A Study on Combustion Characteristics of a High Compression Ratio SI Engine with High Pressure Gasoline Injection
In order to improve the thermal efficiency of spark ignition (SI) engines, an improved technology to avoid irregular combustion under high load conditions of high compression ratio SI engines is required. In this study, the authors focused on high-pressure gasoline direct injection in a high compression ratio SI engine, which its rapid air-fuel mixture formation, turbulence, and flame speed, are enhanced by high-speed fuel spray jet. Effects of fuel injection pressure, fuel mass ratio between direct injection and port fuel injection, and spark ignition timing on combustion characteristics were experimentally investigated. It was found that the heat release rate was drastically increased simultaneously by raising the fuel injection pressure. The increase of direct injected fuel mass ratio can also favorably improve the combustion speed. However, longer delay time between end-of-injection and spark timing worsens the combustion rate due to turbulence dissipation.