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The advantages of gasoline direct-injection are intake air cooling due to fuel vaporization which reduces knocking, additional degrees of freedom in designing a stratified injection mixture, and capability for retarded ignition timing which shortens catalyst light-off time. Stratified mixture combustion designs often require complicated piston shapes which disturb the fluid flow in the cylinder, leading to power reduction, especially in turbocharged gasoline direct-injection engines. Our research replaced the conventional shell-type shallow cavity piston with a dog dish-type curved piston that includes a small lip to facilitate stratification and minimize flow disturbance. As a result, stable stratified combustion and increased power were both achieved.

The atomization structure of the fuel spray is known to be affected by flow conditions and cavitation inside the nozzle hole. In this paper, the cavitation phenomena inside the nozzle hole was visualized by using large-scale transparent nozzles, as well as the effect of length-to-width ratio (l/w ratio) of the nozzle hole on cavitation and on the behavior of injection liquid jet. In addition, various flow patterns inside the nozzle hole same as experimental conditions were simulated by the use of Cavitation model incorporated in Star-CCM+, which was compared with experimental results.