[Footnote 1: Lecture by Mr. Dugald Clerk, before the Literary and
Philosophical Society, Oldham.]
By DUGALD CLERK.
In earlier days of mechanics, before the work of the great Scottish
engineer, James Watt, the crude steam engines of the time were known as
"fire engines," not in the sense in which we now apply the term to
machines for the extinguishing of fires, but as indicating the source from
which the power was derived, motive power engines deriving their vitality
and strength from fire. The modern name--steam engine--to some extent is a
misleading one, distracting the mind from the source of power to the
medium which conveys the power. Similarly the name "Gas Engine" masks the
fact of the motors so called being really fire or heat engines.
The gas engine is more emphatically a "fire engine" than ever the steam
engine has been. In it the fire is not tamed or diluted by indirect
contact with water, but it is used direct; the fire, instead of being kept
to the boiler room, is introduced direct into the motor cylinder of the
engine. This at first sight looks very absurd and impracticable;
difficulties at once become apparent of so overwhelming a nature that the
problem seems almost an impossible one; yet this is what has been
successfully accomplished in the gas engine. Engineers accustomed to the
construction of steam engines would not many years ago have considered any
one proposing such a thing as having taken leave of his senses.
The late Sir William Siemens worked for many years on combustion engines,
some of his patents on this subject dating back to 1860. In the course of
a conversation I had with him on the subject of his earlier patents, I
asked him why he had entitled one of those patents "steam engine
improvements" when it was wholly concerned with a gas engine using
hydrogen and air in the motive cylinder, the combustion of the hydrogen
taking place in the motive cylinder. He answered me that in 1860 he did
not care to entitle his patent gas or combustion engine simply because
engineers at that time would have thought him mad.
Notwithstanding this widespread incredulity among engineers, and the
apparent novelty of the gas engine idea, fire or combustion engines have
been proposed long, long ago. The first Newcomen steam engine ever set to
work was used by a Mr. Back, of Wolverhampton, in the year 1711.
Thirty-one years before this time, in Paris--year 1680--Huyghens presented
a memoir to the Academy of Sciences describing a method of utilizing the
expansive force of gunpowder. This engineer is notable as being the very
first to propose the use of a cylinder and piston, as well as the first
combustion engine of a practical kind.
The engine consists of a vertical open topped cylinder, in which works a
piston; the piston is connected by a chain passing over a pulley above it
to a heavy weight; the upstroke is accomplished by the descent of the
weight, which pulls the piston to the top of the cylinder; gunpowder
placed in a tray at the bottom of the cylinder is now ignited, and expels
the air with which the cylinder is filled through a shifting valve, and,
after the products of combustion have cooled, a partial vacuum takes place
and the atmospheric pressure forces down the piston to the bottom of its
stroke, during which work may be obtained.
On the board I have made a sketch of this engine. Some years previous to
Huyghens' proposal, the Abbe Hautefeuille (1678) proposed a gunpowder
engine without piston for pumping water. It is similar to Savery's steam
engine, but using the pressure of the explosion instead of the pressure of
steam. This engine, however, had no piston, and was only applicable as a
pump. The Savery principle still survives in the action of the well-known
pulsometer steam pump.
Denys Papin, the pupil and assistant of Huyghens, continued experimenting
upon the production of motive power, and in 1690 published a description
of his attempts at Leipzig, entitled "A New Method of Securing Cheaply
Motive Power of Considerable Magnitude."
He mentions the gunpowder engine, and states that "until now all
experiments have been unsuccessful; and after the combustion of the
exploded powder there always remains in the cylinder one-fifth of its
volume of air."
For the explosion of the gunpowder he substituted the generation and
condensation of steam, heating the bottom of his cylinder by a fire; a
small quantity of water contained in it was vaporized, and then on
removing the fire the steam condensed and the piston was forced down. This
was substantially the Newcomen steam engine, but without the separate
boiler.
Papin died about the year 1710, a disappointed man, about the same time as
Newcomen. Thomas Newcomen, ironmonger and blacksmith, of Dartmouth,
England, had first succeeded in getting his engine to work. The hard fight
to wrest from nature a manageable motive power and to harness fire for
industrial use was continued by this clever blacksmith, and he succeeded
when the more profound but less constructively skillful philosophers had
failed.
