Flamelet Model Of G Equation For Large Eddy Simulation And Its Application In Cylinder Process Of Natural Gas Engine

With the development of new energy and the implementation of increasingly stringent emission regulations,Compressed Natural Gas(CNG)engine widely used in the city bus because its advantage in reserves,combustion and emissions.In the process of design and development of natural gas engine,the mechanism of the process of cylinder is indispensable,and with the development of computer,the numerical simulation technology of fluid dynamics(CFD)is essential for the analysis and study of the flow and combustion process in cylinder.In this paper,the flow and combustion process of a gas turbine engine is studied by computational fluid dynamics and combustion theory.By using the large eddy simulation and flame surface concept,the turbulent premixed combustion process in cylinder is simulated,and the model is evaluated by experimental data.The purpose is to establish a higher accuracy and more suitable for the prediction model of the cylinder.Firstly,based on the research results of the combustion model of premixed lean gas engine and the flamelet model of G equation,the control equations and subgrid model of the LES are presented,together with the control equations and the sub grid model of the G equation of the fire island region and the thin reaction zone,the discrete particle ignition kernel model and the methane / air reaction mechanism in GRI-MECH2.11.the model of the large eddy simulation G equation model is built.Based on the mathematical model,the KIVA program is used to simulate the flow and combustion process of a single point injection natural gas engine.The results show that the predicted results of burning development periods and rapid burning periods in defferent combustion chambers are in good agreement with the measured values as far as variation tendency is concerned.But the numerical values differ from the experimental results obviously.Under the condition of high swirl ratio,along with the change of the swirl ratio,the variation tendency of the combustion variation is almost consistent with the measured values,and the numerical values also differ from the experimental results obviously.In order to the get more accurate forecast results,the model of the dynamic combustion velocitycoefficient is developed.The application of the dynamic coefficient show that the dynamic coefficients fluctuate obviously in the process of combustion,and the average values are less than the static one.The error in the calculation of the combustion period witch is less than 7.5% is obviously less than that of the static coefficient,and the accuracy of the cycle fluctuation prediction is improved,witch is within 5% except for the ratio of 1.5.Finally,the dynamic coefficient large eddy simulation G equation model is applied to the optimization of premixed lean gas engine.The simulation is carried out in the Miller systems which combine improving compression ratio with intake vales closing earlier.According to the calculation results,the optimal scheme is selected for experimental study.The results show that the scheme proposed by the simulation is very good at realizing optimization for the original machine.Therefore,the dynamic coefficient large eddy simulation G equation model can improve the design and development efficiency of CNG engine,reduce the development time of new product and save the cost of research and development.