Numerical comparison of H2/air catalytic combustion characteristic of micro–combustors with a conventional, slotted or controllable slotted bluff body

Abstract

The flame instability and low combustion efficiency are still two vital problems to be solved in micro–combustion power field. In this work, the detailed chemical reaction mechanism of H2/O2 is used to numerical study the combustion characteristics of micro–combustors under three kinds of bluff body structures. The results show that a recirculation zone is formed in the conventional bluff body (CBB) micro–combustor, while two symmetric recirculation zones are formed in the slotted bluff body (SBB) micro–combustor and controllable slotted bluff body (CSBB) micro–combustor. Notably, the recirculation zones in the CSBB micro–combustor is significantly prolonged with the increase of controllable flow ratios. Meanwhile, the corresponding equivalence ratio reaching a maximum combustion efficiency is 0.8 in the CSBB micro–combustor, while the CBB and SBB micro–combustors reach the highest combustion efficiency at φ = 1.0. This means that the CSBB micro–combustor exhibits superior combustion performance in the fuel lean condition (φ = 0.8). Additionally, the adjustment of the controllable flow ratios can significantly affect the combustion efficiency of the CSBB micro–combustor. Moreover, the blow–off limits of CBB, SBB and CSBB micro–combustors achieve the maximum at φ = 1.0, which are about 540, 456 and 600 cm3/s, respectively. Thus, the proposed CSBB micro–combustor is of notable advantages compared with the other two micro–combustors in terms of combustion efficiency, temperature distribution, blow–off limit, and so on. Another interesting finding is that the CSBB micro–combustor with a gap width of 0.6 mm has better combustion performance. In conclusion, the controllable slotted bluff body is a good way to stabilize the flame in micro–combustors. This design offers us another way to design such kind of micro–combustors.