DESCRIPTION OF EXISTING GAS ENGINES
_Early Lenoir engine_ (1860).—The motor (Fig. 1) resembled in external
appearance a horizontal double-acting steam engine. This design was in
great favour at that time, being copied from the steam engine, and was
to a certain extent suitable for use with an explosive gas instead of
steam. The valve chest is cylindrical and the valves themselves flat,
and work off two eccentrics; ignition is effected by an electric spark
from a Ruhmkorff coil, which passes through the gas in the cylinder
when the piston is commencing the second half of the forward stroke.
The exploded gases having done their work are driven out through the
exhaust in the return stroke, during which work is being done by a
similar explosion on the other side of the piston. A water jacket
prevents the cylinder walls from becoming overheated. This arrangement
is therefore double-acting, but a compression of the explosive gas
is not possible without the use of a second cylinder. It has been
abandoned because regularity of working is only obtained at the expense
of economy, and by using both sides of the piston as explosive
chambers it is found that the quantity of gas used is quite out of
proportion to the power developed.
[Illustration: FIG. 1.—Early Lenoir Motor (1860).]
_The Bisschop gas engine._—This motor (Fig. 2), based on a mixed
principle, uses the explosion to do work during the forward stroke,
and in the return the atmosphere exerts an excess of pressure on the
other side of the piston, as in the Otto and Langen atmospheric engine
which we have previously mentioned. In its time the Bisschop gas engine
obtained a great measure of success, but it has now almost completely
disappeared. It was, however, well thought out and constructed; the
cylinder was vertical, and relied on longitudinal corrugations, and the
air to keep it cool. Above the cylinder was placed a cylindrical guide;
a connecting rod and cross-head formed the attachment between the
piston rod and crank. The machine was principally constructed for small
workshops requiring small powers of from a quarter to one horse-power,
the cost of fuel for the half horse-power size being about one penny
per hour. The inventor received a prize of 1000 francs from the Société
d’Encouragement for the best small motor applicable to home industries.
[Illustration: FIG. 2.—Bisschop Motor.]
_François motor._—This type, which is now quite obsolete, was somewhat
similar in character to the last, but rather more complicated and
perfect. The crank shaft was not in a line with the cylinder, and was
connected by two connecting rods to the cross-head. Two fly-wheels
were placed one on each side of the cylinder and connected by toothed
wheels. The machine was on the whole too complicated, and although its
consumption of fuel was comparatively small and its speed constant, it
did not succeed in ousting the Bisschop motor from its position.
_Bénier gas engine._—This motor was the first conceived by the
inventors of the combined gas plant and engine which we will describe
later, and is extremely simple. This piston rod is connected to the
crank in a manner similar to a beam engine (Fig. 3). Both the admission
of the gases and their ignition are accomplished by a single spring
valve worked by a cam on the crank-shaft. The cylinder, which is
vertical and inverted, draws in the gases for half the forward stroke,
and then the valve, which has moved still further forward, brings a
flame opposite the admission port and ignites the mixture; a small
auxiliary gas-jet re-ignites the flame at each stroke. The gases
escape from the cylinder by a second port with a special valve and cam.
A water jacket for the cylinder is provided to carry off the surplus
heat. The consumption is high, being about 1400 litres per horse-power
hour, but owing to the extreme simplicity of the working parts this
motor met with a certain amount of success about 1880.
[Illustration: FIG. 3.—Bénier Motor.]
_Forest gas engine_ (Fig. 4).—This motor, being of the single-acting
type without compression, had at one time a considerable sale, being
used where only a small power was required. The rectilinear motion
is changed into a rotary one by means of an Oliver Evans beam, and
a connecting rod which returned alongside of the cylinder to the
crank-shaft and fly-wheel, which are placed at the back. Ignition is
obtained by a burner which is re-lit by a smaller one at each stroke,
and the cylinder is cooled not by a water jacket but by a helical
groove, which increases the surface. This helix is formed by a thin
plate cast on the cylinder. The fuel consumed was about 1400 litres
of gas per horse-power hour, which may be considered good for such an
engine.
[Illustration: FIG. 4.—Forest Motor.]
_Economic motor._—Constructed in New York. This engine is another
example of the early attempts to obtain economy without compression. As
a rule they were not constructed of more than half horse-power size,
and the general arrangement is ingenious, but rather more complicated
than those which we have so far spoken of. The piston rod is guided by
being attached to one end of a lever, connected with crank by means of
a vertical connecting rod. The cylinder is grooved, and cooled by the
circulation of the air round it, and constancy of speed is obtained by
a centrifugal governor, which cuts off the supply of gas when the speed
is too high. The engine seems to have given some very fair results.
_Lentz gas engine._—It is difficult to conceive a more simple mechanism
than is to be found in this motor. The supply of gas is drawn into the
cylinder by an open valve, and a gas flame situated in this admission
port ignites the explosive gases. The force of the explosion closes the
admission valve, and on the return stroke a cam opens an exhaust port
situated underneath the cylinder. There is no water jacket, but the
cylinder is formed of two parts connected together by a non-conducting
joint. In order to smooth down the jerk of the explosion the head of
the connecting rod slides in a groove, and is kept pressed against the
crank-pin by a spring, the result being that the connecting rod is
longitudinally elastic and deadens the shock of the explosion.
