| With the steady progress of micro-machining technology, persistent breakthroughs have been obtained on the development of micro electro-mechanical system(MEMS). Recently, most of the micro devices are driven by the traditional chemical batteries, however, the drawbacks of low energy density and short working time have become the bottleneck of MEMS development. In recent years, due to the advantages of high energy density and long power-supplies time as so as small volume, several micro power generators which based on combustion of hydrocarbon fuel are focused by the researchers. These apparatus inspire high hopes in the solution to the problem of MEMS power, and its potential applications have enlarged rapidly to the portable electronics, wireless communication equipments and unmanned aerial vehicles.As the most important component of the power MEMS, the stability of combustion process and power output of system are directly influenced by the micro combustor design. Not only the short residence time and high heat loss exists in the micro combustion process, but also the disadvantages of narrow and unflexible fuel choices are still prominent. Hence, the combustion characteristics of three types of gaseous fuels are contrasted in a micro-planar combustor. This paper develops a new type micro combustor so as to solve the problem of narrow flammable velocity range of hydrocarbon fuel. Besides, we explore the effect of blended fuels combustion in the micro-scale condition. The main conclusions of this study are as follows:(1) Benefiting from the highly combustible characteristic of hydrogen, the flame locations remain within very close proximity of the inlet and are relatively stable. While the flame locations apparently move towards the outlet with an increase of flow rate in the case of methane and propane, which leading to the matter of narrower flammable velocity range. It is observed that the flammable channel-heights of methane/air and propane/air cases are 2.5mm and 2mm, respectively. However, the hydrogen/air can be ignited in a 1mm height micro-combustor. Besides, under the same chemical energy inputs, the average wall temperatures of methane/air and propane/air cases are apparently higher than the hydrogen case, and the external wall temperature distribution of methane/propane case is most uniform.(2) As for the methane and propane, a micro-planar combustor with cross baffle is an solution to the problem of narrow flammable velocity range. This design not only keeps the flame stable and enlarges the flammable velocity range, but also results in the average wall temperature which is 90 K higher than the micro-planar combustor without cross baffle. The results of the experiments and numerical simulations indicate that the optimum effect is obtained when the length of cross baffle is 10 mm.(3) The results show that the hydrogen addition to the methane/propane can enhance the generative process of key radicals such as OH, which plays a role in improving the flame stability. Along with the increase of the hydrogen mass fraction, the flammable velocity range of blended fuel will have an impressive promotion. When the hydrogen addition ratio is 20%, the upper limit of flammable velocity can reach about 1.4m/s in the methane/propane case. Moreover, the addition of hydrogen can realize the hydrocarbon fuel combust in a smaller channel-height micro combustor. But the actual results of their work are related to the hydrogen addition ratio. In addition, the measures of the hydrogen addition are taken to raise the utilization extent of fuel chemical energy. |
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