An experimental study on flame stability and pollutant emission in a cyclone jet hybrid combustor

The combustion characteristics of a cyclone jet hybrid combustor using a combination of swirling premixed and jet diffusion flames were experimentally investigated to achieve high flame stability and low pollutant emissions. Two kinds of combustion modes were examined: the diffusion combustion (DC) mode, which consists of swirling air flow and jet diffusion flame, and the hybrid combustion (HC) mode, which consists of swirling premixed and jet diffusion flames. In the HC mode, the effects of fuel nozzle geometry on fuel–air mixing were investigated in terms of flame stability and pollutant emissions. The results showed that the HC mode can significantly reduce soot, CO, and NOx emissions in a stable flame region compared to the DC mode. However, CO emission in the HC mode increases drastically when overall equivalence ratios drop below 0.75. By modifying the fuel nozzle for the jet diffusion flame, it was found that increases in fuel–air mixing using the improved nozzle provide a stable flame region approximately twice as wide as that of the fuel nozzle using a single hole. In addition, a multi-hole fuel nozzle shows a NOx reduction of 55% compared to that of the DC mode.