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.Fig. 1 - SECTIONAL ELEVATION - HARGREAVES' THERMO-MOTOR. 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.Fig. 3. 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, P, into the telescopic pipe, L either into the piston, B, or through the pipe, P, into the casing, K - the bottom of the casing being connected by the pipe, P, with the auxiliary boiler, W. The steam generated in the casing, K, is carried to the boiler, W, by the pipe, P, and from the boiler it passes along the pipe, P, through the valve, A, 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, P, and forced through the pipe, P, back to the chamber, Y, through the valve, A, 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.
Diagram from cylinder - 25 in. diam, 18 in. stroke. I.H.P., 63. Scale, 1/30 in. Mean pressure, 28.2 lb..
Diagram from air pump - 15 in. diam., 18 in. stroke. I.H.P., 23. Scale, 1/30 in - Mean pressure, 28.5 lb.
DIAGRAMS FROM CYLINDER AND AIR PUMP.
Net indicated horse power, 40; revolutions per minute, 100; coal tar consumed per hour, 20.5 lb.; coal tar per I.H.P. per hour, 0.512 lb.