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In order to understand premixed charge compression ignition (PCCI) combustion, a new combustion model of kinetic-and-turbulent characteristic-time has been developed. A ununiformity function H(ϕ)was presented by analysis of the effect of fuel/air distributions on the role of turbulent timescale in the combustion model, then an analytical turbulent timescale coefficient f was deduced, which was proved to be able to correlate the fuel ununiformity with the turbulent timescale in the combustion model. The new model was employed for simulation of a PCCI combustion organized by various multi-pulse injection strategies in a heavy duty diesel engine. The simulation results agreed with the experimental data well. The ignition process of a PCCI combustion organized by multi-pulse injection was a separated volume autoignition process, which was strongly influenced by the condition of fuel stratification.

Both in conventional diesel combustion and the low temperature combustion represented by PCCI and EGR-diluted combustion, high mixing rate at the whole combustion history is the key to achieve comparative clean and high-efficiency combustion. In this study, a newly developed combustion chamber, vortex-induced combustion chamber which can enhance middle and late cycle combustion is developed based on BUMP combustion chamber investigated in previous study. And then, the combustion and emission characteristics in the circumstances of diluted combustion are studied. For low oxygen concentration cases, heat release rate goes down and combustion efficiency decreases due to decreased mixing efficiency. The results of chamber design indicate complex structure of flow can be realized by special designed chamber geometry. The velocity difference in the interface of the vortexes will benefit to mixing of fuel and air, therefore combustion and emissions.

The Premixed Charge Compression Ignition (PCCI) engine has the potential to reduce soot and NOx emissions while maintaining high thermal efficiency at part load conditions. However, several technical barriers must be overcome. Notably ways must be found to control ignition timing, expand its limited operation range and limit the rate of heat release. In this paper, comparing with single fuel injection, the superiority of multiple-pulse fuel injection in extending engine load, improve emissions and thermal efficiency trade-off using high exhaust gas recirculation (EGR) and boost in diesel PCCI combustion is studied by engine experiments and simulation study. It was found that EGR can delay the start of hot temperature reactions, reduce the reaction speed to avoid knock combustion in high load, is a very useful method to expand high load limit of PCCI. EGR can reduce the NOx emission to a very small value in PCCI.