| To save the energy sources and protect the environment, the work to exploit new fuel engine is significant. At present, people had paid more and more attention to the CNG engine. Understanding the detail combustion process of CNG engine is very important to improve the engine's performance. In this thesis, a method of multidimensional numerical analysis is used to study the combustion of CNG engine, which will be helpful to optimize the performance of the engine.To study the combustion process of the CNG engine in detail, a chemical kinetics model was coupled with multi-dimension model for the natural gas combustion. In this paper, the mathematical models, the numerical methods and the kinetic mechanism were systemically studied and improved to meet the requirement. The renormalization group (RNG) k-εturbulence model was adopted to simulate in-cylinder flows in this article. The chemical kinetic model which based on the mass action law and used the methane reduced kinetic mechanism, which is extracted from the detailed mechanism, then was adopted to simulate the chemical reaction. This model was run by coupling the KIVA-3V and CHEMKIN2.0 source code. The major problems were how to exchange the thermo data and how to call the relative subroutine to calculate the reaction rate.Experimental results indicated that the model is suitable to describe the in-cylinder combustion process of CNG engine. On the basis of Experimental certification, the main performance parameters and the structural parameters (such as injection timing, swirl ratio, combustion chamber's shape, the excess air ratio, etc.) influence on CNG engine combustion were studied. In this paper, the detailed flow field in-cylinder, the flame propagation and the main species formation were studied and described. Especially, the character of lean burn state and the problem of high exhaust temperature are analyzed respectively. Some important conclusions were worked out after analyzing these simulation results.
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