Modeling of the effects of non-equilibrium excitation and electrode geometry on H2/air ignition in a nanosecond plasma discharge
Modeling of the effects of non-equilibrium excitation and electrode geometry on H2/air ignition in a nanosecond plasma discharge
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DOI：
10.1016/j.combustflame.2022.112046
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发表时间：
2022
影响因子：
4.4
通讯作者：
Xingqian Mao;Hongtao Zhong;Tianhan Zhang;A. Starikovskiy;Y. Ju
中科院分区：
文献类型：
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作者：
Xingqian Mao;Hongtao Zhong;Tianhan Zhang;A. Starikovskiy;Y. Ju
本文研究了纳秒等离子体放电中非平衡激发和电极几何形状对H2/空气点火的影响。基于PASSKEy放电模拟软件包和可压缩多组分反应流求解器ASURF+，开发了等离子体辅助燃烧多尺度自适应约化化学求解器（MARCS PAC），并进行了验证。该模型被应用到模拟的非平衡等离子体激发和电极的几何形状和热损失的影响，从流光放电的动态火花和点火内核的发展与一对圆柱形电极的H2/空气混合物。结果表明，火花和余辉中的等离子体生成物种（N2（A）、N2（B）、N2（a′）、N2（C）、O（1D）、O和H）对点火核的形成有显著的促进作用。在总放电能量相同的情况下，放电电压的增加促进了非平衡活性物种的产生。据发现，在较高的约化电场强度的电子激发的物种的生产是更有效地提高点火相比，振动激发和加热。此外，二维模拟清楚地表明，电场和活性物种分布是高度不均匀的。流光在负电极和正电极的尖锐外边缘处由强电场引发，而在电极的中心线处电场弱得多。此外，模拟结果表明，点火增强是敏感的电极形状，直径和间隙的大小的变化，由于电场分布和流光形成的位置的变化。当放电集中在差距轴附近时，圆柱形电极比抛物形和球形电极产生更大的放电体积和点火核心。结果表明，点火核尺寸与电极直径和电极间距之间存在非单调关系。电极直径和间隙尺寸在最佳条件以上的增加导致点火核心体积减小，这是由于活性组分浓度和气体温度的降低。在较大的电极表面积和电极直径以及较小的电极间隙尺寸下，电极的热损失对减小点火核心尺寸和减缓点火核心发展起着更大的作用。这项工作提供了见解和指导，以了解非平衡等离子体的动力学增强和电极的几何形状对点火的影响，优化点火器在先进的发动机。
This work presents the results of two-dimensional modeling of the effects of non-equilibrium excitation and electrode geometry on H 2/air ignition in a nanosecond plasma discharge. A multiscale adaptive reduced chemistry solver for plasma assisted combustion (MARCS-PAC) based on PASSKEy discharge modeling package and compressible multi-component reactive flow solver ASURF+ is developed and validated. This model is applied to simulate the impact of non-equilibrium plasma excitation and electrode geometry and heat loss on the dynamics of the discharge from streamer to spark and ignition kernel development in a H 2/air mixture with a pair of cylindrical electrodes. The results show that the plasma-generated species (N 2 (A), N 2 (B), N 2 (a′), N 2 (C), O (1 D), O and H) in the spark and afterglow significantly accelerate the ignition kernel development. The increase of discharge voltage at the same total discharge energy promotes the non-equilibrium active species production. It is found that the production of electronically excited species at higher reduced electric field strength is more efficient in enhancing ignition in comparison to the vibrational excitation and heating. Moreover, the 2D simulation clearly reveals that the electric field and active species distribution are highly non-uniform. The streamers are initiated at the sharp outer edges of the negative and positive electrodes by a strong electric field while the electric field is much weaker at the centerline of the electrodes. Furthermore, the simulations reveal that the ignition enhancement is sensitive to the variation of electrode shape, diameter, and gap size due to the changes of electric field distribution and location of streamer formation. A cylindrical electrode produces a larger discharge volume and ignition kernel than the parabolic and spherical electrodes, when the discharge is localized near the axis of the gap. It is found that there is a non-monotonic dependence of ignition kernel size on the electrode diameter and inter-electrode distance. The increase of electrode diameter and gap size above the optimal conditions leads to the reduction of ignition kernel volume, due to the decrease of active species concentration and gas temperature. At a larger electrode surface area and electrode diameter as well as smaller electrode gap size, the heat loss to electrode plays a greater role in reducing the ignition kernel size and slowing ignition kernel development. This work provides insights and guidance to understand the kinetic enhancement of non-equilibrium plasma and the effects of electrode geometries on ignition for the optimization ignitors in advanced engines.