Flame-anchoring mechanisms of a micro cavity-combustor for premixed H2/air flame

•Flow recirculation zone anchors flame root and expands at smaller equivalence ratios.•Heat recirculation via the solid wall leads to earlier initiation of chain reactions.•A local equivalence ratio for premixed H2/air combustion was defined.•The preferential transport effect increases local equivalence ratio near flame root.

Our recent work demonstrated that flame blow-off limit of microscale and mesoscale channels can be greatly extended by using wall cavity. In the present paper, we numerically investigate the flame-anchoring mechanisms of H2/air flame in terms of interplays between flow field, heat recirculation, chemical reaction and preferential transport of species. The results show that obvious recirculation zone and low velocity zone are formed in the cavity, and the flame-anchoring location is near the vertical cavity wall. Moreover, the incoming fresh mixture is gradually heated by the upstream inner wall (i.e., heat recirculation effect), which leads to earlier initiation of chain reactions and more intense reaction near the flame-anchoring location. Furthermore, the preferential transport effect, which is caused by the differences in mass diffusivities of various species and two-dimensionality of the flow field, can change the local equivalence ratio (ϕlocal). It is shown that ϕlocal increases in the recirculation zone and low velocity zone in the cavity. More importantly, ϕlocal is much larger in the vicinity of the flame root, which is beneficial for flame-anchoring. In summary, the cavity can simultaneously provide a recirculation zone and low velocity zone, a better heat recirculation effect, and a high ϕlocal region, which are the main flame-anchoring mechanisms of the micro cavity-combustor for premixed H2/air flames.

Graphical abstractThe major flame-anchoring mechanisms of the cavity in a micro combustor include the recirculation zone, low velocity zone and higher local equivalence ratio formed in the cavity and the heat recirculation effect via the upstream wall.Figure optionsDownload full-size imageDownload as PowerPoint slide