Numerical Simulation On Catalytic Combustion Characteristics Of CH₄ In Micro Combustor With Concave Cavities

As a kind of cross disciplinary technology, Micro electro mechanical system combines many kinds of science and technology, and has broad applicated prospects in medical, biological, military, aerospace and other fields.Using hydrocarbon fuels to provide energy, micro electro mechanical system has the advantages of large energy density,small volume, light quality ect. However, micro combustor as the most complex part, has the disadvantage of less combustion space, large surface to volume ratio, big heat loss, instable combustion and inefficient. Based on the analysis of advantages and disadvantages of current stable combustion technology in micro channel, this paper introduces the domestic and foreign research status of the combustion with recirculation zone in the combustor, and proposes the application of concave cavities to construct recirculation zone and using the method of intake through concave cavities wall to improve the combustion characteristics of methane.Based on the detailed reaction mechanism, combustion characteristics of methane with air in micro combustor with convex cavity are simulated and analyzed mainly from the inlet gas and structural parameters in micro combustor.In this paper, we study the intake effect on combustion characteristics of methane by changing total intake, mainstream inlet air intake, air intake of the rear wall inlets of concave cavities and distribution of air intake of inlets of the rear wall and the mainstream. Conclusion: Recirculation zone inside the concave cavity can promote catalytic combustion process of methane.The combustion product inside the concave cavity is rapidly mixed with the mainstream air in the main channel, which improve the temperature of the fuel before combustion and strengthen the combustion in the main channel. Although increasing the mainstream air intake will reduce the average temperature of the combustion channel, it is beneficial to improve the stability of axial temperature distribution in mainstream channel.Increasing air intake of the rear wall inlets of the concave cavities can strengthen the combustion inside the concave cavities,which is conducive to the efficient combustion of the fuel in the main channel and promote the stability of the axial temperature distribution in the combustion channel.Changing the distribution of air intake of inlets of the rear wall of the concave cavities and mainstream,when the total air intake is constant. Increasing air intake of the rear wall inlets of the concave cavities, the corresponding mainstream air intake decreases.The low velocity zone inside the concave cavity is larger, the velocity isoline of the combustion channel is closer, which is conducive to the efficient and stable combustion of the combustion channel.The effects of structural parameters of ratio the depth to width and the shape of the mainstream inlet on the characteristics of methane combustion are studied. The greater ratio of depth to width, recirculation zone inside the concave cavity formed more favorable, and more intense the combustion process. In the mainstream channel, the lager ratio of depth to width, the closer isoline. The axial pressure drops more rapidly,the combustion process more intense. Intake from mainstream inlet of divergent shape disturbances the recirculation zone inside concave cavity, which leads to the combustion intensity in the concave cavity weakened and the combustion intensity in the main channel strengthened. The overall mixing preheating effect in the main channel is better and the temperature is slightly higher than that in the combustor with mainstream inlet of gradual contraction. In the two kinds of combustor, the distribution curve of components of the rear of the concave cavity is coincident. When intake is large but less than1.4134mg/s, the conversion rate of methane in two kinds of the combustor is more than 90 percent. When the intake is more than 1.75729mg/s, conversion rate of methane in the combustor with mainstream inlet of divergent shape is significantly higher than that in the combustor with mainstream inlet of gradual contraction. With increasing intake, flame coverage area inside concave cavity will continue to reduce or even disappear, temperature in the combustor channel is reduced in two kinds of combustor.At the same intake, temperature in the combustor with mainstream inlet of divergent shape is higher, axial temperature gradient is smaller and temperature distribution is more uniform than that in the combustor with mainstream inlet of gradual contraction.In this paper, a relatively comprehensive investigation on the catalytic combustion process of CH₄ are conducted numerically. The effects of inlet gas and structural parameters are obtained. This article's research is helpful to improve and optimize the structure and combustion characteristics of micro combustor, and promote the further research of micro scale combustion technology, which has a good reference value for the optimization design of micro combustion devices.