CH4/air预混气体双层多孔介质燃烧特性数值模拟研究

基于局部热平衡假设,定义了无量纲参数——火焰宽度比,在过量空气系数为1.2条件下,研究了CH_4/air预混气体在双层多孔介质中浸没燃烧和表面燃烧的燃烧特性。结果表明:表面燃烧具有更高的烟气出口温度以及更高的火焰宽度比。浸没燃烧火焰轮廓类似抛物线,而表面燃烧的火焰宽度比则基本不变;入口速度不同时,距离着火面同一位置浸没燃烧火焰宽度基本保持不变,火焰轮廓仍类似于抛物线;而对于表面燃烧,相同位置的火焰宽度比在很小范围内(约为0.03)呈现先增大后减小的变化规律。同时研究也表明表面燃烧具有更高的NO_x排放,且随着速度的增加两种燃烧方式NO_x排放变化规律一致,均呈现先增大后减小再增加的变化规律。在速度为1.1～1.2μm/s左右时,两种燃烧方式NO_x排放大致相当,这表明在不扩大污染的条件下,可以使用表面燃烧获得更多的对外辐射以节约能源。

Combustion characteristics of premixed-air in two-section porous media by numerical simulation

Based on the local heat balance hypothesis, this paper defines the dimensionless parameter-flame width ratio. Under the condition of excess air coefficient of 1.2, the combustion characteristics of CH4/air premixed gas in immersion combustion and surface combustion in double-layer porous media are studied. The results show that surface combustion has a higher flue gas outlet temperature and a higher flame width ratio. The immersion flame profile is similar to a parabola, while the flame width ratio of the surface combustion is substantially unchanged; When the inlet speed is different, the immersion combustion flame width remains substantially the same from the same position on the fire surface, and the flame profile is still similar to the parabola; For surface combustion, the flame width at the same position is increased in a small range and then decreased. At the same time, the research also shows that the surface combustion has higher NOx emission, and the NOx emission changes of the two combustion modes are consistent with the increase of speed, and the changes are firstly increased, then decreased and then increased. At a speed of about 1.1 ~1.2 m/s, the NOx emissions of the two combustion modes are roughly equivalent, which indicates that surface combustion can be used to obtain more external radiation to save energy without expanding pollution.