Effects of fuel injection parameters on the performance of homogeneous charge compression ignition at low-load conditions

With the objective of enhancing the effectiveness of late fuel injection strategy in extending the low-load limit of homogeneous charge compression ignition engines, a numerical study is conducted to investigate the effects of fuel injection parameters, such as the injection pressure and spray cone angle, on the overall combustion efficiency and CO/NO_x emissions. Closed-cycle engine simulations are performed incorporating detailed iso-octane reaction kinetics and combustion submodel based on the spray-interactive flamelet approach. Extensive parametric studies are conducted to provide a detailed map of the combustion efficiency and emission performance. In general, it is found that the in-cylinder charge stratification can be reduced by both an increased injection pressure and a wider spray cone angle, resulting in substantially lower NO_x emissions and reasonably high combustion efficiency simultaneously. The present study demonstrates that an optimal adjustment of the two fuel injection parameters can result in significant extension of the low-load limit of homogeneous charge compression ignition through delayed fuel injection strategy.