Dynamics of a holder-stabilized laminar methane-air premixed flame in a preheated mesoscale combustor at ultra-lean condition

The flame dynamics at ultra-lean condition under the synergistic effect of heat recirculation and flow recirculation is experimentally studied in this work. The previously reported anomalous blow-off of lean H-2/CH4/air premixed flame with Lewis number Le < 1.0 is obtained for the lean CH4/air premixed flame at Le approximate to 1.0, and the underlying mechanisms are analyzed in terms of heat recirculation, flow recirculation, preferential diffusion, and stretch effects. An anomalous standoff distance between the stable flame root and flame holder is also observed for the lean CH4/air premixed flame. The blow-off dynamics at large and small values of Reynolds numbers are quite different. The flame with local extinction and reignition appears in the blow-off process at large Reynold numbers (>= 100), whereas it is absent at small Reynold numbers ( < 100). The results attained in this study can help to gain insights into flame dynamics in many practical combustors.