Effect of bluff body shape on the blow-off limit of hydrogen/air flame in a planar micro-combustor

• Effect of bluff body shape on blow-off limit of a micro-combustor was investigated.
• Blowout occurs due to flame stretching for triangular and semicircular bluff bodies.
• Triangular bluff body has a lower blow-off limit due to stronger flame stretching.
• Heat losses have a negligible effect on the difference of blow-off limit.

We recently developed a micro-combustor with a triangular bluff body, which has a demonstrated 5-time extension in the blow-off limit compared to straight channel. In the present work, the effect of bluff body shape on the blow-off limit was investigated with a detailed H2/air reaction mechanism. The results show that the blow-off limits for the triangular and semicircular bluff bodies are 36 and 43 m/s respectively at the same equivalence ratio of 0.5. Analyses reveal that flame blowout occurs due to the stretching effect in the shear layers for both the triangular and semicircular bluff bodies. Moreover, it is found that the triangular bluff body has a smaller blow-off limit because of the stronger flame stretching as compared with the semicircular case. Calculations indicate that the two cases have negligible differences in heat losses because the reaction zones and high temperature regions are located in the combustor centers. Therefore, the heat losses have a negligible effect on the difference in the blow-off limit of the two micro-combustors.