多孔介质燃烧火焰相比于常规自由火焰，具有功率密度高、可燃性极限宽、燃烧速率高和污染物排放少等优点。为了探究甲烷多孔介质燃烧火焰面及污染物排放特性，采用计算流体力学方法，结合GRI-Mech 3.0机理，针对三维氧化铝小球堆积床多孔介质燃烧器内预混气体燃烧特性进行数值模拟。分析了当量比对甲烷多孔介质燃烧火焰面、燃烧反应速率以及CO和NOx排放特性的影响。结果表明，甲烷/空气多孔介质燃烧经历了预热—燃烧—燃尽3个阶段，并在主燃区达到了温度峰值以及燃烧反应速率峰值，而在主燃区后程及燃尽区内，燃烧温度趋于均匀，这是多孔介质燃烧与传统燃烧的重要区别。当量比对甲烷/空气多孔介质燃烧整体特性的影响不存在线性关系，化学当量比Φ=1.0时，整体燃烧特性较优。NO生成特性方面，受热力型NO生成机制的影响，多孔介质燃烧场内NO浓度先迅速上升，而后由于还原性气氛增强，GRI-Mech 3.0机理中涉及NO还原反应消耗了一定浓度的NO。

Compared with conventional free flame,porous medium combustion flame has higher power density,wider flammability limit,higher combustion rate and lower pollutant emission. In order to investigate the combustion flame and pollutant emission characteristics of methane porous medium,the combustion characteristics of premixed gas in three-dimensional alumina pellet porous medium burner were numerically simulated by using computational fluid dynamics (CFD) method and GRI-Mech 3.0 mechanism. The effects of equivalence ratio on flame surface,combustion reaction rate and emission characteristics of CO and NOx were analyzed. The results show that the CH4/air combustion goes through three stages:preheating-combustion-burnout,and reaches the peak of temperature and combustion reaction rate in the main combustion zone. In the second half of the main combustion zone and the burn out zone,the combustion temperature tends to be uniform,which is an important difference between porous medium combustion and traditional combustion. There is no linear relationship between the effect of chemical equivalence ratio on the overall combustion characteristics of methane/air porous media,when the stoichiometric ratio is 1.0,the overall combustion characteristics are better. The NO concentration in porous media combustion field first increases rapidly due to the influence of thermal NO generation mechanism,and then a certain concentration of NO is consumed by the reduction reaction involving NO in GRI-Mech 3.0 mechanism due to the enhancement of reducing atmosphere.

0 引言

1 计算模型及网格划分

   1.1 物理模型

   1.2 网格划分及网格无关性检验

2 计算方法

3 燃烧模拟结果分析

   3.1 燃烧火焰形状分析

   3.2 燃烧化学反应速率特性

   3.3 燃烧污染物组分分布特性

4 结论