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A new diffusing-oriented spray stratified combustion system for direct injection gasoline engines is proposed in this study. A reflector with multi-impingement wall head attached ahead of multi-hole injector nozzle is used in this system as a strategy of breaking up the fuel spray and directing it in a desired direction to form a perfect atomization and stratification of fuel air mixture. A comparatively rich fuel-air mixture is always formed over a wide range of engine operation conditions in the vicinity of spark plug due to the fuel spray oriented by the special surface shape of impingement wall, and the finely atomized fuel spray is formed in the other areas of combustion chamber due to the impacting of fuel spray against the impingement wall. Therefore, it is possible to achieve stable and fast burn of lean fuel air mixture. The combustion system is preliminary investigated on a single cylinder four-stroke DI gasoline engine which is shifted from a DI diesel engine.

A multizone phenomenological combustion model, in which the fuel bum rate is governed by the rate of fuel vaporization and mixing, is developed to study the effects of split injection schemes on NO and soot emissions of direct injection diesel engines. This model is calibrated with the experimental data of a single injection case. Comparison between the results calculated by the model and experimental results shows that the model has a good predictive capability for cylinder pressure, heat release rate, NO & soot emissions. The study of split injection parameters, including the delay dwell between injection pulses, the fuel quantity injected in the second pulse and the fuel pressure of the second injection, is carried out. The results predicted by the model show that the soot can be effectively reduced without increasing NO emission and fuel consumption with the split injection in which 10-30% of total fuel is injected in the second injection at about 15 °CA after top dead center.