End-gas autoignition characteristics of PREMIER combustion in a pilot fuel-ignited dual-fuel biogas engine

To improve the thermal efficiency of internal combustion engines at high loads, premixed mixture ignition in the end-gas region (PREMIER) combustion is proposed as a precursor to knocking. In the current work, a pilot fuelignited dual-fuel gas engine was operated at constant speed under different intake pressures (101, 150, and 200 kPa). A simulated biogas was served as the primary fuel and diesel as the pilot fuel. The maximum mean effective pressure and thermal efficiency were evident during PREMIER operation because of autoignition in the end-gas region. Similar to knocking combustion, PREMIER combustion features two stages but neither pressure oscillation nor a rapid pressure rise is observed. We here define a new parameter, the PREMIER intensity (PI), which reflects the strength of PREMIER combustion. As the injection timing was advanced and the pressure boosted, more cycles underwent end-gas autoignition; the associated heat release increased and, consequently, the PI value rose. When the pressure and temperature of a premixed fuel mixture rose as injection timing was advanced, end-gas autoignition commenced earlier. The end-gas autoignition delay became shorter as intake pressure was increased and injection timing advanced.