Modelling the impact of non-equilibrium discharges on reactive mixtures for simulations of plasma-assisted ignition in turbulent flows
Modelling the impact of non-equilibrium discharges on reactive mixtures for simulations of plasma-assisted ignition in turbulent flows
复制标题
模拟非平衡放电对反应混合物的影响，以模拟湍流中的等离子体辅助点火
DOI：
10.1016/j.combustflame.2016.01.009
复制
发表时间：
2016
影响因子：
4.4
通讯作者：
C. Laux
中科院分区：
文献类型：
--
作者：
M. Castela;B. Fiorina;A. Coussement;O. Gicquel;N. Darabiha;C. Laux
本文提出了一个模型来描述非平衡等离子体放电对气体温度和组分浓度的影响，在控制燃烧现象的方程组。基于文献报道的结果，通过分析电能沉积的通道来构建模型。放电过程中产生的电子影响气流的两个主要通道被认为是：（1）氮分子的电子态的激发和随后的弛豫，这导致气体温度的超快增加和放电特征时间内的物种解离;和（2）氮分子的振动态的激发和弛豫，这导致气体加热慢得多。该模型是完全耦合的多维流动平衡方程与详细的传输系数和详细的燃烧化学动力学机制。这种高水平的NRP放电建模允许通过直接数值模拟来计算高雷诺数流动，因此，可以更好地理解实际配置中的等离子体辅助点火现象。利用该模型研究了空气和甲烷-空气混合气体在静止和湍流状态下的放电脉冲序列。结果表明，振动能量对混合物点火的影响较小，以及湍流的增加如何将振动能量和中间燃烧物质传播到放电区周围，从而最大限度地减少多个脉冲的累积效应。相反，在放电过程中产生的O原子的点火延迟和点火能量（放电脉冲数）有很大的影响。结果还强调了初始湍流雷诺数和湍流涡流的空间分布的影响，相对于放电通道，点燃混合物所需的脉冲数。
This article presents a model to describe the effects of non-equilibrium plasma discharges on gas temperature and species concentration, in the set of equations governing the combustion phenomena. Based on the results reported in the literature, the model is constructed by analysing the channels through which the electric energy is deposited. The two main channels by which the electrons produced during the discharge impact the flow are considered: (1) the excitation and the subsequent relaxation of electronic states of nitrogen molecules which leads to an ultrafast increase of gas temperature and species dissociation within the discharge characteristic time; and (2) the excitation and relaxation of vibrational states of nitrogen molecules which causes a much slower gas heating. The model is fully coupled with multi-dimensional flow balance equations with detailed transport coefficients and detailed combustion chemical kinetic mechanisms. This high level of NRP discharge modelling allows computing high Reynolds flows by means of Direct Numerical Simulations and, therefore, a better understanding of plasma-assisted ignition phenomena in practical configurations. A sequence of discharge pulses in air and methane–air mixture in quiescent and turbulent flow configurations are studied with this model. The results show the minor impact of the vibrational energy on mixture ignition and how the increase of the turbulence spreads this vibrational energy and intermediate combustion species around the discharge zone, minimizing the cumulative effect of multiple pulses. In contrast, the production of O atoms during the discharge has a strong impact on the ignition delays and ignition energies (number of discharge pulses). The results also underscore the impact of the initial turbulent flow Reynolds number and the spatial distribution of turbulent eddies, relative to the discharge channel, on the number of pulses needed to ignite the mixture.