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With increasingly stringent requirements and regulations related to particulate matter(PM) emissions, manufacturers are paying more and more attention to emissions from gasoline direct injection(GDI) engines. The present paper proposes an improved two-step soot model. The model is applied in the Kiva-Chemkin program to simulate the processes of spray impinging, fuel mixture preparation, combustion and soot formation in a typical turbocharged downsized GDI engine. The simulation results show that soot formation in the GDI engine is attributed to non-uniform distribution of the air-fuel mixture and pool fire of wall film in the cylinder. Under homogeneous mode, increasing the injection advance angle can optimize fuel atomization and improve air-fuel mixing, thus reducing soot formation. However, an excessive injection advance angle may cause spray to impinge on the cylinder wall and this will sharply increase the soot emission.

A transient gas-solid heat transfer model for the 3-D (three-dimensional) coupling components in internal combustion chamber was built. In order to implement this model, a transient heat transfer program based on FEM (finite-element method) was developed, the KIVA3V code was improved, and a KIVA-FEM interface program was developed. A special treatment for the grid generation were designed and utilized. The 3-D transient non-uniform gas temperature field and convective heat transfer coefficient distribution near the combustion chamber wall can be obtained using this heat transfer model. In addition, both steady and transient temperature fields of the 3-D coupling component system of a gasoline engine were calculated and analyzed. The results show that the temporal and spatial non-uniformity of thermal boundary conditions has an important influence on the steady temperature field, transient temperature field and heat flux of the combustion chamber wall.