Abstract
This paper studied the potential of HCCI higher load extension by using there types of stratified charge, including temperature (thermal) stratification, concentration (fuel) stratification and species (EGR) stratification. To isolate the influence of three stratifications on HCCI engine performance, HCCI combustion processes with different equivalence ratios, stratification degree, EGR ratios were simulated. The results show that stratification leads to earlier ignition timing, sequential heat release, longer combustion duration, lower rate of pressure rise compared to pure homogeneous cases at same load. However, both fuel stratification and EGR stratification lead to high NO_x. Temperature stratification is most effective one to significantly reduce pressure rise rate during CI combustion process with least negative effect of high NO_x emission or incomplete combustion. With limit of maximum pressure rise rate at 5bar/CA and maximum NO_x emissions at 100ppm, the maximum IMEP of pure HCCI without EGR is 1.86bar, the maximum IMEP can be further extended to 5.4bar using temperature stratification and EGR dilution, under natural aspiration conditions.
