Study On Combustion Characteristics Of Ethanol In Double-Electrode Microcombustor

With the development of MEMS, the investigations of micro combustors have developed gradually to be one of the hot subjects today. The micro power system based on micro-combustion technology has been one of the ideal alternatives of the chemical batteries due to its advantages such as high energy density and little pollution. However, as the volume of the combustor decreased, the ratio of area/volume increasing, which may result in shorter resistance time of the fuel and larger heat loss,then they do harm to the combustion stability of the combustors.Atomizing the liquid fuel is one of the most important ways to improve fuel efficiency. The traditional method is given priority to mechanical atomizing, and electro-spraying of the fuel is a feasible way to improve the performance of micro combustors as well. In this paper, we chose two structures of combustors, which were nozzle-grid structure with single electrode and nozzle-ring-grid structure with two electrodes respectively, designing the micro combustors. The catalytic combustor was also designed based on the second structure. Experimental investigations on spraying and combustion characteristics were taken in the combustors with ethanol as fuel. The influence factors from atomization and the distribution of electric field to combustion were also considered.Four spraying modes, which were called pulsed-jet mode, cone-jet mode, skewed cone-jet mode and multi-jet mode, were observed successively in two kinds of combustors. The particle size distribution at cone-jet mode was the most uniform at four modes, and the particle size was smallest at multi-jet mode. The droplet size was in the range of 8-28.8μm in single electrode combustor, but 2.3-17μm in double electrodes combustor. The charging way of ethanol changed with the installation of the ring electrode, which may improve the performance of the spraying. The spraying at cone-jet mode and multi-jet mode were more uniform and stable than other modes.In the process of combustion, the flame was blue in double electrode combustor and non-luminous flame in the catalytic combustor, which represented that the combustion was complete. The flame stabilization limits were larger in double electrodes combustor, and the flame temperature was highest at cone-jet mode. The decreasing of the droplet size enhanced the evaporation ratio of the droplet, which extended the residence time of the fuel and increased the stability of the combustion. Part of the large droplets may reach the flame due to the incomplete evaporation when the droplets moving to the mesh, which may reducing the flame temperature and increasing the heat loss. The combustion efficiency could be higher with a fine spraying performance, then the combustion efficiency of ethanol was higher at cone-jet mode. The installing of the catalytic grid promoted the decomposition and oxidation of ethanol at high temperature, and reduced the harmful exhaust emissions. The highest value of combustion can reach 90.5% in double electrodes micro-combustor,94.5% in double electrodes micro-combustor with catalytic. The stable combustion and flame lasted till all the fuel was consumed. The addition of the ring electrode changed the electric field, enhanced the performance of atomization and combustion. The catalytic combustion enhanced the combustion efficiency obviously. It was an ideal way to enhance the performance of micro combustors by optimizing the parameters of the electric field.