多孔介质微燃烧器内的火焰驻定机理研究

Flame Stabilization Mechanism in Porous Micro-Combustors

关键词:  微尺度燃烧  多孔介质  回热  驻定火焰  传热特性

Key words:  Microscale combustion  Porous medium  Heat recirculation  Stationary flame  Heat transfer characteristic

摘要:

为解释毫米尺度多孔介质燃烧器中火焰可在一个当量比范围内驻定的物理现象，搭建了二维非稳态数学物理模型，利用数值计算方法定性研究了氢气/空气预混气在部分填充不锈钢网的微通道内的火焰传播特性。通过分析浸没火焰及表面火焰的温度分布特点并量化燃烧室内的预热和散热发现：火焰驻定在多孔介质内的不同位置时对应的传热特性存在差异，是控制火焰传播速度在一定当量比范围内保持恒定的关键因素，而预热及散热的相对大小可作为衡量传热对火焰宏观影响的重要参数。对火焰的总预热与总散热之比R越临近多孔介质入口边界，变化越剧烈，导致浸没火焰易驻定在多孔介质的中上游区域；多孔介质对火焰的预热虽在多孔介质出口边界外减小，但与多孔介质散热之比R_p呈上升趋势，使得低流速工况下易形成表面火焰。同时，R随当量比的变化规律导致多孔介质下游火焰的稳定性相对较弱。

Abstract:

In order to investigate the mechanism that the stationary flame can be achieved over a range of equivalence ratios in porous micro-combustors， a two-dimensional unsteady physical model was established. The hydrogen/air premixed combustion in micro-channels partially filled with stainless steel mesh was qualitatively studied by using numerical approaches. By analyzing the temperature distribution characteristics of the submerged flame and the surface flame， as well as quantifying the preheating and heat loss in micro-combustors， it is found that the heat transfer characteristics varying with the flame positions in porous medium is the key factor to control the flame propagation velocity to keep constant within an equivalence ratio range. Furthermore， the relative magnitude of preheating and heat loss can be used as an important parameter to characterize the effect of heat transfer on flame. The ratio（R） of total preheating and total heat loss changes more dramatically as it gets closer to the porous medium inlet boundary， resulting in that the submerged flame is easy to be stabilized at the middle upper region of porous medium. Although the preheating of porous medium decreases near the outlet boundary of porous medium， the ratio （R_p） of the preheating to heat loss of porous medium increases rapidly， which makes surface flame easy to be stabilized under low flow rate conditions. At the same time， the responses of R to equivalence ratios leads to the flame stabilization more feeble when the flame is stabilized at downstream of porous medium.