Gas-Engines and Producer-Gas Plants
by Rodolphe Edgard Mathot · English · Gutenberg #38415 · 406,509 chars · public domain (US)
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Title: Gas-Engines and Producer-Gas Plants
Author: Rodolphe Edgard Mathot
Author of introduction, etc.: Sir Dugald Clerk
Translator: Waldemar Kaempffert
Release date: December 26, 2011 [eBook #38415]
Most recently updated: January 8, 2021
Language: English
Other information and formats: www.gutenberg.org/ebooks/38415
Credits: Produced by Erik Reh, Henry Gardiner and the Online
Distributed Proofreading Team at https://www.pgdp.net
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Gas-Engines and Producer-Gas Plants
A PRACTICE TREATISE SETTING FORTH THE PRINCIPLES OF GAS-ENGINES AND
PRODUCER DESIGN, THE SELECTION AND INSTALLATION OF AN ENGINE, CONDITIONS
OF PERFECT OPERATION, PRODUCER-GAS ENGINES AND THEIR POSSIBILITIES, THE
CARE OF GAS-ENGINES AND PRODUCER-GAS PLANTS, WITH A CHAPTER ON VOLATILE
HYDROCARBON AND OIL ENGINES
BY R. E. MATHOT, M.E.
Member of the Societe des Ingenieurs Civils de France, Institution of
Mechanical Engineers, Association des Ingenieurs de l'Ecole des Mines du
Hainaut of Brussels
TRANSLATED FROM ORIGINAL FRENCH MANUSCRIPT BY WALDEMAR B. KAEMPFFERT
WITH A PREFACE BY DUGALD CLERK, M. INST. C.E., F.C.S.
ILLUSTRATED
NEW YORK
MUNN & COMPANY
OFFICE OF THE SCIENTIFIC AMERICAN
361 BROADWAY
1905
PREFACE TO
"MATHOT'S GAS-ENGINES AND PRODUCER-GAS PLANTS"
BY
DUGALD CLERK, M. INST.C.E., F.C.S.
Mr. Mathot, the author of this interesting work, is a well-known Belgian
engineer, who has devoted himself to testing and reporting upon gas and
oil engines, gas producers and gas plants generally for many years past.
I have had the pleasure of knowing Mr. Mathot for many years, and have
inspected gas-engines with him. I have been much struck with the ability
and care which he has devoted to this subject. I know of no engineer
more competent to deal with the many minute points which occur in the
installation and running of gas and oil engines. I have read this book
with much interest and pleasure, and I consider that it deals
effectively and fully with all the principal detail points in the
installation, operation, and testing of these engines. I know of no work
which has gone so fully into the details of gas-engine installation and
up-keep. The work clearly points out all the matters which have to be
attended to in getting the best work from any gas-engine under the
varying circumstances of different installations and conditions. In my
view, the book is a most useful one, which deserves, and no doubt will
obtain, a wide public recognition.
DUGALD CLERK.
_March, 1905._
INTRODUCTION
The constantly increasing use of gas-engines in the last decade has led
to the invention of a great number of types, the operation and care of
which necessitate a special practical knowledge that is not exacted by
other motors, such as steam-engines.
Explosion-engines, driven by illuminating-gas, producer-gas, oil,
benzin, alcohol and the like, exact much more care in their operation
and adjustment than steam-engines. Indeed, steam-engines are regularly
subjected to comparatively low pressures. The temperature in the
cylinders, moreover, is moderate.
On the other hand, the explosion-motor is irregularly subjected to high
and low pressures. The temperature of the gases at the moment of
explosion is exceedingly high. It is consequently necessary to resort to
artificial means for cooling the cylinder; and the manner in which this
cooling is effected has a very great influence on the operation of the
motor. If the cooling be effected too rapidly, the quantity of gas
consumed is considerably increased; if the cooling be effected too
slowly, the motor parts will quickly deteriorate.
In order to reduce the gas consumption to a minimum, a matter which is
particularly important when the motor is driven by street-gas, the
explosive mixture is compressed before ignition. Only if all the parts
are built with joints absolutely gas-tight is it possible to obtain this
compression. The slightest leakage past the valves or around the piston
will sensibly increase the consumption.
The mixture should be exploded at the exact moment the piston starts on
its working stroke. If ignition occurs too soon or too late, the result
will be a marked diminution in the useful effect produced by the
expansion of the gas. All ignition devices are composed of delicate
parts, which cannot be too well cared for.
It follows from what has thus far been said that the causes of
perturbation are more numerous in a gas than in a steam engine; that
with a gas-engine, improper care will lead to a much greater increase in
consumption than with a steam-engine, and will cause a waste in power
which would hardly be appreciable in steam-engines, whether their joints
be tight or not.
It is the purpose of this manual to indicate the more elementary
precautions to be taken in the care of an engine operating under normal
conditions, and to explain how repairs should be made to remedy the
injuries caused by accidents. Engines which are of less than 200
horse-power and which are widely used in a small way will be primarily
considered. In another work the author will discuss more powerful
engines.
Before considering the choice, installation, and operation of a
gas-engine, it will be of interest to ascertain the relative cost of
different kinds of motive power. Disregarding special reasons which may
favor the one or the other method of generating power, the net cost per
horse-power hour will be considered in each case in order to show which
is the least expensive method of generating power in ordinary
circumstances.
R. E. MATHOT.
MARCH, 1905.
TABLE OF CONTENTS
CHAPTER I
PAGE
MOTIVE POWER AND COST OF INSTALLATION 17
CHAPTER II
SELECTION OF AN ENGINE
The Otto Cycle.--The First Period.--The Second Period.--The Third
Period.--The Fourth Period.--Valve Mechanism.--Ignition.--
Incandescent Tubes.--Electric Ignition.--Electric Ignition by
Battery and Induction-Coil.--Ignition by Magnetos.--The Piston.--
Arrangement of the Cylinder.--The Frame.--Fly-Wheels.--Straight
and Curved Spoke Fly-Wheels.--The Crank-Shaft.--Cams, Rollers,
etc.--Bearings.--Steadiness.--Governors.--Vertical Engines.--
Power of an Engine.--Automatic Starting 21
CHAPTER III
THE INSTALLATION OF AN ENGINE
Location.--Gas-Pipes.--Dry Meters.--Wet Meters.--Anti-Pulsators,
Bags, Pressure-Regulators.--Precautions.--Air Suction.--
Exhaust.--Legal Authorization 69
CHAPTER IV
FOUNDATION AND EXHAUST
The Foundation Materials.--Vibration.--Air Vibration, etc.--
Exhaust Noises 87
CHAPTER V
WATER CIRCULATION
Running Water.--Water-Tanks.--Coolers 98
CHAPTER VI
LUBRICATION
Quality of Oils.--Types of Lubricators 111
CHAPTER VII
CONDITIONS OF PERFECT OPERATION
General Care.--Lubrication.--Tightness of the Cylinder.--
Valve-Regrinding.--Bearings.--Crosshead.--Governor.--Joints.--
Water Circulation.--Adjustment 121
CHAPTER VIII
HOW TO START AN ENGINE.--PRELIMINARY PRECAUTIONS
Care during Operation.--Stopping the Engine 128
CHAPTER IX
PERTURBATIONS IN THE OPERATION OF ENGINES AND
THEIR REMEDY
Difficulties in Starting.--Faulty Compression.--Pressure of Water
in the Cylinder.--Imperfect Ignition.--Electric Ignition by
Battery or Magneto.--Premature Ignition.--Untimely
Detonations.--Retarded Explosions.--Lost Motion in Moving
Parts.--Overheated Bearings.--Overheating of the Cylinder.--
Overheating of the Piston.--Smoke arising from the Cylinder.--
Back Pressure to the Exhaust.--Sudden Stops 134
CHAPTER X
PRODUCER-GAS ENGINES
High Compression.--Cooling.--Premature Ignition.--The Governing
of Engines 153
CHAPTER XI
PRODUCER-GAS
Street-Gas.--Composition of Producer-Gases.--Symptoms of
Asphyxiation.--Gradual, Rapid Asphyxiation.--Slow, Chronic
Asphyxiation.--First Aid in Cases of Carbon Monoxide
Poisoning.--Sylvester Method.--Pacini Method.--Impurities of
the Gases 165
CHAPTER XII
PRESSURE GAS-PRODUCERS
Dowson Producer.--Generators.--Air-Blast.--Blowers.--Fans.--
Compressors.--Exhausters.--Washing and Purifying.--
Gas-Holder.--Lignite and Peat Producers.--Distilling-Producers.--
Producers Using Wood Waste, Sawdust, and the like.--
Combustion-Generators.--Inverted Combustion 174
CHAPTER XIII
SUCTION GAS-PRODUCERS
Advantages.--Qualities of Fuel.--General Arrangement.--
Generator.--Cylindrical Body.--Refractory Lining.--Grate and
Support for the Lining.--Ash-pit.--Charging-Box.--
Slide-Valve.--Cock.--Feed-Hopper.--Connection of Parts.--Air
Supply.--Vaporizer.--Preheaters.--Internal Vaporizers.--
External Vaporizers.--Tubular Vaporizers.--Partition
Vaporizers.--Operation of the Vaporizers.--Air-Heaters.--
Dust-Collectors.--Cooler, Washer, Scrubber.--Purifying
Apparatus.--Gas-Holders.--Drier.--Pipes.--Purifying-Brush.--
Conditions of Perfect Operation of Gas-Producers.--
Workmanship and System.--Generator.--Vaporizer.--Scrubber.--
Assembling the Plant.--Fuel.--How to Keep the Plant in Good
Condition.--Care of the Apparatus.--Starting the Fire for the
Gas-Producer.--Starting the Engine.--Care of the Generator
during Operation.--Stoppages and Cleaning 199
CHAPTER XIV
OIL AND VOLATILE HYDROCARBON ENGINES
Oil-Engines.--Volatile Hydrocarbon Engines.--Comparative Costs.--
Tests of High-Speed Engines.--The Manograph.--The Continuous
Explosion-Recorder for High-Speed Engines.--Records 264
CHAPTER XV
THE SELECTION OF AN ENGINE
The Duty of a Consulting Engineer.--Specifications.--Testing the
Plant.--Explosion-Recorder for Industrial Engines.--Analysis of
the Gases.--Witz Calorimeter.--Maintenance of Plants.--Test of
Stockport Gas-Engine with Dowson Pressure Gas-Producer.--Test of
a Winterthur Engine.--Test of a Winterthur Producer-Gas
Engine.--Test of a Deutz Producer-Gas Engine and Suction
Gas-Producer.--Test of a 200-H.P. Deutz Suction Gas-Producer and
Engine 279
CHAPTER I
MOTIVE POWER--COST OF INSTALLATION
The ease with which a gas-engine can be installed, compared with a
steam-engine is self-evident. In places where illuminating gas can be
obtained and where less than 10 to 15 horse-power is needed, street-gas
is ordinarily employed.[A] The improvements which have very recently
been made in the construction of suction gas-generators, however, would
seem to augur well for their general introduction in the near future,
even for very small powers.
The installation of small street-gas-engines involves simply the making
of the necessary connections with gas main and the mounting of the
engine on a small base.
An economical steam-engine of equal power would necessitate the
installation of a boiler and its setting, the construction of a
smoke-stack, and other accessories, while the engine itself would
require a firm base. Without exaggeration it may be asserted that the
installation of a steam-engine and of its boiler requires five times as
much time and trouble as the installation of a gas-engine of equal
power, without considering even the requirements imposed by storing the
fuel (Fig. 1). Small steam-engines mounted on their own boilers, or
portable engines, the consumption of which is generally not economical,
are not here taken into account.
[Illustration: FIG. 1.--30 H.P. Gas-engine and suction gas-producer.]
[Illustration: FIG. 1_A_.--30 H.P. Steam-engine, boiler and smoke-stack.]
So far as the question of cost is concerned, we find that a 15 to 20
horse-power steam-engine working at a pressure of 90 pounds and having a
speed of 60 revolutions per minute would cost about 16-2/3 per cent.
more than a 15 horse-power gas-engine, with its anti-pulsators and other
accessories. The foundation of the steam-engine would likewise cost
about 16-2/3 per cent. more than that of the gas-engine. Furthermore the
installation of the steam-engine would mean the buying of piping, of a
boiler of 100 pounds pressure, and of firebrick, and the erection of a
smoke-stack having a height of at least 65 feet. Beyond a little
excavating for the engine-base and the necessary piping, a gas-engine
imposes no additional burdens. It may be safely accepted that the
steam-engine of the power indicated would cost approximately 45 per
cent. more than the gas-engine of corresponding power.
The cost of running a 15 to 20 horse-power steam-engine is likewise
considerably greater than that of running a gas-engine of the same size.
Considering the fuel-consumption, the cost of the lubricating oil
employed, the interest on the capital invested, the cost of maintenance
and repair, and the salary of an engineer, it will be found that the
operation of the steam-engine is more expensive by about 23 per cent.
This economical advantage of the gas over the steam-engine holds good
for higher power as well, and becomes even more marked when
producer-gas is used instead of street-gas. Comparing, for example, a 50
horse-power steam-engine having a pressure of 90 pounds and a speed of
60 revolutions per minute, with a 50 horse-power producer-gas engine,
and considering in the case of the steam-engine the cost of a boiler of
suitable size, foundation, firebrick, smoke-stack, etc., and in the case
of the gas-engine the cost of the producer, foundation, and the like, it
will be found that the installation of a steam-engine entails an
expenditure 15 per cent. greater than in the case of the producer-gas
engine. However, the cost of operating and maintaining the steam-engine
of 50 horse-power will be 40 per cent. greater than the operation and
maintenance of the producer-gas engine.
From the foregoing it follows that from 15 to 20 up to 500 horse-power
the engine driven by producer-gas has considerably the advantage over
the steam-engine in first cost and maintenance. For the development of
horse-powers greater than 500, the employment of compound
condensing-engines and engines driven by superheated steam considerably
reduces the consumption, and the difference in the cost of running a
steam- and gas-engine is not so marked. Still, in the present state of
the art, superheated steam installations entail considerable expense for
their maintenance and repair, thereby lessening their practical
advantages and rendering their use rather burdensome.
FOOTNOTES:
[A] Recent improvements made in suction gas-producers will probably lead
to the wide introduction of producer gas engines even for small power.
CHAPTER II
THE SELECTION OF AN ENGINE
Explosion-engines are of many types. Gas-engines, of the four-cycle
type, such as are industrially employed, will here be principally
considered.
=The Otto Cycle.=--The term "four-cycle" motor, or Otto engine, has its
origin in the manner in which the engine operates. A complete cycle
comprises four distinct periods which are diagrammatically reproduced in
the accompanying drawings.
=The First Period.=--_Suction:_ The piston is driven forward, creating a
vacuum in the cylinder, and simultaneously drawing in a certain quantity
of air and gas (Fig. 2).
[Illustration: FIG. 2.--First cycle: Suction.]
=The Second Period.=--_Compression:_ The piston returns to its initial
position. All admission and exhaust valves are closed (Fig. 3). The
mixture drawn in during the first period is compressed.
=The Third Period.=--_Explosion and Expansion:_ When the piston has
reached the end of its return stroke, the compressed mixture is ignited.
Explosion takes place at the dead center. The expansion of the gas
drives the piston forward (Fig. 4).
[Illustration: FIG. 3.--Second cycle: Compression.]
[Illustration: FIG. 4.--Third cycle: Explosion and expansion.]
=The Fourth Period.=--_Exhaust:_ The piston returns a second time. The
exhaust-valve is opened, and the products of combustion are discharged
(Fig. 5).
[Illustration: FIG. 5.--Fourth cycle: Exhaust.]
These various cycles succeed one another, passing through the same
phases in the same order.
=Valve Mechanism.=--It is to be noted that in modern motors valves are
used which are better adapted to the peculiarities of explosion-engines
than were the old slide-valves used when the Otto engine was first
introduced. The slide-valve may now be considered as an antiquated
distributing device with which it is impossible to obtain a low
consumption.
In old-time gas-engines rather low compressions were used. Consequently
a very low explosive power of the gaseous mixture, and low temperatures
were obtained. The slide-valves were held to their seats by the pressure
of external springs, and were generously lubricated. Under these
conditions they operated regularly. Nowadays, the necessity of using
gas-engines which are really economical has led to the use of high
compressions with the result that powerful explosions and high
temperatures are obtained. Under these conditions slide-valves would
work poorly. They would not be sufficiently tight. To lubricate them
would be difficult and ineffective. Furthermore, large engines are
widely used in actual practice, and with these motors the frictional
resistance of large slide-valves, moving on extensive surfaces would be
considerable and would appreciably reduce the amount of useful work
performed.
[Illustration: FIG. 6.--Modern valve mechanism.]
By reason of its peculiar operation, the slide-valve is objectionable,
the gases being throttled at the time of their admission and discharge.
As a result of these objections there are losses in the charge; and
obnoxious counter-pressures occur. The necessity of using elements
simple in their operation and free from the objections which have been
mentioned, has naturally led to the adoption of the present valve. This
valve is used both for the suction of the gas and of the air, as well as
for the exhaust, with the result that either of these two essential
phases in the operation of the motor can be independently controlled.
The valves offer the following advantages: Their tightness increases
with the pressure, since they always open toward the interior of the
cylinder (Fig. 6). They have no rubbing surfaces, and need not,
therefore, be lubricated. Their opening is controlled by levers provided
with quick-acting cams; and their closure is effected by coiled springs
almost instantaneous in their action (Fig. 7). Each valve, depending
upon the purpose for which it is used, can be mounted in that part of
the cylinder best suited for its particular function. The types of
valved motors now used are many and various. In order to attain economy
in consumption and regularity in operation they should meet certain
essential requirements which will here be reviewed.
Apart from proportioning the areas properly and from providing a
suitable means of operation, it is indispensable that the valves should
be readily accessible. Indeed, the valves should be regularly examined,
cleaned and ground. It follows that it should be possible to take them
apart easily and quickly.
[Illustration: FIG. 7.--Controlling mechanism of valve.]
It is necessary that the exhaust-valve be well cooled; otherwise the
valve, exposed as it is to high temperatures, will suffer derangement
and may cause leakage. The water-jacket should, therefore, surround the
seat of the exhaust-valve, care being taken that the cooling water be
admitted as near to it as possible (Fig. 8). The motor should control
the air-let valve or that of the gaseous mixture. Hence these valves
should not be actuated simply by springs, because springs are apt to
move under the influence of the vacuum produced by suction.
[Illustration: FIG. 8.--Water-jacketed valve.]
The mixture of gas and air should not be admitted into the cylinder at
too low a pressure; otherwise the weight of the mixture admitted would
be lower than it ought to be, inasmuch as under these conditions the
valve will be opened too tardily and closed prematurely. At the
beginning as well as at the end of its stroke the linear velocity of the
piston is quite inadequate to create a vacuum sufficient to overcome the
resistance of the spring. It is, therefore, generally the practice
separately to control the opening or closing of the one or the other
valve (gas-valve or mixture-valve). Consequently these valves must be
actuated independently of each other. Nowadays they are mechanically
controlled almost exclusively,--a method which is advocated by
well-known designers for industrial motors in particular. Valves which
are not actuated in this manner (free valves) have only the advantage of
simplicity of operation. Nevertheless, this arrangement is still to be
found in certain oil and benzine engines, notably in automobile-motors.
In these motors it is necessary to atomize the liquid fuel by means of
aspired air, in order to produce an explosive, gaseous mixture.
=Ignition.=--In the development of the gas-engine, the incandescent tube
and the electric spark have taken the place of the obsolete naked flame.
The last-mentioned mode of exploding the gaseous mixture will not,
therefore, be discussed.
The hot tube of porcelain or of metal has the indisputable merit of
regularity of operation. The methods by which this operation is made as
perfect as possible are many. Since certainty of ignition is obtained by
means of the tube, it is important to time the ignition, so that it
shall occur exactly at the moment when the piston is at the dead
center. It has been previously stated that premature or belated ignition
of the explosive mixture appreciably lessens the amount of useful work
performed by the expansion of the gas. If ignition occur too soon, the
mixture will be exploded before the piston has reached the dead center
on its return stroke. As a result, the piston must overcome a
considerable resistance due to the premature explosion and the
consequent pressure. Furthermore, by reason of the high temperature of
explosion, the gaseous products are very rapidly cooled. This rapid
cooling causes a sudden drop in the pressure; and since a certain
interval elapses between the moment of explosion and the moment when the
piston starts on its forward stroke, the useful motive effort is the
more diminished as the ignition is more premature.
