Effects of internal exhaust gas recirculation on controlled auto-ignition in a methane engine combustion

The effects of internal exhaust gas recirculation (IEGR) on controlled auto-ignition were evaluated with a single cycle simulator consisting of a rapid intake compression and expansion machine (RICEM) using methane as the fuel. The fuel–air mixture and simulated residual gas were introduced to the combustion chamber through the spool-type valves. Simulated residual gas representing the internal exhaust gas recirculation (IEGR) was generated by burning the fuel–air mixture in the IEGR chamber during the intake stroke. Various supply timings, homogeneities, and equivalence ratios of simulated residual gas were tested to investigate their effects on the auto-ignition of the fuel–air mixture. Multi-point ignitions and faster combustion were observed along with realized controlled auto-ignition combustion. The supply timing of simulated residual gas correlates with its temperature which subsequently affects the auto-ignition timing and burning duration. Stratification between the fuel–air mixture and simulated residual gas can maintain locally high temperatures of the simulated residual gas and enhance the auto-ignition of the fuel–air mixture. The auto-ignition temperature under the stratified mixing condition was more than 100 K lower than that under homogeneous mixing conditions. Relatively lean mixtures had more difficulty with auto-ignition and frequently showed misfire even at high temperatures.