Controlled auto-ignition characteristics of methane–air mixture in a rapid intake compression and expansion machine

The characteristics of controlled auto-ignition (CAI) were investigated with a methane–air mixture and simulated residual gas, that represents internal exhaust gas recirculation (IEGR). Supply systems were additionally installed on the conventional rapid compression machine (RCM), and this modified machine—a rapid intake compression and expansion machine (RICEM)—was able to simulate an intake stroke for the evaluation of controlled auto-ignition with fuel–air mixture. The fuel–air mixture and the simulated residual gas were introduced separately into the combustion chamber through the spool valves. Various IEGR rates and temperatures of the IEGR gas were tested. The initial reaction and the development in controlled auto-ignition combustion were compared with spark-ignited combustion by visualization with a high-speed digital camera. Under the controlled auto-ignition operation, multi-point ignition and faster combustion were observed. With increasing the temperature of IEGR gas, the auto-ignition timing was advanced and burning duration was shortened. The higher rate of IEGR had the same effects on the combustion of the controlled auto-ignition. However, this trend was reversed with more than 47 per cent of IEGR.