The success of the steam method and the fight necessary to perfect it to
the utmost absorbed the energy of most able engineers--Beighton, John
Smeaton--accomplishing much in applying and perfecting it before the
appearance of James Watt upon the scene.
It is interesting to note that in England alone over 2,000 horse power of
Newcomen engines were at work before Watt commenced his series of
magnificent inventions; he commenced experimenting on a Newcomen engine
model in 1759 at Glasgow University, and in 1774 came to Birmingham,
entered into partnership with Boulton, and 1781 we find his beautiful
double acting beam condensing engine in successful work.
From that time until now the steam engine has steadily advanced,
increasing in economy of fuel from 10 lb. of coal per horse power per hour
to about 1¾ lb. per horse power per hour, which is the best result of
to-day's steam engine practice. This result, according to the highest
authorities, is so near to the theoretical result possible from a steam
engine that further improvement cannot now be looked for. Simultaneously
with the development of the steam engine, inventors continued to struggle
with the direct acting combustion or gas engine, often without any
definite understanding of why they should attempt such apparent
impossibilities, but always by their experiments and repeated failures
increasing knowledge, and forming a firm road upon which those following
them traveled to success.
In 1791 John Barber obtained a patent for an engine producing inflammable
gas, mixing it with air, igniting it, and allowing the current so produced
to impinge upon a reaction wheel, producing motion similar to the well
known Aelopile, which I have at work upon the table. About this time,
Murdoch (Jas. Watt's assistant at Birmingham) was busy introducing coal
gas into use for lighting; in 1792 Boulton and Watt's works were lighted
up with coal gas. From this time many gas engines were proposed, and the
more impracticable combustion of gunpowder received less attention.
In 1794 Thomas Mead obtained a patent for an engine using the internal
combustion of gas; the description is not a clear one, his ideas seem
confused.
In the same year Robert Street obtained a patent for an engine which is
not unlike some now in use. The bottom of a cylinder, containing a piston,
is heated by a fire, a few drops of spirits of turpentine are introduced
and evaporated by the heat, the piston is drawn up, and air entering mixes
with the inflammable vapor. A light is applied at a touch hole, and the
explosion drives up the piston, which, working on a lever, forces down the
piston of a pump for pumping water. Robt. Street adds to his description a
note: "The quantity of spirits of tar or turpentine to be made use of is
always proportional to the confined space, in general about 10 drops to a
cubic foot." This engine is quite a workable one, although the
arrangements described are very crude.
The first gas engine that was actually at work for some years; and was
applied to a variety of purposes, was Samuel Buren's. His patent was
granted in 1823, and in 1826 he built a locomotive carriage with which he
made several experimental runs in London; he also propelled a vessel with
it upon the Thames, and fitted up a large engine for pumping purposes. A
company was formed to introduce his engine, but it proved too wasteful of
fuel, and the company went into voluntary liquidation. Like almost all
engines of this time, the combustion of gas and air was used to produce a
vacuum, the piston being driven by atmospheric pressure.
Buren's locomotive carriage was thus in action three years before the
great trial in 1829, from which George Stephenson emerged victorious with
his wonderful engine "The Rocket." To those curious in the matter, I may
mention that S. Buren's patents are dated 1823, No. 4,874, and 1826, No.
5,350.
From this time on, a continuous series of gas engine patents appear, 20
engines being patented between 1826 and 1860, which is the next date
worthy of particular mention.
In this year, 1860, the famous "Lenoir" engine appeared. The use of high
pressure steam engines had long been common, and Lenoir's engine was
analogous to the high pressure engine, as Buren's was to the condensing
engine. It created a very general interest, and many engines were
constructed and used in France, England, and America; it resembled very
much in external appearance an ordinary high pressure horizontal steam
engine, and it was double acting.
During the following six years, other 20 British patents were granted, and
the gas engine passed from the state of a troublesome toy to a practicable
and widely useful machine.