GROUP II., CLASS I.—ONE CYCLE PER REVOLUTION.
_Dugald-Clerk gas engine._—In the ideal motor we should have at least
one explosion per revolution of the fly-wheel, which is not the case in
the Otto cycle. For this reason many inventors have tried to construct
gas engines with one cycle per revolution, but experience has taught
us that though they may be mechanically more simple, they lose in
efficiency what they gain in simplicity, and in spite of many eminent
inventors attempting to solve the problem. Even the best-designed
motors of this type have been unable to hold their own against the Otto
cycle because they are not as efficient.
The first attempt was made by Dugald-Clerk in 1881. His engine is
simple in the extreme, containing no gear-wheels, and working steadily
and noiselessly at a fairly constant speed (Fig. 5).
There are two cylinders of equal diameter placed side by side, and
projecting over the end of a cast-iron bed-plate. The first of these
is the motive cylinder in which the explosion takes place; the other
is used for compressing the explosive mixture, this compression taking
place in the Otto cycle in the motive cylinder itself.
This secondary cylinder also serves for another purpose; it draws in a
certain volume of air directly after the explosion, which is afterwards
driven through the motive cylinder, effectively clearing out the waste
gases. The advantage which this arrangement of double cylinders has
over the Otto cycle, lies in the fact that one explosion can take place
during each revolution of the crank, and consequently such very heavy
fly-wheels as are used for the Otto type of engine are not necessary.
The great disadvantage which the Dugald-Clerk motor possesses is the
extreme suddenness of the explosion, which is practically complete
before the piston begins to move. In spite of this defect the machines
have a fairly high efficiency. The gases are ignited by a gas-jet
situated in a sliding valve. A water jacket is used for cooling the
cylinder, and in some of these motors a mechanism is attached for
converting the engine from simple to compound. The compression cylinder
then becomes double-acting, and the gases are further expanded in what
was previously the motor cylinder only.
[Illustration: FIG. 5.—Plan of Dugald-Clerk Engine.]
Owing to the fact that this motor was not as efficient as those of the
Otto type it never became a commercial success, and it is doubtful if
any are working at the present date.
_Early Stockport gas engine._—The working of this motor affords a good
example of British ingenuity. The compression cylinder is situated
behind the motive cylinder, being a prolongation of it on the same
axis; the two are firmly bolted together end on. The active piston is
in front and connected to the crank, drawing behind it the piston of
the compression chamber. Each cylinder has a separate sliding valve.
The rear cylinder having aspirated and compressed a volume of the
explosive gases, they are passed into the motive cylinder through a
sliding valve which also serves to ignite them. The waste gas escapes
into the air by a special valve. The aspiration and compression take
place in the auxiliary cylinder once in every revolution of the crank,
and besides, the motive piston also compresses the gases a trifle
before the explosion takes place. The exhaust valve is made to open
slightly before the piston reaches the end of its stroke. The motor
was rather inefficient, and since its appearance a new type has been
brought out with an Otto cycle which we will describe later on.
_Benz motor_ (Fig. 6).—In this motor the inventor attempts to drive out
the whole of the exhaust gases before the second half of the backward
stroke of the piston is reached. To do this he injects a certain volume
of air under pressure, driving out the burnt gases and substituting
itself in their place. Before the end of this return stroke a small
auxiliary pump introduces the requisite amount of coal gas, which is
then compressed during the rest of the stroke. The ignition is effected
by a small magneto machine driven by the engine itself, the sparks
being generated between two fine metallic points in the cylinder.
The jet of air required to drive out the product of the combustion
is furnished from a reservoir, pressure in it being maintained by
using the other side of the piston as an air-pump. This arrangement
is an advantage, because cold air is being continually drawn into the
cylinder which keeps it cool, and enables the lubrification to take
place more effectively. There is also an external cooling apparatus in
the form of a water jacket, which uses about 40 litres of water per
horse-power hour, and keeps the cylinder at about 75° C. The Benz
motor is very well known on the Continent, and much of its success is
due to the fact that it seems to work as well with gasoline as with
coal gas! It is constructed by M. Roger of Paris, and in consequence of
the extreme constancy of its speed, it has been successfully applied to
driving dynamos, and also to launches, motor cars, etc.
[Illustration: FIG. 6.—Benz Gas Engine.]
_Baldwin gas engine._—The cycle of this engine is somewhat similar to
that of the Benz motor, one side of the piston being used for expansion
and the other side for compression. Part of the bed-plate casting is
arranged so as to form a reservoir for the compressed gases. The coal
gas is also admitted into this vessel, so that it contains an explosive
mixture. As the vessel is only made of cast-iron this arrangement
is rather dangerous. There are three valves, the admission valve
being regulated by the governor. The power developed is, therefore,
always kept proportional to the demand, and the constancy of speed is
sufficient to warrant the use of these engines for running dynamos for
electric light. The ignition is by an electric spark, and is generally
obtained from some extra apparatus, such as accumulators or batteries,
and an induction coil. The engine is constructed by Messrs. Otis Bros.
of New York.
