1907.] on Flame in Gas and Petrol 3Iotors. 511 



the specific heat of the gases had been changed, and they considered 

 combustion to be complete at the maximum temperature, or nearly 

 so. My experience with engine indicator cards, supplementing the 

 experhnents made with gas and air mixtures in a closed vessel, led 

 me to conclude that combustion was not complete, and that therefore 

 it was not safe to draw deductions as to varying specific heat, in the 

 absence of definite knowledge that chemical combination was com- 

 pleted before determinations were made of specific heat value. In 

 engine experiments, it was found that the same phenomena occurred, 

 that is, maximum pressure never reached that to be expected on the 

 constant specific heat theory. My view, then, was in opposition to 

 that of the French physicists, as I considered that no proof had been 

 furnished by them, either of the absence of continued combustion, or 

 the absence of dissociation at the very high temperatures of the flame. 

 The absence of definite knowledge as to specific heats at high tem- 

 peratures, dissociation, or 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 assumed as a perfect gas, and tlie chemical action 

 considered as merely a means of heating the air through the desired 

 temperature range. Calculating on this simplified theory, it became 

 evident that the efiiciency to be obtained in an air engine without 

 heat losses was dependent upon compression mainly. Working out 

 this theory showed that while the utmost thermal efficiency that 

 could be theoretically expected from a non-compression engine of the 

 Lenoir type was 22 per cent., compression supplied means of getting 

 theoretical efficiencies of as high as 60 per cent., with practicable 

 ranges of pressures and temperatures. Considering, then, gas and 

 petrol engines as air engines, the theory is very simple. Tliere are 

 three symmetrical cycles of compression air engines. They may be 

 called constant temperature, constant volume, and constant pressure 

 engines, from the method of adding lieat. In the constant tem- 

 perature engines, the heat is added on an isothermal expanding line, 

 but in the constant volume engines the heat is added while the 

 volume is constant ; and in the constant pressure engines the heat 

 is added at constant pressure, while the volume varies. I have four 

 diagrams on the wall illustrating these different engines, calculated 

 as air engines. The first cycle you will recognise to be the Carnot 

 cycle applied to an air engine. It is a perfect engine, between the 

 limits of temperature. It will be seen, however, from the diagram, 

 that assuming 500 lb. per square inch to be the maximum pressure 

 allowable, although the efficiency is great, being equal indeed to 

 " 64, yet the mean pressure is very small — only 6 lb. per square 

 inch for a maximum pressure of 500 lb. absolute. In the constant 