=Incandescent Tubes.=--In Figs. 9 and 10 two systems most commonly used
are illustrated. In these two arrangements, in which no valve is used,
the length or height to which the tube is heated by the outer flame is
so controlled that the gaseous mixture, which has been driven into the
tube after compression, reaches the incandescent zone as nearly as
possible at the exact moment when ignition and explosion should take
place. The temperature of the flame of the burner, the richness of the
gaseous mixture, and other circumstances, however, have a marked
influence on the time of ignition, so that the mixture is never fired at
the exact moment mentioned.
[Illustration: FIGS. 9-10.--Valveless hot tubes.]
These considerations lead to the conclusion that motors in which the
mixture is exploded by hot tubes provided with an ignition-valve are
preferable to valveless tubes. By the use of a special valve, positively
controlled by the motor itself, the chances of untimely ignition are
lessened, because it is necessary simply to regulate the temperature and
the position of the tube in order that ignition may be surely effected
immediately upon the opening of the valve, at the very moment the
cylinder gases come into contact with the incandescent portion of the
tube (Fig. 11). Many manufacturers, however, do not employ the
ignition-valve on motors of less than 15 to 20 horse-power, chiefly
because of the cheaper construction. The total consumption is of less
moment in a motor of small than of great power, and the loss due to the
lack of an ignition-valve not so marked. In a high-power engine,
premature explosion may be the cause of the breaking of a vital part,
such as the piston-rod or the crank-shaft. For this reason, a valve is
indispensable for engines of more than 20 to 25 horse-power. A breakage
of this kind is less to be feared in a small motor, where the parts are
comparatively stout. The gas consumption of a well-designed burner does
not exceed from 3.5 to 5 cubic feet per hour.
[Illustration: FIG. 11.--Ignition-tube with valve.]
=Electric Ignition.=--Electric ignition consists in producing a spark in
the explosion-chamber of the engine. The nicety with which it can be
controlled gives it an undeniable advantage over the hot tube. But the
objection has been raised, perhaps with some force, that it entails
certain complications in installing the engine. Its opponents even
assert that the power and the rapidity of the deflagration of the
explosive mixture are greater with hot-tube ignition. This reason may
have caused the hot-tube system to prevail in England, where
manufacturers of gas-engines are very numerous and not lacking in
experience.
Electric ignition is effected in gas-engines by means of a battery and
spark-coil, or by means of a small magneto machine which mechanically
produces a current-breaking spark.
[Illustration: FIG. 12.--Electric ignition by spark-coil and battery.]
[Illustration: FIG. 13.--Spark-plug.]
=Electric Ignition by Battery and Induction-Coil.=--The first system is
the cheaper; but it exacts the most painstaking care in maintaining the
parts in proper working condition. It comprises three essential
elements--a battery, a coil, and a spark-plug (Fig. 12). The battery may
be a storage-battery, which must, consequently, be recharged from time
to time; or it may be a primary battery which must be frequently
renewed and carefully cleaned. The induction-coil is fitted with a
trembler or interrupter, which easily gets out of order and which must
be regulated with considerable accuracy. The spark-plug is a
particularly delicate part, subject to many possible accidents. The
porcelain of which it is made is liable to crack. It is hard to obtain
absolutely perfect insulation; for the terminals deteriorate as they
become overheated, break, or become foul (Fig. 13). In oil-engines,
especially, soot is rapidly deposited on the terminals, so that no spark
can be produced. In benzine or naphtha motors, such an accident is less
likely to happen. In automobile-motors, however, the spark-plug only too
often fails to perform its function. The one remedy for these evils is
to be found in the most painstaking care of the spark-plug and of the
other elements of the ignition system.
[Illustration: FIG. 14.--Magneto ignition apparatus.]
[Illustration: FIG. 15.--General view and details of a magneto ignition
apparatus.]
=Ignition by Magnetos.=--Magneto apparatus, on the other hand, are
noteworthy for the regularity of their operation. They may be used for
several years without being remagnetized, and require no exceptional
care. Magneto ignition devices are mechanically actuated, the necessary
displacement of the coil being effected by means of a cam carried on a
shaft turning with half the motor speed (Figs. 14 and 15). At the moment
when it is released by the cam, the coil is suddenly returned to its
initial position by means of a spring. This rapid movement generates a
current that passes through terminals, which are arranged within the
cylinder and which are immediately separated by mechanical means. Thus a
much hotter circuit-breaking spark is produced, which is very much more
energetic than that of a battery and induction-coil, and which surely
ignites the gaseous mixture in the cylinder. The terminals are generally
of steel, sometimes pointed with nickel or platinum (Fig. 16). The only
precaution to be observed is the exclusion of moisture and occasional
cleaning. For engines driven by producer-gas magneto-igniters are
preferable to cells and batteries. In general, electrical ignition is to
be recommended for high-pressure engines.
[Illustration: FIG. 16.--Contacts of a magneto-igniter.]
[Illustration: FIG. 17.--Device for regulating the moment of ignition.]
In order to explain more clearly modern methods of ignition a diagram is
presented, showing an electric magneto-igniter applied to the
cylinder-head of a Winterthur motor, and also a sectional view of the
member varying the make-and-break contacts which are mounted in the
explosion-chamber (Figs. 18 and 19)
1. The magneto _A_ consists of horseshoe-magnets, between the poles of
which the armature rotates. At its conically turned end, the
armature-shaft carries an arm _B_, held in place by a nut.
[Illustration: FIG. 18.--Winterthur electric ignition system.]
2. The igniter _C_ is a casting secured to the cylinder-head by a
movable strap and provided with two axes _D_ and _M_, of which the one,
_D_, made of bronze, is movable, and is fitted with a small interior
contact-hammer, a percussion-lever, and an exterior recoil-spring; the
other, _M_, is fixed, insulated, and arranged to receive the current
from the magneto _A_, by means of an insulated copper wire _E_.
3. The spring _F_ comprises two continuous coils contained in a brass
casing, and actuating a steel striking or percussion-pin.
4. The controlling devices of the magneto include a stem or rod _G_,
slidable in a guide _H_, provided with a safety spring and mounted on an
eccentric spindle, the position of which can be varied by means of a
regulating-lever (_I_). The rod is operated from the distributing-shaft,
on the conical end of which a cam _J_ carrying a spindle is secured.
[Illustration: FIG. 19.--Contacts of the Winterthur system.]
_Regulation of the Magneto._--The position assumed by the armature when
at rest is a matter of importance in obtaining a good spark on breaking
the circuit. The marks on the armature should be noted. The position of
the armature may be experimentally varied, in order to obtain a spark of
maximum intensity, by changing the position of the arm B on the
armature-shaft.
_Control of the Magneto._--The controlling gear should enable the
armature to oscillate from 20 to 25 degrees. The time at which the
breaking of the circuit is effected can be regulated by shifting the
handle (_I_). In starting the engine, the circuit can be broken with a
slight retardation, which is lessened as the engine attains its normal
speed.
_Igniter._--It is advisable that there should be a play of 1/2 mm.
(0.0196 in.) between the lever _Z_ when at rest and the striking-pin.
The axis _D_ of the circuit-breaking device should be easily movable;
and the hammer which it carries at its end toward the interior of the
cylinder should be in perfect contact with the stationary spindle _M_,
which is electrically insulated. This spindle _M_ should be well
enclosed, in order to prevent any leakage that might cause a
deterioration of the insulating material.
The subject of ignition is of such extreme importance that the author
will recur to it from time to time in the various chapters of this book.
Too much stress cannot be laid upon proper timing; otherwise there will
be a needless waste of power. Cleanliness is a point that must be
observed scrupulously; for spark-plugs are apt to foul only too readily,
with the result that short-circuits and misfires are apt to occur. In
oil and volatile hydrocarbon engines the tendency to fouling is
particularly noticeable. In the chapter devoted to these forms of
motors the author has dwelt upon the precautions that should be taken to
forestall a possible derangement of the ignition apparatus. As a general
rule the ignition apparatus installed by trustworthy manufacturers will
be found best suited for the requirements of the engine.
The apparatus should be fitted with a device by which the ignition can
be duly timed by hand during operation (Fig. 17).
[Illustration: FIG. 20.--Design of the piston.]
=The Piston.=--Coming, as it does, continually in contact with the
ignited gases, the piston is gradually heated to a high temperature. The
rear face of the piston should preferably be plane. Curved surfaces are
not to be recommended because they cool off badly. Likewise, faces
having either inserted parts or bolt-heads are to be avoided, since they
are liable to become red-hot and to ignite the mixture prematurely (Fig.
20).
[Illustration: FIG. 21.--Piston with lubricated pin.]
Among the parts of the piston which rapidly wear away because constant
lubrication is difficult, is the connection with the piston-rod (Fig.
21). It is important that the bearing at the piston-pin be formed of two
parts which can be adjusted to take up the wear. The pin itself should
be of case-hardened steel. For large engines, some manufacturers have
apparently abandoned the practice of locking the pin, by set-screws, in
flanges cast in one piece with the piston. Indeed, the piston is often
fractured by reason of the expansion of the pins thus held on two sides.
It seems advisable to secure the pin by means of a single screw in one
of the flanges, fitting it by pressure against the opposite boss. The
use of wedges or of clamping-screws, introduced from without the piston
to hold the pin, should be avoided. It may happen that the wedges will
be loosened, will move out, and will grind the cylinder, causing
injuries that cannot be detected before it is too late. The strength of
the piston-pin should be so calculated that the pressure per square inch
of projected surface does not exceed 1,500 to 2,850 pounds per square
inch. It should be borne in mind that the initial pressure of the
explosion is often equal to 400 to 425 pounds per square inch. Some
manufacturers mount the pin as far to the back of the piston as
possible, so as to bring it nearer the point of application of the
motive force of the explosion. Other manufacturers, on the other hand,
mount the pin toward the front of the piston. No great objection can be
raised against either method. In the former case the position of the
rings will limit that of the pin.
The number of these rings ought not to be less than four or five,
arranged at the rear of the piston. It is to be observed that makers of
good engines use as many as 8 to 10 rings in the pistons of fair-sized
motors.
Piston-rings of gray pig-iron can be adjusted with the greatest nicety
in such a manner that, by means of tongues fitting in their grooves,
they are held from turning in the latter, whereby their openings are
prevented from registering and allowing the passage of gas. As a general
rule, a large number of rings may be considered a distinguishing feature
of a well-built engine. In order to prevent a too rapid wear of the
cylinder, several German manufacturers finish off the front of the
piston with bronze or anti-friction metal in engines of more than 40 to
50 horse-power. It is to be observed, however, that this expedient is
not applicable to motors the cylinders of which are comparatively cold;
otherwise the bronze or anti-friction metal will deteriorate.
=Arrangement of the Cylinder.=--The cylinder shell or liner, in which
the piston travels, and the water-jacket should preferably be made in
separate pieces and not cast of the same metal, in order to permit a
free expansion (Figs. 22 and 23). If for want of care or of proper
lubrication, which frequently occurs in gas-engines, the cylinder should
be injured by grinding, it can be easily renewed, without the loss of
all the connecting parts.
[Illustration: FIG. 22.--Head, jacket and liner of cylinder, cast in one
piece.]
[Illustration: FIG. 23.--Cylinder with independent liner and head.]
For the same reason, the cylinder and its casing should be independent
of the frame. In many horizontal engines, the cylinders overhang the
frame throughout the entire length, by reason of the joining of their
front portions with the frames. Although such a construction is attended
with no serious consequences in small engines, nevertheless in large
engines it is exceedingly harmful. Indeed, in most modern single-acting
engines, the pistons are directly connected with the crank-shaft by the
piston-rod, without any intermediate connecting-rod or cross-head. The
vertical reaction of the motive effort on the piston is, therefore,
taken up entirely by the thrust of the cylinder, which is also vertical
(Fig. 24). This thrust, acting against an unsupported part, may cause
fractures; at any rate, it entails a rapid deterioration of the cylinder
joint.
[Illustration: FIG. 24.--Single-acting engines.]
[Illustration: FIG. 25.--Engine with inclined bearings.]
=The Frame.=--Gas-engines driven as they are, by explosions, giving rise
to shocks and blows, should be built with frames, heavy, substantial,
and broad-based, so as to rest solidly on the ground. This essential
condition is often fulfilled at the cost of the engine's appearance; but
appearance will be willingly sacrificed to meet one of the requirements
of perfect operation. For engines of more than 8 to 10 horse-power,
frames should be employed which can be secured to the masonry foundation
without a separate pedestal or base. Some manufacturers, for the purpose
of lightening the frame, attach but little importance to the foundation
and to strength of construction, and employ the design illustrated in
place of the crank-shaft bearing (Fig. 25); others, in order to
facilitate the adjusting of the connecting-rod bearings, prefer the
second form (Fig. 26). It is evident that, in the first case, a part of
the effort produced by the explosion reacts on the upper portion of the
connecting-rod bearing, on the cap of the crank-shaft bearing, and
consequently on the fastening-bolts. In the second case, if the
adjustment be not very carefully made, or if the rubbing surfaces are
insufficient, the entire thrust due to the explosion will be received
by the meeting parts of the two bushings, thus injuring them and causing
a more rapid wear. In the construction of large engines, some
manufacturers take the precaution of forming the connecting-rod bearings
of four parts, adjustable to take up the wear, so that the effort is
exerted against the parts disposed at right angles to each other. A form
that seems rational is that shown in Fig. 27, in which the reaction of
the thrust is taken up by the lower bearing, rigidly supported by the
braced frame, in the direction opposite to that of the explosive effort.
[Illustration: FIG. 26.--Engine with straight bearings.]
[Illustration: FIG. 27.--Engine with correctly designed bearings.]
The sum of the projecting surfaces of the two bearings should be so
calculated that a maximum explosive pressure of 405 to 425 pounds per
square inch will not subject the bearings to a pressure higher than 425
to 550 pounds per square inch.
=Fly-Wheels.=--In gas-engines particularly, the fly-wheel should be
secured to the crank-shaft with the utmost care. It should be mounted as
near as possible to the bearings; otherwise the alinement of the shaft
will be destroyed and its strength impaired. If the fly-wheel be
fastened by means of a key or wedge having a projecting head, it is
advisable to cover the end of the shaft by a movable sleeve. The
fly-wheel should run absolutely true and straight even if the explosion
be premature. In well-built engines the fly-wheels are lined up and
shaped to the rim. The periphery is slightly rounded in order the better
to guide the belt when applied to the wheel.
[Illustration: FIG. 28.--Single fly-wheel engine with external bearing.]
Furthermore, fly-wheels should be nicely balanced; those are to be
preferred which have no counter-weights cast or fastened to the hub, the
spokes, or the rim. The system of balancing the engine by means of two
fly-wheels, mounted on opposite sides, is used chiefly for the purpose
of equalizing the inertia effects. Special engines, employed for driving
dynamos, and even industrial engines of high power, are preferably
fitted with but a single fly-wheel, with an outer bearing, since they
more readily counteract the cyclic irregularities or variations of speed
occurring in a single revolution (Fig. 28). If in this case a pulley be
provided, it should be mounted between the engine and the outer
bearing. The following advantages may be cited in favor of the single
fly-wheel, particularly in the case of dynamo-driving engines:
1. The single fly-wheel permits a more ready access to the parts to be
examined.
2. It involves the employment of a third bearing, thus avoiding the
overhang caused by two ordinary fly-wheels.
3. It avoids the torsional strain to which the two-wheel crank is
subjected when starting, stopping, and changing the load, the peripheral
resistance varying in one of the fly-wheels, while the other is
subjected to a strain in the opposite direction on account of the
inertia.
4. Two fly-wheels, keyed as they are to projecting ends of the shaft,
will be so affected at the rims by the explosions that the belts will
shake.
The third bearing which characterizes the single-fly-wheel system, is
but an independent support, resting solidly on the masonry bed of the
engine. The bearing with its independent support is sufficiently rigid,
and is not subjected to any stress from the crank at the moment of
explosion, the reaction of the crank affecting only the frame bearings.
With such fly-wheels, reputable firms guarantee a cyclic regularity
which compares favorably with that of the best steam-engines. For a duty
varying from a third of the load to the maximum load, these engines,
when driving direct-current dynamos for directly supplying an
electric-light circuit, will insure perfect steadiness of the light;
and the effectually aperiodic measuring instruments will not indicate
fluctuations greater than 2 to 3 per cent. of the tension or intensity
of the current. The coefficient of the variations in the speed of a
single revolution will thus be not far from 1/60.
[Illustration: FIG. 29.--Curved spoke fly-wheel.]
=Straight and Curved Spoke Fly-Wheels.=--The spokes of fly-wheels are
either straight or curved. In assembling the motor parts it too often
occurs that curved spoke fly-wheels are mounted with utter disregard of
the direction in which they are to turn. It is important that curved
spokes should be subjected to compression and not to traction. Hence the
fly-wheels should be so mounted that the concave portions of the spokes
travel in the direction of rotation, as shown in the accompanying
diagram (Fig. 29). If a single fly-wheel be employed on an engine of the
type in which the speed is governed by the "hit-and-miss" system, the
fly-wheel should be extra heavy to counteract the irregularities of the
motive impulses when the engine is not working at its full load, or in
other words, when no explosion takes place at every cycle.
[Illustration: FIG. 30.--Forged crank-shafts.]
=The Crank-Shaft.=--The crank-shaft should be made of the best mild
steel. Those shafts are to be preferred the cranks of which are not
forged on (Fig. 30), but cut out of the mass of metal; furthermore, the
brackets or supports should be planed and shaped so that they are square
in cross-section.
[Illustration: FIG. 31.--Correct design of crank-shaft.]
Such a design involves fine workmanship and speaks well for the
construction of the whole engine. Moreover, it enables the bearings to
be brought nearer each other, reduces to a minimum that part of the
crank-shaft which may be considered the weakest, and permits a rational
and exact counterbalancing of the moving parts, such as the crank and
the end of the connecting-rod. The best manufacturers have adopted the
method of fastening to the cranks balancing weights secured to the
brackets, especially for high-speed engines or for engines of high
power. The projecting surface of the crank-pin should, as a rule, be
calculated for a pressure of 1,400 pounds per square inch.
[Illustration: FIG. 32.--Crank-shaft with balancing weight.]
=Cams, Rollers, etc.=--The cams, rollers, thrust-bearings, as well as
the piston-pin in particular, should be made of good steel,
case-hardened to a depth of at least .08 of an inch. Their hardness and
the degree of cementation may be tested by means of a file. This is the
method followed by the best manufacturers.
=Bearings.=--All the bearings and all guides should be adjustable to
take up the wear. They are usually made of bronze or of the best
anti-friction metal.
=Steadiness.=--The steadiness of engines may be considered from two
different standpoints.
[Illustration: FIG. 33.--Inertia governor.]
1. _Variation of the Number of Revolutions at Different Loads._--This
depends chiefly on the sensitiveness of the governor, which should be of
the "inertia" or of the "ball" (or centrifugal) type. The first form is
rarely employed, except in small engines up to 10 horse-power, and is
applicable only to engines in which the "hit and miss" system is
employed (Fig. 33). The second form is more widely used, and is
applicable to engines having "hit-and-miss" or variable admission
devices. In the first form, the governor simply displaces a very light
member, whatever may be the size of the engine, for which reason the
dimensions are very small. In the second form, on the other hand, the
governor acts either on a conical sleeve or on some other regulating
member offering resistance. Evidently, in order to overcome the
reactions to which it is subjected, it must be as heavy and powerful as
a steam-engine governor. Sufficient allowance is made in a good engine
for variation in the number of revolutions between no load and full
load, not greater than two per cent. if the admission be of the
"hit-and-miss" type, and five per cent. if it be of the variable type.
