Analysis of different modes of low temperature combustion by ultra-high EGR and modulated kinetics in a heavy duty diesel engine

Simulation is performed to analyze the characteristics of different modes of low temperature combustion (LTC), by ultra-high exhaust gas recirculation (EGR) (UHE) and modulated kinetics (MK) in a CI engine. The physical models and numerical methods in KIVA-CMC are validated against measured pressure traces and NOx, CO and PM emissions for selected test cases. It is shown that the two LTC modes involve different fuel evaporation histories and turbulent flame structures in the tested ranges of EGR rates and injection timings. LTC is confirmed with simultaneous reduction of NOx and PM above the critical EGR rate and SOI timing in the UHE and the MK mode respectively. The UHE mode at the EGR rate 68% shows conditional temperature between 1000 K and 1600 K, while the MK mode at the EGR rate 48% shows conditional temperature distribution between 1000 K and 2200 K. It is shown that the temperature is the most sensitive parameter to suppress NOx in the UHE mode, while a longer ignition delay leads to more homogeneous mixture to result in reduced CO and PM in the MK mode.