Abstract
Improving the flame stability and thermal behavior of the micro-combustor (MC) are major challenges in microscale combustion. In this paper, the micro combustions of an H2/air premixed flame in a swirl MC with various channel diameters (Din = 2, 3, 4 mm) were analyzed based on an established three-dimensional numerical model. The effects of hydrogen mass flow rate, thermal conductivity of walls, and the preferential transport of species were investigated. The results indicated that the flame type was characterized by the presence of two recirculation zones. The flame was anchored by the recirculation zones, and the anchoring location of the flame root was the starting position of the recirculation zones. The recirculation zones had a larger distribution of local equivalence ratio, especially in the proximity of the flame root, indicating the formation of a radical pool. The combustion efficiency increased with an increasing Din due to the longer residence time of the reactants. Furthermore, the MC with Din = 2 mm obtained the highest outer wall temperature distribution. However, the MC with Din = 4 mm had a better uniformity of outer wall temperature and large emitter efficiency due to the larger radiation surface. An increase in thermal conductivity boosts the thermal performance of combustion efficiency, emitter efficiency, and wall temperature uniformity. But there is a critical point of thermal conductivity that can increase the thermal performance. The above results can offer us significant guidance for designing MC with high thermal performance.
Highlights
With the development of micro electro-mechanical systems (MEMS), micro power generators with high energy density and low weight are pressingly required [1,2,3,4]
The emitter efficiency ηe is calculated by η e = ( Q 0 mHQLHV ) × 1 0 0 %, where QLHV is the to 3.60 g/h, the average wall temperature of the swirl MC with Din = 2 mm was 116.2 K, 82.2 K, 61.5 K, lower heating value hydrogen isin119.96
Was due to the swirling flow facilitating flame anchoring; The local equivalence ratio was larger in the recirculation zones, which confirms that the recirculation zones helped to create a radical pool, thereby anchoring the flame to there; parameters such as channel diameter, inlet mass flow rate, and thermal conductivity of the solid wall changed, the flame root was firmly anchored to the starting position of the recirculation zones; The combustion intensity was stronger in the MC with a small Din of 2 mm, which had a higher wall temperature
Summary
With the development of micro electro-mechanical systems (MEMS), micro power generators with high energy density and low weight are pressingly required [1,2,3,4]. For the application of a micro thermophotovoltaic power generator, many studies are working to improve the thermal performance of MCs in order to further increase the energy output power or efficiency. In order to acquire higher energy output, Yang et al [31] proposed a converging–diverging channel MC for micro thermophotovoltaic power generator They pointed out that the flow disturbance caused by the converging–diverging channel improves the heat transfer between the gas and the solid wall. We developed a swirl MC [39] fueled by hydrogen/air based on a swirl-stabilized flame configuration, and the combustion and thermal performances under premixed modes and non-premixed modes were compared and analyzed. The energy output performance of the MC was affected by the combustion and thermal performance was investigated based on three-dimensional numerical channel diameter.
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