2. _Cyclic Regularity._--This term means simply that the speed of the
engine is constant in a single revolution. In practice this is never
attained. Allowance is made in engines used for driving direct-current
dynamos for a variation of about 1/60; while in industrial engines a
variation of 1/25 is permissible. Cyclic variation depends only on the
weight of the fly-wheel; whereas variation in the number of revolutions
is determined chiefly by the governor.
=Governors.=--Diagrams are here presented of the principal types of
governors--the inertia governor, the ball or centrifugal governor
controlling an admission-valve of the "hit-and-miss" type (Fig. 34), and
the ball or centrifugal governor controlling a variable gas-admission
valve (Fig. 35).
In distinguishing between the operation of the two last-mentioned types,
it may be stated that the former bears the same relation to the
hit-and-miss gear as it does, for example, to the valve gear of a
Corliss steam-engine. In other words, it is an apparatus that
_indicates_ without _inducing_, admission or cut-off. The second type,
on the other hand, operates by means of slides and the like, as in the
Ridder type of engine, in which it controls the displacement of the
cut-off or distribution slide-valve and is subjected to variable forces,
depending on the pressure, lubrication, the condition of the
stuffing-boxes, and the like.
In gas as well as in steam engines, designs are to be commended which
shield the delicate mechanism from strains and stresses that are likely
to destroy its sensitiveness, as is the case in the automatic cut-off of
the Corliss steam-engine.
[Illustration: FIG. 34.--"Hit-and-miss" governor.]
Governors should be provided with means to permit the manual variation
of the speed while the engine is in operation.
For small motors, one of the most widely used admission devices is that
of the "hit-and-miss" type. As its name indicates, this admission
arrangement allows a given quantity of gas to enter the cylinder for a
number of consecutive intervals, until the engine is about to exceed its
normal speed. Thereupon the governor cuts off the gas entirely. The
result is that, in this system, the number of admissions is variable,
but that each admitted charge is composed of a constant proportion of
gas and air.
The governors employed for the "hit-and-miss" type are either "inertia"
or "centrifugal" governors.
Inertia governors (Fig. 33) are less sensitive than those of the
centrifugal type. They are generally applied only to industrial engines
of small power, in which regularity of operation is a secondary
consideration.
Centrifugal governors employed for gas-engines with "hit-and-miss"
regulation are, as a general rule, noteworthy for their small size,
which is accounted for by the fact that, in most systems, merely a
movable member is placed between the admission-controlling means and the
valve-stem (Fig. 34). It follows that this method of operation relieves
the governor of the necessity of overcoming the resistance of the weight
of moving parts, more or less effectually lubricated, and subjected to
the reaction of the parts which they control.
In engines equipped with variable admission devices for the gas or the
explosive mixture, the governor actuates a sleeve on which the
admission-cam is fastened (Fig. 35). Or, the governor may displace a
conical cam, the reaction of which, on contact with the lever, destroys
the stability of the governor. These conditions justify the employment
of powerful governors which, on account of the inertia of their parts,
diminish the reactionary forces encountered.
The centrifugal governor should be sufficiently effectual to prevent
variations in the number of revolutions within the limits of 2 to 3 per
cent. between no load and approximately full load. Under equivalent
conditions, the inertia governor can hardly be relied upon for a
coefficient of regularity greater than 4 to 5 per cent.
[Illustration: FIG. 35.--Variable admission governor.]
The manner of a governor's operation is necessarily dependent on the
admission system adopted. And the admission system varies essentially
with the size, the purpose of the engine, and the character of the fuel
employed.
[Illustration: FIG. 36.--Vertical engine.]
[Illustration: FIG. 37.--Section through an engine of the vertical or
"steam-hammer" type.]
=Vertical Engines.=--For some years past there seems to have been a
tendency in Europe to use horizontal instead of vertical engines,
especially since engines of more than 10 or 15 horse-power have been
extensively used for industrial purposes. The vertical type is used for
1 to 8 horse-power engines, with the cylinder in the lower part of the
frame, and the shaft and its fly-wheel in the upper part (Fig. 36). The
only merit to be attributed to this arrangement is a great saving of
space. It is evident, however, that beyond a certain size and power,
such engines are unstable. In America particularly, many manufacturers
of high-power engines (50 to 100 horse-power or more) prefer the
vertical or "steam-hammer" arrangement, which consists in placing the
cylinder in the upper part, and the shaft in the lower part of the frame
as close to the ground as possible (Figs. 37 and 38). The problem of
saving space, as well as that of insuring stability, is thus solved, so
that it is easily possible to run up the speed of the engine. There is
also the advantage that the shaft of a dynamo can be directly coupled
up with the crank-shaft of the engine, thus dispensing with a belt,
which, at the least, absorbs 4 to 6 per cent. of the total power. It
should, nevertheless, be borne in mind that the direct coupling of
electric generators to engine-shafts implies the use of extremely large
and, therefore, of extremely costly dynamos. Furthermore, by reason of
this arrangement, groups of electro-generators can be disposed in a
comparatively small amount of space. Some English manufacturers are also
beginning to adopt the "steam-hammer" type of engine for high powers,
the result being a marked saving in material and lowering of the cost of
installation.
[Illustration: FIG. 38.--Side and end elevations of a vertical or
"steam-hammer" engine.]
=Power of the Engine.=--The first thing to be considered is that the
power of a gas-engine is always given in "effective" horse-power, and
that the power of a steam-engine is always given in "indicated"
horse-power in contracts of sale. In England and in the United States,
the expression "nominal" horse-power is still employed. It may be
advisable to define these various terms exactly, since unscrupulous
dealers, to the buyer's loss, have done much to confuse them.
"Indicated" horse-power is a designation applied to the theoretical
power produced by the action of the motive agent on the piston. The work
performed is measured on an indicator card, by means of which the
average pressure to be considered in the computation of the theoretical
power is ascertained.
The "effective" or brake horse-power is equal to the "indicated"
horse-power, less the energy absorbed by passive resistance, friction of
the moving parts, etc.
The "effective" work is an experimental term applied to the power
actually developed at the shaft. This work is of interest solely to the
engine user.
In a well-built motor, in which the passive resistance by reason of the
correct adjustment and simplicity of the parts, is reduced to a minimum,
the "effective" horse-power is about 80 to 87 per cent. of the
"indicated" horse-power, when the engine runs under full load. This
reduced output is usually called the "mechanical efficiency" of the
engine.
"Nominal" horse-power is an arbitrary term in the sense in which it is
used in England and America, where it is quite common. The manufacturers
themselves do not seem to agree on its absolute value. A "nominal"
horse-power, however, is equal to anything from 3 to 4 "effective"
horse-power. The uncertainty which ensues from the use of the term
should lead to its abandonment.
In installing a motor, the determination of its horse-power is a matter
of grave importance, which should not be considered as if the motor were
a steam-engine or an engine of some other type. It must not be forgotten
that, especially at full load, explosion-engines are most efficient, and
that, under these conditions, it will generally be advisable to
subordinate the utility of having a reserve power to the economy which
follows from the employment of a motor running at a load close to its
maximum capacity. On the other hand, the gas-engine user is unwilling to
believe that the stipulated horse-power of the motor which is sold to
him is the greatest that it is capable of developing under industrial
conditions. Business competition has led some firms to sell their
engines to meet these conditions. It is probably not stretching the
truth too far to declare that 80 per cent. of the engines sold with no
exact contract specifications are incapable of maintaining for more than
a half hour the power which is attributed to them, and which the buyer
expects. It follows that the power at which the engine is sold should be
both industrially realized and maintained, if need be, for an entire
day, without the engine's showing the slightest perturbation, or
faltering in its silent and regular operation. To attain this end, it is
essential that the energy developed by the engine in normal or constant
operation should not exceed 90 to 95 per cent. of the maximum power
which it is able to yield, and which may be termed its "utmost power".
As a general rule, especially for installations in which the power
fluctuates from the lowest possible to double this, as much attention
must be paid to the consumption at half load as at full load; and
preference should be given to the engine which, other things being
equal, will operate most economically at its lowest load. In this case
the consumption per effective horse-power is appreciably higher.
Generally, this consumption is greater by 20 to 30 per cent. than that
at full load. This is particularly true of the single-acting engines so
widely used for horse-powers less than 100 to 150.
In some double or triple-acting engines, according to certain writers,
the diminution in the consumption will hardly be proportional to the
diminution of the power, or at any rate, the difference between the
consumption per B.H.P. at full load and at reduced load will be less
than in other engines. It should be observed, however, that this
statement is apparently not borne out by experiments which the author
has had occasion to make. To a slight degree, this economy is obtained
at the cost of simplicity, and consequently, at the cost of the engine.
At all events, the engines have the merit of great cyclic regularity,
rendering them serviceable for driving electric-light dynamos; but this
regularity can also be attained by the use of the extra heavy fly-wheels
which English firms, in particular, have introduced.
=Automatic Starting.=--When the gas-engine was first introduced,
starting was effected simply by manually turning the fly-wheel until
steady running was assured. This procedure, altogether too crude in its
way, is attended with some danger. In a few countries it is prohibited
by laws regulating the employment of industrial machinery. If the engine
be of rather large size one, moreover, which operates at high
pressure--such a method of starting is very troublesome. For these
reasons, among others, manufacturers have devised automatic means of
setting a gas-engine in motion.
Of such automatic devices, the first that shall be mentioned is a
combination of pipes, provided with cocks, by the manipulation of which,
a certain amount of gas, drawn from the supply pipe, is introduced into
the engine-cylinder. The piston is first placed in a suitable position,
and behind it a mixture is formed which is ignited by a naked flame
situated near a convenient orifice. When the explosion takes place the
ignition-orifice is automatically closed, and the piston is given its
motive impulse. The engine thus started continues to run in accordance
with the regular recurrence of the cycles. In this system, starting is
effected by the explosion of a mixture, without previous compression.
Some designers have devised a system of hand-pumps which compress in the
cylinder a mixture of air and gas, ignited at the proper time by
allowing it to come into contact with the igniter, through the
manipulation of cocks (Fig. 39).
These two methods are not absolutely effective. They require a certain
deftness which can be acquired only after some practice. Furthermore,
they are objectionable because the starting is effected too violently,
and because the instantaneous explosion subjects the stationary piston,
crank, and fly-wheel to a shock so sudden that they may be severely
strained and may even break. Moreover, the slightest leakage in one of
the valves or checks may cause the entire system to fail, and,
particularly in the case of the pump, may induce a back explosion
exceedingly dangerous to the man in charge of the engine.
These systems are now almost generally supplanted by the compressed-air
system, which is simpler, less dangerous, and more certain in its
effect.
The elements comprising the system in question include essentially a
reservoir of thick sheet iron, capable of resisting a pressure of 180 to
225 pounds and sufficient in capacity to start an engine several times.
This reservoir is connected with the engine by piping, which is disposed
in one of two ways, depending upon whether the reservoir is charged by
the engine itself operatively connected with the compressor, or by an
independent compressor, mechanically operated.
[Illustration: FIG. 39.--Tangye starter.]
In the first case, the pipe is provided with a stop-cock, mounted
adjacent to the cylinder, and with a check-valve. When the engine is
started and the gas cut off, the air is drawn in at each cycle and
driven back into the reservoir during the period of compression. When
the engine, running under these conditions by reason of the inertia of
the fly-wheel, begins to slow down, the check-valve is closed and the
gas-admission valve opened, so as to produce several explosions and to
impart a certain speed to the engine in order to continue the charging
of the reservoir with compressed air. This done, the valve on the
reservoir itself is tightly closed, as well as the check-valve, so as to
avoid any leakage likely to cause a fall in the reservoir's pressure.
In the second case, which applies particularly to engines of more than
50 horse-power, the charging pipe connected with the reservoir is
necessarily independent of the pipe by means of which the motor is
started. The reservoir having been filled and the decompression cam
thrown into gear, starting is accomplished:
1. By placing the piston in starting position, which corresponds with a
crank inclination of 10 to 20 degrees in the direction of the piston's
movement, from the rear dead center, immediately after the period of
compression;
2. By opening the reservoir-valve;
3. By allowing the compressed air to enter the cylinder rapidly, through
the quick manipulation of the stop-cock, which is closed again when the
impulse is given and reopened at the corresponding period of the
following cycle, this operation being repeated several times in order to
impart sufficient speed to the motor;
4. By opening the gas-valve and finally closing the two valves of the
compressed-air pipe.
The pipes and compressed-air reservoirs should be perfectly tight. The
reservoirs should have a capacity in inverse ratio to the pressure under
which they are placed, _i.e._, they increase in size as the pressure
decreases. If, for example, the reservoirs should be operated normally
at a pressure of 105 to 120 pounds per square inch, their capacity
should be at least five or six times the volume of the engine-cylinder.
If these reservoirs are charged by the engine itself, the pressure will
always be less by 15 to 20 per cent. than that of the compression.
CHAPTER III
THE INSTALLATION OF AN ENGINE
In the preceding chapter the various structural details of an engine
have been summarized and those arrangements indicated which, from a
general standpoint, seem most commendable. No particular system has been
described in order that this manual might be kept within proper limits.
Moreover, the best-known writers, such as Hutton, Hiscox, Parsell and
Weed, in America; Aime Witz, in France; Dugald Clerk, Frederick Grover,
and the late Bryan Donkin, in England; Gueldner, Schottler, Thering, in
Germany, have published very full descriptive works on the various types
of engines.
We shall now consider the various methods which seem preferable in
installing an engine. The directions to be given, the author believes,
have not been hitherto published in any work, and are here formulated,
after an experience of fifteen years, acquired in testing over 400
engines of all kinds, and in studying the methods of the leading
gas-engine-building firms in the chief industrial centers of Europe and
America.
=Location.=--The engine should be preferably located in a well-lighted
place, accessible for inspection and maintenance, and should be kept
entirely free from dust. As a general rule, the engine space should be
enclosed. An engine should not be located in a cellar, on a damp floor,
or in badly illuminated and ventilated places.
=Gas-Pipes.=--The pipes by which fuel is conducted to engines, driven by
street-gas, and the gas-bags, etc., are rarely altogether free from
leakage. For this reason, the engine-room should be as well ventilated
as possible in the interest of safety. Long lines of pipe between the
meter and the engine should be avoided, for the sake of economy, since
the chances for leakage increase with the length of the pipe. It seldom
happens that the leakage of a pipe 30 to 50 feet long, supplying a 30
horse-power engine, is much less than 90 cubic feet per hour. The
beneficial effect of short supply pipes between meter and engine on the
running of the engine is another point to be kept in mind.
An engine should be supplied with gas as cool as possible, which
condition is seldom realized if long pipe lines be employed, extending
through workshops, the temperature of which is usually higher than that
of underground piping. On the other hand, pipes should not be exposed to
the freezing temperature of winter, since the frost formed within the
pipe, and particularly the crystalline deposition of naphthaline,
reduces the cross section and sometimes clogs the passage. Often it
happens that water condenses in the pipes; consequently, the piping
should be disposed so as to obviate inclines, in which the water can
collect in pockets. An accumulation of water is usually manifested by
fluctuations in the flame of the burner. In places where water can
collect, a drain-cock should be inserted. In places exposed to frost, a
cock or a plug should be provided, so that a liquid can be introduced to
dissolve the naphthaline. To insure the perfect operation of the engine,
as well as to avoid fluctuations in nearby lights, pipes having a large
diameter should preferably be employed. The cross-section should not be
less than that of the discharge-pipe of the meter, selected in
accordance with the prescriptions of the following table:
GAS-METERS.
Table Headings--
Column A: Capacity.
Column B: Normal hourly flow.
Column C: Height.
Column D: Width.
Column E: Depth.
Column F: Diameter of pipe.
Column G: Power of engine to be fed.
_________________________________________________________________
| | |
| | Dimension in inches. |
| |_______________________________________|
| | | | | |
A. | B. | C. | D. | E. | F. | G.
________|_________|_________|__________|__________|_______|______
| | | | | |
burners | cu. ft. | | | | | h.-p.
3 | 14.726 | 13 | 11 | 9-13/16 | 0.590 | 1/2
5 | 24.710 | 18 | 13-3/4 | 10-5/8 | 0.787 | 3/4
10 | 49.420 | 21-1/4 | 18-1/2 | 12-9/16 | 0.984 | 1-2
20 | 98.840 | 23-3/16 | 19-11/16 | 15-5/16 | 1.181 | 3-4
30 | 148.260 | 25-5/8 | 21-11/16 | 18-3/16 | 1.456 | 5-6
50 | 247.100 | 29-1/2 | 24-5/16 | 20-7/16 | 1.592 | 7-10
60 | 296.520 | 30-5/16 | 25-5/8 | 25-5/8 | 1.671 | 11-14
80 | 395.360 | 33-5/16 | 30-5/16 | 27-1/8 | 1.968 | 15-19
100 | 494.200 | 35 | 33-7/16 | 29-15/16 | 1.968 | 20-25
150 | 741.300 | 40-3/16 | 40-3/16 | 33-13/16 | | 30-40
________|_________|_________|__________|__________|_______|______
The records made are exact only when the meters (Fig. 40) are installed
and operated under normal conditions. Two chief causes tend to falsify
the measurements in wet meters: (1) evaporation of the water, (2) the
failure to have the meter level.
Evaporation occurs incessantly, owing to the flowing of the gas through
the apparatus, and increases with a rise in the temperature of the
atmosphere surrounding the meter. Consequently this temperature must be
kept down, for which reason the meter should be placed as near the
ground as possible. The evaporation also increases with the volume of
gas delivered. Hence the meter should not supply more than the volume
for which it was intended. In order to facilitate the return of the
water of condensation to the meter and to prevent its accumulation, the
pipes should be inclined as far as possible toward the meter. The
lowering of the water-level in the meter benefits the consumer at the
expense of the gas company.
[Illustration: FIG. 40.--Wet gas-meter.]
Inclination from the horizontal has an effect that varies with the
direction of inclination. If the meter be inclined forward, or from left
to right, the water can flow out by the lateral opening at the level,
and incorrect measurements are made to the consumer's cost.
During winter, the meter should be protected from cold. The simplest way
to accomplish this, is to wrap substances around the meter which are
poor conductors of heat, such as straw, hay, rags, cotton, and the like.
Freezing of the water can also be prevented by the addition of alcohol
in the proportion of 2 pints per burner. The water is thus enabled to
withstand a temperature of about 5 degrees F. below zero. Instead of
alcohol, glycerine in the same proportions can be employed, care being
taken that the glycerine is neutral, in order that the meter may not be
attacked by the acids which the liquid sometimes contains.
[Illustration: FIG. 41.--Dry gas-meter.]
=Dry Meters.=--Dry meters are employed chiefly in cold climates, where
wet meters could be protected only with difficulty and where the water
is likely to freeze. In the United States the dry meter is the type most
widely employed. In Sweden and in Holland it is also generally
introduced (Fig. 41).
In the matter of accuracy of measurement there is little, if any,
difference between wet and dry meters. The dry meter has the merit of
measuring correctly regardless of the fluctuations in the water level.
On the other hand, it is open to the objection of absorbing somewhat
more pressure than the wet meter, after having been in operation for a
certain length of time. This is an objection of no great weight; for
there is always enough pressure in the mains and pipes to operate a
meter.
[Illustration: FIG. 42.--Section through a dry gas-meter.]
In many cases, where the employment of non-freezing liquids is
necessary, the dry meter may be used to advantage, since all such
liquids have more or less corroding effect on sheet lead and even tin,
depending upon the composition of the gas.
[Illustration: FIG. 43.--Section through a dry gas-meter.]
The dry meter comprises two bellows, operating in a casing divided into
two compartments by a central partition. The gas is distributed on one
or the other side of the bellows, by slides _B_. The slides _B_ are
provided with cranks _E_, controlled by levers _M_, actuated by
transmission shafts _O_, driven by the bellows. The meter is adjusted by
a screw which changes the throw of the cranks _E_ and consequently
affects the bellows. The movement of the crank-shaft _D_ is transmitted
to the indicating apparatus. In order to obviate any leakage, this shaft
passes through a stuffing-box, _G_. The diagrams (Figs. 42-43) show the
construction of a dry meter, the arrows indicating the course taken by
the gas.
