Plasma-assisted ignition of methane/air and ethylene/air mixtures: Efficiency at low and high pressures
Plasma-assisted ignition of methane/air and ethylene/air mixtures: Efficiency at low and high pressures
复制标题
等离子体辅助点燃甲烷/空气和乙烯/空气混合物： 低压和高压下的效率
DOI：
10.1016/j.proci.2020.06.126
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发表时间：
2021-04-13
影响因子：
3.4
通讯作者：
Bisetti, Fabrizio
中科院分区：
文献类型：
--
作者：
Deak, Nicholas;Bellemans, Aurelie;Bisetti, Fabrizio
使用零维等容绝热反应器对纳秒脉冲放电 (NSPD) 引起的甲烷/空气和乙烯/空气混合物的点火进行了数值研究。燃烧动力学模型与非平衡等离子体机制相结合，其特点是通过电子碰撞实现中性粒子（O 2 和 N 2 ）的振动和电子激发、解离和电离。点火时间指标 ?定义，并执行涵盖各种压力（0.5-30 atm）和每种燃料的脉冲条件的点火模拟。对于每种燃料，我们发现 tau 主要取决于初始压力和能量沉积速率，并推导出比例定律。为了量化等离子体辅助点火 (PAI) 带来的好处，将 tau 与热点火时间进行了比较。研究发现，对于这两种燃料，PAI 在低压下会导致更快的点火，而在较高压力（p 0 >= 5 atm）下，甲烷/空气点火变得低效（这意味着与热点火相比，相同输入能量的点火时间更长）。乙烯/空气 PAI 仅显示出适度的恶化。研究发现，性能随压力的下降是由于脉冲期间获得的平均电子能量造成的，这与压力呈反比关系，导致激发物质和燃烧自由基减少。通过对反应路径的分析解释了高压下甲烷/空气混合物点火性能不佳的原因。在高压下（p 0 类似于30 atm），H主要被消耗以形成氢过氧基（HO 2 ），导致从甲醛（CH 2 O）形成甲酰基（HCO）的瓶颈。相反，对于乙烯/空气点火，在低压和高压下都存在多个旁路路径，有助于直接从各种中间体形成 HCO 和 CO，这解释了 PAI 在压力下对乙烯具有更稳健的性能。(C) 2020 The Combustion Institute。由爱思唯尔公司出版。保留所有权利。
The ignition of methane/air and ethylene/air mixtures by nanosecond pulsed discharges (NSPD) is investigated numerically using a zero-dimensional isochoric adiabatic reactor. A combustion kinetics model is coupled with a non-equilibrium plasma mechanism, which features vibrational and electronic excitation, dissociation, and ionization of neutral particles (O 2 and N 2 ) via electron impact. A time to ignition metric ? is defined, and ignition simulations encompassing a wide range of pressures (0.5-30 atm) and pulsing conditions for each fuel are executed. For each fuel, it is found that tau depends primarily on initial pressure and energy deposition rate, and scaling laws are derived. In order to quantify the benefit gained from plasmaassisted ignition (PAI), tau is compared with a thermal ignition time. It is found that for both fuels, PAI leads to a faster ignition at low pressures, while at higher pressures ( p 0 >= 5 atm), methane/air ignition becomes inefficient (meaning a longer ignition time for the same input energy compared to thermal ignition). Ethylene/air PAI shows only a modest deterioration. The drop in performance with pressure is found to be due to the mean electron energy achieved during the pulse, which shows an inverse relationship with pressure, leading to fewer excited species and combustion radicals. The poor performance of methane/air mixture ignition at high pressure is explained by an analysis of the reaction pathways. At high pressures ( p 0 similar to 30 atm), H is consumed mostly to form hydroperoxyl (HO 2 ), leading to a bottleneck in the formation of formyl (HCO) from formaldehyde (CH 2 O). Instead, for ethylene/air ignition, at both low and high pressures there exist several bypass pathways that facilitate the formation of HCO and CO directly from various intermediates, explaining the more robust performance of PAI for ethylene at pressure.(C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.