Concerns about environmental pollution and energy shortages have increased worldwide. One approach to reduce CO2 emissions from gasoline engines is to achieve stratified charge combustion with various injection ratios using port fuel injection(PFI) and direct injection. The combustion and emission characteristics of a 4-valve direct injection spark ignition(DISI) engine equipped with a dual injection system were investigated while the injection ratio was varied. When the direct injection ratio increased, the lean limit A/F was extended. This suggests that the dual injection gasoline engine with both PFI and direct injection can meet severe vehicle emission and fuel economy requirements. The dual injection system had higher combustion pressure than that of either a conventional or direct injection systems. Therefore, the engine power of a dual injection DISI engine would be higher than that of a single injection DISI engine. However, NOx emissions increased compared with the emission levels in both PFI and DISI systems. Concerns about environmental pollution and energy shortages have increased worldwide. One approach to reduce CO2 emissions from gasoline engines is to achieve stratified charge combustion with various injection ratios using port fuel injection (PFI) and direct injection. The combustion and emission characteristics of a 4- valve direct injection spark ignition (DISI) engine equipped with a dual injection system were investigated while the injection rate was varied. When the direct injection ratio increased, the lean limit A / F was extended. PFI and direct injection can meet severe vehicle emission and fuel economy requirements. The dual injection system had higher combustion pressure than that of either a conventional or direct injection systems. Thus, the engine power of a dual injection DISI engine would be higher than that of a single injection DISI engine. However, NOx emissions increased compared with the emission le vels in both PFI and DISI systems.