[Illustration: FIG. 44.--Rubber bag to prevent fluctuations of the
ignition flame.]
[Illustration: FIG. 45.--Rubber bags on gas-pipes.]
Care should be taken to provide the gas-pipe with a drain-cock, at a
point near the engine. By means of this cock, any air in the pipe can be
allowed to escape before starting; otherwise the engine can be set in
motion only with difficulty. If the engine be provided with an
incandescent tube, the gas-supply pipe of the igniter should be fitted
with a small rubber pouch or bag, in order to obviate fluctuations in
the burner flame, caused by variations in the pressure (Fig. 44). As a
general rule, the supply-pipe should be connected with the main pipe on
the forward side of the bags and gas-governors. The main pipe and all
other piping near the engine should extend underground, so that free
access to the motor from all sides can be obtained, without possibility
of injury.
=Anti-pulsators, Bags, Pressure-Regulators.=--The most commonly employed
means of preventing fluctuation of nearby lights, due to the sharp
strokes of the engine, consists in providing the gas-supply pipe with
rubber bags (Fig. 45), which form reservoirs for the gas and, by reason
of their elasticity, counteract the effect produced by the suction of
the engine. Nevertheless, in order to insure a supply of gas at a
constant pressure, which is necessary for the perfect operation of the
engine, there are generally used, in addition to the bags, devices
called gas-governors, or anti-pulsators (Fig. 46).
Although these devices are constructed in different ways, the underlying
principle is the same in all. They comprise a metallic casing,
containing a flexible diaphragm of rubber or of some fabric impermeable
to gas. Suction of the engine creates a vacuum in the casing. The
diaphragm bends, thereby actuating a valve, which cuts off the gas
supply. During the three following periods (compression, explosion, and
exhaust) the gas, by reason of its pressure on the diaphragm, opens the
valve and fills the casing, ready for the next suction stroke.
[Illustration: FIG. 46.--An anti-pulsator.]
Other devices, which are never sold with the engine, but are rendered
necessary by reason of the conditions imposed by the gas supply are sold
under the name "pressure-regulators" (Fig. 47). They consist of a bell,
floating in a reservoir containing water and glycerine (or mercury), and
likewise actuate a valve which partially controls the flow of gas. This
valve being balanced, its mechanical action is the more certain. Such
devices are very effective in maintaining the steadiness of lights. On
the other hand, they are often an obstacle to the operation of the
engine because they reduce the flow and pressure of the gas too much. In
order to obviate this difficulty, a pressure-regulator should be chosen
with discrimination, and of sufficiently large size to insure the
maintenance of an adequate supply of gas to the engine. Frequent
examinations should be made to ascertain if the bell of the regulator is
immersed in the liquid. In the case of anti-pulsators, care should be
taken that they are not spattered with oil, which has a disastrous
effect on rubber. Anti-pulsators are generally mounted about 4 inches
from a wall, in order that the diaphragm may be actuated by hand, if
need be.
[Illustration: FIG. 47.--A pressure-regulator.]
=Precautions.=--In order not to strain the rubber of the bags or of the
anti-pulsators, it is advisable to place a stop-cock in advance of these
devices so that they can not be filled while the motor is at rest.
The capacity of the rubber bags that can be bought in the market being
limited, it is necessary to place one, two, or three extra bags in
series (Figs. 48 and 49), for large pipes; but it should be borne in
mind that the total section of the branch pipes should be at least equal
to that of the main pipe. It is also advisable to extend the tube
completely through the bag as shown in Figs. 48 and 49.
[Illustration: FIGS. 48-49.--Arrangement of rubber bags.]
If there be two branch pipes the minimum diameter which meets this
requirement is ascertained as follows: Draw to any scale a semicircle
having a diameter equal or proportional to that of the main pipe (Fig.
50). The sides of the isosceles triangle inscribed within this
semicircle give the minimum diameter of each of the branch pipes.
Sometimes engines are provided with a cock having an arrangement by
means of which the gas feed is permanently regulated, according to the
quality and pressure of the gas and according to the load at which the
engine is to run. This renders it possible to open the cock always to
the same point (Fig. 51).
[Illustration: FIG. 50.]
[Illustration: FIG. 51.]
=Air Suction.=--In a special chapter the precautions to be taken to
counteract the influence of the suction of the engine in causing
vibration will be treated. The manner in which the suction of air is
effected necessarily has as marked an influence on the operation of the
engine as the supply of gas, since air and gas constitute the explosive
mixture.
Resistance to the suction of air should be carefully avoided, for which
reason the length of the pipe should be reduced to a minimum, and its
cross-section kept at least equal to that of the air inlet of the
engine. Since the quality of street-gas varies with each city, the
proper proportions of gas and air are not constant. In order that these
proportions may be regulated, it is a matter of some importance to fit
some suitable device on the pipe. Good engines are provided with a plug
or flap valve. Generally the air-pipe terminates either in the hollowed
portion of the frame, or in an independent pot, or air chest. The first
arrangement is not to be recommended for engines over 20 to 25
horse-power. Accidents may result, such as the breaking of the frame by
reason of back firing, of which more will be said later. If an
independent chest be employed, its closeness to the ground renders it
possible for dust easily to pass through the air-holes in the walls at
the moment of suction, and even to enter the cylinder, where its
presence is particularly harmful, leading, as it does, to the rapid wear
of the rubbing surfaces. This evil can be largely remedied by filling
the air-chest with cocoa fiber or even wood fiber, provided the latter
does not become packed down so as to prevent the air from passing
freely. Such fibers act as air-filters. Regular cleaning or renewal of
the fiber protects the cylinder from wear. In a general way, care should
be taken, before fitting both the gas and air pipes, to tap the pipes,
elbows, and joints lightly with a hammer on the outside in order to
loosen whatever rust or sand may cling to the interior; otherwise this
foreign matter may enter the cylinder and cause perturbations in the
operation of the engine. Under all circumstances, care should be taken
not to place the end of the air-pipe under the floor or in an enclosed
space, because leakage may occur, due to the bad seating of the
air-valve, thereby producing a mixture which may explode if the flame
leaps back, as we shall see in the discussion of suction by pipes
terminating in the hollow of the frame. On the other hand, sand or
sawdust should not be sprinkled on the floor.
=Exhaust.=--For the exhaust, cast-iron or drawn pipes as short as
possible should be used. Not only the power of the engine, but also its
economic consumption, can be markedly affected by the employment of long
and bent pipes. Resistance to the exhaust of the products of combustion
not only causes an injurious counter-pressure, but also prevents the
clearing of the cylinder of burnt gases, which contaminate the aspired
mixture and rob it of much of its explosiveness. The necessity of
evacuating the cylinder as completely as possible is, nevertheless, not
always reconcilable with local surroundings. To a certain extent, the
objections to long exhaust-pipes are overcome by rigorously avoiding the
use of elbows. Gradual curves are preferable. In the case of very long
pipes it is advisable to increase their diameter every 16 feet from the
exhaust. The exhaust-chest should be placed as near as possible to the
engine; it should never be buried; for the joints of the inlet and
outlet pipes of the exhaust-chest should be easily accessible, so that
they may be renewed when necessary. The author recommends the placing
of the exhaust-chest in a masonry pit, which can be closed with a
sheet-metal cover. For engines of 20 horse-power and upward, these
joints should be entirely of asbestos. Pipes screwed directly into the
casting are liable to rust. Exposed as they are to the steam or water of
the exhaust, they cannot be detached.
[Illustration: FIG. 52.--Method of mounting pipes.]
The water, which results from the combination of the hydrogen of the gas
with the oxygen of the air, is deposited in most cases at the bottom of
the exhaust-chest. It is advisable to fit a plug or iron cock in the
base of the chest. Alkaline or acid water will always corrode a bronze
cock. In order that the pipes may not also be attacked, they are not
disposed horizontally, but are given a slight incline toward the point
where the water is drained off. If pipes of some length be employed,
they should be able to expand freely without straining the joints, as
shown in the accompanying diagram (Fig. 52), in which the exhaust-chest
rests on iron rollers which permit a slight displacement.
For the sake of safety, at least that portion of the piping which is
near the engine should be located at a proper distance from woodwork and
other combustible material. By no means should the exhaust discharge
into a sewer or chimney, even though the sewer or chimney be not in use;
for the unburnt gases may be trapped, and dangerous explosions may ensue
at the moment of discharge.
The joints or threaded sleeves employed in assembling the exhaust-pipe
should be tested for tightness. The combined action of the moisture and
heat causes the metal to rust and to deteriorate very rapidly at leaky
spots.
When several engines are installed near one another, each should be
provided with a special exhaust-pipe; otherwise it may happen, when the
engines are all running at once, that the products of combustion
discharged by the one may cause a back pressure detrimental to the
exhaust of the next.
It is possible to employ a pipe common to all the exhausts if the pipe
starts from a point beyond the exhaust-chests, in which case Y-joints
and not T-joints are to be used.
The manner of securing the pipes to walls by means of detachable
hangers, lined with asbestos, is shown in a general way in the
accompanying Fig. 53. The object of this arrangement is to render
detachment easy and to prevent the transmission of shocks to the
masonry.
The precautions to be taken for muffling the noise of the exhaust will
be discussed later.
The end of the exhaust-pipe should be slightly curved down in order to
prevent the entrance of rain. Exhaust-pipes are subjected to
considerable vibration, due to the sudden discharge of the gases. To
protect the joints, the pipes should be rigidly fastened in place.
[Illustration: FIG. 53.--Method of securing pipes to walls.]
=Legal Authorization.=--In most countries gas-engines may be installed
only in accordance with the provision of general or local laws, which
impose certain conditions. These laws vary with different localities,
for which reason they are not discussed here.
CHAPTER IV
FOUNDATION AND EXHAUST
The reader will remember from what has already been said that a
gas-engine is a motor which, more than any other, is subjected to
forces, suddenly and repeatedly exerted, producing violent reactions on
the foundation. It follows that the foundation must be made particularly
resistant by properly determining its shape and size and by carefully
selecting the material of which it is to be built.
=The Foundation Materials.=--Well-hardened brick should be used. The top
course of bricks should be laid on edge. It is advisable to increase the
stability of the foundation by longitudinally elongating it toward the
base, as shown in the accompanying diagram (Fig. 54).
As a binding material, only mortar composed of coarse sand or river sand
and of good cement, should be used. Instead of coarse sand, crushed
slag, well-screened, may be employed. The mortar should consist of 2/3
slag and 1/3 cement. Oil should not in any way come into contact with
the mortar; it may percolate through the cement and alter its resistant
qualities.
As in the construction of all foundations, care should be taken to
excavate down to good soil and to line the bottom with concrete, in
order to form a single mass of artificial stone. A day or two should be
allowed for the masonry to dry out, before filling in around it.
When the engine is installed on the ground floor above a vaulted cellar,
the foundation should not rest directly on the vault below or on the
joists, but should be built upon the very floor of the cellar, so that
it passes through the planking of the ground floor without contact.
[Illustration: FIG. 54.--Method of building the foundation.]
When the engine is to be installed on a staging, the method of securing
it in place illustrated in Fig. 55 should be adopted.
Although a foundation, built in the manner described, will fulfill the
usual conditions of an industrial installation, it will be inadequate
for special cases in which trepidation is to be expected. Such is the
case when engines are to be installed in places where, owing to the
absence of factories, it is necessary to avoid all nuisance, such as
noise, trepidations, odors, and the like.
[Illustration: FIG. 55.--Elevated foundation.]
=Vibration.=--In order to prevent the transmission of vibration, the
foundation should be carefully insulated from all neighboring walls. For
this purpose various insulating substances called "anti-vibratory" are
to be recommended. Among these may be mentioned horsehair, felt packing,
cork, and the like. The efficacy of these substances depends much on the
manner in which they are applied. It is always advisable to interpose a
layer of one of these substances, from one to four inches thick, between
the foundation and the surrounding soil, the thickness varying with the
nature of the material used and the effect to be obtained. Between the
bed of concrete, mentioned previously, and the foundation-masonry and
between the foundation and the engine-frame, a layer of insulating
material may well be placed. Preference is to be given to substances not
likely to rot or at least not likely to lose their insulating property,
when acted upon by heat, moisture or pressure.
Here it may not be amiss to warn against the utilization of cork for the
bottom of the foundation; for water may cause the cork to swell and to
dislocate the foundation or destroy its level.
The employment of the various substances mentioned does not entail any
great expense when the foundations are not large and the engines are
light. But the cost becomes considerable when insulating material is to
be employed for the foundation of a 30 to 50 horse-power engine and
upwards. For an engine of such size the author recommends an arrangement
as simple as it is efficient, which consists in placing the foundation
of the engine in a veritable masonry basin, the bottom of which is a bed
of concrete of suitable thickness. The foundation is so placed that the
lateral surfaces are absolutely independent of the supporting-walls of
the basin thus formed. Care should be taken to cover the bottom with a
layer of dry sand, rammed down well, varying in thickness with each
case. This layer of sand constitutes the anti-vibratory material and
confines the trepidations of the engine to the foundation.
As a result of this arrangement, it should be observed that, being
unsupported laterally, the foundation should be all the more resistant,
for which reason the base-area and weight should be increased by 30 to
40 per cent. The expense entailed will be largely offset by saving the
cost of special anti-vibratory substances. In places liable to be
flooded by water, the basin should be cemented or asphalted.
When the engine is of some size and is intended for the driving of one
or more dynamos which may themselves give rise to vibrations, the
dynamos are secured directly to the foundation of the engine, which is
extended for that purpose, so that both machines are carried solidly on
a single base.
The foregoing outline should not lead the proprietor of a plant to
dispense with the services of experts, whose long experience has brought
home to them the difficulties to be overcome in special cases.
It should here be stated, as a general rule, that the bricks should be
thoroughly moistened before they are laid in order that they may grip
the mortar.
After having been placed on the foundation and roughly trimmed with
respect to the transmission devices, the engine is carefully leveled by
means of hardwood wedges driven under the base. This done, the bolts are
sealed by very gradually pouring a cement wash into the holes, and
allowing it to set. When the holes are completely filled and the bolts
securely fastened in place, a shallow rim, or edge of clay, or sand is
run around the cast base, so as to form a small box or trough, in which
cement is also poured for the purpose of firmly binding the engine frame
and foundation together. When, as in the case of electric-light engines,
single extra-heavy fly-wheels are employed, provided with bearings held
in independent cast supports, the following rule should be observed to
prevent the overheating due to unlevelness, which usually occurs at the
bushings of these bearings: That part of the foundation which is to
receive such a support should rest directly on the concrete bed and
should be rigidly connected at the bottom with the main foundation. When
the foundation is completely blocked up, the fly-wheel bearing with its
support is hung to the crank-shaft; and not until this is effected is
the masonry at the base of the support completed and rigidly fixed in
its proper position.
For very large engines, the foundation-bolts should be particularly well
sealed into the foundation. In order to attain this end the bricks are
laid around the bolt-holes, alternately projected and retracted as shown
in Fig. 54. Broken stone is then rammed down around the fixed bolt; in
the interstices cement wash is poured.
=Air Vibration, etc.=--Vibration due chiefly to the transmission of
noises and the displacement of air by the piston should not be confused
with the trepidations previously mentioned.
The noise of an engine is caused by two distinct phenomena. The one is
due to the transmitting properties of the entire solid mass constituting
the frame, the foundation, and the soil. The other is due to vibrations
transmitted to the air. In both cases, in order to reduce the noise to a
minimum, the moving parts should be kept nicely adjusted, and above all,
shocks avoided, the more harmful of which are caused by the play between
the joint at the foot of the connecting-rod and the piston-pin, and
between the head of the connecting-rod and the crank-shaft.
Although smooth running of the engine may be assured, there is always an
inherent drawback in the rapid reciprocating movement of the piston. In
large, single-acting gas-engines, a considerable displacement of air is
thus produced. In the case of a forty horse-power engine having a
cylinder diameter and piston-stroke respectively of 13-3/4 inches and
21-3/5 inches, it is evident that at each stroke the piston will
displace about 2 cubic feet of air, the effect of which will be doubled
when it is considered that on the forward stroke back pressure is
created and on the return stroke suction is produced.
The air motion caused by the engine is the more readily felt as the
engine-room is smaller. If the room, for example, be 9 feet by 15 feet
by 8 feet, the volume will be 1,080 cubic feet. From this it follows
that the 2 cubic feet of air in the case supposed will be alternately
displaced six times each second, which means the displacement of 12
cubic feet at short intervals with an average speed of 550 feet per
minute. Such vibrations transmitted to halls or neighboring rooms are
due entirely to the displacement of the air.
In installations where the air-intake of the engine is located in the
engine-room, a certain compensation is secured, at the period of
suction, between the quantity of air expelled on the forward stroke of
the piston and the quantity of air drawn into the cylinder. From this it
follows that the vibration caused by the movement of the air is felt
less and occurs but once for two revolutions of the engine.
This phenomenon is very manifest in narrow rooms in which the engine
happens to be installed near glass windows. By reason of the elasticity
of the glass, the windows acquire a vibratory movement corresponding in
period with half the number of revolutions of the engine. It follows
from the preceding that, in order to do away with the air vibration
occasioned by the piston in drawing in and forcing out air in an
enclosed space, openings should be provided for the entrance of large
quantities of air, or a sufficient supply of air should be forced in by
means of a fan.
The author ends this section with the advice that all pipes in general
and the exhaust-pipe in particular be insulated from the foundation and
from the walls through which they pass as well as from the ground, as
metal pipes are good conductors of sound and liable to carry to some
distance from the engine the sounds of the moving parts.
=Exhaust Noises.=--Among the most difficult noises to muffle is that of
the exhaust. Indeed, it is the exhaust above all that betrays the
gas-engine by its discharge to the exterior through the exhaust-pipe.
The most commonly employed means for rendering the exhaust less
perceptible consists in extending the pipe upward as far as possible,
even to the height of the roof. This is an easy way out of the
difficulty; but it has a bad effect on the operation of the engine. It
reduces the power generated and increases the consumption, as will be
explained in a special paragraph.
Expansion-boxes, more commonly called exhaust-mufflers, considerably
deaden the noise of explosion by the use of two or three successive
receptacles. But this remedy is attended with the same faults that mark
the use of extremely long pipes. The best plan is to mount a single
exhaust-muffler near the discharge of the engine in the engine-room
itself, where it will serve at least the purpose of localizing the
sound.
[Illustration: FIG. 56.--Exhaust-muffler.]
The employment of pipes of sufficiently large cross-section to
constitute expansion-boxes in themselves will also muffle the exhaust. A
more complete solution of the problem is obtained by causing the
exhaust-pipe, after leaving the muffler, to discharge into a masonry
trough having a volume equal to twelve times that of the engine-cylinder
(Fig. 56). This trough should be divided into two parts, separated by a
horizontal iron grating. Into the lower part, which is empty, the
exhaust-pipe discharges; in the upper part, paving-blocks or hard stones
not likely to crumble with the heat, are placed. Between this layer of
stones and the cover it is advisable to leave a space equal to the
first. Here the gases may expand after having been divided into many
parts in passing through the spaces left between adjacent stones. The
trough should not be closed by a rigid cover; for, although efficient
muffling may be attained, certain disadvantages are nevertheless
encountered. It may happen that in a badly regulated engine, unburnt
gases may be discharged into this trough, forming an explosive mixture
which will be ignited by the next explosion, causing considerable
damage. Still, the explosion will be less dangerous than noisy. It may
be mentioned in passing that this disadvantage occurs rarely.
A second arrangement consists in superposing the end of the exhaust-pipe
upon a casing of suitable size, which casing is partitioned off by
several perforated baffle-plates. This casing is preferably made of
wood, lined with metal, so that it will not be resonant. The size of the
casing, the number of partitions and their perforations, and the manner
of disposing the partitions have much to do with the result to be
obtained. Here again the experience of the expert is of use.
Various other systems are employed, depending upon the particular
circumstances of each case. Among these systems may be mentioned those
in which the pipe is forked at its end to form either a yoke (Fig. 57)
or a double curve, each branch of which terminates in a muffler (Fig.
58).
[Illustration: FIG. 57.]
[Illustration: FIG. 58.--Two types of exhaust-mufflers.]
