The air standard cycle, the ideal fuel-air cycle and the fundamental concepts of combustion in a spark ignition engine are briefly described. The effect of combustion processes at various air fuel ratios on power, efficiency and composition of exhaust products are reviewed. It is recognized some degree of incomplete combustion is always present, and the effects of “poor” combustion on engine operations are discussed.
FOREWORD Recently, a number of investigators (1), (2), and (3) have reported detection by means of ionization gaps of flame fronts other than those initiated by the spark discharge. Since some of the findings in these studies appeared to be contrary to road-test experience at the General Motors Research Laboratories, the significance of ionization-gap data was questioned. For example, Reference (1) shows abnormal flame fronts occurring in an engine in the absence of combustion chamber deposits, whereas in road testing, it is usually necessary to accumulate deposits before abnormal flame fronts become noticeable. Reference (2) shows data wherein abnormal combustion was unaffected by fuel octane number, while in road testing, objectionable abnormal combustion is usually eliminated by increasing fuel octane number. In order to investigate these apparent anomalies, engine tests were made using special independent ionization gaps.
THE 18-cyl turbine-compounded engine developed by Wright is claimed to be an attractive powerplant for aircraft designed to fly up to speeds of about 450 mph. The compounding of this engine is accomplished by means of three blowdown turbines. This type of turbine is used because, according to the authors, it is more efficient than the pressure turbine up to an altitude of about 30,000 ft. It is estimated that at take-off a suitable pressure turbine would provide about 8% increased engine output. The present Turbo Compound engine, with its blowdown turbines, gives an 18% increase.
ALTHOUGH the new Ford V-8 engine has displacement and compression ratio as the old V-8 does, the new engine develops 130 hp and 214 ft-lb maximum torque to only 110 hp and 196 ft-lb torque for the old. Specific fuel consumption is also lower in the new engine over the entire speed range. The new engine has a very short stroke, to increase mechanical and thermal efficiencies. It also has overhead valves to permit maximum volumetric efficiency to be attained, if required by future increases in compression ratio.