氧气/空气源低温等离子体发生器的性能对比分析

为对比不同气源的介质阻挡放电型低温等离子体发生器的性能参数,分别以氧气和空气为气源,对发生器进行了静态对比试验,研究了放电电极面积、放电电压峰峰值、气体体积流量对放电功率、单周期电荷传输量、O_3浓度、O_3产量和O_3产率的影响。结果表明,当放电电极面积增大时,放电功率和单周期电荷传输量均线性增大,但空气源对应的放电功率和单周期电荷传输量及其增长速率较低;此时,氧气和空气源的O_3浓度整体呈上升趋势而O_3产率则呈下降趋势。当放电电压峰峰值增大时,氧气和空气源的放电功率和单周期电荷传输量均显著增大,且后期增大速率加快;O_3浓度均先升后降而O_3产率则逐渐减小,高浓度和高产率不可兼得。不同放电频率下,氧气源的最大臭氧浓度大于55 mg/L,空气源的最大臭氧质量浓度在4~8 mg/L之间。当气体体积流量增大时,氧气源的放电功率和单周期电荷传输量均先上升后趋于平缓,而空气源的放电功率和单周期电荷传输量则逐渐增大;氧气源的O_3浓度下降,O_3产量上升直至平缓,而空气源的O_3浓度则先增后减,O_3产量逐渐上升但上升速率放缓;氧气源和空气源的O_3产率均随气体体积流量的增大而缓慢上升。以氧气为气源时,气体体积流量不宜超过10 L/min;以空气为气源时,气体体积流量可选取为9 L/min左右。研究结果可为低温等离子体喷射系统优化及柴油机颗粒物捕集器的再生研究提供参考。

Comparative analysis on characteristics in non-thermal plasma reactor with oxygen and air

Diesel engines have been favored in heavy trucks and passenger cars due to their low fuel consumption, high power output and durability. However, particulate matter (PM) and nitrogen oxide (NOx) emitted from diesel bring about deterioration of air pollution, which has an adverse impact on human health. Stricter emission regulations have been implemented worldwide. As a solution, diesel particular filter (DPF) has become a mainstay in PM control. However, there are some problems with DPF regeneration technologies, such as thermal damage, sulfur poisoning of the catalyst and low regeneration efficiency. So it is meaningful to find out a new regeneration method. Recently, non-thermal plasma (NTP) has become a research focus in the field of diesel emission control with its high efficiency, safety, no secondary pollution and a wide range of application. The active materials, mainly including O3,NO2,OH and O, can start complex chemical reactions, which is impossible in a conventional condition. So, it can be used to remove PM deposits in DPF and realize DPF regeneration. In term of NTP reactor, dielectric barrier discharge is widely used in the laboratory and industry for its simple type, safety and reliability. There are many influence factors concerning discharge, such as discharge voltage and frequency, gas type and flow, materials of barrier and electrode type. In this paper, a coaxial type NTP reactor was designed. In order to have a detailed recognition of NTP reactor, comparative analysis on oxygen and air dielectric discharge were investigated, with the studies on the influence of discharge electrode area (SE), peak-peak voltage (Up-p) and volume flow rate (qv) on discharge power (P), charge flux (Q), ozone concentration, ozone output and ozone output efficiency.SEwas changed by the length of wire tightly wrapped around the barrier,Up-pwas adjusted by a plasma source andqv was controlled by gas valves and flow meters. The results indicated thatSEhad a similar effect both on oxygen and air dielectric discharge. With the increase ofSE,P andQhad a linear growth but there were lower values and growth rate in air discharge. Ozone concentration increased asSE increased while its output efficiency decreased both in oxygen and air discharge.Up-phad remarkably positive impacts onP and Q, both of which had a rising growth rate. Ozone concentration rose at first and decreased afterwards with increasingUp-p while ozone output efficiency declined, which indicated a contradiction between them. Under the different discharge frequency, the maximum ozone mass concentration in oxygen discharge was larger than 55 mg/L while the maximum ozone mass concentration in oxygen discharge was between 4-8 mg/L. Excessive increase inUp-p was useless after the maximum ozone concentration point. In addition, under the sameUp-p, ozone concentration increased with growing discharge frequency in oxygen discharge but it showed an opposite trend in air discharge. Ozone output efficiency was higher than 100 g/kW·h when Up-p was lower than 17.5 kV in oxygen discharge and it maintained at 20 g/kW·h whenUp-p was lower than 17 kV in air discharge. Oxygen and air discharge differed whenqvchanged.P andQ showed a sharp climb and then kept steady with the growth ofqv in oxygen discharge while they kept growing in air discharge. Ozone concentration fell with increasingqvand its output grew at first and then flattened in oxygen discharge, but they increased to the highest, and then descended, and its output grew with a smaller rate in air discharge. The same was that their output efficiency rose slowly with increasingqv. In consideration of the trade-off between ozone concentration, ozone output and output efficiency,qvshould better not exceed 10 L/min when the gas source was oxygen and 9 L/min could be chosen when the gas source was air. This study founds a theoretical and experimental basis for optimization of non-thermal plasma injection system and its application on diesel particular filter regeneration.