_De Ravel motors._—The first motor constructed by M. de Ravel was
exhibited in Paris in 1878, and was of the oscillating cylinder
type, with a variable centre of gravity. The explosion drove up a
heavy piston whose rod was directly connected to the crank-pin. The
revolution of the crank-pin caused the whole cylinder to move in the
same manner as that of the early oscillating steam engines. This
movement was used as a means of opening and closing the ports. The
efficiency of the engine was low, using some 600 to 700 litres of
gas per horse-power hour; and besides the motor had, owing to faulty
mechanism, the unhappy knack of suddenly stopping dead. These defects
caused M. de Ravel to abandon this type and to bring out a second motor
in 1885, performing one cycle per revolution. This new motor only had
one cylinder, whose rear half acted as a compression chamber during the
backward stroke of the piston, whilst the explosion took place in the
front end of the cylinder. The consumption of gas was slightly more
than an Otto engine, and the motor ran exceedingly silently and evenly,
but this advantage was not of much service in the struggle against the
all-conquering Otto motor.
_Midland motor (Taylor)._—Constructed in Nottingham, this engine is
of the horizontal double-cylinder type. One cylinder compresses the
explosive mixture and passes it on to the other, where it is ignited
and does work. The cranks connected to the two pistons are placed
65° apart, and a complete cycle in the cylinders is performed every
revolution. The makers of this engine claim a consumption of only 600
litres of gas per horse-power hour.
_Campbell gas engine._—The mechanism of this engine is very much
like that of the Dugald-Clerk motor, two cylinders being placed side
by side. The utilization of the heat is, however, far superior, and
only about 500 litres of coal gas per horse-power hour are required.
A result which the inventor of this type of cycle never succeeded in
obtaining, but as far as we know the motor has never had any official
trial, and the above figures are only taken from the makers prospectus.
However, there is only a hardly perceptible shock from the explosion,
and the motor can be safely recommended to anybody requiring a silent
gas engine. There still exist gas engines worked on this same cycle
per revolution principle, such as the Conelly, Day, De Ravel motors,
descriptions of which must be sought elsewhere. The limited space at
our disposal prevents us from discussing all those types which have
only obtained a very small measure of success. The only remaining
engine based on this principle worth mentioning is the Bénier motor,
which is exceedingly instructive, but we shall speak of it later under
the head of poor-gas engines. We shall at present pass on to the
consideration of engines based in principle on the patent of Beau de
Rochas, and first practically realized in 1877 by Dr. Otto.
_Otto gas engine_ (Fig. 7).—The principle on which this engine is based
is known as the Otto cycle, named after Dr. Otto, but first suggested
by Beau de Rochas. Since the patents have expired numerous copies and
imitations have been brought out, but very few surpass or even equal
some of the earlier types.
[Illustration: FIG. 7.—Otto Gas Engine.]
The explanation of the working of the Otto motor, which we are about
to give, will save us from returning to it in the descriptions of
analogous types brought out after this famous system. The cylinder is
continued in a backward direction so as to form a compression chamber,
into which the mixture of gas and air is drawn during the forward
stroke of the piston. The mixture is compressed during the return
stroke in this chamber, the pressure rising at the end of the stroke to
about 3 or 4 atmospheres. At this point in the cycle a flame is brought
into contact with the compressed gases and they explode. This explosion
raises the temperature of the gases to 1500° C., and drives forward the
piston under a pressure of about 150 lbs. to the square inch. During
the second return stroke, corresponding to the latter half of the
second revolution of the crank, the piston drives out the products of
the combustion into the air under a pressure of about an atmosphere.
The heating of the cylinder is avoided by keeping water automatically
circulating through a jacket surrounding it. This is necessary, because
if the cylinder walls became heated, the oil upon them would become
decomposed, and lose its lubricating properties. Dr. Otto paid special
attention to the efficiency of the engine, and in order to increase
it, he diluted the air and gas drawn into the cylinder with a portion
of the gases already burnt in the previous stroke. Consequently the
explosion at the beginning of the stroke is less violent, and the
gases continue burning while the piston moves forward. The cause of
this slow combustion has been wrongly attributed to stratification
of superimposed layers of gas and air, but it is probably due to the
action of the cylinder walls.
The Otto gas engine is a marvel of simplicity from a mechanical
point of view, very much more so than a Corliss steam engine for
instance. The admission and exhaust valves are worked by cams, and the
ignition takes place under pressure. The governor is sometimes of the
centrifugal type, and at others of the inertia type, but in both it
is a case of all or nothing, the supply being completely shut off if
the engine is going too fast. The connecting rod joins the crank to
the piston rod by a cross-head running into a bored out-guide. It is
necessary to have a heavy fly-wheel, because, as only one explosion
takes place per two revolutions, the fly-wheel must store up enough
energy during that explosion to carry it through the rest of the cycle.
