Mitani, S., Hashimoto, S., Nomura, H., Shimizu, R. et al., "New Combustion Concept for Turbocharged Gasoline Direct-Injection Engines," SAE Int. J. Engines 7(2):551-559, 2014, doi:10.4271/2014-01-1210.
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.