介质阻挡体放电对甲烷扩散火焰CH*自发辐射影响实验研究

Experimental Study for Effects of Volumetric Dielectric Barrier Discharge on Methane/Air Diffusion Flame CH Chemiluminescence

为分析非平衡等离子体对空气/甲烷扩散火焰的助燃效果,实验以发射中心谱线430nm的激发态自由基CH*表征火焰燃烧状态,采用同轴圆柱构型激励器在高频交流模式下激发等离子体,分析了火焰CH*自发辐射图像、火焰高度、CH*径向分布和燃烧释热速率等火焰特性在不同空气流量和当量比下随放电电压的变化规律。结果表明:等离子体激励在空气流量较低时,会显著增强火焰上游甲烷燃烧,从而降低CH*空间分布高度和火焰高度;空气流量增大后,有利于促进甲烷充分燃烧,增大火焰下游CH*辐射强度和分布范围。在火焰上游区域,等离子体气动效应可有效扩展甲烷径向分布,实现剪切层更宽范围燃烧,其活化效应会明显提高剪切层燃烧强度,并随电压增大作用效果逐渐增强。此外,等离子体激励会使燃烧器喷嘴出口附近火焰释热速率显著增大,该现象在空气-甲烷动量比较大时更容易发生。

To study the combustion-assisted effects of nonequilibrium plasma on a CH4/air diffusion flame,a spectral line at 430 nm is selected to indicate the excited state radical CH* chemiluminescence occurred in the flame. The plasma is generated by a co-axial cylindrical actuator with high frequency alternating current source.The variations of CH* chemiluminescence images,flame heights,CH* radial profiles,and the combustion heat release rates of the flame with discharge voltage are analyzed under different air flow rates and equivalence ratios.Results show that the combustion upstream of the flame is enhanced by the plasma leading to the decrease of the height of CH* spatial distribution and flame,when the air flow rate is relatively low. As the flow rate rises,the fuel methane burns better. Then,the intensity and the extent of CH* increases in the downstream part of the flame.Due to the gas dynamic effect of the plasma,the radial distribution of CH4 is extended in the upstream region of the flame,which results in a larger range of combustion within the shear layer. The combustion intensity around the shear layer increases by the kinetic effect of the plasma,especially for a higher voltage. Moreover,the heat release rate increases notably near the injector outlet of the burner by the plasma. This phenomenon occurs easier,when the ratio of the momentum of air to the momentum of CH4 is large.