Many different types of Otto gas engines now exist, some having two
cylinders and a single crank, and others two fly-wheels, in order
to ensure constancy of speed for driving dynamos. Dr. Otto devised
a compound gas engine, but it did not succeed, and also a cheaper
vertical type (Fig. 8), which is very convenient for small workshops.
Since the invention of carburetted air the creator of the Otto cycle
has devised another motor for use with gasoline instead of coal gas.
Otto devised the first practical gas engine and opened up the path for
others, who, following in his footsteps, have confined their attention
to improvement of detail. Some have undoubtedly succeeded, and by
avoiding waste of heat, and by raising the initial temperature of the
gases, they have considerably reduced the consumption of fuel. We shall
now discuss different types of motors which have appeared during the
last fifteen years, confining ourselves to the really successful ones.
[Illustration: FIG. 8.—Otto Gas Engine (vertical type).]
_Second Lenoir motor._—Twenty-five years separated the appearances of
the first and second Lenoir motors, and during this time M. Lenoir
gained a great deal of practical experience, so that if reference be
made to Figs. 1 and 9 they will be seen to have very little in common.
In the later type the cylinder projects over the back of the bed-plate,
and is provided with deep circular grooves on the outside to increase
the cooling surface. Ignition is obtained by the spark from a coil
supplied by a battery as in the early form. The consumption of gas is
about 800 litres per horse-power hour. Later on we shall discuss a
petroleum motor for motor cars, and also a stationary petroleum engine
by the same inventor. These engines were originally constructed by
Mignon and Rouart, but later by the Compagnie Parisienne du Gaz, and
are very well designed and constructed.
[Illustration: FIG. 9.—Lenoir Gas Engine (second type).]
_Koerting-Lieckfeld motor._—The first of these motors was constructed
in 1877, and was based on the Dugald-Clerk cycle. The original type
has, however, been abandoned, and the firm of Brûlé et Cie. of Paris
now construct these engines on the Otto system. All the moving parts
are attached to a vertical frame of cast-iron (Fig. 10), the lower half
containing the cylinder. The admission and exhaust valves are situated
in front and near the base. The governor is of the centrifugal type and
acts directly on the levers of the valves. The flame ignition makes it
necessary to occasionally clean out the valves, but otherwise the motor
has few drawbacks, and is very neat and compact. The consumption of
coal gas for engines of 8 horse-power and upwards is about 800 litres
per horse-power hour. The crank-shaft is placed horizontally across
the top of the frame, and the cams acting upon the valves are rotated
by a bevel gear enclosed in a case, driving a thin supplementary shaft
on which they are placed. The motor is self-lubricating, and is also
constructed as a horizontal gas engine.
[Illustration: FIG. 10.—Koerting-Boulet Motor.]
_Andrews’ motor._—The governing apparatus in this engine is exceedingly
simple and ingenious, consisting of a weight fixed to an oscillating
lever which controls the admission valve. The position which the weight
takes up depends upon the rapidity with which the lever oscillates, and
consequently upon the speed of the engine. If, therefore, the engine
is running too fast or too slow the weight takes up a new position,
and the effect upon the admission valve is to either slow down or
quicken the speed. The gases are ignited by means of a tube kept
red-hot by a gas flame. This engine possesses the special advantage
of being self-starting, that is to say, it is not necessary, as in
many other motors, to start the engine by giving the fly-wheel a few
rapid turns by hand. The motor is stopped with the crank in a position
slightly in advance of the point corresponding to ignition. The gas is
allowed to enter by a small auxiliary valve, which closes after the
first explosion. This volume of gas entering the cylinder mixes with
the air already in it, forming an explosive mixture. This explosive
mixture then begins to escape by similar automatic self-closing valves
situated at the top of the red-hot ignition tube. Ignition takes place,
and is communicated to the rest of the gas in the cylinder, closing the
two small valves by the force of the explosion. The piston is therefore
driven forward, and the energy of this combustion is sufficient to
start the engine. It must be understood that this operation is only
performed once at starting, for immediately afterwards the engine
falls into its normal cycle of operations. Two fly-wheels are as a
rule provided to ensure constancy of speed. The consumption of gas is
as low as 580 litres per horse-power hour in the large units of 100
horse-power.
The Andrews gas engine is also constructed of a special type for
consuming poor gas produced by the Dowson process, and gives very
good results. As a rule, about 600 to 800 grammes of anthracite are
necessary to produce one horse-power hour. In one particular plant
generating electricity, the cost has been certified to be as low as one
penny per kilowatt hour, including lubrication.
