From the researches and investigations of Carnot, Joule, Rankine,
Clausius, and Sir William Thomson, the science of thermo-dynamics has
not only been brought into existence, but fully matured. We learn from
it that whereas in the steam engine, on account of the limited range of
temperature in the working cylinder and the rapid conduction of steam
during condensation, no combination of cylinders can materially affect
its present efficiency, internally fired engines, such as gas and
caloric engines--being, as it were, less fettered--can have their
already high efficiency increased by simply overcoming mechanical
difficulties. To this fact is no doubt due the recent remarkable
development of gas and caloric engines. The first caloric or hot air
engine was invented by Sir George Cayley in 1807, and in 1827 Dr. Robert
Stirling, a Scotch minister, took out his first patent for a hot air
engine, which was the foundation of many subsequent machines, and by the
invention of the regenerator he converted what was practically a
scientific toy into an efficient machine.
One of the most ardent workers in this field at the present time is Mr.
James Hargreaves, of Widnes, who, with a thorough theoretical knowledge
of the subject has, after many years of patient perseverance, over come
many of the mechanical difficulties, and designed the engine of which
the above is an illustration.
The sectional elevation, shown in Fig. 1, is an expanded view of the
machine, shown thus to enable the action of the machine to be more
clearly understood; the relative position of the different parts, as
actually made, is shown in the side elevation (Fig. 4). The principal
working parts of the machine are the combustion chamber, D, which is of
the form shown, lined with fire brick, and having an entrance, with the
door screwed down like a manhole lid; the working cylinder, A,
surrounded by the water casing, K; the piston, B, with a water lining,
and coupled to the end of the working beam by a parallel motion, the
beam being supported by two rocking columns, Z, as in engines of the
"grasshopper" type; the air compressor, C, coupled directly to the
piston of the working cylinder; the injection pump, F, for supplying the
fuel--creosote or coal tar--to the combustion chamber; the regenerator
E; the receiver and separator, V Y; the feed and exhaust valves, M.
[Illustration: Fig. 1--SECTIONAL ELEVATION--HARGREAVES' THERMO-MOTOR.]
[Illustration: Fig. 2.]
The action of the machine is as follows: Assuming the engine to be in
condition for starting, the sides of the combustion chamber, D, are red
hot, the chamber charged with air, and the spray of creosote, injected
by the pump, F, is ignited; the expansion of the gases produced by the
combustion acts upon the bottom of the piston, B, forcing it to the top
of the cylinder, and thus, by intermediate mechanism, causing the crank
shaft to revolve. By the same stroke a charge of air is forced by the
compressor, C, into the receiver through the pipe, R. The cylinder is,
of course, single acting, and on the down stroke of the piston, B--which
falls by its own weight and the momentum of the fly wheel--the exhaust
gases are forced through the regenerator, E, which absorbs most of their
heat; they then pass through the exhaust valve, placed immediately under
the feed valve, M, along the pipe, Q, up through the pipes, T, fitted
into the receiver, V, down the pipes, T, fitted into the saturator, Y,
and out of the funnel fixed to the bottom of Y.
[Illustration: Fig 3.]
[Illustration: Fig. 4.]
The charge of air for supplying the combustion chamber is forced by the
compressor, C, through the pipe, R, _outside_ the tubes, T, in the
chambers, V and Y, along the pipe, P, through the feed valve, M, and the
regenerator, E, into the combustion chamber. In its passage from the
compressor, it first picks up the residual heat of the exhaust gases in
the tubes, T, and finally the heat absorbed by the regenerator, E, thus
entering the combustion chamber in a highly heated state. Having
described generally the passage of the air from the compressor to the
working cylinder, and back again to the funnel, we will now describe the
details. The working cylinder, A, is fitted into the casting which forms
the water casing, K, a space being left between the bottom of the
cylinder and the casing, which is filled with a non-conducting mixture
of asbestos to protect it from the heat of combustion; the bottom of the
piston, B, has a similar protection, and the regenerator has a lining
of the same mixture, to prevent any heat from escaping through the
casting which holds it. The water in the casing, K, and in the piston,
B, is supplied by a small pump, G, which forces the water through the
pipe, P4, into the telescopic pipe, L either into the piston, B, or
through the pipe, P6, into the casing, K--the bottom of the casing
being connected by the pipe, P10, with the auxiliary boiler, W. The
steam generated in the casing, K, is carried to the boiler, W, by the
pipe, P3, and from the boiler it passes along the pipe, P2,
through the valve, A2, into the chamber, V, thus giving up its heat
to the incoming air, with which it mixes. The vapor gradually condenses
at the bottom of the vessel, Y, and the water so formed is drawn by the
pump, J, along the suction pipe, P9, and forced through the pipe,
P8, back to the chamber, Y, through the valve, A1, and in the form
of spray plays on the tubes, T, and absorbing any residual heat. The
heat generated by compression in the cylinder, C, is absorbed by a spray
of water from the pump, H, the vapor being carried along with the air
through the pipe, R, to the chamber, Y, where it is separated, and
falling to the bottom is circulated, as just described, by the pump, J.
X is a small auxiliary air compressor, to obtain the necessary
compression to start the engine, and is worked from the boiler, W. In
future engines this compressor will be superseded by a specially
designed injector, which will produce the necessary pressure at a
considerable reduction in cost. When once the engine is started, the
fire of the auxiliary boiler can, of course, be drawn, as the main
engine afterward makes its own steam. The regenerator, E, has circular
ends of fire clay perforated, the body being filled with fire clay
spirals of the shape clearly shown in elevation in Fig. 2. The injector
valve for the creosote is shown to a larger scale in Fig. 3. This valve
has, however, been since considerably modified and improved. The feed
and exhaust valves, M, are actuated by cams keyed to a countershaft
driven by bevel wheels from the main shaft. The creosote pump, F, is
also worked by a cam on the same shaft, but the pumps, G H J, are worked
by eccentrics. A stop valve, N, is fixed to the supply pipe, P, under
which is place a back pressure valve to retain the pressure in the
combustion chamber. The engine is regulated by an ordinary Porter
governor actuating the throttle valve, O. An engine, as described, has
been constructed by Messrs. Adair & Co., engineers, Waterloo Road,
Liverpool, and has been running most satisfactorily for several weeks,
the results being clearly shown by the indicator diagrams (Figs. 5 and
6). The results obtained by this motor are very remarkable, and are a
long way in advance of any previous performance, as only a little over ½
lb. of fuel is used per i.h.p. per hour. It may be mentioned that the
temperature of the combustion chamber is calculated to be about
2,500°F., and that of the exhaust gases does not exceed
180°F.--_Industries._
[Illustration: Diagram from cylinder--25 in. diam, 18 in. stroke.
I.H.P., 63. Scale, 1/30 in. Mean pressure, 28.2 lb. FIG. 5.]
[Illustration: Diagram from air pump--15 in. diam., 18 in. stroke.
I.H.P., 23. Scale, 1/30 in--Mean pressure, 28.5 lb. FIG. 6.