Numerical investigation of dual-fuel direct injection on RCCI combustion performance at low load condition

A numerical study was performed to investigate the combustion characteristics of hydrogenated catalytic biodiesel (HCB)/gasoline reactivity controlled compression ignition (RCCI) with dual-fuel direct injection at low load condition. The results indicated that compared with the conventional port injection RCCI, the dual-fuel direct injection can effectively control the distribution of in-cylinder gasoline mixture and improve the incomplete combustion phenomenon. The delay of start of injection (SOI) of gasoline can weaken stratified combustion, shorten combustion duration, reduce combustion efficiency, decrease NOx emission and increase soot emission. In contrast, the delay of SOI of HCB can intensify stratified combustion, prolong combustion duration, increase combustion efficiency, increase NOx emission and reduce soot emission. Compared with gasoline injection timing, HCB injection timing has a more profound effect on combustion efficiency and indicated thermal efficiency. When HCB injection timing was in the range of -25° ATDC (after top dead center) to -20° ATDC and gasoline injection timing of -50° ATDC to -45°ATDC, the engine has a better performance, with the combustion efficiency about 94 %, the indicated thermal efficiency around 45 %, and the NOx and soot emissions in the original exhaust less than the limit value of Euro VI standard.