Abstract
The effect of mixture heterogeneity on PCCI combustion was analyzed using the Large Eddy Simulation model in combination with the reaction kinetics. The aim of this analysis is to find the statistical characteristics of the mixture heterogeneity of the fuel, EGR-gas and temperature distributions in a turbulent flow field for moderating extreme pressure rise and for extending an output limit. The initial velocity field at the beginning of compression was given by a new method, which generated statistically reasonable turbulent velocity fluctuations. The auto-ignition and combustion behaviors were analyzed for several different sets of the rms and the length scale of the spatial fluctuations in the fuel mass fraction, EGR-gas mass fraction and temperature. The analysis shows that the combination of a larger rms value and a longer length scale of the spatially fluctuating fuel mass fraction is effective to slow the combustion in a hot flame reaction phase and to extend a knock limit, and that the heterogeneous distribution of the EGR-gas gives a similar effect. The result shows that non-uniform temperature distribution is not so effective under the conditions tested.
