Study of Fuel Distribution on Diesel PCCI Combustion by Development of a New Characteristic-Time Combustion Model

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. The combustion temperature of richer zones were drawn down by mass and heat transfer into surrounding lean zones, so that lower combustion temperature and lower formation rate of NO were observed in richer area. Moreover, a “V” type distribution of equivalence ratio was found to be beneficial to retardence of high temperature reaction.