Experimental study on electro-spraying and combustion characteristics in meso-scale combustors

•A new meso-scale combustor with nozzle-ring-mesh was designed.•Four typical electro-spraying modes were visualized.•Droplet sizes were measured and electric field distributions were simulated.•Additional ring electrode reduces the droplet size and improves its distribution.•Smaller droplet size results in less evaporation time and more complete combustion. Electro-spraying and combustion of ethanol in meso-scale combustors were experimentally investigated by using two different structures of combustors. Type A combustor consisted of two section quartz glass tubes. The glass tube served as the combustor wall and had an inner diameter of 12mm. The inner tube was used as a stainless capillary tube with an inner diameter of 0.9mm served as the fuel nozzle and the positive DC electrode. Type B combustor consisted of three sections of quartz glass tubes. A fuel nozzle as a positive electrode, a second ring electrode, and a grounded steel mesh forming a combined electric field. Electro-spraying behaviors under the effect of electric field were visually investigated, and the stable and uniform spraying mode which could enhance the combustion was identified and analyzed. The results demonstrated that the combined electrode design with an additional ring electrode improved the electric field distribution at the spraying region, resulting in a decrease of droplet size and an increase of droplet uniformity. Comparing with Type A combustor, CO emissions decreased and combustion efficiency increased in Type B combustor. The combustion efficiency reached its maximum value when the equivalent ratio was equal to 1.0 for both of the two combustors. For Type B combustor, the combustion efficiency was up to a maximum value of 90.5%. The results also showed that droplet size and size distribution had a dramatic impact on the performance of meso-scale combustors.