_Fielding gas engine._—The characteristic point in these engines is
the extreme simplicity of the valve gear, only one valve being ever
subjected to pressure. Even in the small engines of this type all
sliding valves are replaced by those of the spring pattern, in fact,
the valve mechanism consists simply of two spring-valves, one of which
fulfils two functions, controlling the admission and the escape of the
gases. The two valves are moved by a double lever actuated by a single
cam. The cycle is that of Dr. Otto. When the piston is starting on the
return stroke after an explosion has taken place, the lever lifts
one of the valves, and the products of the combustion escape into a
circular space situated below. In the next forward stroke this valve
is still further lifted, opening the admission port, while at the same
moment the exhaust port is closed by the second valve; a new charge is
therefore drawn into the cylinder. At the end of the admission stroke
the valves are released by the lever, and the compression can now take
place during the second return stroke. The movement causing the lifting
of the valve continuously throughout one whole revolution is effected
by means of a cam with two prominences on it, which act in succession
on the lever. There is only one valve, therefore, which is subjected
to pressure, and even this is well provided against risk of leakage by
the second valve being placed behind it, acting as a double seating.
A chamber is also provided in which the gases are first mixed, and
this mixing is regulated by a second lever and a special valve. The
governor is of the inertia type, and is attached to the upper side of
the double lever. It consists of a straight rod with a ball at one end
and a knife edge at the other, pivoted at its centre to the end of the
valve lever. As this lever is thrown forward the knife edge strikes the
end of the spring-valve admitting gas to the mixing chamber. If the
speed is too great the sudden jerk on the ball at the other end of the
knife edge causes it to miss the valve, and no gas is admitted till
the speed is reduced to the normal number of revolutions per minute.
This arrangement is very sensitive, and keeps the speed exceedingly
constant. Mr. Fielding has constructed some large gas engines of 350
horse-power which are started by compressed air, this air having been
previously stored up under pressure when the motor was stopping.
_Niel motor._—As will be seen from Fig. 11, the valves are actuated
by cams rotating on a supplementary shaft placed parallel to the
cylinder. A pair of toothed wheels transmit the rotation of the crank
to this valve-shaft, and it is arranged so as to give one rotation to
every two of the crank. The cycle of operations is somewhat similar
to the Otto cycle; gas is only admitted to the cylinder for two-thirds
of the forward stroke, so that the compression on the back stroke is
somewhat lessened. It is doubtful whether there is much advantage in
this method, but the Niel motors have had a large sale, which is a
sufficient proof of their good qualities.
[Illustration: FIG. 11.—Niel Gas Engine (elevation and sectional plan).]
_Lombart, Martini_ (Fig. 12), _Adam, Le Parisien, and Le Kientzy
motors._—All these motors, each of which is constructed by a different
maker, are based in principle on the Otto engine, and except for slight
modifications of the working parts, they do not call for any particular
notice. The small amount of space at our disposal only admits of our
mentioning them.
[Illustration: FIG. 12.—Martini Motor.]
_Lablin motor_ (Fig. 13).—M. Lablin of Nantes set himself to produce
a motor which should correspond with the Brotherood and Westinghouse
steam engine, that is to say, a motor developing the maximum of
power for the minimum of space and weight. This might be termed the
dynamic density of the motor, which M. Lablin sought to increase. He
has succeeded in constructing gas motors of ½ horse-power weighing
about 90 lbs., and of 8 horse-power weighing 7 cwt. Unfortunately
they consume a rather large quantity of fuel—about 1000 litres of
coal gas, or 500 grammes of gasoline per horse-power hour. There are
three cylinders grouped at equal distances round the same shaft,
and all attached to one single crank. By this arrangement a more
constant torque or twisting movement on the shaft is obtained, and
consequently the weight of the fly-wheel can be considerably reduced.
Three explosions are produced during every revolution, that is to say,
each cylinder performs a complete cycle of operations during every
revolution, a fact which accounts for the low efficiency. Ignition
is obtained by a platinum tube heated to incandescence when using
coal gas, and by an electric spark when carburetted air is used. The
governor is centrifugal, and controls the admission of gas.
[Illustration: FIG. 13.—Lablin Three-cylinder Motor.]
_Crossley Bros. gas engine_ (Figs. 14, 15).—This engine is from the
cycle point of view purely and simply an Otto gas engine. A light
shaft runs parallel to the cylinder, being driven by a worm-gear of
the crank-shaft. On it are situated the cams which force open the four
spring-valves, controlling respectively the admission of air gas and
the ignition and exhaust.
[Illustration: FIG. 14.—Crossley Gas Engine (X type).]
[Illustration: FIG. 15.—Crossley Gas Engine.]
The pressure of the gases is raised during compression to about four
atmospheres, and immediately after the explosion it rises to about 180
lbs. on the square inch; during the exhaust it averages about 10 lbs.
per square inch. Ignition is obtained by a tube heated to a bright red
incandescence by a Bunsen flame. At the right moment a valve is opened,
placing the explosive mixture in contact with it and causing the
explosion. When starting the machine the ignition is retarded or takes
place a little after passing the dead point, so that the machine cannot
start the wrong way by mistake. Two or three other features call for
special notice, especially the device for lubricating the cylinder. In
the illustration (Fig. 14) will be seen a small bell-shaped receptacle.
