Anomalous blow-off limit of methane-air premixed flame in a micro preheated combustor with a flame holder

Abstract

The present work first reports the combustion characteristics of methane/air premixed fuel mixture (Lewis number Le ≈ 1.0) at different Reynolds numbers (Re) in a micro preheated combustor with a flame holder which can be used as heat source for the micro power generators. Unexpectedly, the previously reported anomalous blow-off of lean H2/CH4/air (Le < 1.0) premixed flame in the mesoscale combustor appears in the present micro combustor, which is observed for the first time. The flame dynamics in the micro combustor also presents other new features comparing with that in the similar mesoscale combustor. Three neighboring cases (Re = 40, 80, and 120) are adopted to reveal the underlying mechanisms of the anomalous blow-off in terms of the flow field, stretch effect, conjugate heat exchange, and preferential transport effect. A better heat recirculation effect results in the increase of blow-off limit from Re = 120 to 80. A worse flow recirculation effect, a larger heat loss ratio to the environment, and a worse preferential transport effect lead to the decrease of blow-off limit from Re = 80 to 40. In the end, the critical standoff distance between the flame root and flame holder presents a second-order function relation with the change of Re.