Blowout limit of premixed flame in a micro preheated combustor with a flame holder at different blockage ratios

Abstract

A micro preheated combustor with a flame holder was developed to take full advantage of both heat and flow recirculation. In the present study, the effect of blockage ratio (ξ) on the blowout limit of methane/air premixed flame is investigated. The blockage ratio increases by increasing the width of the flame holder in a combustion chamber with a constant height, while the inflow channel width correspondingly decreases. It is interesting to find that the blowout limit first increases and then decreases with increased ξ. Then, the underlying mechanisms are analyzed in terms of the flow field, stretch effect, heat transfer effect, and preferential transport. The analysis indicates that the direct effect of flow field on the present non-monotonic blowout limit is marginal. A larger stretch effect and heat-loss to the flame holder can induce the decrease in blowout limit from ξ = 0.6 to ξ = 0.7. The change rules of the heat recirculation and preferential transport effects are consistent with that of the blowout limit. The heat recirculation effect on the fresh mixture and preferential transport effect on the flame root are the best at ξ = 0.6, which contributes to the largest blowout limit at ξ = 0.6. Thus, a larger width of flame holder does not always guarantee a bigger blow-off limit. The present work not only provides guideline for reasonably choosing the size of the flame holder in the similar micro combustors but also helps us to gain insights into the combustion characteristics under the aforementioned competitive effects.