This vessel contains oil, and also a small crank inside driven by a
belt off the valve-shaft. As this crank rotates it dips into the oil at
the bottom of the vessel, and at the top of its path it wipes off the
oil which it has gathered on to a cup which allows it to flow into the
cylinder.
The water jacket is cast separately from the cylinder, and not, as in
many engines, in one piece with it. There is an advantage in this,
because there is less likelihood of flaws or blow-holes in the cylinder
wall passing unobserved when the engine is leaving the maker’s hands.
The governor in some of the sizes is centrifugal, and in others of the
inertia type similar to that described in the Fielding gas engine.
_Pygmée motor (Lefebvre)._—This motor, shown in Fig. 16, gives one the
idea of solidity and compactness. It possesses the peculiar property of
working equally well in any position, either horizontal or vertical.
This is due to the fact that it is particularly well balanced, and when
running does not vibrate at all. Easily started, these engines run at
a very constant speed, and their power in relation to their size is
truly remarkable, hence the name Pygmée. They have been especially
designed for self-propelled vehicles, and are not affected by the worst
running conditions, such as inclement weather or bad roads. In this
type they are constructed with two cylinders in order to obtain a more
constant torque, and also have an arrangement by which the speed can be
changed. For stationary purposes the motor is mounted on a cast-iron
stand (Fig. 16). In virtue of their exceedingly small dimensions and
reduced weight they are specially suitable where small-power motors
are required for home industries or small workshops, and also for
driving private electric installations and pumping water. They have
economically replaced steam engines in agricultural operations, both on
a large and small scale. The working parts being entirely enclosed they
stand a good deal of rough usage, and will work in positions in which
other motors would be useless. Where it is necessary to bring the motor
to the work it is required to perform they are bolted to a carriage
instead of a cast-iron base.
[Illustration: FIG. 16.—Pygmée Gas Engine.]
_The “National” gas engine._—As a gas engine this machine is
constructed in all sizes, from one horse-power up to large units
requiring a gas plant of their own. As petroleum motors they range from
one to ten horse-power. They are all provided with two fly-wheels,
which keep them well balanced and steadies their speed. They have
besides been especially designed with a view to economy of coal gas
or petroleum. An idea of the general arrangement of the parts will be
obtained by glancing at Fig. 17. The petroleum motors are provided in
addition with a vaporizer and a petroleum lamp placed at the front end
of the machine, and the oil reservoir is situated immediately above the
cylinder. M. Herckenrath has specially devoted himself to simplifying
the mechanism and making it more self-contained and less unsightly. Up
to 50 horse-power only one cylinder is found necessary, and for larger
powers two are provided. The patent governor is centrifugal and rather
novel in construction, and to it is partly due the high efficiency of
these engines. The large sizes are as easily started as the smaller
ones, and the lubrication is perfectly automatic. Besides these
advantages they require a minimum of attention, in fact, a skilled
attendant can be dispensed with, a few explanations and instructions
being all that is necessary to enable a boy or labourer to take
competent charge of them.
[Illustration: FIG. 17.—Herckenrath National Gas Engine.]
_Forest motor_ (Figs. 18, 19, 20).—We have already described the
earlier attempts of M. Forest to produce a practical gas engine. The
idea embodied in the motor depicted in Fig. 20, if not particularly
advantageous, is none the less highly original. The ends of the single
cylinder are open, and within it are two pistons, between which the
explosive mixture is introduced. The explosion drives these pistons
out in different directions, but by means of a suitable mechanism they
are each connected to one of two cranks on the same shaft. The whole
forms a very neat and compact arrangement. In another type by the same
inventor (Figs. 18, 19), also working on the Otto cycle, the cylinders
are vertical, there being one, two, or four placed side by side. In
the last case two explosions per revolution are obtained, ensuring a
very constant torque throughout. M. Forest has, however, particularly
applied himself in collaboration with M. Gallice to designing petroleum
engines for small boats. These two inventors have conceived a highly
ingenious arrangement for reversing the direction of rotation of the
engine, which is absolutely necessary in the propulsion of boats. All
the cams which actuate the valves are grouped together on a light
shaft, and by a simple twisting of this shaft from one end by a handle
the engine is reversed. The engines are self-starting, and are so
especially suitable for the propulsion of boats that they have been
adopted by the French navy, who at the present date have a number of
small vessels propelled by this motive power.
[Illustration: FIG. 18. FIG. 19. De Forest Gas Engines.]
[Illustration: FIG. 20.—De Forest Double Piston Motor.]
_Cuinat gas engines._—These engines are constructed in four types.
The A type is vertical with the cylinder above and fly-wheel and
shaft below. This is a more stable arrangement than placing them in
the reversed order, as is more frequently done. For small engines
the vertical type is undoubtedly the best, space, or rather lack of
space, being very often an important consideration to the purchaser.
