Three-Dimensional Numerical Simulation of Flame Propagation in Spark Ignition Engines 932713

Multi-dimensional numerical simulation of the combustion process in spark ignition engines were performed using the Coherent Flame Model (CFM) which is based on the flamelet assumption. The CFM uses a balance equation for the flame surface area to simulate flame surface advection, diffusion, production and destruction in a turbulent reacting flow. There are two model constants in CFM, one associated with the modeling of flame surface production and the other with the modeling of flame surface destruction. Previous experimental results on two test engines charged with propane-air mixtures were used to compare with the computations for different engine speeds, loads, equivalence ratios and spark plug locations. Predicted engine cylinder pressure histories agree well with the experimental results for various operating conditions after the model constants were calibrated against a reference operating condition. It was found that only the production term constant must be calibrated for each engine. However, when the ignition site is moved away from the center of the combustion chamber, predicted burning rates are too fast for the higher engine speed cases. Contour plots of gas temperature and density show that the Coherent Flame Model predicts a highly convoluted flame surface in the combustion chamber. These contour plots were also used to aid understanding of the difficulties encountered in the side wall ignition cases.