Experimental And Numerical Studies Of Premixed Hydrogen/Oxygen Combustion In Micro-combustors With Different Structures

With the rapid development of miniaturization, high efficiency and integration of electronic mechanical system, there is an urgent need for a small power plant with light weight and long life. The micro power system based on the combustion of hydrocarbon fuels has obvious advantages in terms of power density, fuel supply and energy output. Micro-combustor is the core component of the system of energy conversion, due to the small scale of combustor, making the face to volume ratio of combustor increase, and then leads to a sharp increase in the rate of heat dissipation, which can make it harder to obtain the stable flame in the combustor. In addition, flame propagation of free radicals is easier to lose activity due to the collision with the wall. In view of this, the optimization and improvement of micro-combustor has drawn wide attention from scholars.Two combustors with different structures have been designed in this paper, that is, the combustion chamber with sudden expansion and the combustor with symmetrical convex. Using experimental method and numerical simulation method, the combustion characteristics of premixed hydrogen / oxygen combustion in micro-combustor with sudden expansion have been analyzed. In addition, with the aid of numerical calculation software Ansys Fluent, the combustion characteristics of the combustor with symmetrical convex have been analyzed. In addition, the combustion characteristics of two combustors with different structures are compared and analyzed in order to obtain better combustion efficiency. The main research contents and main conclusions of this paper are as follows:(1) For the characteristics of hydrogen and oxygen premixed combustion in the micro-combustor, a comparison between the combustor with abrupt changes in the cross-sectional area and no abrupt changes in the cross-sectional area with the experimental methods, by changing the equivalent ratio and inlet velocity of mixed gas, the analysis of the combustor has been obtained. The results show that the average temperature of the external wall of the combustor with cross section reach the highest when the equivalence ratio is 1, and the average temperature of the combustion chamber decreases with the increasing of the equivalence ratio. The increase of the inlet velocity of the mixture will aggravate the combustion process, which will increase the average temperature of the external wall surface.(2) Based on the experimental verification, coupled with the hydrogen / oxygen chemical kinetic mechanism, the three-dimensional numerical calculation model of the micro-combustor, and the experimental verification was achieved. According to temperature and species distribution in the combustor, the analysis of combustor with sudden expansion of cross section were obtained. The results show, with the increasing size of the sudden expansion, the high temperature area in the micro-combustor is enlarged. Increasing the inlet flow rate of the mixed gas will increase the temperature of the fluid in the micro-combustor. The use of the structure with sudden expansion of cross section is beneficial to slow down the flow rate and the trend of the decrease of the hydrogen conversion rate.(3) The combustor with symmetrical convex has been designed, and the combustion characteristics have been analyzed by numerical simulation. The results show that the increase of the height of the symmetric convex has little effect on the temperature of the mixed gas in the combustion chamber. In order to obtain the high efficiency of combustion chamber, the inlet velocity needs to be controlled within the proper range. With the increase of the inlet flow rate, the temperature of the fluid increases, and the outlet temperature also increases.(4) Through means of numerical simulation, the combustion characteristics of two combustors with different structures were compared and analyzed in order to obtain a better combustor structure. The results show that the combustion performance of the combustor with sudden expansion is superior to that with symmetric convex sets.