The B type is similar to the previous one, except that two fly-wheels
are provided so as to make it suitable for small electric light
installations. The C type is horizontal, having all the valves placed
vertically, which plan seems to work better for engines of power
greater than 10 horse-power. The D type is also horizontal, but has
two fly-wheels, having been specially designed for electric lighting
purposes. In order to take up as little space as possible the dynamo
is situated underneath the projecting cylinder, both the engine and
dynamo being bolted down on to a special bed-plate. This arrangement is
more stable than placing them on separate foundations. In the petroleum
engines an electric spark is used to ignite the gases, and in the gas
engines both electricity and a gas flame.
It is best not to use animal or vegetable oils for lubricating the
inside of the cylinder, because they decompose, forming fatty acids
which have a corrosive action. Besides this, when they have fulfilled
their function of lubrication they settle down to a thick paste, which
has a most injurious effect on the working of the engine. It is best,
therefore, to use nothing but perfectly pure mineral oils and to avoid
all others. This does not only apply to the type of engine we have just
been describing, but to all gas engines. The Cuinat gas and petroleum
motors do not mix a portion of their exhausted gases with the fresh
charge as is frequently done, but completely sweep away the products
of the explosion before admitting a new charge. The result is, that
combustion is more complete but at the same time rather more violent.
An examination of an indicator diagram taken from one of these engines
shows that the combustion takes place at once as an explosion, and
that the final expanded pressure is as low as it is possible to get
it. These being the conditions necessary for a high efficiency, it is
needless to state that the consumption of fuel in these engines is as
low as in any other engine.
_Noël motor._—This type, constructed at Provins, has the advantage of
being exceedingly simple. The entries to the cylinder are controlled by
spring-valves, and the gases are ignited by electricity. From the ¼
up to the 2 horse-power size the cylinder is not provided with a water
jacket, and the general arrangement is either vertical or horizontal.
These engines work equally well with coal gas or carburetted air; in
the latter case the carburator is placed inside the cast-iron frame of
the motor. The guaranteed consumption of fuel is about 900 litres of
gas or 500 grammes of gasoline per horse-power hour, which is quite
satisfactory.
_Tenting motor._—This is a horizontal motor with the cylinder cooled
atmospherically, and the gases ignited by electricity. The governor
acts upon the exhaust valve; the products of the explosion remain in
the cylinder if the speed is too great, and then the admission valve,
which is automatic, no longer rises to admit a fresh charge until the
speed has once more fallen to the normal. This little motor is one of
the most practical small-power engines existing, partly because of the
great simplicity of the mechanism. It works well with carburetted air,
and the vertical type has been successfully applied to the propulsion
of small pleasure-boats.
_Atkinson motor_ (Figs. 21, 22).—This apparatus, constructed by the
British Gas Engine Company, was until recently the most efficient
heat engine in existence, its indicated efficiency being 22·8%. Mr.
Atkinson, the inventor, has arrived at this result by making the gases
burn gradually and by shortening the compression stroke. The discharge
of the residual gases is complete, this being directly opposite to Dr.
Otto’s procedure, for he diluted his explosive mixture largely with
the exhausted gases. In order, however, to make the piston execute two
strokes relative to the cylinder of different lengths, the inventor has
had to devise a rather complicated mechanism (Fig. 21). The result,
however, quite neutralizes this slight disadvantage.
[Illustration: FIG. 21.—Diagram of Atkinson Mechanism.]
[Illustration: FIG. 22.—Section of Charon Motor.]
_Charon motor_ (Fig. 23).—M. Charon has attempted to obtain a
prolonged combustion without the complicated devices resorted to by
Atkinson. He has obtained the same result by means of a regulator
controlling a double cam, one half of which actuates the admission
valve and the other half an auxiliary valve, which opens into a tube
forming a sort of reservoir, into which part of the explosive mixture
passes during the compression. After the explosion this stored-up
mixture is gradually allowed to re-enter the cylinder and prolong the
combustion. By this means a considerable gain in economy is obtained,
so that engines of this type only use about 500 litres of coal gas
per horse-power hour. In appearance the motor much resembles the
Otto motor, the crank-shaft and valve-shaft and valves being placed
in the same relative positions. Although these motors are rather
more expensive than others working with the Otto cycle, they are
nevertheless widely used. This is due to the fact that if cost of coal
gas in a particular district is high it is cheaper in the end to pay a
higher price for an efficient engine than to buy a less expensive and
at the same time less economical machine.
[Illustration: FIG. 23.—Charon Motor (latest type).]
_Roger motor._—This excellent little engine (Fig. 24) was especially
designed for small workshops. The extreme simplicity of the working
parts in no way lessens the efficiency, for the two horse-power only
burns 700 litres of gas per horse-power hour. The simple design also
keeps the cost of construction low, and the price averages about £30
per horse-power.
[Illustration: FIG. 24.—Roger Vertical Gas Engine.]
The governor controls the admission valve. Ignition is obtained by
means of an incandescent tube; the cylinder is cooled by a water
jacket; the mean speed is about 200 revolutions per minute, and this
speed is constant enough to allow the engine to drive a dynamo for
electric lighting. The motor has been very favourably received abroad,
but is not much known in this country.
