光谱方法研究大气压氩气等离子体喷枪的放电特性

摘要

利用同轴介质阻挡放电喷枪，通过氩气的流动在大气压空气中产生了均匀的等离子体羽。等离子体羽沿气流方向较为均匀，但在喷嘴处为白色且亮度较高，远离喷嘴处为蓝色，亮度较低。研究了等离子体羽长度与外加电压幅值、驱动频率和气体流速的关系，气流小于4 L·min-1时等离子羽的长度随气流的增大而增大，而当气流大于4 L·min-1时长度随气流的增大而减小。当气流保持恒定时，等离子体羽的长度随外加电压幅值或驱动频率的增大而增大。结合气体放电理论以及分析湍流和平流对放电的影响，对等离子体羽长度随实验参数的变化进行了定性解释。光学方法研究发现在外加电压正半周期等离子羽有一个发光脉冲，而负半周期没有发光信号。同轴介质阻挡放电正半周期有两个发光脉冲，负半周期有一个发光脉冲。通过对该N2现象的分析，为等离子体羽的产生机制提供了一种可能的解释。采集了同轴介质阻挡放电和等离子体羽的发射光谱，研究发现除等离子体羽存在明显的OH 和N2的发射谱线外，其发射光谱没有明显差别。利用光学发射谱N＋2第一负带系，对等离子体羽转动温度进行了测量，发现转动温度沿远离喷嘴的方向逐渐降低，且转动温度随电压幅值的增大而增大。%A uniform plasma plume was generated in a coaxial dielectric barrier discharge j et through blowing argon into the am-bient air at atmospheric pressure.The plasma plume was uniform along the direction of the gas flow.The length of the plasma plume was investigated as a function of the peak voltage,the driving frequency and the gas flow rate.It was found that with in-creasing the gas flow rate,the plume length increases when the flow rate is lower than 4 L·min-1 ,and decreases when it is higher than 4 L·min-1 .Under constant gas flow rate,the length of the plasma plume increases with the increase in the peak value of the applied voltage and the driving frequency.According to the discharge theory and based on the analysis of the turbu-lence and the advection,a qualitative explanation was given for the variance of plume length as functions of the experimental pa-rameters.Results also show that there is a discharge pulse for the plasma plume in every positive half cycle,while there is no pulse in negative half cycle.The coaxial dielectric barrier discharge shows two pulses in every positive half cycle and a pulse in every negative half cycle.Analyzing these experimental phenomena mentioned above,a formation mechanism of the plasma plume was proposed.The optical emission spectra were obtained for both the coaxial dielectric barrier discharge and the plasma plume.There was no apparent difference except that some emission lines from reactive species such as OH and N2 were found in the plasma plume.Using the first negative band of,the rational temperature of the plasma plume was measured.Results show that the rational temperature of the plasma plume decreases away from the jet nozzle,and increases with increasing the peak val-ue of the applied voltage.