Effects of trapezoidal bluff bodies on blow out limit of methane/air combustion in a micro-channel

Abstract

Effects of five trapezoidal bluff bodies on blow out limit of methane/air (equivalence ratio ϕ = 0.9) combustion in a micro-channel were numerically investigated in this paper. The results show that four different flow fields successively emerge with the increase of blockage ratio and inlet velocity. They are the stable flow field in front of the bluff body, the flow field with vortex, the inclined flow field and the stable flow field behind the bluff body, respectively. The shape change of trapezoidal bluff body has a slight effect on expansion of combustion recirculation zone and increase of blow out limit at the same blockage ratio while the combustion recirculation zone expands obviously with increasing blockage ratio. In addition, the expansion of recirculation zone is favorable to improve the channel temperature and extend the mixed gas residence time. At the same time, the blow out limit of methane/air combustion increases. Among all five trapezoidal bluff bodies, the optimum choice is the one whose blockage ratio is 0.4 and blow out limit reaches 2 m/s. Furthermore, the extinction limit occurs at a relatively low inlet velocity, which is due to the less imported fuel in the micro-reactor and relatively high heat loss while the blow out limit arises at a relatively high inlet velocity, which is attributed to the high heat loss and short residence time of mixture. This study could provide some useful information for the design and operation of the micro-combustor with trapezoidal bluff body, and is helpful to understand the methane/air combustion phenomena in the micro-combustor with trapezoidal bluff body.