Numerical Study And Optimization Analysis Of Skeletal Mechanism

Actual fires generally involve mixed burning process of a variety of fuels, the study on the combustion characteristic of mixture can provide fundamental information for the understanding of fire phenomenon. Numerical simulation is one of the most important means to study the combustion characteristic, to represent combustion process accurately, the detailed chemical kinetic mechanism used in the simulation should be as detailed as possible. However, the coupled flow and combustion brings difficulty to numerical simulation with great numerical stiffness problem, which is emerged mainly by the great differences involved in detailed combustion chemical kinetic. Therefore, the simplification of the detailed combustion kinetic with the assurance of precision is significant for fire simulation research.In this paper, the combustion characteristic was studied by kinetic modeling of mixture fuels with a coupled detailed reaction mechanism, and emphasis on the influence of mixture ratio on the ignition delay time and the laminar burning velocity in premixed flame. The combustion characteristics of the ethylene/methyl ether blended fuel were investigated numerically in this paper. The result shows that the addition of methyl ether can enhance the ignition delay time at higher temperature, especially when the mixture blends is less than20%. Both the laminar burning velocity and the maximum mole fraction of O+OH decreased with the methyl ether increase, combined with the analysis of sensitivity and component concentration, a linear equation describing the relationship between the laminar burning velocity and maximum O+OH mole fraction was achieved. The increased levels of methyl ether can reduce the emission of toxic gases CO.In this paper, an analysis based on principal component analysis of matrix S and genetic algorithms was also established to simplify and optimize the detailed chemical reaction mechanisms globally. First, by identifying the main oxidation path with element flux analysis, a global analysis of the major component involved in the oxidation reaction was carried out to simplify the chemical mechanism by reducing the number of component and element reactions. Then, the genetic algorithm was applied in global optimization of the reaction parameters of the simplified mechanism to improve calculation accuracy. Finally, the simplified mechanism with high accuracy and high efficiency was achieved. Methane combustion reaction mechanism is the simplest of hydrocarbon fuels chemical kinetic mechanism. Simplification and optimization of the methane chemical reaction mechanism by the above numerical study platform was performed. Compared with the detailed mechanism, optimized and simplified mechanism greatly reduce the computing time, and also have high accuracy in predicting the laminar burning velocity, flame temperature, reactants and products mole fraction. This proved that the simplified and optimized method has high reliability and validity.Two main highlights are presented in this paper: First, the application of the numerical simulation method to study the combustion characteristic of ethylene/dimethyl ether mixed fuels provides basic information for unsaturated hydrocarbon and complex non-hydrocarbon gases mixture combustion. Second, an analysis based on principal component analysis of matrix S and genetic algorithms to simplify and optimize the detailed chemical reaction mechanisms globally is established, it can improve the accuracy and efficiency of the chemical kinetic mechanism.