Prediction of charge effect on SI engine performance for hydrocarbon fuels

A theoretical model is presented in this research to predict the ignition delay and the combustion process in a class of stratified charge engines including the non-spherical flame progress through rich and lean regions. Step by step calculations were carried out in both rich and lean regions. The process continued until all the fuel was burned. At each crank angle، the volume of the mass control changes and the mole fraction of the burned fuel increased due to the flame propagation. Considering the heat transfer from the cylinder contents to the surrounding area and the frictional work، some important operating parameters such as the mean effective pressure، the thermal efficiency and the specific fuel consumption، were predicted. Predicted values obtained by the model for the natural gas were compared to corresponding experimental data. The comparison shows that there is a logical agreement between theoretical and measured values. The flexibility of the model allows having accurate predictions in a wide range of the charge stratification for various hydrocarbon fuels.