Recent direct injection gasoline engines have remarkably improved specific fuel consumption and increased power. These direct injection gasoline engines have a high pressure common rail fuel injection system to operate a mixed strategy using early injection at high load and late injection at low load.

Mixture formation and combustion process in these engines are described in this paper. First, engine operating design concepts are shown and compared with �gclassic�h ones. Next, general fuel system requirements are explained. Fuel vaporization and fuel/air mixing in a cylinder are discussed, based on the fuel property and the theory of momentum. Methods for mixture preparation are introduced, being sorted by the utilization of charge flow and piston crown which dominate the mixture formation. Finally, the combustion process and engine performance of both stratified mode and homogeneous mode are explained. Based on the review of technical publications, the trends and directions of the development of direct injection gasoline engines are discussed.
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