非平衡等离子体控制乙烯-空气旋流反扩散火焰实验研究

Experimental Study on Control of Ethylene-Air Reverse Diffusion Flame by Non-Equilibrium Plasma

关键词:  非平衡等离子体  介质阻挡放电  乙烯  旋流  反扩散火焰

Key words:  Nonequilibrium plasma  Dielectric barrier discharge  Ethylene  Swirl  Reverse diffusion flame

摘要:

为研究非平衡等离子体自身特性及其对乙烯-空气反扩散火焰的影响，基于同轴旋流式等离子体喷嘴，采用交流激励介质阻挡放电（Alternating Current Dielectric Barrier Discharge，AC DBD）方式在乙烯旋流中产生非平衡等离子体，分别从放电图像、温度和流场变化等方面对乙烯等离子体的电学特性、热效应和气动效应进行了研究，最后通过反扩散火焰可见光和CH*自发辐射图像详细分析了等离子体对乙烯-空气反扩散火焰的影响及其机理。结果表明，AC DBD激励方式使乙烯旋流在喷嘴环缝内产生了丝状非平衡等离子体，丝状等离子体通道数目随着激励电压上升而显著增加。与空气等离子体和氧气等离子体相似，乙烯等离子体兼具热效应和气动效应，其热效应主要集中在放电核心区域，对射流加热作用微弱，对燃烧的影响可以忽略不计；气动效应显著，主要体现在增强了射流掺混、扩大了射流覆盖面积以及降低了转捩点高度，射流掺混的增强导致反扩散火焰最大释热强度提升，且在低当量比时较为明显，射流转捩点高度的降低引起了火焰中心位置下降。

Abstract:

To study the characteristics of non-equilibrium plasma and its effect on ethylene-air reverse diffusion flame， an alternating current dielectric barrier discharge （AC DBD） method was used to generate nonequilibrium plasma in the swirl of ethylene based on the coaxial swirl plasma nozzle. The electrical properties， thermal and aerodynamic effects of ethylene plasma were studied by discharge image and changes in temperature and flow field. In the end， the effect of plasma on ethylene-air reverse diffusion flame and its mechanism were analyzed in detail through visible light and CH * spontaneous emission images. The results show that the AC DBD excitation mode causes ethylene swirl to generate filamentous non-equilibrium plasma in the nozzle ring gap， and the number of filamentary plasma channels increases significantly with the increase of the excitation voltage. Similar to air plasma and oxygen plasma， ethylene plasma has both thermal and aerodynamic effects. Its thermal effect is mainly concentrated in the core area of ??the discharge， and it has a weak heating effect on the jet， so its effect on combustion is negligible. The aerodynamic effect is significant， mainly reflected in enhancement of jet blending， enlargement of jet coverage， and reduction of transition point height. The enhancement of jet mixing results in an increase in the maximum heat release intensity of the reverse diffusion flame， which is more pronounced at low equivalent ratios. The decrease in the transition point height of the jet causes the flame center position dropped.