双模式放电中DBD放电参数对甲烷滑动弧火焰光谱及活性粒子的影响分析

对未燃烧的可燃混合气体进行DBD放电，放电后会产生大量的活性粒子，这些活性粒子可以辅助气体燃烧，达到提高燃料燃烧利用率等目的。以DBD激励氩气、甲烷、空气产生的自由基（CH基和OH基）等强化燃烧的关键活性粒子为探索对象，研究DBD放电激励甲烷对滑动弧火焰的影响。为此，采用自主设计的DBD-滑动弧双模式等离子体激励器，利用同轴介质阻挡放电结构对氩气、甲烷、空气混合气进行放电激励，将激励后的氩气、甲烷、空气混合气通入滑动弧端进行点火。固定氩气流量不变，调整空气流量为4.76 L·min-1，并加入甲烷0.5 L·min-1，保证进气通道内氩气与空气-甲烷的气体体积流量比达到Ar∶（CH₄+Air）=1∶30，其中空气、甲烷这两种气体达到了化学燃烧当量比φ=1，氩气、甲烷、甲烷混合气体能实现均匀而稳定的放电并燃烧。DBD段放电电压在15～20 kV范围变化，放电频率在6～10 kHz范围变化，滑动弧段的电压和频率分别保持4 kV与10 kHz恒定，通过改变DBD段放电电压和放电频率，用高速光纤光谱仪检测滑动弧火焰中自由基种类及其光谱强度，分析放电参数激励甲烷对火焰中自由基（CH基和OH基）的影响。结果表明，DBD段放电电压及放电频率的增加可以促进火焰内部的偶联反应发生，可有效提升甲烷滑动弧火焰内部的活性粒子含量，其中OH基团、CH基团在燃烧链式化学反应进程中发挥着较为重要的作用。甲烷经过DBD激励后，随放电电压和频率的增加，火焰中OH基、CH基等主要活性粒子都随之增加。DBD放电后，活性粒子的光谱强度增大，特征谱线比单模式更加明显；甲烷经过DBD激励后，火焰组成发生了变化，滑动弧段出口处甲烷燃烧反应更加充分，火焰温度越高越容易产生OH基。与单模式滑动弧相比，双模式放电可有效促进火焰内部的链式化学反应进程，促进燃料燃烧。

Flame Spectrum and Active Particles Analysis of the Effect of Dielectric Barrier Discharge Induced on Gliding Arc Discharge With the Mixture of Methane-Air-Ar Within A Dual Mode Discharge

The discharge of DBD in unburned gaseous fuel or the combustible mixture will produce a lot of active free radicals, which can promote combustion and improve the combustion characteristics of fuel. In this paper, the effect of DBD excited methane on gliding arc flame is studied by using the key active particles (CH and OH) produced by DBD to enhance combustion. Therefore, a self-designed DBD-Gliding arc dual-mode plasma exciter is used to excite argon, methane and air mixture by using a coaxial Dielectric barrier discharge structure. The argon, methane and air mixture after excitation is fed into the gliding arc end for ignition. The volume flow ratio of argon to Air-methane in the inlet passage can reach Ar∶(CH₄+Air)=1∶30 by adjusting the Airflow rate to 4.76 L·min-1 and adding methane to 0.5 L·min-1, the mixture of argon, methane and methane can be discharged and burned uniformly and stably when the equivalent ratio of chemical combustion isΦ=1. The discharge voltage in the DBD segment varies from 15 to 20 kV, and the discharge frequency varies from 6 to 10 kHz. The voltage and frequency in the gliding arc discharge segment remain constant at 4 kV and 10 kHz, respectively, the type and spectrum intensity of free radicals in gliding arc flame were measured by a high-speed optical fiber spectrometer, and the effect of methane excited by discharge parameters on free radicals (CH and OH) in-flame was analyzed. The results show that the increase of DBD voltage and frequency can promote the coupling reaction in the flame and can effectively increase the content of active particles in the methane gliding arc flame. The OH group and CH group play an important role in the combustion chain reaction. The OH and CH groups in the flame increase with the increase of DBD discharge voltage and frequency. After DBD discharge, the spectrum intensity of the active particles increases, and the characteristic spectrum is more obvious than that of a single-mode. After the methane is excited by DBD, the flame composition changes, and the methane combustion reaction at the exit of the gliding arc is sufficient. The higher the flame temperature, the more likely it to produce an OH group. Compared with the single-mode GAD, the Double mode discharge can promote the chain chemical reaction process and fuel combustion.