Enhancement of combustion performance in a microchannel: Synergistic effects of bluff-body and cavity

Abstract

The stable flame is vulnerable in the micro-scale combustors due to the significant heat loss and the limited residence. In this study, the bluff-body and cavity are integrated in a microchannel to enhance the combustion performance of premixed H2/air flames. The enhancement and combustion characteristics are investigated numerically, using detailed chemical kinematic mechanisms and conjugate heat transfer. It is found that the reaction zones formed behind the bluff-body in center is merged with the flame anchored by the cavity along the side wall, which converts the single flame tip in the micro cavity-combustor to the “M-type” flame. Moreover, the side dual-cavity configuration can significantly improve the anchorage ability of the central bluff-body through extending the recirculation zone and mitigating the flame stretch rate. Due to the synergistic effects of the bluff-body and cavity, the critical velocity increases from 40 m/s in both the single cavity and the single bluff-body combustors to 56 m/s in the proposed combustor. Improved wall temperature uniformity is also observed as the result of the merged reaction zones. Besides, the effects of the equivalence and blockage ratios are investigated. Results suggest that a moderate equivalence ratio is favored to achieve a stable and high efficiency combustion. As the blockage ratio of the bluff-body increases, the flame stability improved due to the enlarged recirculation zones, whereas the combustion efficiency degrades because of the strengthened flame stretch rate and reduced residence time. Finally, an optimal blockage ratio of 0.4 is proposed for the dual-stabilizer micro-combustor.