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. (C) 2008 Elsevier Ltd. All rights reserved.