A Simulation Study of Water Injection Position and Pressure on the Knock, Combustion, and Emissions of a Direct Injection Gasoline Engine.

A turbocharged downsizing spark ignition (SI) engine combined with direct injection technology has the potential to improve the power and fuel economy and reduce emissions. However, gasoline engines are prone to knocking under low-speed and high-load conditions, which limits the application and development of downsizing SI engines. In this study, numerical simulation methods are used to explore the feasibility of water injection in the intake port to reduce the knock tendency of gasoline direct injection (GDI) engines and to explore the effects of different water injection pressures on combustion and emissions. First, the GDI engine is induced to knock by increasing the compression ratio and advancing the spark timing. Then, the influences of low position and no angle (LPNA) and high position and angled water injector arrangements on engine combustion are explored. When the water injector arrangement is LPNA, the turbulent kinetic energy near the spark plug is higher, the equivalence ratio is more evenly distributed, and the engine knock intensity is smaller. Finally, when the arrangement of the water injector is LPNA, the effects of water injection pressure on the knock, combustion, and emissions of the GDI engine are explored. The results show that when the water injection pressure is 5 bar, the knock intensity of the engine is the smallest, the cycle work is the highest, and the emissions of NO and unburned hydrocarbon are the lowest.