A novel flame-anchorage micro-combustor: Effects of flame holder shape and height on premixed CH4/air flame blow-off limit

Maintaining stable combustion is one of the major challenges for microscale combustors. In this study, a novel premixed CH4/air flame micro-combustor combining a flame holder, backward-facing step and preheating channel is developed to enhance the flame anchorage and extend the blow-off limits. The effects of flame holder shape (triangle and rectangle) and height (H = 0.0, 0.5, 1.0, 1.5 and 2.0 mm) on the combustion stability are studied numerically by FLUENT 16.0. The results show that this micro-combustor not only can considerably anchor the flame root owing to flow recirculation but also can further improve CH4 flammability owing to heat recirculation. Compared with the rectangle flame holder, the triangle flame holder achieves the higher blow-off limits owning to the larger recirculation zone and better preheating effect. As the flame holder height increases, (i) the recirculation zone sizes near the flame root decrease, weakening the flame-root anchorage ability, and (ii) the heat recirculation effect becomes stronger, improving CH4 flammability. Under the combined effects of flow recirculation and heat recirculation, the highest flame blow-off limits are attained when H = 0.5 mm. The flame holder with triangle shape and H = 0.5 mm attains the highest flame blow-off limits (10.3 m/s and 6.2 m/s at Phi= 0.7 and 0.5).