We have the theoretical efficiency of a gas engine, neglecting friction, loss to the cylinder walls, and loss through the rejection of heat with the exhaust gas, equal to— 1960 – 520 E = —————————— = 73.5 percent. 1960 In substituting the numerical values in the above calculation it was assumed that the temperature of the burning mixture would be 1500° F above zero, and that the exhaust temperature would be as low as 60. Since the calculation is made from absolute zero, which is 460° below the zero marked on our thermometers, the temperature of the burning charge, T = 1500 + 460° = 1960° above absolute zero. Similarly the absolute temperature of the exhaust would be, t = 60 + 460 = 520° absolute. The application of the absolute temperatures will be seen from the calculation for efficiency. The value given, 73.5 per cent, it should be understood is the theoretical efficiency and is at least 20 per cent above the best results obtained in practice. The best record that we have had to date, is that established by a Diesel engine which returned 48.2 per cent of the calorific value of the fuel in the form of mechanical energy. In order that the reader may have some idea of the losses that occur in the engine, and their extent we submit the following table. These are the results of actual tests obtained from different sources and represent engines built for different services and of various capacities: ═════════════════════════╤══════════╤══════════╤═══════════╤═══════════ LOSSES—DATA │Automobile│Stationary│Stationary │ │ Motor │ Engine │ Engine │ ─────────────────────────┼──────────┼──────────┼───────────┼─────────── Horse-power │ 30. │ 200 │ 1000 │ │ │ │ │Loss at per Heat lost to jacket water│ 35.8% │ 31.0% │2970 B.T.U.│Horse-power │ │ │ │in B.T.U.’s Heat lost in exhaust │ 24.6% │ 30.0% │2835 B.T.U.│ Friction loss │ 8.6% │ 6.5% │810 B.T.U. │ Heat lost by radiation │ 15.4% │ 8.2 │540 B.T.U. │ Heat available as power │ │ │2700 B.T.U.│ Efficiency (per cent) │ 15.6% │ 24.3 │ │ Fuel │ Gasoline │ │ Producer │ │ │ │ Gas │ ─────────────────────────┴──────────┴──────────┴───────────┴─────────── The remarkable efficiency of the Diesel engine is due principally to the extremely high compression pressure, which was from 500 to 600 pounds per square inch. When this is compared to the 60 to 70 pounds compression pressure used with automobile engines it is easy to see where the Diesel gains its efficiency. It is evident that as much depends on the manner in which the fuel is used in the engine as on the calorific value of the fuel.