Effect of distributions of fuel concentration and temperature on ignition processes in a diesel PCCI combustion

Abstract

The distributions of fuel concentration and temperature have significant effect on the ignition processes of diesel premixed charge compression ignition (PCCI) combustion. It was found in this study that the ignition process of PCCI combustion organized by multi-pulse injection was strongly influenced by conditions of fuel stratification. The start of low temperature reactions occurred in the leaner area of the combustion chamber in the test engine because the temperature here first reached the point of low temperature reactions. Ignition always occurred in the position where the mixture featured with equivalence ratios close to the mean equivalence ratio of the overall mixture, while the neighboring area of the initial ignition area accumulate heat with a finite speed until finally autoigniting. Moreover, the appearance of highest combustion temperature occurred in the same area at the combustion chamber. For more homogeneous mixture, a higher amount of mixture reached ignition simultaneously, resulting in a larger initial ignition area and a higher temperature at the ignition area. Furthermore, V-type distribution of equivalence ratio was found to be beneficial to retarding high temperature reaction.

Key words： PCCI; fuel stratification; multi-pulse injection; ignition