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The diesel premixed low-temperature combustion mode avoids the generation of thick mixture and the high temperature region in which a great amount of NOx and PM generates. It makes a significant reduction in the emissions of both NOx and PM available at the same time. However, with the quantity of pre-injection increases and the injection time advances, the emission of HC increases significantly, which causes a decrease in the combustion efficiency. Studies have shown that the flame quench caused by too thick or too lean mixture and the oil film on the chamber is the main source for the emission of HC. As a result, understanding the mechanism of atomization and evaporation of the fuel and the formation of the mixture makes significant sense. This paper focuses on the mixture formation process. And the methods of testing the distribution of the mixture, the influential factors and control methods are studied.

In this study, a composition-based particulate matter (PM) model of direct injection diesel engines has been formulated and developed to simulate PM emission. The PM model is based on formation mechanisms of main compositions of PM: soot and soluble organic fraction (SOF). Firstly, two models for soot and SOF emissions are established respectively, then, the two models are integrated into a whole PM model. The soot emission model is given by the difference between a primary formation model and an oxidation model of soot. The soot primary formation model is the Hiroyasu soot formation model, and the Nagle and Strickland-Constable model for the soot oxidation is adopted. The SOF emission model is based on an unburned hydrocarbons (HC) emission model, and the HC model is given by the difference between a HC primary formation model and a HC oxidation model.