Multi-Dimensional Numerical Simulation For Combustion Process Of SI CNG Engines

Numerical simulation and experiment are two supports of internal-combustion engine research and development. Especially in recent years, along with the enhancement of computer's speed and the maturity of simulation softwares, the numerical simulation has attracted more and more researchers by the development environment due to low cost and high efficiency. The numerical simulation can also provide more comprehensive data then experimental research, for example, it can simulate in-cylinder flow field and temperature tendency, and so on.The 3D numerical simulation model and calculation algorithm of in-cylinder combustion process is introduced in this paper. The turbulence models, combustion models and emission models are explained in detail. The 3D numerical package FIRE developed by AVL is used in this paper. Numerical investigation includes the in-cylinder turbulence flow, temperature distribution and emissions.The numerical simulation in this paper is focused on four aspects of a T6114ZL SI CNG engine, which is transformed by a DI diesel engine.â‘ Compression ratio. Two values of compression ratio are disigned, and comparison is made on the combustion process with these.Finally, the most suitable compression ratio is found.â‘¡Combustion chamber geometric shape. Several shapes of combustion chambers are designed with the same compression ratio. Comparison is made on the velocity field and the flame-propagation among different combustion chambers.â‘¢Spark advance angle. Change the spark advance angle and analysis the combustion process, find out the best value of the spark advance angle finally.â‘£Coefficient of excess air. Several coefficients of excess air are designed, and comparison is made in combustion process and fuel economy. The optimum parameters are obtained through the simulation results, then, the study and qualitative forecast of the emission production and heat load are made with these parameters.According to the result from numerical simulation, bowl-type combustion chamber has a good equilibrium in the diffusion and the distribution of the flame, thus it could achieve lean combustion in CNG engine more conveniently. Experiment results from the test bench showed a good consistency with numerical simulation in the engine design and operation variables which proposed by simulation. As a result, the simulation in the dissertation can provide a good argument for the development of CNG engine, and save much work in test bench.At last, the prospect is given on the 3D engine combustion simulation process.