Estimating Heat-Release and Mass-of-Mixture Burned from Spark-Ignition Engine Pressure Data

A First Law analysis based on the cylinder pressure variation during combustion is a commonly used diagnostic for determining actual spark-ignition engine burning rates. Both simple one-zone and more complex two-zone models have been developed for this purpose. It is shown that the fraction of the fuel's chemical energy which has been released and the fraction of fuel-air mixture burned, within the engine's cylinder, can be accurately estimated from a one-zone analysis if appropriate values for the “average ratio of specific heats”, y¯, of the one-zone contents are used. These values are determined by matching the output of the one-zone analysis to that of the more rigorous two-zone analysis of the same cylinder pressure data. Use of this one-zone burning rate analysis procedure is illustrated.