Effects Of Catalytic Fin On The Premixed Combustion Characteristics In The Micro Combustor

The micro power system based on hydrocarbon fuel has a broad potential application, since it has many distinct advantages in low cost, high energy density, et al. As the core component of micro power system, micro combustor has a great influence on the performance of the whole system. With the size of micro combustor decreasing, the ratio of surface-to-volume increases, and the heat loss increases, which ultimately lead to low stability and efficiency of combustion. Catalytic combustion is an effective way to solve the above problems, for its flammability, low pollution, high efficiency, high combustible limit and stable combustion.Experiments have been conducted in catalytic micro-combustor for the effects of catalyst on combustion characteristic. Visualized micro combustor has been processed for further analysis of the interaction between the surface reaction and gas phase reaction. The flame characteristics in the micro chamber are also observed. Combustion characteristics of catalytic micro-combustor are numerically simulated based on the experimental verification. The interaction between gas-phase and catalytic reaction was analyzed by changing inlet parameters and locations of catalyst. The blow-off limits of micro combustor with and without catalyst were also analyzed. Some conclusions with scientific significance and practical values have been obtained:(1) Through the observation of premixed methane/oxygen combustion flame characteristics in micro combustor, the effects of catalytic fin on flame stability ware analyzed. Results show that, in the methane-rich combustion, stable combustion can be obtained in the micro-combustor with a separator in the middle of entrance. When the flow rate of methane is 300 SCCM, the flame displays steady-volatility-steady propagation with the increase of oxygen flow rate. Reaction area can be fixed with catalysts added, and the flammable limit can be broadened. Gas-phase reaction is weakened with the intermediate products consumed in catalytic reaction, and catalytic reaction is subdued with the high temperature generated by gas-phase reaction on the contrary. Catalytic reaction is dominant near the surface of catalyst, while gas-phase reaction is dominant away from the surface.(2)Through the experimental study, effects of catalytic fin on combustion characteristics in micro combustor were analyzed. Results show that, the mean temperature of combustor external wall rises at the beginning then drops later with the increase of equivalence ratio. The highest mean temperature of catalytic micro-combustor is achieved when the equivalence ratio of premixed hydrogen/ air mixture is 1.1. While in the combustion of premixed hydrogen/ oxygen mixture, the highest mean temperature of catalytic micro-combustor is achieved at the equivalence ratio 1.0. With the increase of inlet velocity, the mean temperature of the combustor external wall rises gradually, and the growth is slowing down. Catalytic fin’s position arrangement has great influences on the temperature distribution of combustor external wall, the higher temperature of combustor external wall is, the farther catalytic fin away from the entrance. The mean temperature of combustor external wall can be improved by changing the size of catalyst and the position arrangement of catalyst.(3) Through the numerical simulation method, the blow-off limits of micro combustor with and without catalyst were analyzed, so were the inlet parameters and locations of catalyst. Results show that, catalytic surface reaction is dominant nearby catalyst surface, while gas-phase reaction is dominant far from the catalyst surface. The blow-off limit can be markedly widened by adding catalysts. The blow-off limits of combustor with and without catalyst are 46m/s and 22m/s, respectively. The highest activity of catalytic reaction is achieved at equivalence ratio 1.0, and the gas-phase reaction is subdued mostly. The outer wall temperature increases with the mixture equivalence ratio increases firstly, and then decreases, the highest outer wall temperature is obtained with equivalence ratio 1.0. With the catalytic fin moving towards the outlet, the mean temperature of external wall tends to be more uniform, and the conversion rate of hydrogen is higher, but the effect of catalytic fin on gas-phase reaction is weakened.In this paper, the catalytic combustion characteristics of micro combustor were detailed studied, which provide a theoretical basis for further research, and provide a reference basis for the design of catalytic combustion chamber.