Combustion of liquid ethanol in an innovatory vortex-tube combustor with Self-evaporating and edge-like flame properties

The combustion performance of a novel self-evaporating vortex-tube combustor for liquid fuel proposed in this study was experimentally explored by taking liquid ethanol as fuel. The new combustor was developed via installing a double-layer self-evaporating tube made of stainless steel and copper into the center of a localized stratified vortex-tube combustor. The evaporation temperature and rate of liquid fuel can be controlled by adjusting the flow rate of cooling air flowing through the tube interlayer. The effects of global equivalence ratio and fuel flow rate on the stability limit, pressure fluctuation, flame configuration, and NO_x and CO emissions were investigated. The results corroborate that the novel vortex-tube combustor can achieve full evaporation of ethanol up to 30 mL/min, corresponding to a heat output of 10.57 kW. The localized stratified distribution of species formed in the combustor results in an edge-like tubular flame structure and correspondingly a wide stability limit, which enables stable ultra-lean combustion with the global equivalence ratio as low as 0.22. The pressure fluctuation amplitudes are always less than 800 Pa throughout the entire operating map. The combustor can achieve low NO_x and CO emissions below 18 ppm under appropriate conditions. The high-steady combustion procedure makes the ultra-lean combustion conducted, whilst the evaporating of liquid fuel can also decrease the temperature of the post-flame zone, then reducing the formation of thermal NO_x. Furthermore, the high-temperature post-flame zone locates in the fuel-rich region with high concentrations of CO and H₂, which can further inhibit the production of NO_x.