微燃烧器外墙壁热损失对微尺度燃烧特性的影响分析

Effect of Heat Loss through the Outer Wall on Combustion Performance of Micro Combustor

以美国麻省理工学院(MIT)研制的硅基六晶片微燃烧器为研究对象,研究其外墙壁热损失状况对该燃烧器燃烧特性的影响程度。采用考虑了基元反应动力学机理燃烧程序的二维CFD数值分析方法,研究在微燃烧器入口处氢气/空气当量比、流量不变的情况下,其外墙壁热损失状况对燃烧器燃烧特性的影响程度。整个计算过程包括混合气体的流动路径、燃烧器的内部区域以及其墙壁面;同时在计算过程中也考虑了混合气体的流体动力学特性、传热学特性和详细的基元反应机理。计算结果表明,燃烧器外墙壁的热传递状况不但影响燃烧器的燃烧性能,还对整个燃烧器的结构寿命影响较大。随着外墙壁热传递状况的改善,如从150 W/(m2·K)增大到250 W/(m2·K),燃烧器排出气体的温度、燃烧性能均出现降低或下降的趋势,但外墙壁的热传递系数过小,如50 W/(m2·K)时,燃烧器的微细通道内将发生回燃。结果表明,利用二维CFD数值模拟的方法研究微尺度燃烧器燃烧特性可行,与国外实际测量结果较为相近,为今后微型燃气轮机燃烧器的研制及改进提供了一定的参考依据。

On the basis of the six-wafer combustor used in a micro-gas turbine engine developed by Massachusetts Institute of Technology（MIT）,a two-dimensional Computational Fluid Dynamics（CFD）simulation is employed in studying the effect of heat loss through the outer wall on the combustion performance in a micro combustor when the ratio and the flow rate of hydrogen/air are fixed. The CFD modeling includes the hydrogen/air flow path,combustion chamber as well as the solid walls of the micro-combustor,and the simulation analysis involves flow mechanics,heat transfer and the numerous chemical reactions occurring in the micro-combustor. The results show that the heat loss through the outer wall will have a great effect on both the combustion behavior and the device lifetime of the micro combustor. With the increase of the heat loss through the outer wall to the environment,e.g. from 150 W/（m^2·K） to 250 W/（m^2·K）,the outer wall temperature and the combustor efficiency will decrease correspondingly. If the heat transfer coefficient on the outer wall is kept so low,e.g.50 W/（m^2·K）,as to reduce the heat loss from the system,the flame will flash back and combust in the recirculation jacket.It comes to a conclusion that the numerical simulation can be one of the most powerful and beneficial tools for design and development of the micro-combustor.