Ar/CH4等离子体射流发射光谱诊断研究

为了更加深入的研究大气压条件下Ar/CH₄等离子体射流的放电机理和其内部电子的状态，通过自主设计的针-环式介质阻挡放电结构，在放电频率10 kHz、一个大气压条件下产生了稳定的Ar/CH₄等离子体射流，并利用发射光谱法对其进行了诊断研究。对大气条件下Ar/CH₄等离子体射流的放电现象及内部活性粒子种类进行诊断分析，重点研究了不同氩气甲烷体积流量比、不同峰值电压对大气压Ar/CH₄等离子体射流电子激发温度、电子密度以及CH基团活性粒子浓度的影响规律。结果表明，大气压条件下Ar/CH₄等离子体射流呈淡蓝色，在射流边缘可观察到丝状毛刺并伴有刺耳的电离声同时发现射流尖端的形态波动较大；通过发射光谱可以发现Ar/CH₄等离子体射流中的主要活性粒子为CH基团，C，CⅡ，CⅢ，CⅣ，ArⅠ和ArⅡ，其中含碳粒子的谱线主要集中在400~600 nm之间，ArⅠ和ArⅡ的谱线分布在680~800 nm之间；可以发现CH基团的浓度随峰值电压的增大而增大，但CH基团浓度随Ar/CH₄体积流量比的增大而减小，同时Ar/CH₄等离子体射流中C原子的浓度随之增加，这表明氩气甲烷体积流量比的增大加速了Ar/CH₄等离子体射流中C-H的断裂，因此可以发现增大峰值电压与氩气甲烷体积流量比均可明显的加快甲烷分子的脱氢效率，但增大氩气甲烷体积流量比的脱氢效果更加明显。通过多谱线斜率法选取4条ArⅠ谱线计算了不同工况下的电子激发温度，求得大气压Ar/CH₄等离子体射流的电子激发温度在6 000~12 000 K之间，且随峰值电压与氩气甲烷体积流量比的增大均呈现上升的趋势；依据Stark展宽机理对Ar/CH₄等离子体射流的电子密度进行了计算，电子密度的数量级可达1017 cm-3，且增大峰值电压与氩气甲烷体积流量比均可有效的提高射流中的电子密度。这些参数的探索对大气压等离子体射流的研讨具有重大意义。

A Study on Emission Spectral Diagnosis of Ar/CH4 Plasma Jet

In order to have abetter understanding on the discharge mechanism of Ar/CH₄plasma jet and the state of its internal electrons under atmospheric pressure,a stable Ar/CH₄plasma jet was produced in the atmosphere through a self-designed needle-ring Dielectric Barrier Discharge structure with a discharge frequency of 10 kHz,and the plasma jet was diagnosed by emission spectroscopy.The discharge phenomenon of Ar/CH₄plasma jet and the types of active particles inside were analyzed under atmospheric conditions.The effects of different argon-methane volume flow ratios and different peak voltages on the electron excitation temperature,electron density and concentration of CH group active particles in atmospheric pressure Ar/CH₄plasma jet were emphasis studied.The results show that the Ar/CH₄plasma jet is light blue under atmospheric pressure,and filamentous burrs can be observed on the edge of the jet.A harsh ionizing sound accompanies the discharge,and the shape of the jet tip fluctuates greatly;The main active particles in Ar/CH₄plasma jet at atmospheric pressure are CH group,C atom,CⅡ,CⅢ,CⅣ,ArⅠand ArⅡ.Among them,the spectral lines of carbon-containing particles are mainly concentrated between 400 and 600 nm,and the spectral lines of ArⅠand ArⅡare distributed between 680 and 800 nm;It can be found that the concentration of the CH group increases with the increase of the peak voltage,however,the concentration of CH group decreases with the increase of the volume flow ratio of Ar/CH₄.At the same time,the concentration of C atoms in the Ar/CH₄plasma jet increases.This means that the increase of the volume flow rate accelerates C—H fracture in the Ar/CH₄plasma jet.Therefore,it can be seen that increasing of the peak voltage and Ar/CH₄volume flow ratio can significantly accelerate the dehydrogenation efficiency of methane molecules,but increasing the Ar/CH₄volume flow ratio dehydrogenation effect is more obvious.Four ArⅠlines was selected to calculate the electron excitation temperature under different operating conditions.The electron excitation temperature of Ar/CH₄plasma jet is between 6000 and 12000 K,and it shows an upward trend with the increase of the peak voltage and the volume flow rate of Ar/CH₄;The electron density of the Ar/CH₄plasma jet was calculated based on the Stark broadening mechanism,the magnitude of electron density can reach 10¹⁷ cm^-3,and plasma jet electron density can be significantly improved by increasing the volume flow ratio of Ar/CH₄and peak voltage.The exploration of these parameters is of great significance to the study of atmospheric pressure plasma jets.