It should be observed that, under ordinary conditions, noises heard as
hissing sounds are often due to the presence of projections, or to
distortion of the pipes near the discharge opening. Consequently, in
connecting the pipes, care should be taken that the joints or seams have
no interior projections. Occasionally, water may be injected into the
exhaust-muffler in order to condense the vapors of the exhaust, the
result being a deadening of the noises; but in order to be truly
efficient this method should be employed with discretion, for which
reason the advice of an expert is of value.
CHAPTER V
WATER CIRCULATION
Circulation of water in explosion-engines is one of the essentials of
their perfect operation. Two special cases are encountered. In the one
the jacket of the engine is supplied with running water; in the other,
reservoirs are employed, the circulation being effected simply by the
difference in specific gravity in a thermo-siphon apparatus. Coolers are
also used.
=Running Water.=--A water-jacket fed from a constant source of running
water, such as the water mains of a town, is certainly productive of the
best results, the supply, moreover, being easily regulated; but the
system is not widely used because the water runs away and is entirely
lost. If running water be employed, the outlet of the jacket is so
disposed that the water gushes out immediately on leaving the cylinder,
and that the flow is visible and accessible, in order that the
temperature may be tested by the hand. Apart from the relatively great
cost of water in towns, the use of running water is objectionable on
account of its chemical composition. Though it may be clear and limpid,
it frequently contains lime salts, carbonates, sulphates, and silicates
which are precipitated by reason of the sudden change of temperature to
which the water is subjected as it comes into contact with the walls of
the cylinder. That part of the water-jacket surrounding the head or
explosion-chamber, where the temperature is necessarily the highest,
becomes literally covered with calcareous incrustations, which are the
more harmful because they are bad conductors of heat and because they
reduce and even obstruct the passage exactly at the point where the
water must circulate most freely to do any good. If the circulating
water be pumped into the jacket, it is preferable, wherever possible, to
use cistern water, which is not likely to contain lime salts in
suspension. If river water be used, it should be free from the
objections already mentioned, which are all the more grave if the water
be muddy, as sometimes happens. The water-jacket can be easily freed
from all non-adhering deposits by flushing it periodically through the
medium of a conveniently placed cock. It is always preferable to pass
the water through a reservoir where its impurities can settle, before it
flows to the cylinder. In the case considered, the water usually has an
average temperature of 54 to 60 degrees F., under which condition the
hourly flow should be at least 5-1/2 gallons per horse-power per hour,
the temperature rising at the outlet-pipe of the cylinder to 140 and 158
degrees F., which should not be surpassed. However, in engines working
with high compression, 104 to 122 degrees F. should not be exceeded.
If the water-jacket be fed by a reservoir, it is essential that the
reservoir comply with the following conditions:
In horizontal engines the water-inlet is always located in the base of
the cylinder, while the outlet is located at the top. By providing the
inlet-pipe extending to the cylinder with a cock, the circulation of
water can be regulated to correspond with the work performed by the
engine. Another cock at the end of the outlet-pipe near the reservoir
serves, in conjunction with the first, to arrest the circulating water.
When the weather is very cold or when the cylinder must be repaired,
these two cocks may be closed, and the pipe and water-jacket of the
cylinder drained by means of the drain-cock _V_ (Fig. 59), mounted at
the inlet of the engine's water-jacket. In order that the pressure of
the atmosphere may not prevent the flowing of the water, the highest
part of the pipe is provided with a small tube, _T_, communicating with
the atmosphere.
[Illustration: FIG. 59.--Thermo-siphon cooling system.]
On account of the importance of preventing losses of the charge in the
pipes the author recommends the utilization of sluice-valves of the type
shown in Fig. 60, instead of the usual cone or plug type.
[Illustration: FIG. 60.--Vanne sluice-cock.]
=Water-Tanks.=--The reservoir is mounted in such a way that its base is
flush with the top of the cylinder; it should be as near as possible to
the cylinder in order to obviate the use of long inlet and return pipes.
This fact, however, does not necessarily render it advisable to place
the reservoir in the engine-room; for such a disposition is doubly
disadvantageous in so far as it does not permit a sufficiently rapid
cooling of the circulating water by reason of the high temperature of
the surrounding air, and in so far as it is liable to cause the
formation of vapors which injuriously affect the engine. Consequently,
the reservoir should be placed in as cool a place as possible,
preferably even in the open air; for the water is not likely to freeze,
except when it has been allowed to stand for a considerable time. The
reservoir should be left uncovered so as to facilitate cooling by the
liberation of the vapors formed on the surface of the water.
Circulation being effected solely by the difference in specific gravity
or density between the warmer water emerging from the cylinder and the
cooler water which flows in from the reservoir, the slightest
obstruction will impede the flow. Hence, the cross-section of the pipes
should not be less than that of the inlet and outlet openings of the
cylinder of the engine. Good circulation cannot be attained if the water
must overcome inclines or obstacles in the pipes themselves. Instead of
elbows, long curves of great radius, limited to the smallest possible
number, should be employed. This is particularly true of the return-pipe
extending from the cylinder back to the reservoir. For this pipe a
minimum incline of 10 to 15 per cent. should be allowed, in order that
the water may run up into the reservoir. The height of the water in the
reservoir should be from 2 to 4 inches above the discharge of the
return-pipe. In order to maintain this level it is advisable to use some
automatic device such as a float-valve, in which case the reservoir
should not be allowed to become too full.
[Illustration: FIG. 61.--Correct arrangement of tanks and piping.]
The size of a reservoir is determined by the engine; it should be large
enough to enable the engine to run smoothly at its maximum load for
several hours consecutively. Under these conditions, the reservoir
should have a capacity of 45 to 55 gallons per horse-power for engines
with "hit-and-miss" admission, and 55 to 65 gallons for engines
controlled by variable admission. It is not advisable to employ
reservoirs having a capacity of more than 330 to 440 gallons, the usual
diameter being about 3 feet.
[Illustration: FIG. 62.--Incorrect arrangement of tanks and piping.]
If the power of the engine be such that several reservoirs are
necessary, then the reservoirs should be connected in such a manner that
the top of the first communicates with the bottom of the next and so
on, the first reservoir receiving the water as it comes from the
cylinder (Fig. 61).
Intercommunication of the reservoirs by means of a common top tube (_a_)
is objectionable; and simultaneous intercommunication at top and bottom
(_a_ and _b_) is ineffective, so far as one of the reservoirs is
concerned (Fig. 62).
[Illustration: FIG. 63.--Tanks connected by inclined pipes.]
The reservoirs are true thermo-siphons. Consequently the water should be
methodically circulated; in other words, the hottest water, flowing from
the engine into the top of the first reservoir and having, for example,
a temperature of 104 degrees F., is cooled off to 86 degrees F. and
drops to the bottom of the reservoir, thence to be driven, at a
temperature sensibly equal to 86 degrees F., to the second reservoir,
where a further cooling of 18 degrees F. takes place. In passing on to
the following reservoirs the temperature is still further lowered, until
the water finally reaches its minimum temperature, after which it flows
back to the engine-cylinder.
[Illustration: FIG. 64.--Circulating pump with by-pass.]
In order to effect this cooling, the reservoirs can be connected in
several ways. The most common method, as shown in Fig. 63, consists in
connecting the reservoirs by oblique pipes. This is open to criticism,
however, since leakage occurs, caused by the employment of elbows which
retard the circulation. A less cumbrous and more efficient method of
connection consists in joining the reservoirs by a single pipe at the
top, as shown in Fig. 61; but care must be taken to extend this pipe at
the point of its entrance into the adjoining reservoir by means of a
downwardly projecting extension, or to fit its discharge-end with a box,
closed by a single partition, open at the bottom.
In order to prevent incrustation of the water-jacket surrounding the
cylinder, a pound of soda per 17 cubic feet of the reservoir capacity is
monthly introduced, and the jacket flushed weekly by a cock conveniently
mounted near the cylinder (Fig. 59). The jacket is thus purged of
calcareous sediments, which are prevented by the soda from adhering to
the metal. The flushing-cock mentioned also serves to drain the
water-jacket of the cylinder in case of intense or persistent cold,
which would certainly freeze the water in the jacket, thereby cracking
the cylinder or the exposed pipes.
In order to regulate the circulation of the water in accordance with the
work performed by the engine, a cock should be fitted to the water
supply pipe at a convenient place.
In engines of large size, driven at full load for long periods, cooling
by natural circulation is often inadequate. In such cases, circulation
is quickened by a small rotary or reciprocating pump, driven from the
engine itself and fitted with a by-pass provided with a cock. This
arrangement permits the renewal of the natural thermo-siphon circulation
in case of accident to the pump (Fig. 64).
[Illustration: FIG. 65.--Water-cooler in which tree branches are
employed.]
=Coolers.=--The arrangement which is illustrated in Fig. 65, and which
has the merit of simplicity, will be found of service in cooling the
water. It comprises a tank _B_ surmounted by a set of trays _E_, formed
of frames to which iron rods are secured, spaced 1 to 2 feet apart, so
as to form superimposed series separated by 1-1/2 to 2-1/3 feet. On
these trays bundles of tree branches are placed. The cold water at the
bottom of the tank is forced by the pump _P_i into the water-jacket,
from which it emerges hot, and flows through the pipe _T_, which ends in
a sprinkler _G_, formed of communicating tubes and perforated with a
sufficient number of holes to enable the water to fall upon the trays in
many drops. Thus finely divided, the water falls from one tray to
another, retarded as it descends by the bundles of tree branches. It
finally reaches the tank in a very cold condition and is then ready to
be pumped to the engine. Birch branches are to be preferred on account
of their tenuity.
Great care should be taken to cover the tank with a sheet-metal closure
in order to prevent twigs and foreign bodies from entering and from
being drawn into the pump.
[Illustration: FIG. 66.--Fan-cooler.]
In the following table the dimensions of an operative apparatus of this
kind are given,--an apparatus, moreover, that may be constructed of wood
or of iron:--
Table Headings--
Column A: Horse-power.
Column B: Volume in cubic ft.
Column C: Base.
Column D: Height.
Column E: Height of tray-base.
Column F: Pump--Capacity in gals. per min.
______________________________________________
| | | |
| | Tank. | |
| |____________________| |
| | | | |
A. | B. | C. | D. | E. | F.
_____|_____|_____________|______|______|______
| | | | |
30 | 105 | 4.9' x 4.9' | 4.4' | 6.6' | 16.71
40 | 154 | 5.2' x 5.2' | 5.6' | 7.4' | 18.69
50 | 190 | 5.7' x 5.7' | 6.4' | 8.1' | 21.99
75 | 350 | 6.6' x 6.6' | 8.1' | 9.1' | 35.18
100 | 490 | 7.4' x 7.4' | 9.1' | 9.1' | 43.98
_____|_____|_____________|______|______|______
In order that the water may not drop to one side, the base of the
apparatus should be made 10 to 12 inches less in width than the tank.
The size of these apparatus may be considerably reduced by constructing
them in the form of closed chests, into the bottom of which air maybe
injected by means of fans in order to accelerate cooling (Fig. 66).
CHAPTER VI
LUBRICATION
Lubrication is a subject that should be studied by every gas-engine
user. So far as the piston is concerned it is a matter of the utmost
importance. The piston does its work under very peculiar conditions. It
is driven at great linear velocities; and it is, moreover, subjected to
high temperatures which have nothing in common with good lubrication if
care be not exercised.
The piston is the essential, vital element of an engine. Upon its
freedom from leakage depends the maintenance of a proper compression,
and, consequently, the production of power and economical consumption.
As it travels forward and as it recedes from the explosion-chamber, it
uncovers more and more of the frictional surface constituting the
interior wall of the cylinder. This surface, as a result, is regularly
brought into contact with the ignited, expanding gases after each
explosion. For this reason the oil which covers the wall is constantly
subjected to high temperatures, by which it is likely to be volatilized
and burned. Therefore, the first condition to be fulfilled in properly
lubricating the piston is a constant and regular supply of oil.
=Quality of Oils.=--For cylinder lubrication only the very best oils
should be used; perfect lubrication is of such importance that cost
should not be considered. Besides, the surplus oil which is usually
caught in the drip-pan is by no means lost. After having been filtered
it can be used for lubricating the bearings of the crank, the cam-shaft,
and like parts.
Cylinder-oil should be exceedingly pure, free from acids, and composed
of hydrocarbons that leave no residue after combustion. Only mineral
oils, therefore, are suitable for the purpose. Those oils should be
selected which, with a maximum of viscosity, are capable of withstanding
great heat without volatilizing or burning. The point at which a good
cylinder-oil ignites should not be lower than 535 degrees F.
Whether an oil possesses this essential quality is easily enough
ascertained in practice without resorting to laboratory tests. All that
is necessary is to heat the oil in a metal vessel or a porcelain dish.
In order that the temperature may be uniform the vessel is shielded from
the direct flame by interposing a piece of sheet metal or a layer of dry
sand. As soon as gases begin to arise a lighted match is held over the
oil. When the gases are ignited the thermometer reading is taken, the
instrument being immersed in the oil. The temperature recorded is that
corresponding with the point of ignition.
For cylinder lubrication American mineral oil is preferable to Russian
oil. The specific gravity should lie somewhere between .886 and .889 at
70 degrees F. Oil of this quality begins to evaporate at about 365
degrees F. Ignition occurs at 535 degrees F. The point of complete
combustibility lies between 625 and 645 degrees F. Oil of this quality
solidifies at 39 or 41 degrees F. Its color is a reddish yellow with a
greenish fluorescence. Compared with water its degree of viscosity lies
between 11.5 and 12.5 at a temperature of 140 degrees F.
Before lubricating other parts of the engine with oil that has been used
for the piston, heavy particles and foreign matter, such as dust,
bearing incrustations, and the like, should be filtered out. The
piston-pivot and the connecting-rod head are preferably lubricated with
fresh oil, because their constant movement renders inspection difficult
and the control of lubrication irksome. A good, industrial mineral oil
of usual market quality will be found satisfactory. In order to bring
home the importance of employing good cylinder-oil and of proper
lubrication the author can only state that in his personal experience he
has frequently detected losses varying from 10 to 15 per cent. in the
power developed by engines poorly lubricated.
=Types of Lubricators.=--Among the more common apparatus employed for
automatically lubricating the cylinder, the author mentions an English
oiler of the type pictured in Fig. 67 which is driven simply by a belt
from the intermediary shaft, and which rotates the pulley _P_ secured on
the shaft _a_ of the apparatus, at a very slow speed. The shaft _a_ is
provided at its end with a small crank, from which a small iron arm _f_
is suspended, which arm dips in the oil contained in the cup _G_ of the
oiler. When the shaft _a_ is turned this arm, as it sweeps through the
oil-bath, collects a certain quantity of oil which it deposits on the
collector _b_. From this spindle the oil passes through an outlet-pipe
opening into the bottom of the oiler, and thence to the cylinder. The
entire apparatus is closed by a cover _D_ which can be easily removed in
order to ascertain the quantity of oil still remaining in the apparatus.
Many other systems are utilized which, like the one that has been
described, enable the feed to be controlled. Often small force-pumps are
employed as cylinder-lubricators. Whatever may be the type selected,
preference should be given to that in which the feed is visible (Fig.
68).
[Illustration: FIG. 67.--An automatic English oiler.]
If the oil be fed under pressure the cylinder is more constantly
lubricated. Pressure-lubricators are nowadays widely used on large
engines. It is advisable to add a little salt to the water contained in
sight-feed lubricators so that the drop of oil is easily freed.
These oil-pumps are provided with small check-valves at their outlets as
well as at the inlets of cylinders. In order that pressure-lubricators
may operate perfectly they should be regularly inspected and the
check-valves ground from time to time.
The lubrication of the crank-shaft and of the two connecting-rod heads
should receive every attention.
[Illustration: FIG. 68.--Sight-feed lubricating-pump.]
[Illustration: FIG. 69.--Method of oiling the piston and end of the
connecting-rod.]
Lubricating devices should be employed which, besides being efficient,
do not necessitate the stopping of the engine in order to oil the
bearings. The foot of the connecting-rod at the point where it is
pivoted to the piston is generally lubricated with cylinder-oil which is
supplied by a tube mounted in the proper place across the piston-wall
(Fig. 69). This arrangement may be adequate enough for small engines;
but it is not sufficiently sure for engines of considerable size. An
independent lubricating system should be employed, lubrication being
effected either by a splasher mounted in front of the cylinder or by a
lubricator secured to the connecting-rod by which the pivot is
lubricated through the medium of a small tube supplying special oil
(Fig. 21). The head of the connecting-rod where it meets the crank, must
also be carefully lubricated because of the important nature of the work
which it must perform, and because of the shocks to which it is
subjected at each explosion. For motors of high power the system which
seems to give most satisfactory results is that illustrated in Fig. 70.
The arrangement there shown consists of an annular vessel secured at one
side of the crank and turning concentrically on its axis; the vessel
being connected with a long tube extending into a channel formed in the
crank and discharging at the surface of the crank-pin within the bearing
at the head of the connecting-rod. An adjustable sight-feed lubricator
conducts the oil along a pipe to the vessel. Turning with the shaft, the
vessel retains the oil in the periphery so that the feed in the
previously mentioned channel in the connecting-rod head, is constant.
[Illustration: FIG. 70.--Method of oiling the crank-shaft.]
The main crank-shaft bearings are more easily lubricated. Among the
systems commonly used with good results may be mentioned that shown in
Fig. 71, in which the half section represents a small tube starting from
the bearing and terminating in the interior of an oil recess or
reservoir cast integrally with the bearing-cap. This reservoir is filled
up to the level of the tube opening. A piece of cotton waste held on a
small iron wire is inserted in the tube, part of the cotton being
allowed to hang down in the reservoir. This cotton serves as a kind of
siphon and feeds the bearing by capillary attraction with a constant
quantity of oil, the supply being regulated by varying the thickness of
the cotton. When the motor is stopped, the cotton should be removed in
order that oil-feeding may not uselessly continue. Glass, sight-feed
lubricators with stop-cocks, are very often used on crank-shafts. They
are cleaner and much more easily regulated. Of all shaft-bearing
lubricators, those which are most to be recommended are of the
revolving-ring type (Fig. 72). They presuppose, however, bearings of
large size and a special arrangement of bushings which renders their
application somewhat expensive. Furthermore, the revolving-ring system
can hardly be used in connection with engines of less than 20
horse-power. Since the system is applied almost exclusively to
dynamo-shafts, it need not here be described in detail. As its name
indicates, it consists of a metal ring having a diameter larger than
that part of the shaft from which it is suspended and by which it is
rotated. The lower part of the ring is immersed in an oil bath so that
a certain quantity of lubricant is continually transferred to the shaft.
[Illustration: FIG. 71.--Cotton-waste lubricator.]
The revolving ring bearing should be fitted with a drain-cock and a
glass tube in order to control the level of the oil in the bearing.
Many manufacturers have adopted lubricating devices for valve-stems, and
especially for exhaust-valves. The system adopted consists of a small
tube curved in any convenient direction and discharging in the
stem-guide. The free end is provided with a plug. A few drops of
petroleum are introduced once or twice a day.
[Illustration: FIG. 72.--Ring type of bearing oiler.]
The lubrication of an engine entails certain difficulties which are
easily overcome. One of these is the splashing of oil by the
connecting-rod head. In order that this splashed oil may be collected in
the base of the engine a suitably curved sheet-metal guard is mounted
over the crank. A more serious difficulty is presented when the oil from
a crank-bearing finds its way to the hub of the fly-wheel, whence it is
driven by the centrifugal force to the rim. The oil is not only splashed
against the walls of the engine-room, but it also destroys the adhesion
of the belt if the fly-wheel be employed as a pulley. In order to
overcome this objection the oil is prevented from spreading along the
shaft by means of a circular guard (Fig. 73) mounted on that portion of
the shaft toward the interior of the bearing.
[Illustration: FIG. 73.--Shaft with oil-guard.]
The problem of lubrication is of particular importance if the engine is
driven for several days at a time without a stop. This happens in the
case of mill and shop engines. Lubricators of large volume or
lubricators which can be readily filled without stopping the engine
should be employed.
