大气压甲烷针-板放电等离子体中粒子密度和反应路径的数值模拟

甲烷针-板放电与重油加氢耦合形成甲烷转化重油加氢,可实现重油高效加氢并增产高附加值低碳烯烃,有实践应用前景和科学研究意义.建立二维流体模型,对大气压甲烷针-板放电等离子体进行数值模拟,得到电场强度、电子温度和粒子密度的空间与轴向分布,总结反应产额并提炼生成各种带电和中性粒子的关键路径.模拟结果表明,CH_3~+和CH_4~+密度与电场强度和电子温度的轴向演化接近且密切相关;CH_5~+和C_2H_5~+密度沿轴向先增大后减小;CH_3与H密度的空间和轴向分布几乎相同;CH_2,C_2H_4与C_2H_5的粒子密度分布在靠近阴极的区域内明显不同而在正柱区内较为相像;电子与CH_4发生电子碰撞电离生成的CH_3~+和CH_4~+,CH_3~+和CH_4~+分别与CH_4发生分子碰撞解离生成C_2H_5~+和CH_5~+;电子与CH_4间的电子碰撞分解是生成CH_3,CH_2,CH和H的主导反应;CH_2与CH_4和电子与C_2H_4发生的反应分别是生成C_2H_4和C_2H_2的关键路径;电子与CH_4间的电子碰撞分解反应和CH_2与CH_4发生的反应的产额各占H_2总产额的52.15%和47.85%.

Numerical simulation on particle density and reaction pathways in methane needle-plane discharge plasma at atmospheric pressure

Methane needle-plane discharge has practical application prospect and scientific research significance since methane conversion heavy oil hydrogenation is formed by coupling methane needle-plane discharge with heavy oil hydrogenation, which can achieve high-efficient heavy oil hydrogenation and increase the yields of high value-added light olefins. In this paper, a two-dimensional fluid model is built up for numerically simulating the methane needle-plane discharge plasma at atmospheric pressure. Spatial and axial distributions of electric intensity, electron temperature and particle densities are obtained. Reaction yields are summarized and crucial pathways to produce various kinds of charged and neutral particles are found out. Simulation results indicate that axial evolutions of CH₃⁺ and CH₄⁺ densities, electric intensity and electron temperature are similar and closely related. The CH₅⁺ and C₂H₅⁺ densities first increase and then decrease along the axial direction. The CH₃ and H densities have nearly identical spatial and axial distributions. Particle density distributions of CH₂, C₂H₄ and C₂H₅ are obviously different in the area near the cathode but comparatively resemblant in the positive column region. The CH₃⁺ and CH₄⁺ are produced by electron impact ionizations between electrons and CH₄. The CH₅⁺ and C₂H₅⁺ are respectively generated by molecular impact dissociations between CH₃⁺ and CH₄ and between CH₄⁺ and CH₄. Electron impact decomposition between electrons and CH₄ is a dominated reaction to produce CH₃, CH₂, CH and H. The reactions between CH₂ and CH₄ and between electrons and C₂H₄ are critical pathways to produce C₂H₄ and C₂H₂, respectively. In addition, the yields of electron impact decomposition reactions between electrons and CH₄ and reactions between CH₂ and CH₄ account for 52.15% and 47.85% of total yields of H₂ respectively.