APRIL 4, 1907 | 
NAL Thee 
By 
also operated by gunpowder. This paper gives an account 
of the first gas engine which appears to have been worked 
in Britain or elsewhere. 
Six years later Samuel Brown invented and built an 
ingenious engine, depending on the flame-vacuum method, 
which appears to have been the earliest gas engine ever 
worked on any considerable scale. In an early number 
of the Mechanics’ Magazine it is stated that Brown 
succeeded with his engine in propelling a boat upon the 
Thames and in actuating a road locomotive. This vacuum 
method, however, never produced a really commercial 
engine, its only survival being the small engine shown as 
illustrating a modified form of class (1). 
Many engines have been built using the atmospheric, or, 
as it is more commonly known, the non-compression ex- 
plosion principle, but the most successful was that of 
Lenoir. The simplest engine of this type was one which 
was used in considerable numbers until a comparatively 
recent date—the Bischoff engine. In it a mixture of gas 
and air is drawn into the cylinder through suitable valves. 
As the piston passes an igniting aperture the flame is 
sucked in, the mixture ignites, and a small check valve 
closes the flame or touch-hole aperture. In the Lenoir 
engine, which was the most successful of this type, how- 
ever, many of the modern characteristics are found, such 
as the water-jacket and ignition by the electric spark. 
The gas consumption, however, of all these engines was 
very high, rather more than go cubic feet per indicated 
horse-power per hour. The power obtained for given 
dimensions, too, was very small. 
The first and second methods accordingly are not now 
used. Their disadvantages proved too great. In all 
modern gas or petrol engines the third method is used, 
that is, the charge of inflammable mixture is compressed 
before ignition. 
Many attempts to construct engines operating on the 
compression principle were made before success was 
obtained. In such attempts England had a full share. 
One of the very earliest feasible compression gas engines 
was that described by William Barnett, an Englishman, 
in the year 1838. This engine had many of the features 
of successful engines of to-day. Later proposals were 
made for similar engines, both in France and in Germany ; 
but the first inventor to succeed in overcoming difficulties 
to a sufficient extent to produce a commercial engine was 
the late Dr. Otto, of Deutz. To Dr. Otto belongs the 
honour of producing the first successful compression gas 
engine. The great majority of modern gas and petrol 
engines operate on what is now known as the Otto cycle. 
The production of a compressed charge in a motor cylinder 
in a safe, quiet, and economical manner is a much more 
difficult problem than appears at first sight. Those of us 
upon whom fell the brunt of working out this problem 
about thirty years ago appreciate fully the ability and 
knowledge displayed by the late Dr. Otto in producing 
his famous engine. In the Otto engine the characteristic 
feature is found in the alternate use of the same piston 
and cylinder for the purpose of pump and motor. In one 
complete revolution the cylinder is used as a pump, and 
in another complete revolution as a motor. The cycle is 
very simple. 
The Otto cycle has many great advantages. The 
charging and discharging of the gases is accomplished 
easily. The heat flow through the sides of the cylinder 
is not too continuous, and consequently the cycle can be 
operated at very high speeds. Many attempts, however, 
have been made to obviate the main disadvantage of the 
Otto cycle, that is, the necessity for two complete revolu- 
tions for every power impulse. In 1881 the lecturer 
invented a cycle of operations which gave in the same 
cylinder one power impulse at each revolution. This cycle 
is now known as the Clerk cycle, and it comes next to the 
Otto cycle in order of number of engines now running in 
the world. Sections showing the operation of the Clerk 
cycle were shown. Its characteristic consists of open ports 
at the outer end of the stroke, which are overrun by the 
piston. The pressure in the cylinder rapidly falls to atmo- 
sphere, and a charge is forced into the cylinder at low 
pressure, about 2 lb. above atmosphere. This displaces 
the exhaust products remaining in the cylinder, and 
furnishes the fresh charge, which is compressed on the 
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return stroke into a space at the end of the cylinder. 
This charge is ignited, and in this way a power impulse 
is obtained for every forward stroke of the piston. A 
second cylinder is required in order to supply the charge. 
The second cylinder is very light in construction, both as 
to the cylinder itself, the piston, and the connecting rod 
and cranks driving it. Working sections of a Clerk engine 
and Lanchester engine were shown. 
The last thirty years have seen the greatest development, 
so far as practical matters are concerned, so that now more 
than two million horse-power of stationary gas engines 
operated by flame are in use in the world. It is difficult 
to form an estimate of the power of motor-car engines 
in use, but probably it now exceeds a million horse-power. 
Although great progress has been made in the practical 
control and utilisation of flame and gaseous explosions 
for the purpose of producing motive power, little is as 
yet known as to the actual properties of the flame-working 
fluid so utilised. Accordingly, for the present it is not’ 
possible to formulate a complete theory of the internal- 
combustion motor. The subject is a difficult one, and 
involves not only the statical properties of these gases, 
but requires a knowledge of the conditions and rate of 
chemical combinations occurring in minute fractions of a 
second, and of the conditions of dissociation of compounds 
such as carbonic acid and steam at high temperatures 
under varying conditions of temperature and_ pressure. 
Many distinguished investigators have given the subject 
some attention. Bunsen in 1866 arranged a small glass 
tube with a safety valve, and weights to apply pressure 
to the valve. He provided platinum points between which 
the electric spark could be passed the whole length of the 
tubular vessel. This vessel was filled with various ex- 
plosive mixtures, and ignited by the spark. The valve 
was loaded until it just blew off. This blow-off pressure 
was considered to be the maximum pressure produced by 
the explosion. Bunsen’s apparatus was very crude, and 
could not have been expected to give accurate results. 
The maximum pressures must have far exceeded the 
pressures registered by his apparatus. Messrs. Mallard 
and Le Chatelier, and Berthelot and Vieulle, took up the 
subject of gaseous explosions, and made experiments also 
with numerous gases and oxygen, and coal-gas and air. 
A series of experiments was made by the lecturer in 1883. 
A Richards indicator, of the best construction known at 
that date, was used, and secured indications which were 
fairly trustworthy. Curves of explosion and cooling with 
coal-gas so obtained were shown. These experiments also 
showed clearly that the whole of the heat present was not 
evolved at maximum temperature, assuming the gases to 
have their ordinary specific heat at the high temperatures 
as well as low. Messrs. Mallard and Le Chatelier, and 
Berthelot and Vieulle, had come to the conclusion that 
the specific heat of the gases had been changed, and they 
considered combustion to be complete at the maximum 
temperature, Or nearly so. The lecturer’s experience with 
engine indicator cards, supplementing the experiments 
made with gas and air mixtures in a closed vessel, led 
to the view that combustion was not complete, and that 
therefore it was not safe to draw deductions as to vary- 
ing specific heat without quite definite knowledge that 
chemical combination was completed before determinations 
were made of specific heat value. The absence of definite 
knowledge as to specific heats at high temperatures, dis- 
sociation, and rates of continued combustion, made it 
impossible to develop any complete theory of the internal- 
combustion motor. 
To enable some investigation, however, to be made on 
different engine cycles, it appeared desirable to consider 
the gas engine as an air engine pure and simple, operated 
with air of constant specific heat, the air being a perfect 
gas and the chemical action being assumed as merely a 
means of heating the air through the desired temperature 
range. Calculating on this simplified theory, it became 
evident that the efficiency to be obtained in an air engine 
without heat losses was dependent upon compression 
mainly. Working out this theory showed that while the 
utmost that could be theoretically expected from a non- 
compression engine of the Lenoir type was 22 per cent., 
compression supplied means of getting theoretical effici- 
encies as high as 60 per cent., with practicable ranges 
