CFD simulation of stratified combustion process in a direct injection spark ignition engine

A three-dimensional simulation technique for the stratified combustion process in direct injection gasoline engines is developed. The effects of a widely distributed mixture equivalence ratio and a large amount of EGR on laminar flame speed are briefly modeled taking into account only the temperature of the unburned mixture and the flame temperature. The suggested laminar flame speed model is incorporated into a CFD code in combination with the coherent flame model. In burned gas, chemical equilibrium depending on the local equivalence ratio is assumed so that the post flame reaction upon mixing rich burned gas and lean burned gas or fresh air can be simply modeled as a change of the equilibrium. The calculated flame propagation process, heat release rate and exhaust emissions are confirmed by the results of measurements including the LIF technique. The good agreements obtained under various conditions indicate the applicability of this method.