Temperature Gradients in Spark Ignition Engine Combustion Chambers

A computer model has been developed to simulate the combustion process in a Renault IFP spark ignition research engine. The model enables the gradients in temperature and composition in the burnt gases behind the flame front to be predicted in a more accurate manner than has henceforth been possible. This is due to the incorporation into the model of heat exchanges due to mixing between adjacent zones in the, burnt gases. The temperature gradients in the burnt gases are reduced quite markedly as the turbulent eddy diffusivity, ɛ, of the flow in the combustion chamber is increased. The NO gradients are not so significantly affected.

The ability of the model to predict accurate values of burnt gas temperature behind the flame front is verified from the correlations noted between predicted and spectroscopically measured burnt gas temperatures at certain locations in the combustion chamber. Good agreement is also obtained between the predicted and measured NO levels in the engine exhaust. The errors involved in NO prediction by using a “homogeneous” or a “non-mixing” model in place of the more accurate “mixing” model are investigated. Comparisons are also made between these models with regard to combustion time intervals and pressure development