Influence of CH4/air injection location on non-premixed flame blow-off limits in a novel micro-combustor

Abstract

Stable flame is still one of the challenging issues in the micro-combustors. Besides, the premixed flame may flash back under the large equivalence ratio, and the non-premixed combustion is an effective way to avoid the flame flash-back issue. In this work, a novel non-premixed CH4/air micro-combustor with the flame holder, the backward-facing steps and the separated preheating channels is developed to avoid the flame flash-back issue and extend the flame blow-off limits. This paper investigates the influence of two different CH4/air injection locations on the flame blow-off limits numerically and profoundly reveals the mechanisms in this micro-combustor. Results show that this novel configuration can considerably anchor the flame without the flame flash-back issue and significantly extend flammability owning to the flow & heat recirculations. Compared with the “Air(out)/CH4(in)” injection location, the “Air(in)/CH4(out)” injection location exhibits a comparatively larger size of recirculation, causing a more vital anchorage ability. In addition, after the preheating in the preheating channels, the CH4/air mixture of the “Air(in)/CH4(out)” injection location presents a higher temperature level than that of the “Air(out)/CH4(in)” injection location. Consequently, compared to the “Air(out)/CH4(in)” injection location, the larger blow-off limits are attained for the “Air(in)/CH4(out)” injection location. These results provide new insights into the stable non-premixed flame and give valuable guidance for designing the similar non-premixed micro-combustor.