From 1791 to the end of 1866, in all 46 British patents were granted for
gas engines, and in these patents are to be found the principles upon
which the gas engines of to-day are constructed, many years elapsing
before experience enough was gained to turn the proposals of the older
inventors to practical account.
The most important of these patents are:
No. Year.
Robert Street 1,983 1794 Direct-acting engine.
Samuel Buren 4,874 1823 Vacuum engine.
Samuel Buren 5,350 1826 Vacuum engine.
W.L. Wright 6,525 1833 Direct-acting engine.
Wm. Barnett 7,615 1838 Compression first proposed.
Barsante & Matteucci 1,072 1854 Rack & clutch engine.
Drake 562 1855 Direct-acting engine.
Lenoir 335 1860 D.I. engine, electric ignition.
C.W. Siemens 2,074 1860 Compression, _constant
pressure_.
Hugon 2,902 1860 Platinum ignition.
Millein 1,840 1861 Compression, both constant vol. and
_pressure_.
F.H. Wenham 1,873 1864 Free piston.
Hugon 986 1865 Flame ignition.
Otto and Langen 434 1866 Rack and clutch, flame ignition.
Leaving for the present the history of the gas engine, which brings us to
a stage comparable to the state of the steam engine during the Newcomen's
time, it will be advisable to give some consideration to the principles
concerned in the economical and efficient working of gas engines, in order
to understand the more recent developments.
It has been seen that gunpowder was the explosive used to produce a vacuum
in Huyghens' engine, and that it was abandoned in favor of gas by Buren in
1823. The reason of departure is very obvious: a gunpowder explosion and a
gaseous explosion differ in very important practical points.
Gunpowder being a solid substance is capable of being packed into a very
small space; the gas evolved by its decomposition is so great in volume
that, even in the absence of any evolution of heat, a very high pressure
would result. One cubic inch of gunpowder confined in a space of one cubic
inch would cause a pressure by the gas it contains alone of 15,000 lb. per
square inch; if the heating effect be allowed for, pressures of four times
that amount, or 60,000 lb. per square inch, are easily accounted for.
These pressures are far too high for use in any engine, and the bare
possibility of getting such pressure by accident put gunpowder quite
outside the purpose of the engineer, quite apart from any question of
comparative cost. In a proper mixture of inflammable gas and air is found
an exceedingly safe explosive, perfectly manageable and quite incapable of
producing pressures in any sense dangerous to a properly constructed
engine.
The pressure produced by the explosion of any mixture of gas and air is
strictly determined and limited, whereas the pressure produced by the
explosion of gunpowder depends greatly upon the relation between the
volume of the gunpowder and the space in which it is confined.
Engines of the "Lenoir" type are the simplest in idea and construction; in
them a mixture of gas and air is made in the cylinder during the first
half of the piston stroke, air being taken from the atmosphere and drawn
into the cylinder by the forward movement of the piston. At the same time
gas entering by a number of holes, and streaming into the air to form an
explosive mixture, the movement of a valve cuts off the supply, and brings
the igniting arrangement into action. The pressure produced by the
explosion acting upon the piston makes it complete its stroke, when the
exhaust valve opens exactly as in the steam engine. The Lenoir and Hugon
engines, the earlier forms of this type, were double acting, receiving two
impulses for every revolution of the crank, the impulse differing from
that in a high pressure steam engine in commencing at half stroke.
The Lenoir igniting arrangement was complicated and troublesome. I have it
upon the table; the mixture was ignited at the proper time by the electric
spark produced from a primary battery and Ruhmkorff coil.
The Hugon engine was an advance in this respect, using a flame ignited,
and securing greater certainty of action in a comparatively simple manner.
It is really a modification of Barnett's lighting cock described in his
patent of 1838.
Other difficulties were found in using these engines; the pistons became
exceedingly hot. In the case of the Lenoir larger engines, it sometimes
became red hot, and caused complete ruin of the cylinder by scoring and
cutting up. Hugon to prevent this injected some water.
In the all important question of economy, these engines were found
grievously wanting, Lenoir consuming 95 cubic feet per I.H.P. per hour;
Hugon consuming 85 cubic feet per I.H.P. per hour.
