Flammability limit of methane-air nonpremixed mixture in a micro preheated combustor with a flame holder

In this study, a novel micro nonpremixed combustor, which could act as a microthruster, was developed. The flammability limits of a methane-air nonpremixed mixture in this combustor were investigated by numerical simulation. The results indicated that the flammability limit of the nonpremixed mixture could reach a significantly low value, and the flame remained stable until it blew off. It was found that the flammability limit first increased slightly (normal blow-off) and then decreased sharply (anomalous blow-off) with the decrease in Re. This is the first report of the anomalous blow-off phenomenon for a nonpremixed flame. Additionally, the underlying mechanisms were systematically revealed in terms of the mixed performance of methane and air, combustion reaction intensity, flow field, stretch effect, heat exchange effect, and preferential transport effect. This study provides insights into the combustion characteristics of the microscale nonpremixed mixture. (C) 2020 Elsevier Ltd. All rights reserved.