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. The HC primary formation model considers that fuel injected and mixed beyond the lean combustion limit during ignition delay and fuel effusing from the nozzle sac volume at low pressure and low velocity.
In order to validate the model, experiments were performed on a six-cylinder, turbocharged and intercooled, direct injection diesel engine. The simulation results show good agreement with the experimental data, and it indicates the validity of the PM model. The calculation results show distinctions between PM and soot formation rates are mainly in the early combustion stage. The SOF formation has important influence on the PM formation at lower loads, and the soot formation dominates the whole PM formation process at higher loads. The PM model is helpful for better understanding the PM emission formation process of diesel engines, and useful for the simulation of PM emission, as well as PM emission control of diesel engines.