CHAPTER VII
THE CONDITIONS OF PERFECT OPERATION
=General Care.=--Gas-engines, as well as most machines in general,
should be kept in perfect condition. Cleanliness, even in the case of
parts of secondary importance, is indispensable. Unpainted and polished
surfaces such as the shaft of the engine, the distributing cam-shafts,
the levers, the connecting-rod and the like, should be kept in a
condition equal to that when they were new. The absence of all traces of
rust or corrosion in these parts affords sufficient evidence of the care
taken of the invisible members such as the piston, the valves, ignition
devices, and the like.
=Lubrication.=--The rubbing surfaces of a gas-engine should be regularly
and perfectly lubricated. The absence of lost motion and backlash in the
bearings, guides, and joints is of particular importance not only
because of its influence on steady and silent running, but also on the
power developed and on the consumption. As we have already seen in the
chapter on lubrication, a special quality of oil should be employed for
the lubrication of the cylinder. The feed of the lubricator supplying
this most vital part of the engine is so regulated that it meets the
actual requirements with the utmost nicety possible. In a subsequent
chapter, in which faulty operation will be discussed, it will be shown
how too much and too little oil may cause serious trouble.
=Tightness of the Cylinder.=--The amount of power developed depends
principally on the degree of compression to which the explosive mixture
is subjected. The economical operation of the engine depends in general
upon perfect compression. It is, therefore, necessary to keep those
parts in good order upon which the tightness of the cylinder depends.
These parts are the piston, the valves, and their joints, and the
ignition devices whether they be of the hot-tube or electrical variety.
In order to prevent leakage at the piston, the rings should be protected
from all wear. It is of the utmost importance that the surfaces both of
the piston and of the cylinder, be highly polished so that binding
cannot occur. In cleansing the cylinder, emery paper or abrasive powder
should not be employed; for the slightest particle of abrasive between
the surfaces in contact will surely cause leakage. The oil and dirt,
which is turned black by friction and which may adhere to the piston
rings, should be washed away with petroleum. Similarly the other parts
of the cylinder should be cleaned to which burnt oil tends to adhere.
=Valve-Regrinding.=--The valves should be regularly ground. Even in
special cases where they may show no trace of rapid wear they should be
removed at least every month. In order to avoid any accident, care
should be taken in adjusting the valves after the cap has been unbolted
not to introduce a candle or a lighted match either in the
valve-chambers or in the cylinder, without first closing the gas-cock.
Furthermore, a few turns should be given to the engine, in order to
drive out any explosive mixture that may still remain in the cylinder or
the connected passages. The exhaust-valve, by reason of the high
temperature to which the disk and the seat are subjected, should receive
special attention. The valve should be ground on its seat every two or
three months at least, depending upon the load of the engine.
=Bearings and Crosshead.=--The bushings of the engine shaft should
always be held tightly in place. The looseness to which they are liable,
particularly in gas-engines on account of the sharp explosions, tends to
unscrew the nuts and to hasten the wear of the brass, which is the
result of frequent tightening. The slightest play in the bearings of the
engine-shaft as well as in the bearings of connecting-rods increases the
sound that engines naturally produce.
=Governor.=--The governor should receive careful attention so far as its
cleanliness is concerned; for if its operation is not easy it is apt to
become "lazy" and to lose its sensitiveness. If the governor be of the
ball type, or of the conical pendulum type operated by centrifugal
force, it is well to lubricate each joint without excess of oil. In
order to prevent the accumulation and the solidification of oil, the
governor should be lubricated from time to time with petroleum. If the
governor is actuated by inertia, which is the case in most engines of
the hit-and-miss variety, it needs less care; still, it is advisable to
keep the contact at which the thrust takes place well oiled.
The operation of any of these governors is usually controlled by the
tension of a spring, or by a counterweight. In order to increase the
speed of the engine, or in other words, to increase the number of
admissions of gas in a given time, all that is usually necessary is to
tighten up the spring, or to change the position of the counterweight.
It should be possible to effect this adjustment while the engine is
running in such a manner that the speed can be easily changed.
=Joints.=--In most well-built engines the caps of the valve-chests and
other removable parts are secured "metal on metal" without interposing
special joints. In other words, the surfaces are themselves sufficiently
cohesive to insure perfect tightness. In engines which are not of this
class, asbestos joints are very frequently employed, particularly at the
exhaust-valve cap and the suction-valve.
In some engines, where for any reason it is necessary frequently to
detach the caps, certain precautions should be taken to protect the
joints so that they may not be exposed to deterioration whenever they
are removed. For this purpose, they are first immersed in water in order
to be softened, then dried and washed with olive or linseed oil on the
side upon which they rest in the engine. On the cap side they are dusted
with talcum or with graphite. Treated in this manner, the joint will
adhere on one side and will be easily released on the other.
Joints that are liable to come in contact with the gases in the
explosion-chamber should be free from all projections toward the
interior of the cylinder; for during compression these uncooled
projections may become incandescent and may thus cause premature
ignition. As a general rule when the cap is placed in position the joint
should be retightened after a certain time, when the surfaces have
become sufficiently heated. In order to tighten the joints the bolts and
nuts should not be oiled; otherwise the removal of the cap becomes
difficult.
=Water Circulation.=--In a previous chapter, the importance of the water
circulation and the necessity of keeping the cylinder-jacket hot, have
been sufficiently dwelt upon. As the cylinder tends to become hotter
with an increase in the load, because of the greater frequency of
explosions, it is advisable to regulate the flow of the water in order
to prevent its becoming more than sufficient in quantity when the engine
is lightly loaded; for under these conditions the cylinder will be cold
and the explosive mixture will be badly utilized. A suitable temperature
of 140 to 158 degrees F. is easily maintained by adjusting the
circulation of the water. This can be accomplished by providing the
water-inlet pipe leading to the cylinder with a cock which can be opened
more or less, as may be necessary. The temperature of 140 to 158 degrees
F., which has been mentioned, may, at first blush, seem rather high
because it would be impossible to keep the hand on the outlet-pipe. The
cylinder, however, will not become overheated so long as it is possible
to hold the hand beneath the jacket near the water-inlet. This relates
only to engines having a compression of 50 to 100 lbs. per square inch.
For engines of higher compression, a lower running temperature will be
safer. On this matter the instructions of the engine maker should be
carried out.
=Adjustment.=--Gas-engines, at least those which are built by
trustworthy firms, are always put to the brake test before they are sent
from the shops, and are adjusted to meet the requirements of maximum
efficiency. But since the nature and quality of gas necessarily vary
with each city, it is evident that an engine adjusted to develop a
certain horse-power with a gas of a certain richness, may not fulfil all
expectations if it is fed with a gas less rich, less pure, hotter, and
the like. The altitude also has some influence on the efficiency of the
engine. As it increases, the density of the mixture diminishes; that is
to say, for the same volume the engine is using a smaller amount. From
this it follows that a gas-engine ought to be adjusted as a general rule
on the spot where it is to be used.
The fulfilment of this condition is particularly important in the case
of explosion-engines, because an advancement or retardation of only
one-half a second in igniting the explosive mixture will cause a
considerable loss in useful work. From this it would follow that
gas-engines should be periodically inspected in order that they may
operate with the highest efficiency and economy. As in the case of
steam-engines, it is advisable to take indicator records which afford
conclusive evidence of the perturbations to which every engine is
subject after having run for some time.
Most gas-engine users either have no indicating instruments at their
disposal or else are not sufficiently versed in their employment and the
interpretation of their records to study perturbations by their means.
For this reason the advice of experts should be sought,--men who
understand the meaning of the diagrams taken and who are able by their
means to effect a considerable saving in gas.
CHAPTER VIII
HOW TO START AN ENGINE--PRELIMINARY PRECAUTIONS
The first step which is taken in starting an engine driven by street-gas
is, naturally, the opening of the meter-cock and the valves between the
meter and the engine. When the gas has reached the engine, the rubber
bags will swell up and the anti-pulsator diaphragm will be forced out.
The drain-cock of the gas-pipe is then opened. In order to ascertain
whether the flow of gas is pure, a match is applied to the outlet of the
cock. The flame is allowed to burn until it changes from its original
blue color to a brilliant yellow.
If the hot-tube system of ignition be employed, the Bunsen burner is
ignited, care being taken that the flame emerging from the tube is blue
in color. If necessary the admission of air to the burner is regulated
by the usual adjusting-sleeve. A white or smoky flame indicates an
insufficient supply of air to the burner. A characteristic sooty odor is
still other evidence of the same fact. Sometimes a white flame may be
produced by the ignition of the gas at the opening of the
adjusting-sleeve. A blue or greenish flame is that which has the highest
temperature and is the one which should, therefore, be obtained. About
five or ten minutes are required to heat up the tube, owing to the
material of which it is made. When the proper temperature has been
attained the tube becomes a dazzling cherry red in color. While the tube
is being heated up, it is well to determine whether the engine is
properly lubricated and all the cups and oil reservoirs are duly filled
up. The cotton waste of the lubricators should be properly immersed, and
the drip lubricators examined to determine whether they are supplying
their normal quantity of oil.
The regulating-levers of the valves should be operated in order to
ascertain whether the valves drop upon their seats as they should. The
stem of the exhaust-valve should be lubricated with a few drops of
petroleum.
If the ignition system employed be of the electric type, with batteries
and coils, tests should be made to determine whether the current passes
at the proper time on completing the circuit with the contact mounted on
the intermediary shaft. This contact should produce the characteristic
hum caused by the operation of the coil.
If a magneto be used in connection with the ignition apparatus, its
inspection need not be undertaken whenever the engine is started,
because it is not so likely to be deranged. Still, it is advisable, as
in the case of ignition by induction-coils, to set in position the
device which retards the production of the spark. This precaution is
necessary in order to avoid a premature explosion, liable to cause a
sharp backward revolution of the fly-wheel.
After the ignition apparatus and the lubricators have been thus
inspected, the engine is adjusted with the piston at the starting
position, which is generally indicated by a mark on the cam-shaft. The
starting position corresponds with the explosion cycle and is generally
at an angle of 40 to 60 degrees formed by the crank above the horizontal
and toward the rear of the engine. The gas-cock is opened to the proper
mark, usually shown on a small dial. If there be no mark, the cock is
slowly opened in order that no premature explosion may be caused by an
excess of gas.
The steps outlined in the foregoing are those which must be taken with
all motors. Each system, however, necessitates peculiar precautions,
which are usually given in detailed directions furnished by the builder.
As a general rule the engines are provided on their intermediary shafts
with a "relief" or "half-compression" cam. By means of this cam the
fly-wheel can be turned several times without the necessity of
overcoming the resistance due to complete compression. Care should be
taken, however, not to release the cam until the engine has reached a
speed sufficient to overcome this resistance.
Engines of considerable size are commonly provided with an automatic
starting appliance. In order to manipulate the parts of which this
appliance is composed, the directions furnished by the manufacturer
must be followed. Particularly is this true of automatic starters
comprising a hand-pump by means of which an explosive mixture is
compressed,--true because in the interests of safety great care must be
taken.
The tightness and free operation of the valves or clacks which are
intended to prevent back firing toward the pump should be made the
subject of careful investigation. Otherwise, the piston of the pump is
likely to receive a sudden shock when back firing occurs.
When the engine has been idle for several days, it is advisable, before
starting, to give it several turns (without gas) in order to be sure
that all its parts operate normally. The same precaution should be taken
in starting an engine, if a first attempt has failed, in order to
evacuate imperfect mixtures that may be left in the cylinder. Before
this test is made, the gas-cock should, of course, be closed in order to
prevent an untimely explosion. It is advisable in starting an engine not
to bend the body over the ignition-tube, because the tube is likely to
break and to scatter dangerous fragments.
Under no condition whatever should the fly-wheel be turned by placing
the foot upon the spokes. All that should be done is to set it in motion
by applying the hand to the rim.
=Care During Operation.=--When the engine has acquired its normal speed,
the governor should be looked after in order that its free operation may
be assured and that all possibility of racing may be prevented. After
the engine has been running normally for a time, the cocks of the water
circulation system should be manipulated in order to adjust the supply
of water to the work performed by the engine. In other words the
cylinder should be kept hot, but not burning, as previously explained in
the paragraph in which the water-jacket is discussed. The maintenance of
a suitable temperature is extremely important so far as economy is
concerned. All the bearings should be inspected in order that hot boxes
may be obviated.
=Stopping the Engine.=--The steps to be taken in stopping the engine are
the following:
1. Stopping the various machines driven by the engine,--a practice which
is followed in the case of all motors;
2. Throwing out the driving-pulley of the engine itself, if there be
one;
3. Closing the cock between the meter and the gas-bags in order to
prevent the escape of gas and the useless stretching of the rubber of
the bags or of the anti-pulsating devices;
4. Actuating the half-compression or relief cam as the motor slows down,
in order to prevent the recoil due to the compression;
5. Closing the gas-admission cock;
6. Shutting off the supply of oil of free flowing lubricators, and
lifting out the cotton from the others.
If the engine be used to drive a dynamo, particularly a dynamo provided
with metal brushes, the precaution should be taken of lifting the
brushes before the engine is stopped in order to prevent their injury
by a return movement of the armature-shaft;
7. Shutting off the cooling-water cock if running water is used.
If the engine is exposed to great cold, the freezing of the water in the
jacket is prevented while the engine is at rest, either by draining the
jacket entirely, or by arranging a gas jet or a burner beneath the
cylinder for the purpose of causing the water to circulate. If such a
burner be used the cocks of the water supply pipe should, of course, be
left open.
CHAPTER IX
PERTURBATIONS IN THE OPERATION OF ENGINES AND THEIR REMEDY
In this chapter will be discussed certain perturbations which affect the
operations of gas-engines to a more marked degree than lack of care in
their construction. In previous chapters defects in operation due to
various causes have been dwelt upon, such as objectionable methods in
the construction of an engine, ill-advised combination of parts, defects
of installation, and the like; and an attempt has been made to determine
in each case the conditions which must be fulfilled by the engine in
order to secure efficiency and economy at a normal load.
=Difficulties in Starting.=--The preliminary precautions to be taken in
starting an engine having been indicated, it is to be assumed that the
advice given has been followed. Nevertheless various causes may prevent
the starting of the engine.
=Faulty Compression.=--Defective compression, as a general rule,
prevents the ignition of the explosive mixture. Whether or not the
compression be imperfect can be ascertained by moving the piston back to
the period corresponding with compression, in other words, that position
in which all valves are closed. If no resistance be encountered, it is
evident that the air or the gaseous mixture is escaping from the
cylinder by way of the admission-valve, the exhaust-valve, or the
piston. The valves, ordinarily seated by springs, may remain open
because their stems have become bound, or because some obstruction has
dropped in between the disk and the seat. In a worn-out or badly kept
engine the valves are likely to leak. If that be the case grinding is
the only remedy. If a valve be clogged, which becomes sufficiently
evident by manipulating the controlling levers, it is necessary simply
to clean the stem and its guides in order to remove the caked oil which
accumulates in time. If the engine be new, the binding of the
valve-stems is often caused by insufficient play between the stems and
their guides. Should this prove to be the case, the defect is remedied
by rubbing the frictional surface of the stem with fine emery paper and
by lubricating it with cylinder-oil. The exhaust-valve, however, should
be lubricated only with petroleum.
It is not unlikely that the exhaust-valve may leak for two other
reasons. In the first place, the tension of the spring which serves to
return the valve may have lessened and may be insufficient to prevent
the valve from being unseated during suction. Again, the screw or roller
serving as a contact between the lever and the valve-stem, may not have
sufficient play, so that the lengthening of the stem on account of its
expansion may prevent the valve from falling back on its seat. The
first-mentioned defect is remedied by renewing the spring, or by the
provision of an additional spring or of a counterweight in order to
prevent the stoppage of the motor. The second defect can be remedied by
regulating the contact.
Leakage past the piston may be caused by the breaking of one or more
rings, by wear or binding of the rings, or by wear or binding of the
cylinder. The whistling caused by the air or the mixture as it passes
back proves the existence of this fault.
=Presence of Water in the Cylinder.=--It may sometimes happen that water
may find its way into the cylinder with the gas by reason of the bad
arrangement of the piping. It may also happen that water may enter the
cylinder through the water-jacket joint. Again, the presence of water in
the cylinder may be due to condensation of the steam formed by the
chemical union of the hydrogen of the gas and the oxygen of the air,
which condensation is caused by the cool walls of the cylinder. The
water may sometimes accumulate in the exhaust pipe and box, when they
have been improperly drained, and may thus return to the cylinder.
Whatever may be its cause, however, the presence of water in the cylinder
impedes the starting of the engine, because the gases resulting from the
explosion are almost spontaneously chilled, thereby diminishing the
working pressure.
If electric ignition be employed, drops of water may be deposited
between the contacts, thereby causing short circuits which prevent the
passing of the spark.
If there be no drain-cock on the cylinder, the difficulty of starting
the engine can be overcome only by ceaseless attempts to set it in
motion. The leaky condition of a joint as well as the presence of a
particle of gravel in the cylinder-casting, through which the water can
pass from the jacket, is attested by the bubbling up of gas in the
water-tank at the opening of the supply tube. These bubbles are caused
by the passage of the gas through the jacket after the explosion. If
such bubbles be detected, the cylinder should be renewed or the defect
remedied. In order to obviate any danger, the stop-cocks of the
water-jacket, which have already been described in a previous chapter,
should be closed while the engine is idle.
=Imperfect Ignition.=--The difficulties encountered in starting an
engine, and caused by imperfect ignition, vary in their nature with the
character of the ignition system employed, whether that system, for
example, be of the electric, or of the incandescent or hot tube type.
Frequently it happens that in starting an engine a hot tube may break.
If the tube be of porcelain the accident may usually be traced to
improper fitting or to the presence of water in the cylinder. If the
tube be of metal, its breaking is caused usually by a weakening of the
metal through long use--an accident that occurs more often in starting
the engine than in normal operation, because the explosions at starting
are more violent, owing to the tendency of the supply-pipes to admit an
excess of gas at the beginning.
A misfire arising from a faulty tube in starting may be caused by an
obstruction or by leaks at the joints or in the body of the tube
itself, thereby allowing a certain quantity of the mixture to escape
before ignition. This defect in the tube is usually disclosed by a
characteristic whistling sound.
A tube may leak either at the bottom or at the top. In the first case,
starting is very difficult, because the part of the mixture compressed
toward the tube will escape through the opening before it reaches the
incandescent zone. In the second case, ignition may be simply retarded
to so marked an extent that a sufficient motive effect cannot be
produced. An example of this retardation, artificially produced to
facilitate the starting and to obviate premature explosions, is found in
a system of ignition-tubes provided with a small cock or variable valve
(Figs. 74 and 75).
[Illustration: FIG. 74.]
[Illustration: FIG. 75.--Ignition-tubes provided with needle valves to
facilitate starting.]
The mere enumeration of defects caused by leakage is sufficient to
indicate the remedy to be adopted. It may be well to recall in this
connection the important part played by the ignition-valve. If it be
leaky, or if its free operation be impeded, starting will always be
difficult.
=Electric Ignition by Battery or Magneto.=--If the electric ignition
apparatus, whatever may be the method by which the spark is produced, be
imperfect in operation, the first step to be taken is to ascertain
whether the spark is produced at the proper time, in other words,
slightly after the dead center in the particular position given to the
admission device at starting. If a coil and a battery be employed, it is
advisable to remove the plug and to place it with its armature upon a
well-polished metal surface to produce an electrical contact,
preventing, however, the contact of the binding post with this metallic
surface. The same method of inspection is adopted with the
make-and-break apparatus of an electric magneto. In both cases it should
be ascertained whether or not there is any short-circuiting. The
contacts should be cleaned with a little benzine if they are covered
with oil or caked grease.
If no spark is produced at the plug or at the make-and-break device it
may be inferred that the wires are broken or that the generating
apparatus is out of order. A careful examination will indicate what
measures are to be taken to cure the defects.
=Premature Ignition.=--It has several times been stated that the moment
of ignition of the gaseous mixture has a pronounced influence on the
operation of gas-engines and upon their economy.
