Anomalous blow-off behavior of a holder-stabilized premixed flame in a preheated mesoscale combustor

Abstract

The present study investigates the blow-off limits of a laminar methane–air premixed flame under the synergistic effect of heat and flow recirculation by means of experimentation and three-dimensional numerical simulation. An anomalous blow-off phenomenon (the blow-off limit decreases with the decrease in Reynolds number (Re)) is experimentally observed and reproduced via simulation. First, the flame base structures for various Re values are studied. Subsequently, the underlying mechanisms are revealed in terms of flow field, stretch effect, preferential transport effect, and conjugate heat transfer. The main causes of the present anomalous blow-off phenomenon are the flow recirculation effect, preferential transport effect, and conjugate heat transfer, rather than the stretch effect. Specifically, a weaker flow recirculation effect, a weaker preferential transport effect, a larger heat loss ratio from the combustor to the ambient environment, and a lower preheated temperature of the fresh mixture altogether lead to a smaller blow-off limit at a smaller Re. In addition, the sharp reductions in both the local equivalence ratio and preheated temperature of the fresh fuel-oxidizer mixture explain why the blow-off limit sharply decreases from Re = 80 to 40. This work offers insights into flame blow-off behaviors under the synergistic effect of heat and flow recirculation in many practical combustors.