The oxygen-deficient combustion and its effect on the NOx emission in a localized stratified vortex-tube combustor

Abstract

The oxygen-deficient combustion characteristics of methane in a localized stratified vortex-tube combustor (LSVC) are studied by diluting combustion air with nitrogen. The influences of oxygen mole fraction (0.13–0.21) on flame configuration, combustion stability, combustion efficiency, and NOx emission characteristics are experimental investigated at the inlet temperature of 300 K. Combined with the numerical simulation method, the NOx generation, and emission mechanisms are analyzed in this combustor. Results show that the LSVC can achieve a wide stability limit, in which the global equivalence ratio can be as low as 0.22 at the lowest oxygen mole fraction (β) of 0.13. To ensure high combustion efficiency, the β should be kept above 0.16 since the oxygen-deficient condition reduces the reaction rate and flame temperature. The combustor can achieve ultra-low NOx emission of below 10 ppm (@ 15 vol% O2) due to low oxygen concentration and flame temperature. Furthermore, part of NOx entrained into the fuel-rich reduction zone by the swirl flow field is reduced by the reductive species (i.e., CO and H2) to further lowering NOx emissions. The results of this paper can guide the development of the LSVC in the high-efficiency and low-emission combustion fields.