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The limits on reciprocating engine performance are set by the idealized constant-volume cycle. Heretofore, fuel-air cycles have been computed by tracing them out on thermodynamic charts -- a long and tedious process. By programming the thermodynamic characteristics of the fuel-air media and the cycle processes on a digital computer, it has been possible to compute the characteristics of fuel-air cycles over a wide range of fuel-air ratios, compression ratios, and initial conditions and present the results in graphic form. The results are used to compute equivalent theoretical cycles for comparison with real engine performance. The ratio of actual to ideal thermodynamic performance of engines can be computed using equivalent cycles. The method to evaluate engine performance is illustrated, and a number of actual cycles are compared with their equivalent fuel-air cycles, and losses are considered.

REPORTED here are the results of work carried on to determine the effect of variations in engine exhaust pressure on the performance at various altitudes of compressor-engine-turbine combinations for aircraft, in which the turbine is geared to the engine crankshaft. Measurements were made of indicated mean effective pressure, fuel consumption, and exhaust temperature on a liquid-cooled aircraft-engine cylinder at various inlet and exhaust pressures. The author concludes that this combination unit can give high specific output and low specific fuel consumption, particularly at high altitudes. He also determines the ratio of engine exhaust pressure to engine inlet pressure required for maximum net output, as well as for lowest net fuel consumption. He found further that high exhaust pressures did not appear to impose undue mechanical or thermal stresses on the engine.

IN the investigations reported in this paper flame-trace photographs were taken on a moving film through a glass-window slot in an engine cylinder to show the effects of various operating conditions on the rate of flame travel across the combustion-chamber. The tests were made with a small L-head single-cylinder engine in the Sloan Automotive Laboratories at the Massachusetts Institute of Technology. The technique is similar to that used by Withrow and Boyd in flame studies reported in 1931. This investigation covers a considerable range of operating conditions, including altitude, with and without supercharging, inlet temperature, humidity of the intake air, engine speed, ignition timing, and fuel-air ratio. In general, the results show that flame speed decreases with increasing altitude in an unsupercharged engine. Either supercharging or reducing the exhaust pressure with inlet pressure constant, tends to increase flame speed.

THIS paper refers to previous literature on the subject and discusses the fundamental factors involved. It also gives the results of tests showing the effect of variations in atmospheric pressure and temperature on one particular engine. In conclusion it points out the need for further research on this subject.

SUPPLEMENTING the results of an investigation at the Massachusetts Institute of Technology on supercharging a single-cylinder automobile engine which were presented at the 1928 Annual Meeting, this paper reports a study that was made to determine whether the mechanical action of a high-speed centrifugal supercharger improves engine performance by increasing the degree of atomization and vaporization of the fuel in the inlet manifold. While changes in the degree of fuel atomization and vaporization might be measured directly by sampling the gases as they pass to each cylinder, an indirect evaluation of these changes by measuring their effect on engine performance was considered more practicable. Tests were made on a six-cylinder automobile engine connected to an electric cradle-dynamometer.

SUPPLEMENTING the results of an investigation at the Massachusetts Institute of Technology on supercharging a single-cylinder automobile engine which were presented at the 1928 Annual Meeting, this paper reports a study that was made to determine whether the mechanical action of a high-speed centrifugal supercharger improves engine performance by increasing the degree of atomization and vaporization of the fuel in the inlet manifold. While changes in the degree of fuel atomization and vaporization might be measured directly by sampling the gases as they pass to each cylinder, an indirect evaluation of these changes by measuring their effect on engine performance was considered more practicable. Tests were made on a six-cylinder automobile engine connected to an electric cradle-dynamometer.