The surviving engines of this type are only used for very small powers,
from one to four man power, or 1/8 to 1/2 horse, the most widely known of
this kind being the "Bischoff," which is very largely used; its
consumption of gas is even greater than the Lenoir, being 110 cubic feet
per horse power per hour, as tested with a half-horse engine at a late
exhibition of gas apparatus at Stockport.
So large a consumption of gas prevented these engines coming into extended
use for engines of moderate power, and led inventors to work to obtain
better results. The force generated by the explosion of a mixture of gas
and air is very short lived, and if it is to be fully utilized must be
used quickly; a high pressure is produced, but it very quickly disappears.
The quicker the piston moves after the maximum pressure is reached, the
less will be the loss of heat to the sides of the cylinder. The flame
which fills the cylinder and causes the increase of pressure rapidly loses
heat, and the pressure falls.
The idea of using a free piston was proposed as a remedy; it was thought
that a piston connected to a crank in the ordinary manner could not move
fast enough to utilize the pressure before it was lost. Many inventors
proposed to perform work upon a piston free from any direct connection
with the crank or shaft of the engine; the explosion after attaining its
maximum pressure expends its force in giving velocity to a piston; the
velocity so acquired carries it on against atmospheric pressure until the
energy is all absorbed, and a vacuum or deficit of pressure exists in the
cylinder instead of an excess of pressure. The return stroke is
accomplished by the atmospheric pressure, and the work is now done upon
the engine shaft on the return only. The method of connecting on the
return stroke while leaving the piston free on the out stroke varies, but
in many engines the principle was the same.
Barsante and Matteucci, year 1857, British patent No. 1,625, describe the
first engine of this kind, but Messrs. Otto and Langen were the first to
successfully overcome all difficulties and make a marketable engine of it.
Their patent was dated 1866, No. 434. To distinguish it from Otto's later
patents, it may be called the rack and clutch engine.
The economy obtained by this engine was a great advance upon the Lenoir.
According to a test by Prof. Tresca, at the Paris Exhibition of 1867, the
gas consumed was 44 cubic feet per indicated horse power per hour.
According to tests I have made myself in Manchester with a two horse power
engine, Otto and Langen's free piston engine consumes 40 cubic feet per
I.H.P. per hour. This is less than one-half of the gas used by the Hugon
engine for one horse power.
The igniting arrangement is a very good modification of Barnett's lighting
cock, which I have explained already, but a slide valve is used instead of
a cock.
Other engines carried out the same principle in a different manner,
including Gilles' engine, but they were not commercially so successful as
the Otto and Langen. Mr. F.H. Wenham's engine was of this type, and was
working in England, Mr. Wenham informed me, in 1866, his patent being
taken out in 1864.
The great objection to this kind of engine is the irregularity and great
noise in working; this was so great as to prevent engines from being made
larger than three horse power. The engine, however, did good work, and was
largely used from 1866 until the end of 1876, when Mr. Otto produced his
famous engine, now known as "The Otto Silent Gas Engine." In this engine
great economy is attained without the objectionable free piston by a
method proposed first by Burnett, 1838, and also by a Frenchman, Millein,
in 1861; this method is compression before ignition. Other inventors also
described very clearly the advantages to be expected from compression, but
none were able to make it commercially successful till Mr. Otto. To him
belongs the great credit of inventing a cycle of operations capable of
realizing compression in a simple manner.
Starting from the same point as inventors did to produce the free piston
engine--namely, that the more quickly the explosive force is utilized, the
less will be the loss, and the greater the power produced from a quantity
of burning gas--it is evident that if any method can be discovered to
increase the pressure upon the piston without increasing the temperature
of the flame causing this pressure, then a great gain will result, and
the engine will convert more of the heat given to it into work. This is
exactly what is done by compression before ignition. Suppose we take a
mixture of gas and air of such proportions as to cause when exploded, or
rather ignited (because explosion is too strong a term), a pressure of 45
lb. above atmosphere, or 60 lb. per square inch absolute pressure. Then
this mixture, if compressed to half volume before igniting and kept at
constant temperature, would give, when ignited, a pressure of 120 lb.
total, or 105 lb. above atmosphere, and this without any increase of the
temperature of the flame.
