Experimental Investigation On Electrospray Characteristics And Performance Of Small-scale Combustors

With the rapid development of micro electro mechanical systems,small devices have increasingly involved in many areas. But a growing amount of research about power plant of small devices can’t still solve some combustor’s problems,such as incomplete combustion,unstable flame,large heat loss and so on,which hinder the development of small combustors.In this paper,in order to resolve the difficulties of short residence time of fuel in small combustor causing low heat release,electrospray technology was applied to small scale combustion of liquid fuel. Two kinds of small combustor including capillary-grid single electrode and capillary-ring-grid compound electrodes were designed and fabricated. Experimental research on electrospray characteristics and performance of the small combustor was carried out using liquid ethanol as fuel.The electrospray modes of pulsed-jet,cone-jet,skewed cone-jet,and multi- jet were observed by optical visualization method. The operating ranges of differe nt modes for ethanol were divided into several regions based on present experimental results. The formation mechanism and influence factors of electrospray were analyzed. Specific charges were measured based on mesh target method, and its uncertainty were estimated. The angle of Taylor cones in the mode of cone-jet were measured. The experimental results showed that liquid ethanol was charged inside the capillary which was connected to high voltage DC power supply and between capillary-ring induced electric field. Capillary-grid or ring- grid electric field had little effect charging process and mainly supplied driving force for the motion of liquid droplets in the spraying region. The steel grid was a key component for the movement,capture and burning of liquid ethanol droplets.The flame in the single electrode combustor was blue mixed yellow and can’t maintain invariant shape. The flame in the compound electrodes combustor existed on the gird with a blue luminosity and looked like slice on the grid which had function of flame holder. The stable combustion and flame lasted for more than 20 minutes till liquid ethanol was consumed. The temperatures of flame in the single electrode combustor increased along with the increase of the capillary potentials. There was a maximum amplification at the moment that the electrospray modes of pulsed-jet transformed into cone-jet. The combustion efficiency could reach 90.13%. Kept ring electrode potential as constant,the temperatures of flame in the combustor with compound electrodes,increased with the capillary potential at first then declined. The combustion efficiency could reach 96.72%. These results showed that the electrospray modes impacted the performance of the small combustor.