Premature ignition takes place when there is a violent shock at the
moment when the piston leaps from the rear dead center to the end of the
compression stroke. The violent effects produced are all the more
harmful because they tend to overheat the interior of the engine and
thereby to increase in intensity.
Premature ignition may be due to several causes. If a valveless hot tube
be employed it may happen that the incandescent zone is too near the
base. If the tube be provided with a valve, it very frequently happens
that the valve leaks or that it opens too soon. In the case of electric
ignition, the circuit may be completed before the proper time, because
of faulty regulation. The suggestions made in the preceding chapters
indicate the method of remedying these defects.
Faulty ignition may have its origin not only in the method of ignition
employed, but also in excessive heating of the internal parts of the
engine, caused by continual overloading or by inadequate circulation of
water.
Passing to those cases of premature ignition of a special nature which
are not due to any functional defect in the engine, but which are purely
accidental in origin, such as the uncleanliness of the parts within the
cylinder or the presence of some projecting part which becomes heated to
incandescence during compression, it should first be stated that these
ignitions, usually termed spontaneous, often occur well in advance of
the end of the compression stroke. They are characterized by a more
marked shock than that caused by ordinary premature ignition and
usually result in bringing the engine to a complete stop in a very short
time. These spontaneous explosions counteract to such an extent the
impulse of the compression period, during which the piston is moving
back, that they have a tendency to reverse the direction in which the
engine is running. In such cases a careful inspection and a scrupulous
cleaning of the cylinder and of the piston should be undertaken.
The bottom of the piston is particularly likely to retain grease which
has become caked, and which is likely to become heated to incandescence
and spontaneously to ignite the explosive mixture.
=Untimely Detonations.=--The sound produced by the explosions of a
normally operating engine can hardly be heard in the engine-room.
Untimely detonations are produced either at the exhaust, or in the
suction apparatus, near the engine itself. These detonations are noisier
than they are dangerous; still, they afford evidence of some fault in
the operation which should be remedied.
Detonations produced at the exhaust are caused by the burning of a
charge of the explosive mixture in the exhaust-pipe, which charge, for
some reason, has not been ignited in the cylinder, and has been driven
into the exhaust-pipe, where it catches fire on coming into contact with
the incandescent gases discharged from the cylinder after the following
explosion.
Detonations produced in the suction apparatus of the engine, which
apparatus is either arranged in the base itself or in a separate chest,
are often noisier than the foregoing. They are caused by the accidental
backward flowing of the explosive mixture, and by its ignition outside
of the cylinder. The accident may be traced to three causes:
1. The suction-valve of the mixture may not be tight and may leak during
the period of compression, allowing a certain quantity of the mixture to
pass into the suction-chest or into the frame. When the explosion takes
place in the cylinder that part of the mixture which has passed back is
ignited, as we have just seen, thereby producing a very loud
deflagration. The obvious remedy consists in making the suction-valve
tight by carefully grinding it.
2. It may happen that at the end of the exhaust stroke incandescent
particles may remain in the cylinder, which particles may consist of
caked oil or may be retained by poorly cooled projections. The result is
that the mixture is prematurely ignited during the suction period.
3. The engine is so regulated, particularly in the case of English-built
engines, as to effect what is technically called "scavenging" the
products of combustion. In order to obtain this result, the
mixture-valve is opened before the end of the exhaust stroke of the
piston and the closing of the exhaust-valve. Owing to the inertia and
the speed acquired by the products of combustion shot into the
exhaust-pipe after explosion, a lowering of the pressure is produced in
the cylinder toward the end of the stroke, causing the entrance of air
by the open admission-valve and consequently effecting the scavenging of
the burnt gases, part of which would otherwise remain in the cylinder.
It is evident that if a charge of the mixture has not been normally
exploded, either because its constituents have not been mingled in the
proper proportion, or because the ignition apparatus has missed fire,
this charge at the moment of exhausting will pass out of the cylinder
without any acquired speed, and will flow back in part at the end of the
exhaust stroke past the prematurely opened admission-valve, thereby
lodging in the air suction apparatus. Despite the suction which takes
place immediately following the re-entrance of the gas into the
cylinder, a certain quantity of the mixture is still confined in the
suction-pipe and its branches, where it will catch fire at the end of
the exhaust stroke after the opening of the mixture-valve.
In order to avoid these detonations it is necessary simply to see to it
that the mixture is regularly ignited. This is accomplished by mixing
the gas and air in proper proportions or by correcting the ignition
time.
=Retarded Explosions.=--Retarded explosions considerably reduce the
power which an engine should normally yield, and sensibly increase the
consumption. They are due to three chief causes: (1), faulty ignition;
(2), the poor quality of the mixture; (3), compression losses. The
existence of the defect cannot be ascertained with any certainty without
the use of an indicator or of some registering device which gives
graphic records. Nevertheless, it is possible in some degree to detect
retarded explosions, simply by observing whether there is a diminution
in the power or an excessive consumption, despite the perfect operation
and good condition of all the engine parts.
In order to remedy the defect it should be ascertained if the
compression is good, if the supply of gas is normal, and if the
conditions under which the mixture of air and gas is produced have not
been changed. Lastly, the ignition apparatus is gradually adjusted to
accelerate its operation until a point is reached when, after explosion,
shocks are produced which indicate an excessive advance. The ignition
apparatus is then adjusted to a point slightly ahead of the
corresponding position. Recalling the descriptions already given of the
various systems of ignition, the manner of regulating the moment of
ignition in each case may be summarized as follows:
1. For the valveless incandescent tube, provided with a burner the
position of which can be varied, ignition can be accelerated by bringing
the burner nearer to the base. Retardation is effected by moving the
burner away from the base.
2. In the case of the incandescent tube of the fixed burner type, the
moment of ignition will depend upon the length of the tube. The
retardation will be greater as the tube is shorter, and _vice versa_.
3. If the tube be provided with an ignition-valve, the time of ignition
having been regulated by the maker, regulation need not be undertaken
except if the valve-stem be worn or the controlling-cam be distorted.
If these defects should be noted, the imperfect parts should be repaired
or renewed.
4. In electric igniters the controlling apparatus is generally provided
with a regulating device which may be manipulated during the operation
of the motor. If the manual adjustment of the regulating apparatus be
unproductive of satisfactory results, it is advisable to ascertain
whether the spark is being produced normally. Before the engine has come
to a stop, one of the valve-casings is raised, and through the opening
thus produced it is easily seen whether the spark is of sufficient
strength, the engine in the meanwhile being turned by hand. Care should
always be taken to purge the cylinder of the gas that it may contain, in
order to prevent dangerous explosions. If the spark should prove to be
too feeble, or if there be no spark at all, despite the fact that every
part of the mechanism is properly adjusted, it may be inferred that the
fault lies with the current and is caused by
1. Imperfect contact with the binding-posts, with the conducting wire,
or with the contact-breaking members;
2. A short circuit in one of the dismembered pieces;
3. The presence of a layer of oil or of caked grease forming an
insulator, injurious to induction, between the armature and the magnets;
4. A deposit of oil or moisture on the contact-breaking parts;
5. The exhaustion of the magnets, which, however, occurs only after
several years of use, except when the magneto has been subjected for a
long time to a high temperature.
The mere discovery of any of these defects sufficiently indicates the
means to be adopted in remedying them.
=Lost Motion in Moving Parts.=--Lost motion of the moving parts is due
to structural errors. Its cause is to be found in the insufficient size
of the frictional bearing surfaces, and improper proportioning of
shafts, pins, and the like. The result is a premature wear which cannot
be remedied. Imperfect adjustment, lack of care, and bad lubrication,
may also hasten the wear of certain parts. This wear is manifested in
shocks, occurring during the operation of the engine,--shocks which are
particularly noticeable at the moment of explosion.
Besides the inconveniences mentioned, wearing of the gears and of the
moving parts leads to derangement of the power-transmitting members.
So far as the admission and exhaust valves are concerned, the wearing of
the cams, rollers, and lever-pivots is evidenced by a retardation in the
opening of these valves and an acceleration in their closing.
The ignition, whatever may be the system employed, is affected by lost
motion and is retarded. The engine appreciably loses in power, and its
consumption becomes excessive.
=Overheated Bearings.=--Apart from the imperfect adjustment of a member,
it may happen that the bushings of the main bearings of the ends of the
connecting-rod, and of the piston-pivot, may become heated because of
excessive play, or of too much tightening, or of a lack of oil, or of
the employment of oil of bad quality. The overheating may lead to the
binding of frictional surfaces and even to the fusion of bushings if
they be lined with anti-friction metal. In order to avoid the
overheating of parts, it is advisable, while the engine is running, to
touch them from time to time with the back of the hand. As soon as the
slightest overheating is felt, the temperature may be lowered often by
liberal oiling. If this be inadequate and if for special reasons it is
impossible to stop the engine, the overheated part may be cooled by
spraying it with soapy water.
If the overheating has not been detected or reduced in time, a
characteristic odor of burnt oil will be perceived, accompanied by
smoke. The part overheated will then have attained a temperature so high
that it cannot be touched with the hand. Should this occur, it is
inadvisable to employ oil, because it would immediately burn up and
would only aggravate the conditions. Cotton waste should be carefully
applied to the overheated member, and gradual spraying with soapy water
begun.
In special cases where the lubricating openings or channels are not
likely to be obstructed, a little flowers of sulphur may be added to the
oil, if this be very fluid. Castor oil may also be successfully
employed.
If the binding of the rubbing surfaces should prevent the reduction of
the overheated member's temperature, the engine must necessarily be
stopped, and the parts affected detached. All causes of binding are
removed by means of a steel scraper. The surfaces of the bushings and of
the shaft which they receive are smoothed with a soft file and then
polished with fine emery paper. Before the parts are replaced, the
precaution of ascertaining whether they touch at all points should be
taken. Careful inspection and copious lubrication should, of course, be
undertaken when the engine is again started.
=Overheating of the Cylinder.=--The overheating of the cylinder may be
due to a complete lack of water in the jacket or to an accidental
diminution in the quantity of water supplied. If this discovery is made
too late, and if the cylinder has reached a very high temperature, the
circulation of the water should not be suddenly re-established, because
of the liability of breaking the casting. It is best to stop the engine
and to restore the parts to their normal condition.
It is well to recall at this point that if the calcareous incrustation
of the water-jacket or the branch pipes should hinder the free
circulation of water, cleaning is, of course, necessary. The jacket may
be washed several times with a twenty per cent. solution of hydrochloric
acid. After this treatment the jacket should, of course, be rinsed with
fresh water before the piping of the water-circulating apparatus is
again connected.
=Overheating of the Piston.=--If the overheating of the piston is not
due to faulty adjustment, it may be caused by lack of oil or to the
employment of a lubricant not suitable for the purpose. In a previous
chapter the importance of using a special oil for cylinder lubrication
has been insisted upon. The overheating of the piston can also result
from that of the piston-pin. Should this be the case it is advisable to
stop the engine, to ascertain the condition and the degree of
lubrication of this member and its bearing. Overheating of the piston is
manifested by an increase of the temperature of the cylinder at the
forward end. If this overheating be not checked, binding of the piston
in the cylinder is likely to result.
=Smoke Arising from the Cylinder.=--This is generally a sign either of
overheating, which causes the oil to evaporate, or of an abnormal
passage of gas, caused by the explosion. Abnormal passage of gas may
result from wear or from distortion of the cylinder, or from wear or
breakage of the piston-rings. The result is always the overheating of
the cylinder and a reduction in compression and power.
If the engine is well kept and shows no sign of wear, leakage may be
caused simply by the fouling of the piston-rings, which then adhere in
their grooves and have but insufficient play. This defect is obviated by
cleaning the rings in the manner explained in Chapter VII.
Lubrication is faulty when the quantity of lubricant supplied is either
insufficient or too abundant, or when the oils employed are of bad
quality. It has already been shown that insufficient lubrication and the
utilization of bad oils leads to the overheating of the moving parts.
Insufficient lubrication may be caused by imperfect operation of the
lubricators, or, particularly during cold weather, by too great a
viscosity or congelation of the oil. If a lubricator be imperfect in its
operation, the condition of its regulating mechanism should be
ascertained, if it has any, and an examination made to discover any
obstruction in the oil-ducts. Such obstructions are very likely to occur
in new devices which have been packed in cotton waste or excelsior, with
the result that the particles of the packing material often find their
way into openings.
An oil may be bad in quality because of its very nature, or because of
the presence of foreign bodies. In either case an oil of better quality
should be substituted.
The freezing of oil by intense cold may be retarded by the addition of
ordinary petroleum to the amount of 10 to 20 per cent.
An excess of oil in the bearings results simply in an unnecessary waste
of lubricant, and the splashing of oil on the engine and about the room.
If too much oil be used in the cylinder, grave consequences may be the
result; for a certain quantity of the oil is likely to accumulate within
the cylinder, where it burns and forms a caky mass that may be heated to
incandescence and prematurely ignite the explosive mixture. Especially
in producer-gas engines is an excess of cylinder-lubricant likely to
cause such accidents. Indeed, the temperature of explosion not being as
high as in street-gas engines, the excess oil cannot be so readily
removed with certainty by evaporation or combustion. On the other hand,
the compression of the mixture being generally higher, premature
ignition is very likely to occur.
=Back Pressure to the Exhaust.=--How the pipes and chests for the
exhaust should be arranged in order not to exert a harmful influence on
the motor has already been explained. Even if the directions given have
been followed, however, the exhaust may not operate properly from
accidental causes. Among these causes may be mentioned obstructions in
the form of foreign bodies, such as particles of rust, which drop from
the interior of the pipes after the engine has been running for some
time and which, accumulating at any place in the pipe, are likely to
clog the passage. Furthermore, the products of combustion may contain
atomized cylinder oil which finds its way into the exhaust-pipe. This
oil condenses on the walls of the elbows and bends of the pipe in a
deposit which, as it carbonizes, is converted into a hard cake and which
reduces the cross-section of the passage, thereby constituting a true
obstacle to the free exhaust of the gases.
These various defects are manifested in a loss in engine power as well
as in an abnormal elevation of the temperature of the parts surrounding
the exhaust opening.
=Sudden Stops.=--Sudden stops are occasioned by faulty operation of the
engine, and by imperfect fuel supply. Among the first class the chief
causes to be mentioned are the following:
1. Overheating, which has already been discussed and which may block a
moving part.
2. Defective ignition.
3. Binding of the admission-valve or of the exhaust-valve, preventing
respectively suction or compression.
4. The breaking or derangement of a member of the distributing
mechanism.
5. A weakening of the exhaust-valve spring, so that the valve is opened
by the suction of fresh quantities of mixture.
These faults are due to carelessness and improper inspection of the
engine.
So far as the fuel supply of the engine is concerned, the causes of
stoppage will vary if street-gas or producer-gas be employed. In the
former case the difficulty may be occasioned by the improper operation
of the meter, by the formation of a water-pocket in the piping, by the
binding of an anti-pulsator valve, by the derangement of a
pressure-regulator, or by a sudden change in the gas pressure when no
pressure-regulator is employed. If producer-gas be used, stoppages may
be occasioned by a sudden change in the quality, quantity, or
temperature of the gas. These defects will be examined in detail in the
chapter on Gas-Producers.
CHAPTER X
PRODUCER-GAS ENGINES
Thus far only street-gas or illuminating-gas engines have been
discussed. If the engine employed be small--10 to 15 horse-power, for
instance--street-gas is a fuel, the richness, purity and facility of
employment of which offsets its comparatively high cost. But the
constantly increasing necessity of generating power cheaply has led to
the employment of special gases which are easily and cheaply generated.
Such are the following:
Blast-furnace gases,
Coke-oven gases,
Fuel-gas proper,
Mond gas,
Mixed gas,
Water-gas,
Wood-gas.
The practical advantages resulting from the utilization of these gases
in generating power were hardly known until within the last few years.
The many uses to which these gases have been applied in Europe since
1900 have definitely proved the industrial value of producer-gas engines
in general.
The steps which have led to this gradually increasing use of
producer-gas have been learnedly discussed and commented upon in the
instructive works and publications of Aime Witz, Professor in the
Faculty of Sciences of Lille, in those of Dugald Clerk, of London, F.
Grover, of Leeds, and Otto Gueldner, of Munich, and in those of the
American authors, Goldingham, Hiscox, Hutton, Parsell and Weed, etc. The
new tendencies in the construction of large engines may be regarded as
an interesting verification of the forecasts of these men--forecasts
which coincide with the opinion long held by the author. Aime Witz has
always been an advocate of high pressures and of increased piston speed.
English builders who made experiments in this direction conceded the
beneficial results obtained; but while they increased the original
pressure of 28 to 43 pounds per square inch employed five or six years
ago to the pressure of 85 to 100 pounds per square inch nowadays
advocated, the Germans, for the most part, have adopted, at least in
producer-gas engines, pressures of 114 to 170 pounds per square inch and
more.
=High Compression.=--In actual practice, the problem of high pressures
is apparently very difficult of solution, and many of the best firms
still seem to cling to old ideas. The reason for their course is,
perhaps, to be found in the fact that certain experiments which they
made in raising the pressures resulted in discouraging accidents. The
explosion-chambers became overheated; valves were distorted; and
premature ignition occurred. Because the principle underlying high
pressures was improperly applied, the results obtained were poor.
High pressures cannot be used with impunity in cylinders not especially
designed for their employment, and this is the case with most engines of
the older type, among which may be included most engines of English,
French, and particularly of American construction. In American engines
notably, the explosion-chamber, the cylinder and its jacket, are
generally cast in one piece, so that it is very difficult to allow for
the free expansion of certain members with the high and unequal
temperatures to which they are subjected (Fig. 22).
Some builders have attempted to use high pressures without concerning
themselves in the least with a modification of the explosive mixture.
The result has been that, owing to the richness of the mixture, the
explosive pressure was increased to a point far beyond that for which
the parts were designed. Sudden starts and stops in operation,
overheating of the parts, and even breaking of crank-shafts, were the
results. The engines had gained somewhat in power, but no progress had
been made in economy of consumption, although this was the very purpose
of increasing the compression.
High pressures render it possible to employ poor mixtures and still
insure ignition. A quality of street-gas, for example, which yields one
horse-power per hour with 17.5 cubic feet and a mixture of 1 part gas
and 8 of air compressed to 78 pounds per square inch, will give the same
power as 14 cubic feet of the same gas mixed with 12 parts of air and
compressed to 171 pounds per square inch.
"Scavenging" of the cylinder, a practice which engineers of modern
ideas seem to consider of much importance, is better effected with high
pressures, for the simple reason that the explosion-chamber, at the end
of the return stroke, contains considerably less burnt gases when its
volume is smaller in proportion to that of the cylinder.
In impoverishing the mixture to meet the needs of high pressures, the
explosive power is not increased and in practice hardly exceeds 365 to
427 pounds per square inch. With the higher pressures thus obtained
there is consequently no reason for subjecting the moving parts to
greater forces.
[Illustration: FIG. 76.--Method of cooling the cylinder-head.]
=Cooling.=--The increase in temperature of the cylinder-head and of the
valves, due wholly to high compression, is perfectly counteracted by an
arrangement which most designers seem to prefer, and which, as shown in
the accompanying diagram (Fig. 76), consists in placing the mixture and
exhaust-valves in a passage forming a kind of antechamber completely
surrounded by water. The immediate vicinity of this water assures the
perfect and equal cooling of the valve-seats. This arrangement, while it
renders it possible to reduce the size of the explosion-chamber to a
minimum, has the additional mechanical advantage of enabling the builder
to bore the seats and valve-guides with the same tool, since they are
all mounted on the same line. From the standpoint of efficiency, the
design has the advantage of permitting the introduction of the explosive
mixture without overheating it as it passes through the admission-valve,
which obtains all the benefit of the cooling of the cylinder-head,
literally surrounded as it is by water.
In large engines the cooling effect is even heightened by separately
supplying the jackets of the cylinder-head and of the cylinder. In
engines of less power the top of the cylinder-head jacket is placed in
communication with that of the cylinder, so that the coldest water
enters at the base of the head and, after having there been heated,
passes around the cylinder in order finally to emerge at the top toward
the center. The water having been thus methodically circulated, the
useful effect and regularity of the cooling process is increased.
