Effect of direct injected water distribution pattern on performance and emission characteristics of a gasoline direct injection engine - A CFD analysis

Gasoline direct injection (GDI) engines have better fuel efficiency and higher power output than conventional engines. However, they tend to produce higher nitrogen oxide (NOx) emissions, particularly at high-load conditions. Several strategies have been employed to mitigate these emissions, including exhaust gas recirculation (EGR), fuel injection timing optimisation, fuel additives, etc. However, it is found that direct water injection into the combustion chamber is one of the promising methods. Proper in-cylinder distribution of water can reduce emissions and improve engine performance. Therefore, in this study, an attempt has been made to evaluate the effect of variation of in-cylinder water distribution on the performance and emission characteristics of a GDI engine using computational fluid dynamics (CFD) analysis. The analysis is made for the base engine without water injection and with water direct injection for the cases of homogenous, linear, and Gaussian distributions. A naturally aspirated, spray-guided, four-stroke GDI engine is considered for the analysis. Water distributions are achieved by carefully dividing the engine into spherical zones such that water quantity at the spark plug location is negligible and goes on to a maximum near the cylinder liner. The analysis is done under high-load conditions at a constant speed of 1000 rev/min with a compression ratio (CR) of 10. The water injector orientation angle is initially determined based on the engine design constraints and literature data. Then, a comparative analysis is done between various cases of water distributions along with the base case. The results showed that Gaussian water distributions inside the combustion chamber marginally improved the engine performance and reduced NOx emissions.