The effect of compression is to make a small piston do the work of a large
one, and convert more heat into work by lessening the loss of heat through
the walls of the cylinder. In addition to this advantage, greater
expansions are made possible, and therefore greatly increase economy.
The Otto engine must be so familiar in appearance to all of you, that I
need hardly trouble you with details of its external appearance. I shall
briefly describe its action. Its strong points and its weak points are
alike caused by its cycle. One cylinder and piston suffices to carry out
its whole action. Its cycle is: First outstroke, gas and air sucked into
the cylinder; first instroke, gas and air compressed into space; second
outstroke, impulse due to ignition; second instroke, discharge of
exhausted gases. When working at full power, it gets one impulse for every
two revolutions; this seems to be a retrograde movement, but,
notwithstanding, the advantages obtained are very great. The igniting
arrangement is in the main similar to that used on the rack and clutch
engine. The engine has been exceedingly successful, and is very
economical. The Otto compression engine consumes 21 cubic feet of gas per
I.H.P. per hour, and runs with great smoothness.
In 1876 I commenced my work upon gas engines, and very soon concluded that
the compression system was the true line to proceed upon. It took me two
years to produce a workable engine. My efforts have always been directed
toward producing an engine giving at least one impulse every revolution
and, if possible, to start without hand labor, just as a steam engine
does. My first gas engine was running in 1878, and patented and exhibited
in 1879. It was first exhibited at the Kilburn Royal Agricultural
Society's show.
This engine was self-starting, gave an ignition at every revolution, and
ignited without external flame. It consisted of two cylinders, a motor,
and a compressing pump, with a small intermediate reservoir. Suitable
valves introduced the mixture of gas and air into the pump, and passed it
when compressed from the reservoir to the motor cylinder. The igniting
arrangement consisted of a platinum cage firmly fixed in a valve port;
this cage was heated in the first instance by a flame of gas and air
mixed; it became white hot in a few seconds, and then the engine was
started by opening a valve.
The platinum was kept hot by the heat derived from the successive
ignitions, and, the engine once started, no further external flame was
required. I have here one of these platinum cages which has been in use.
Finding this method not well suited for small engines, I produced the
engine which is at present in the market under my name.
The cycle is different, and is designed for greater simplicity and the
avoidance of back ignitions. It also consists of two cylinders, motor
cylinder and the displace or charging cylinder. There is no intermediate
reservoir. The displace crank leads the motor by a right angle, and takes
into it the mixed charge of gas and air, in some cases taking air alone
during the latter part of its stroke.
The motor on the outstroke crosses V-shaped parts about from one-sixth to
one-seventh from the out end, the displacer charge now passing into the
motor cylinder, displacing the exhaust gases by these ports and filling
the cylinder and the space at the end of it with the explosive mixture.
The introduction of some air in advance of the charge serves the double
purpose of cooling down the exhaust gases and preventing direct contact of
the inflammable mixture with flame which may linger in the cylinder from
the previous stroke. The instroke of the motor compresses the charge into
the conical space at the end of the cylinder, and, when fully compressed,
ignition is effected by means of the slide I have upon the table.
This system of ignition has been found very reliable, and capable of
acting as often as 400 times per minute, which the Otto ignite is quite
incapable of doing. By this cycle the advantages of compression are gained
and one step nearer to the steam engine is attained, that is, an impulse
is given for every revolution of the engine.
As a consequence, I am able with my engine to give a greater amount of
power for a comparatively small weight. In addition to this, I have
introduced a method of self-starting; in this I believe I was the
first--about 100 of my engines are now using self-starting.
The largest single engine I have yet made indicates 30 H.P. The
consumption of gas in Glasgow is: Clerk engine consumes in Glasgow 18
cubic feet per I.H.P. per hour; Clerk engine consumes in Manchester 22
cubic feet per I.H.P. per hour. So far as I know, the Otto engine and my
own are the only compression engines which have as yet made any success in
the market. Other engines are being continually prepared, gas engine
patents being taken out just now at the rate of 60 per annum, but none of
them have been able as yet to get beyond the experimental stage. The
reason is simply the great experience necessary to produce these machines,
which seem so very simple; but to the inexperienced inventor the subject
fairly bristles with pitfalls.