Notwithstanding the care which is devoted to water circulation, it is
advisable to run the producer-gas engine "colder" than the older
street-gas types, in which the more economic speed is that at which the
water emerges from the jacket at about a temperature of 104 degrees F.
It would seem advisable to meet the requirements of piston lubrication
by reducing to a minimum the quantity of heat withdrawn by the
circulating water. Indeed, the personal experiments of the author bear
out this principle.
For street-gas engines, however, the cylinders should be worked at the
highest possible temperature consistent with the requirements of
lubrication. It should not be forgotten that, in large engines fed with
producer-gas, economy of consumption is a secondary consideration,
because of the low quantity of fuel required. The cost, moreover, may
well be sacrificed to that steadiness of operation which is of such
great importance in large engines furnishing the power of factories; for
in such engines sudden stops seriously affect the work to be performed.
For this reason engine builders have been led to the construction of
motors provided with very effective cooling apparatus. Since the
circulation of the water around the explosion-chamber and the cylinder
is not sufficient to counteract the rise of temperature, it has become
the practice to cool separately each part likely to be subjected to
heat. The seats of the exhaust-valves, the valves themselves, the
piston, and sometimes the piston-rod, have been provided with
water-jackets.
=Premature Ignition.=--Returning to the causes of the discouragements
encountered by some designers who endeavored to use high pressures, it
has already been mentioned that premature ignition of the explosive
mixture in cylinders not suited for high pressures is one reason for the
bad results obtained. An explanation of these results is to be found in
the high theoretical temperature corresponding with great pressures and
in the quantity of heat which must be absorbed by the walls of the
explosion-chamber. These two circumstances are in themselves sufficient
to produce spontaneous ignition of excessively rich mixtures, compressed
in an overheated chamber unprovided with a sufficient circulation of
water. A third cause of premature ignition may also be found in the old
system of ignition which, in most English engines, consists of a
metallic or porcelain tube, the interior of which communicates with the
explosion-chamber, an exterior flame being employed to heat the tube to
incandescence. In tubes of this type which are not provided with a
special ignition-valve, the time of ignition is dependent only on the
moment when the explosive mixture, driven into the tube, comes into
contact, at the end of the compression stroke, with the incandescent
zone, thereby causing the ignition. This very empirical method leads
either to an acceleration or retardation of the ignition, depending upon
the temperature of the tube, the position of the red-hot zone, its
dimensions, and the temperature of the mixture, which is determined by
the load of the engine. Although this system, the only merit of which is
its simplicity, may meet the requirements of small engines, there is not
the slightest doubt that it is quite inapplicable to those of more than
20 to 25 horse-power, for in such engines greater certainty in operation
is demanded. Even if only the more improved of the two types of hot-tube
ignition be considered, with or without valves, it must still be held
that they are inapplicable to high compression engines. The
ignition-valve is the part which suffers most from the high temperature
to which it is subjected. Its immediate proximity to the incandescent
tube, and its contact with the burning gas when it flares up, render it
almost impossible to employ any cooling arrangement. Although with the
exercise of great care it may work satisfactorily in engines of normal
pressure, it is evident that it cannot meet the requirements of high
pressure engines, because the temperature of the compressed mixture is
such that the charge is certain to catch fire by mere contact with the
overheated valve. In industrial engines of small size, premature
ignition has little, if any, effect except upon silent operation and
economic consumption. This does not hold true, however, of large
engines. Besides the inconveniences mentioned, there is also the danger
of breaking the cranks or other moving parts. The inertia of these
members is a matter of some concern, because of their weight and of the
linear speed which they attain in large engines. Some idea of this may
be obtained when it is considered that in a producer-gas or
blast-furnace-gas engine having a piston diameter of 24 inches and an
explosive pressure of 299 pounds per square inch, the force exerted at
the moment of explosion is about 132,000 pounds. Naturally, engine
builders have adopted the most certain means of avoiding premature
ignition and its grave consequences.
The method of ignition which at present seems to be preferred to any
other for producer-gas is that employing a break-spark obtained with
the magneto apparatus previously described. Some builders of large
engines, particularly desirous of assuring steadiness of running, have
provided the explosion-chamber with two independent igniters. It may be
that they have adopted this arrangement largely for the purpose of
avoiding the inconveniences resulting from a failure of one of the
igniters, rather than for the purpose of igniting the mixture in several
places so as to obtain a more uniform ignition and one better suited for
the propagation of the flame.
=The Governing of Engines.=--Various methods have been adopted for the
purpose of varying the motive power of an engine between no load and
full load, still preserving, however, a constant speed of rotation.
These methods consist in changing either the quantity or the quality of
the mixture admitted into the cylinder. Thus it may happen that an
engine may be supplied:
1. With a mixture constant in quality and in quantity;
2. With a mixture variable in quality and constant in quantity;
3. With a mixture constant in quality and variable in quantity.
1. _Mixture Constant in Quality and Quantity._--This method implies the
use of the hit-and-miss system of admission, in which the number of
admissions and explosions varies, while the value or the composition of
each admitted charge remains as constant as the compression itself (Fig.
34). This system has already been referred to and its simplicity fully
set forth. By its use a comparatively low consumption is obtained, even
when the engine is not running at full load. On the other hand, it has
the disadvantage of necessitating the employment of heavy fly-wheel to
preserve cyclic regularity.
2. _Mixture Variable in Quality and Constant in Quantity._--The
governing system most commonly employed to obtain a mixture variable in
quality and constant quantity is based upon the control of the
gas-admission valve by means of a cam having a conical longitudinal
section, as shown in Fig. 35. This cam, commonly called a "conical cam,"
is connected with a lever actuated from the governor. As the lever
swings under the action of the governor, the cam is shifted along the
half-speed shaft of the engine. The result is that the gas-admission
valve is opened for a longer or shorter period.
In another system a cylindrical valve is mounted between the chamber in
which the mixture is formed and the gas-supply pipe, the valve being
carried on the same stem as the mixture-valve itself. The cylindrical
valve is displaced by the governor so as to vary the quantity of gas
drawn in with relation to the quantity of air.
When the engines are fed with producer-gas the parts which have just
been described should be frequently inspected and cleaned; for they are
only too easily fouled.
Engines thus governed should be run at high pressure so as to insure
the ignition of the producer-gas mixtures formed when the position of
the cam corresponds with the minimum opening of the gas-valve. Powerful
governors should be employed, capable of overcoming the resistance
offered by the cylindrical valve or the cam.
It may often happen that variations in the load of the engine render it
necessary to actuate the air valve, so as to obtain a mixture which will
be ignited and exploded under the best possible conditions.
3. _Mixture Constant in Quality and Variable in Quantity._--In supplying
an engine with a mixture constant in quality and variable in quantity,
the compression does not remain constant. The quantity of mixture drawn
in by the cylinder may even be so far reduced that the pressure drops
below the point at which ignition takes place. For that reason engines
of this type should be run at high pressures.
The variation of the quantity of mixture may be effected in various
ways. The simplest arrangement consists in mounting a butterfly-valve in
the mixture pipe, which valve is controlled by the governor and
throttles the passage to a greater or lesser degree. A very striking
solution of the problem consists in varying the opening of the
mixture-valve itself. To attain this end the valve is moved by levers.
The point of application of one of these levers is displaced under the
action of the governor so as to vary the travel of the valve within
predetermined limits. Under these conditions a mixture of constant
homogeneity is introduced into the cylinder, so proportioned as to
insure ignition even at low pressures.
[Illustration: FIG. 76_a_.--Governing system for producer-gas engines.]
In recent experiments conducted by the author it was proved that with
this governing system ignition still takes place even though the
pressure has dropped to 43 pounds per square inch. This system has the
merit of rendering it possible to employ ordinary governors of moderate
size, since the resistance to be overcome at the point of application of
the lever is comparatively small. In the accompanying illustration the
Otto Deutz system is illustrated.
CHAPTER XI
PRODUCER-GAS
It may here be not amiss to point out the differences between
illuminating gas and those gases which are called in English "producer"
gases, and in French "poor" gases, because of their low calorific value.
=Street-Gas.=--This gas, the composition of which varies with different
localities, has a calorific value, which is a function of its
composition, and which varies from 5,000 to 5,600 calories per cubic
meter (19,841 to 24,896 B.T.U. per 35.31 cubic feet) measured at
constant pressure and corrected to 0 degrees C. (32 degrees F.) at a
pressure of 760 millimeters (29.9 inches of mercury, or atmospheric
pressure), not including the latent heat of the water of condensation.
The following table gives the average volumetric composition of
illuminating gas in various cities:
____________________________________________________________________
|
| Cities.
|______________________________________________
| | | | |
| | Manches- | New | |
| London. | ter. | York. | Paris. | Berlin.
_____________________|_________|__________|_______|________|________
| | | | |
Hydrogen | 48 | 46 | 40 | 52 | 50
Carbon monoxide | 4 | 7 | 4 | 6 | 9
Methane | 38 | 35 | 37 | 32 | 33
Various hydrocarbons | 4 | 6 | 7 | 6 | 5
Carbon dioxide | | 4 | 3 | | 2
Nitrogen | 5 | 2 | 8 | 4 | 1
Oxygen | 1 | ... | 1 | ... | ...
|_________|__________|_______|________|________
| | | | |
| 100 | 100 | 100 | 100 | 100
_____________________|_________|__________|_______|________|________
Furthermore, these constituents vary within certain limits. This is also
true of the calorific value. Experiments made by the author have
demonstrated that in the same place at an interval of a few hours,
variations of approximately ten per cent. occur.
=Composition of Producer-Gases.=--The average chemical composition of
producer-gases varies with the conditions under which they are generated
and the nature of the fuel. The following are the proportions of its
constituents expressed volumetrically:
Table Headings--
A: Blast Furnace.
B: Producer.
C: Mond.
D: Mixed (Fichet).
E: Water (Stache).
F: Wood (Riche).
________________________________________________________________________
|
| Gas.
|_________________________________________________
| | | | | |
| A. | B. | C. | D. | E. | F.
______________________|_______|_______|_______|________|________|_______
| | | | | |
Nitrogen and oxygen | 60 | 59 | 42 | 50 | 5 | 1
Carbon monoxide | 24 | 25 | 11 | 20 | 40 | 29
Carbon dioxide | 12 | 5 | 16 | 7 | 4 | 11
Hydrocarbons | 2 | 2 | 2 | 3 | 1 | 15
Hydrogen | 2 | 9 | 29 | 20 | 50 | 44
|_______|_______|_______|________|________|_______
| | | | | |
| 100 | 100 | 100 | 100 | 100 | 100
|_______|_______|_______|________|________|_______
Calorific value | | | | | |
in calories. | 950 | 1,100 | 1,400 | 1,300 | 2,400 | 2,960
Average weight of a | | | | | |
cubic meter in kilos| 1.30 | 1.1 | 1.02 | 1.05 | 0.680 | 0.824
Or of a cubic foot | | | | | |
in pounds | 0.008 | 0.007 | 0.006 | 0.0068 | 0.0042 | 0.0051
______________________|_______|_______|_______|________|________|_______
Blast-furnace gas has been used for generating power by means of
gas-engines for about ten years. At the present time it is used in
engines of very high power, a discussion of which engines more properly
belongs to a work on metallurgy, and has no place, therefore, in a
manual such as this.
Producer-gas, in the true sense of the term, is generated in special
apparatus either under pressure or by suction in a manner to be
described in the following chapters.
Mond gas is produced in generators of the blowing or pressure type from
bituminous coal, necessitating the employment of special purifiers and
permitting the collection of the by-products of the fractional
distillation of the coal. Mond gas plants are, therefore, rather
complicated and can be advantageously utilized only for large engines.
More exhaustive information can be obtained from the descriptions
published by the builders of Mond gas generators.
Mixed gas is generated in apparatus arranged so that the retort is kept
at a high temperature, thereby producing a gas richer in hydrogen than
that made by producers. It should be observed that in practice the
generators at present used yield a producer-gas, the calorific value of
which fluctuates between 1,000 and 1,400 calories per cubic meter (3,968
to 5,158 B.T.U. per 35.31 cubic feet); and the composition varies
accordingly, in the manner that has already been indicated in the tables
for producer-gas and mixed gas. There is no necessity, therefore, for
drawing a distinction between these two qualities of gas.
Water-gas should theoretically be composed of 50 per cent. carbon
monoxide and 50 per cent. hydrogen, resulting from the decomposition of
steam by incandescent coal. In practice, however, it contains a little
nitrogen and carbon dioxide. The gas is obtained from generators in
which air is alternately blown in to fan the fire and then steam to
produce gas. Water-gas is employed in soldering on account of its
reducing properties and of the high temperature of its flame. The great
quantity of carbon monoxide which it contains renders it very poisonous
and exceedingly dangerous, because it is generated under pressure. From
the economical standpoint, its generation is more expensive than that of
producer-gas, for which reason its employment in gas-engines is hardly
of much value.
Wood-gas, the composition of which has already been given, is generated
in apparatus of the Riche type, the principle of which consists in
heating a cast retort charged with any kind of fuel, namely wood, and
vertically mounted on a masonry base.
This apparatus should be of particular interest to the proprietors of
sawmills, furniture factories, and the like, since it offers a means of
using the waste products of their plants.
The relatively high proportion of carbon monoxide in producer-gas is
objectionable from a hygienic standpoint, so much so, indeed, that it
has attracted the attention of manufacturers. Carbon monoxide, the
specific gravity of which is 0.967, is a gas peculiarly poisonous and
dangerous. It cannot be breathed without baneful effects, and is even
more dangerous than carbonic-acid gas, which eventually causes
asphyxiation by reducing the quantity of oxygen in the air. For this
reason, it is necessary to take the utmost precaution in efficiently and
continuously ventilating the rooms in which the gas-generators and their
accessories are installed. This suggestion should be followed, above
all, when the apparatus in question are installed in cellars and
basements. As a further precaution, where the plant is rather large a
workman should not be allowed to enter the generator room alone.
Blowing-generators, or those in which the gas is produced under
pressure, are more dangerous than suction-generators. In the former a
leaky joint may cause the vitiation of the surrounding air as the
producer-gas escapes; in the suction apparatus the same fault simply
causes more air to be drawn in.
Dr. Melotte recommends the following procedure in cases of carbon
monoxide asphyxiation:
CARBON MONOXIDE ASPHYXIATION
Cases of poisoning by carbon monoxide are both frequent and dangerous.
The gas is extremely poisonous, and all the more dangerous because it is
odorless, colorless and tasteless. When it comes into contact with the
blood, it forms a combination so stable that it is reacted upon by the
oxygen of the air only with difficulty. It follows, therefore, that with
each respiration of air charged with carbon monoxide, a certain quantity
of blood is poisoned. In consequence of this, there is a possibility of
poisoning in open air.
=Symptoms.=--The symptoms observed will vary with the manner in which
the blood has been poisoned. There are two ways in which this poisoning
can occur. The one depends upon whether the atmosphere contains an
excess of carbon monoxide; the other whether the air breathed contains
only traces of the gas.
=Gradual, Rapid Asphyxiation.=--At first a vague sickness is felt,
rapidly followed by violent headaches, vertigo, anxiety, oppression,
dimness of vision, beating of the pulse at the temples, hallucinations,
and an irresistible desire to sleep. If at this stage the patient has a
sufficient idea of danger to prompt him to open a window or door, he
will escape death.
In the second stage, the victim's legs are paralyzed, but he can still
move his arms and his head. The mind still preserves its clearness, and
in a measure assists the further process of asphyxiation because of its
impotency. Then follow coma and death.
=Slow, Chronic Asphyxiation.=--Slow, chronic asphyxiation is not
infrequent. Its symptoms are often difficult to detect. Poisoning is
manifested by weakness, cephalalgia, vomiting, pallor, general anemia,
lassitude, and local paralysis. If any of these symptoms appear in the
men who work in the vicinity of the producers, immediate steps should be
taken to prevent the possibility of carbon monoxide asphyxiation.
FIRST AID IN CASES OF CARBON MONOXIDE POISONING
It has already been stated that the oxygen of the air has no oxidizing
effect upon blood contaminated by carbon monoxide. Only a liberal
current of pure oxygen can oxidize the combination formed and render
hematosis possible. This liberal current can be obtained from an oxygen
tank of the portable variety, provided with a tube carrying at its free
end a mask which is held over the mouth and the nostrils. The
absorption of gas takes place by artificial respiration, which is
effected in several ways. The most practical of these are the Sylvester
and Pacini methods.
=Sylvester Method.=--The patient is laid on his back. His arms are
raised over his head and then brought back on each side of the body.
This operation is repeated fifteen times per minute approximately. The
method is very frequently employed and is excellent in its results.
=The Pacini Method.=--Four fingers are placed in the pit of the arm,
with the thumb on the shoulder. The shoulder is then alternately raised
and lowered, producing a marked expansion of the chest. This method is
the more effective of the two. The movements described are repeated
fifteen to twenty times each minute very rhythmically.
One or the other of these two methods of treatment should be immediately
applied in serious cases. Certain preliminary precautions should be
taken in all cases, however. The patient should be carried to a
well-ventilated and moderately heated room, stripped of his clothes, and
warmed by water-bottles and heated linen. Reflex action should be
excited, the peripheral nervous system stimulated in order to contract
the heart and the respiratory muscles, and the precordial region
cauterized. In addition to this treatment, the region of the diaphragm
should be rubbed and pinched, the skin rubbed, cold showers given,
flagellations administered, urtications (whipping with nettles)
undertaken, the skin and the mucous membranes excited, the mucous
membrane of the nose and of the pharynx titillated with a feather dipped
in ammonia, alcohol, vinegar, or lemon juice. Rhythmic traction of the
tongue is effective when carried out as follows: The tongue is seized
with a forceps and kept extended by means of a coarse thread. It is then
pulled out from the mouth sharply and allowed to reenter after each
traction. These movements should be rhythmic and should be repeated
fifteen to twenty times a minute.
All these efforts should be continued for several hours. When the
patient has finally been revived, he should be placed in a warm bed.
Stimulants such as wine, coffee, and the like should be administered. If
the head should be congested, local blood-letting should be resorted to
and four or six leeches applied behind the ears. It should be borne in
mind that the various steps enumerated are to be taken pending the
arrival of a physician.
IMPURITIES OF THE GASES
Most of the coal used in generating producer-gas contains sulphur.
Sulphuretted hydrogen is thus produced, which mixes with the gas and
imparts to it its characteristic odor. In some gas-generators, purifiers
are employed in which sawdust mixed with iron salts is utilized, with
the result that a combination is formed with the sulphuretted hydrogen,
thereby removing it from the producer-gas. In other forms of generators
a more summary method of purification is adopted, so that traces of
sulphuretted hydrogen still remain. Since this gas attacks copper, the
employment of this metal is not advisable for the following apparatus:
Generator (openings, cock for testing the gas); piping (gas-pressure
cocks, drain and pet cocks); engine (gas-admission cock, lubricating
joint in the cylinder, valves and cocks of the compressed-air
starting-pipe).
The distillation of coal in generators results in the formation of
ammonia gas. This also has a corrosive action on copper and its alloys;
but owing to its great solubility, it is eliminated by the waters of the
"scrubber" and does not reach the engine.
PRODUCTION AND CONSUMPTION
The quantity of gas produced in most generators varies from 6.4 to 8.2
pounds per cubic foot of raw coal burnt in the generator. The engine
consumes per horse-power per hour 70 to 115 cubic feet of gas, depending
upon its richness.
CHAPTER XII
PRESSURE GAS-PRODUCERS
As we have already seen, producer-gas as a fuel for engines may be
generated in two kinds of apparatus, the one operating under pressure,
and the other by suction.
=Dowson Gas-Producers.=--The first pressure-generators were introduced
by Dowson of London and necessitated installations of quite a
complicated nature. Later improvements made by the designers contributed
much to the general employment of their system. Many installations
varying from 50 to 100 horsepower and more may be found in the United
Kingdom, all of them made by Dowson. Indeed, for a long time the name of
Dowson was coupled with producer-gas itself. The Dowson system
necessitates the utilization of anthracite or of comparatively hard
coal, such as that mined in Wales and Pennsylvania. Owing to the
necessity of employing this specia
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