Impact of fuel injection pressure on GDI engine performance: a numerical study with pre-combustion chamber

The automotive industry needs to develop engines with higher efficiency and lower emissions. Gasoline direct injection (GDI) engines address these demands, with better fuel economy and reduced carbon dioxide (CO2) emissions, but face challenges in optimizing combustion processes and fuel injection strategies. The purpose of this study is to examine the combined impact of injection and pre-chamber design parameters on both pre and main-chamber combustion in order to achieve improved engine performance and emissions. Previous studies suggested that the 2% pre-chamber model achieved better combustion performance than both the standard engine (without a pre-chamber) and the 5% pre-chamber model. Therefore, in this study, a 2% pre-chamber model was numerically tested using computational fluid dynamics (CFD) codes available on the STAR-CD platform with three distinct injection pressures (IPs): 150 bar, 100 bar, and 50 bar (standard). The objective was to examine the combined impact of these pressures on mixture formation during the suction and compression strokes, as well as on combustion and emission formation. The outcome of the research reveals that the 100-bar model had superior fuel evaporation and produced a more homogenous mixture in comparison to the other two models. The same model recorded the highest peak pressure, and the difference in pressure between the three IP models was minimal. The formation of carbon monoxide (CO) increased with increasing IP during the combustion, with CO2 formed almost similar for all three cases. The development of nitrogen oxide (NO) is lesser for both 100 and 150-bar IPs when compared to the standard IP model, whereas soot formation was negligible for all three IP models. From the study, it is concluded that the engine with 2% pre-chamber volume and 100 bar IP model yielded better performance than the standard IP model.