I have here sections of some of the earlier engines, including Dr.
Siemens' and Messrs. Simon and Beechy. Although interesting and containing
many good points, these have not been practically successful.
The Simon engine is an adaptation of the well-known American petroleum
motor, the Brayton, the only difference consisting in the use of steam as
well as flame.
Dr. Siemens worked for some twenty years on gas engines, but he aimed
rather high at first to attain even moderate success. Had he lived, I
doubt not but that he would have succeeded in introducing them for large
powers. In 1882 he informed me that he had in hand a set of gas engines of
some hundreds of horse power for use on board ship, to be supplied with
gas from one of his gas producers modified to suit the altered
conditions.
Summarizing the ground over which we have passed, we find the origin of
the gas engine in the minds of the same men as were first to propose the
steam engine, Huyghens and Papin, 1680 and 1690. Greater mechanical
difficulties and ignorance of the nature of explosives caused the
abandonment of the internal combustion idea, and the mechanical
difficulties with steam being less, the steam engine became successful,
and triumphed over its rival. The knowledge and skill gained in the
construction of steam engines made it possible once again to attack the
more difficult problem, and simultaneously with the introduction and
perfecting of the steam engine, the gas engine idea became more and more
possible, the practicable stage commencing with Lenoir and continuing with
Hugon, Millein, Otto and Langen, F.H. Wenham, then Otto and Clerk. In
1860, 95 cubic feet of gas produced one horse power for an hour; in 1867,
40 cubic feet accomplished the same thing; and now (1885) we can get one
horse power for an hour for from 15 to 20 cubic feet of gas, depending on
the size of the engine used.
Considered as a heat engine, the gas engine is now twice as efficient as
the very best modern steam engine. It is true the fuel used at present
is more expensive than coal, and for large powers the steam engine is
the best because of this. But the way is clearing to change this. Gas
engines as at present, if supplied with producer gas, produced direct
from coal without leaving any coke, as is done in the Siemens, the
Wilson, and the Dawson producers, will give power at one-half the cost
of steam power. They will use 7/8 of a pound of coal per horse power per
hour, instead of 1-3/4 lb., as is done in the best steam engines. The
only producer that makes gas for gas engines at present is the Dawson,
and in it anthracite is used, because of the difficulty of getting rid
of the tar coming from the Siemens and Wilson producers, using any
ordinary slack.
When this difficulty has been overcome, and that it will be overcome there
can be no manner of doubt, gas engines will rapidly displace the steam
engine, because a gas engine with a gas producer, producing gas from any
ordinary coal with the same ease as steam is produced from a boiler, will
be much safer, and will use one-half the fuel of the very best steam
engines for equal power. The first cost also will not be greater than that
of steam. The engine itself will be more expensive than a steam engine of
equal power, but the gas producer will be less expensive than the boiler
at present. Perfect as the gas engine now is, considered as a machine for
converting heat into work, the possibility of great development is not yet
exhausted. Its economy may be increased two or even three fold; in this
lies the brilliant future before it. The steam engine is nearly as perfect
as it can be made; it approaches very nearly the possibility of its
theory. Its defect does not lie in its mechanism, but in the very
properties of water and steam itself. The loss of heat which takes place
in converting liquid water into gaseous steam is so great that by far the
greater portion of the heat given out by the fuel passes away either in
the condenser or the exhaust of a steam engine; but a small proportion of
the heat is converted into work.
The very best steam engines convert about 11 per cent. of the heat given
them into useful work, the remaining 89 per cent. being wasted,
principally in the exhaust of the engine.
Gas engines now convert 20 per cent. of the heat given to them into work,
and very probably will, in a few years more, convert 60 per cent. into
useful work. The conclusion, then, is irresistible that, when engineers
have gained greater experience with gas engines and gas producers, they
will displace steam engines entirely for every use--mills, locomotives,
and ships.
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