Some Factors Affecting Combustion in an Internal-Combustion Engine

An investigation of the combustion of gasoline, safety, and diesel fuels was made in the N. A. C. A. combustion apparatus under conditions of temperature that permitted ignition by spark with direct fuel injection, in spite of the compression ration of 12.7 employed. The influence of such variables as injection advance angle, jacket temperature, engine sped, and spark position was studied, The most pronounced effect was that an increase in the injection advance angle (beyond a certain minimum value) caused a decrease in the extent and rate of combustion. In almost all cases, combustion improved with increased temperature. For an increase in engine speed, the rate of pressure rise increased and the time interval in seconds between injection and the spark necessary to effect ignition was considerably shortened. Although all these fuels reacted in the same manner to these variable conditions, the reactions differed decidedly in extent. The results show that at low air temperatures the rates on combustion vary with the volatility of the fuel, but that at high temperatures this relationship does not exist and the rates depend to a greater extent on the chemical nature of the fuel.