Flame Temperatures Vary with Knock and Combustion-Chamber Position 350091
TEMPERATURE measurements have been made along three lines through the combustion chamber of a gasoline engine running under non-knocking and under knocking conditions. The results show that, after passage of the flame fronts through portions of the charge located either near the point of ignition or near the center of the combustion chamber, the temperature rises continually until shortly before maximum pressure is reached. When the charge is completely inflamed, there is a temperature gradient along the length of the combustion space, the temperature at the spark-plug end being as much as 600 deg. fahr. higher than at the opposite end. These effects are explained on the basis of adiabatic compression and expansion of the gases during the combustion process.
Comparison of knocking and non-knocking explosions shows that in the knocking case: (a) the maximum temperatures are higher, (b) the maximum temperatures are attained earlier in the cycle, (c) the rate of cooling during the expansion stroke is greater, and (d) the exhaust temperatures are lower.