Numerical Study Of Catalytic Combustion Characters For Methane/Air In Micro-channel With Different Cavities

With the development of MEMS, it is widely used in daily life, military, spaceflight, biology and so on. As a significant energy provision system in micro-dynamic device, micro-combustor is becoming a main research subject in today’s society. Micro combustor, because of its small size, fuel is difficult to combust stably and efficiently. Catalytic combustion is a way of stabilizing flame and appropriate changes in the structure can stabilize combustion. Porous media and Swiss-roll combustor are specially adopted in micro-combustion. Concave cavity The concave cavity technology,which can increase the combustion efficiency and stability, is commonly used to increase the stability of supersonic combustion. But the effect of concave cavity on the slow flow combustion is not further studied and even the convex cavity. So it is necessary to have a research on the catalytic combustion in micro-channels with different cavities.In this thesis, the catalyst combustion of CH4/O2 based the detailed reaction mechanism in straight micro-channel and the micro-channel with concave or convex cavity. The effects of equivalence ratio, inlet velocity and wall temperature on methane catalytic combustion are investigated. Then for the micro-channel with convex cavity, mainly study the effect of width-length ratio, depth- diameter ratio,position and numbers on methane conversion, combustion temperature and extinctive limit. The results show that:①The micro-channel with convex wall cavity is conductive to methane catalytic micro-combustion. In the micro-channel with convex wall cavity, the inner wall pressure increases, because the fuel is disrupted when it flows through the cavity. Then the mixture of methane contact with catalyst is enhanced, which favors the combustion of methane. The recirculation zone which is the largest area formed in the micro-channel with convex wall cavity absorbs more high temperature gas and raises the combustion temperature. Heat transfer in the convex micro-channel is enhanced which makes the temperature distribution more uniform. The maximum value of the extinction limit is 16.5 m/s, which occurs in the micro-channel with convex cavity.②With the increasing of width-length ratio, depth-diameter ratio, numbers of convex cavity and setting in the downstream, the CH4 conversion increases. Increasing the cavity depth-diameter ratio works more on methane combustion than the width-length ratio. When the inlet velocity becomes faster, the cavity, which is set in the downstream, plays a more positive role in combustion.③With the increasing of width-length ratio, depth-diameter ratio, numbers of convex cavity and setting in the downstream, the extinction limit expands. With the width-length ratio increasing, the inner wall pressure increases, because the fuel is disrupted when it flows through the cavity. The temperature goes up and the extinction limit expands. With the depth-diameter ratio increasing, the recirculation zone becomes larger and the vortex comes out. Both of them help the combustion to be more stable and extend the extinction limit. This also helps to shorten the ignition distance. Placing the cavity to the downstream has the same effect. Increasing the number of convex cavity contributes to changing the wall temperature, expanding the recirculation zone, enhancing the inner wall heat transfer and delivering heat to the downstream, which make the temperature get raised and extend the extinction limit.④With the CH4/O2 equivalence ratio increasing, the CH4 conversion first increases and then decreases, the peak value comes out at the equivalence ratio of 1. The CH4 conversion presents a increasing-decreasing trend as the wall temperature increases, the peak value comes out at the temperature of 1200 K. The CH4 conversion goes down with the increasing of inlet velocity. The equivalence ratio whose methane conversion reaches max value tends to the lean oxygen zone and high wall temperature.In this paper, a relatively comprehensive investigation on the catalytic combustion of micro-channel with concave or convex cavity is conducted numerically. The rules of channel structure on catalytic combustion are obtained. It has important academic significance and researching value for the development of micro power devices.