Effects of flame impingement on the stability and NO/CO emissions of laminar premixed methane-ammonia impinging flame

This study investigates the stable combustion range and CO/NO emissions of laminar premixed CH4-NH3 4-NH 3 impinging flames experimentally. Effects of flame impingement on the flame stability and CO/NO formations are analyzed quantitatively. The result shows that the flame impingement improves the flame stability considerably through decelerating the unburned gases velocity in the stagnation region, with smaller nozzle-to-wall distance (H) H ) exerting stronger improvement on the flame stability. The NO emission is increased initially but dropped finally with the increased H . This trend is ascribed to the suppressed NO productions at both small and large H due to the intensive cooling effects of cold wall and ambient air entrainment respectively in consideration of the relatively inferior reactivity of NH3. 3 . Additionally, due to the insufficient oxidizer in the fuel-rich flame, the more NH3 3 molecule can also facilitate the NO destruction via the DeNOx pathways at small or large H . In contrast, the CO emissions show similar variation trends with H like the NO emission for the fuel-lean and stoichiometric flames, while the CO emission has a "N" type variation trend with H for the fuel-rich flames. Since the CH4 4 reactivity can be improved by the NH3 3 addition at low temperatures, a low-temperature environment at small H due to the strong cooling effect, as well as more available NH3 3 in the flame, can effectively highlight the improvement of NH3 3 on the CH4 4 reactivity in the fuel-rich flame. This makes for the CO production at small H combined with the insufficient oxidizer and eventually results in the higher CO emission of the fuel-rich flame at small H . Additionally, the decreased CO emission at large H results from the improved CO oxidation that is caused by the increased residence time and more oxidizer from ambient air.