Predictions of Autoignition in a Spark-Ignition Engine Using Chemical Kinetics

A model developed to predict outoignition is used with data from a premixed charge, spark-ignition engine. A detailed chemical kinetics mechanism is used to predict the reactions which occur in the end-gas and lead to autoignition. Experimental pressure data from a CFR engine are used in the model to determine end-gas temperatures.

The initial temperature at the time of spark must be increased above the bulk temperature for the predicted time of outoignition to agree with the observed time. A method for estimating the initial temperature based on an adiabotic compression from the time of intake valve closing is presented.

The predictions of the model are examined over a range of engine speeds and fuel-air equivalence ratios. The magnitude by which the initial temperature must be increased above the bulk temperature decreases with increasing engine speed. This magnitude follows a trend which can be related to a heat transfer correlation. The magnitude of the temperature correction shows no dependence on equivalence ratio for propane; for methane and ethane, the temperature correction decreases with increasing equivalence ratio.