_Motor of the Compagnie Parisienne du Gaz_ (Fig. 25).—Owing to its very
large consumption of gas the engine can only be used if the price of
gas is low, but it has several advantages which to a certain extent
neutralize this defect. It runs at a high speed of 400 revolutions per
minute, and the parts are arranged so as to be easily accessible.
[Illustration: FIG. 25.—Vertical Gas Engine of the Compagnie Parisienne
du Gaz.]
_Letombe motor._—Constructed by the firm of Mollet-Fontaine of Lille,
this engine presents several interesting features which we will briefly
enumerate. The cylinder is double-acting, giving one impulse to the
piston during every revolution. The speed is therefore maintained
fairly constant. The efficiency is high owing to the gases in the
cylinder being made to burn slowly as in the Charon motor. The machine
on the whole works exceedingly satisfactorily and reflects great credit
on its inventors.
_Robuste (Levasseur) motor._—The composition, admission, and ignition
of explosive mixture are regulated by a sliding valve as in the Otto
motor; in this case, however, it is a piston-valve and not a flat one.
The valve-chest is at the back of the cylinder. The governor is of
the inertia type, and suppresses the admission if the speed becomes
higher than the normal. A double water jacket is provided for cooling
the cylinder walls. Although not presenting any new features, this
motor fully merits its name, and its solid construction enables it to
withstand a surprising amount of bad handling.
_Richardson and Norris gas engine._—Yet another high-speed engine,
running at a speed of 230 revolutions per minute. Roby & Co. construct
this machine especially for driving dynamos, and for this purpose
two fly-wheels are provided in order to make it run smoothly without
variation of speed. The gases are ignited through a valve with a double
seating by means of a red-hot tube. The motor is reversible, which
is an advantage under certain conditions. Poor gas can also be used
instead of coal gas, consuming about 510 grammes of anthracite per
horse-power hour for an 86 horse-power engine supplied with Dowson gas.
This works out to a thermal efficiency of 21%, a result which places
this engine above criticism.
_H. C. motor._—This is an enclosed motor for use in mines or dusty
places, the fly-wheel alone of the moving parts being visible. It
works equally well with coal gas, carburetted air, or petroleum, and
is constructed in sizes from ½ to 60 horse-power. In spite of its
original features it has not met with much success up to the present
time.
_Le Marcel and Le Maurice motors (Cadiot)_ (Fig. 26).—The smallest
types of the Marcel motors are of one man-power, and the largest of
one horse-power, so that they are only suitable for small operations.
One impulse is given to the piston every two revolutions, the cycle
being that of Dr. Otto. The gas is compressed in a red-hot tube
during half of the backward stroke. There are only two valves, one
for the admission and the other for the escape of the gases, actuated
by a single cam on the crank-shaft. The cylinder is cooled by a water
jacket. The governor works on the all or nothing principle, the supply
of gas being completely shut off if the speed rises above the normal of
350 revolutions per minute.
[Illustration: FIG. 26.—Maurice Motor (de Cadiot).]
The Maurice motors are somewhat similar in construction, but are
designed for operating dynamos. For this purpose two fly-wheels are
provided. Many of these little motors are to be seen about the country
working fans, lathes, pumps, etc.
_Various._—We have described about thirty different sorts of motors,
selected from the best-known and most original types. About one hundred
other motors exist in Europe, which are similar in one way or another
to those already described, such as the engines of Dürkopp, Forward,
Brouhot, Debry de Soissons, Narjot, Archat, Wertenbruch, the “Acmé”
motor, and many others. But we are obliged to limit our descriptions,
and to conclude the chapter by a couple of examples of motors
performing one cycle of operations per three revolutions.
_Griffin motor._—In this engine we have only two explosions over three
revolutions, but as it is double-acting this number is reduced to one
explosion per revolution and a half. The different operations are as
follows:—(1) gases drawn into the cylinder, (2) compression of gases,
(3) ignition and expansion, (4) products of combustion driven out of
the cylinder, (5) a volume drawn into it to completely sweep away any
residue of the exhaust gases, (6) this volume of air drawn out.
Admission and ignition are obtained by the action of a sliding valve
and eccentric. The governor causes the gas admission valve to remain
open for a shorter or longer time, so as to ensure constancy of
speed. The exhaust gases escape by two valves actuated by a pair of
cams, opening them at every turn and a half, so that the gases are
alternately discharged from the back and front parts of the cylinder.
The consumption of fuel for a 12 horse-power motor was about 792 litres
of coal gas per horse-power hour in an official trial. The speed is
very constant in spite of the long cycle.
_Rollason gas engine._—This is also an engine using a long cycle of
operations, the arrangement of the parts being copied off the Otto
motor. The governor is electric, and acts on the admission valve,
varying the amount of gas admitted to the cylinder in proportion to the
demand for power. In the larger size of from 20 to 100 horse-power a
self-starting arrangement has been added. This engine, like the Griffin
motor, has proved that it is possible, by completely getting rid of
the products of combustion, to use a very dilute explosive mixture,
which would be impossible in the Otto motor. The Rollason engine is
constructed by Messrs. Beck and Co. of Newcastle-on-Tyne.