空气旋流数对甲烷燃烧NO_(x)生成影响数值模拟研究

Numerical Simulaion Research on Effect of Air Swirl on NO_(x)Generation during Methane Combustion

为研究甲烷-空气非预混燃烧下空气旋流数对流动特性、温度分布及其对污染物NO_(x)生成的影响,利用CFD软件,采用标准的k-ε湍流模型、P-1辐射模型和涡流耗散模型进行数值模拟。结果表明:空气旋流数从0提高到0.8的过程中,形成的中心内回流区会强化燃料和空气混合,中心火焰向燃烧室两侧逐渐扩散,火焰长度变短,且高温区移动到燃烧室的前端,局部高温的产生得到了抑制,燃烧室内的温度场更加均匀,进而导致NO_(x)生成量的下降。同时研究燃烧器几何尺寸对气体停留时间及NO_(x)排放浓度的影响,发现缩小空气入口孔隙半径r和燃空径向隔板间距L会导致气流速度增大,促进反应更快地弥散到整个空间,能够进一步抑制NO_(x)的产生。

In order to study the effect of the air swirl number on the flow characteristics,temperature distribution and pollutant NO_(x) generation during methane-air non-premixed combustion,the numerical simulations were carried out by using CFD software,the standard k-εturbulence model,P-1 radiation model and eddy current dissipation model.The results show that when the air swirl number is increased from 0 to 0.8,the combustion zone will form a central recirculation zone to enhance fuel and air mixing,the central flame spreads to both sides of the combustion chamber,the flame length becomes shorter,and the high temperature zone moves to the front end of the combustion chamber,local high temperatures are inhibited,and the temperature field in the entire combustion chamber becomes more uniform,which in turn leads to a decrease in NO_(x) generation.At the same time,the effect of the geometrical size of the burner on the gas residence time and NO_(x) emission concentration is studied.It is found that reducing the air inlet pore radius r and the fuel-air radial baffle spacing L will lead to the increase of air flow velocity,promote the reaction to spread to the entire space faster,and furtherly suppress the generation of NO_(x).