Investigation of two-stage split-injection strategies for a Dieseline fuelled PPCI engine

Two-stage split-injection strategies for partially premixed compression ignition (PPCI) combustion mode were investigated in a light duty 2.2 L four cylinder compression ignition engine fuelled with G50-Dieseline (50% ULG95 gasoline in EN590 diesel by volume). The investigation of two-stage split-injection has been focused on injection quantity-ratios and timings and it aims to achieve improved charge premixing and consequently reduce the oxides of nitrogen (NOx) and particulate matter (PM) emissions simultaneously. Other parameters affecting combustion process (e.g. compression ratio) were fixed to identify the individual effects of parameters under study on the combustion and emission characteristics by the Taguchi-DOE (design of experiment) analysis. The investigation was conducted for two load groups of 1.37 and 2.97 bar BMEP selected from the new European driving cycle (NEDC) at an engine speed of 1800 RPM. Optimum operating values of injection parameters for generating the minimum and maximum combustion and emission characteristics were identified. Furthermore, very early first injection-timings were investigated for 2.97 bar BMEP with the combustion phase of 50% accumulative heat release (AHR-50) fixed. Compared with the single-injection strategy, BSNOx was reduced by approximately 39% to 59% through applying the two-stage split-injection. Accumulation particulate concentration as well as smoke number were reduced by approximately 90%. It is believed that with very early first-injection timings, fuel wall-impingement and over mixing may have resulted in lower combustion efficiency and thus BMEP drop. Consequently, the premixing process can reach a limit where the effect of required higher injected fuel quantity dominates combustion and emission characteristics. The two-stage split-injection developed in this study appears to be effective in improving the premixing process for PPCI combustion.