Diesel engine combustion characteristics variation under switching process

In order to study the way how to identify the combustion region between conventional combustion and low temperature combustion (LTC) under combustion mode switching process in diesel engine, and the effect of different injection parameters on combustion characteristics, experimental investigations were carried out on a common rail diesel engine by single injection and EGR to switch combustion mode at 1500 r·min-1 and 30% load condition. The results show that, with the promotion of exhaust gas recirculation (EGR) from 0% to 55%, the position of start of combustion (SOC) is delayed a little but not too much. However, when the EGR ratio is over 45%, the LTC region is attained. The point of inflection at the beginning of heat release rate (HRR) profile can be used as an indicator to identify the LTC region and control the combustion event. When the injection timing retards from -14°CA ATDC to -7°CA ATDC, it shows little effect on ignition delay and combustion duration on conventional combustion region, but it influences greatly on LTC region. What's more, it almost misses fire when the injection timing is tuned to -7°CA ATDC. With the fuel injection pressure increasing from 75 MPa to 140 MPa, it promotes the air-fuel mixing both in conventional combustion region and LTC region. The peak point of in-cylinder pressure and HRR are risen and the indicated heat efficiency slightly increased. © 2016, Editorial Department of Transaction of Beijing Institute of Technology. All right reserved.