甲基过氧自由基对氨和氨氧自由基氢提取反应动力学计算

Kinetics Study of H-Atom Abstractions from NH3 and H2NO by CH3Ȯ2

摘要

在新型燃烧概念兴起及氨作为能源载体日益普及的背景下，氨的低温化学及其与碳氢化合物相互作用成为掺氨燃料燃烧反应动力学中的关键科学问题。碳一氮（C- N）交叉反应对氨与碳氢燃料混合燃烧特性具有重要影响。针对 NH₃/CH₄ 混合物中低温点火特性，研究了甲基过氧自由基 $\left(\mathrm{CH}_{3} \dot{\mathrm{O}}_{2}\right)$从氨（NH₃）和氨氧自由基（H₂NO）中提取氢原子的两条 C-N 相互作用反应路径的动力学。基于 M06-2X/6-311++G(d,p) 理论水平优化几何结构并计算转-振动性质，采用 CASPT2 方法结合不同基组确定反应能垒，通过过渡态理论计算了 298.15∼2000 K 温度范围内的速率常数.将这两条反应路径及其速率常数引人 NH₃/CH₄ 动力学模型研究其对模型预测的影响.结果表明，$\mathrm{NH}_{3}+\mathrm{CH}_{3} \dot{\mathrm{O}}_{2} \rightleftharpoons \dot{\mathrm{~N}} \mathrm{H}_{2}+\mathrm{CH}_{3} \mathrm{O}_{2} \mathrm{H}$显著缩短了混合物低温点火延迟时间，而 $\mathrm{H}_{2} \mathrm{NO}+\mathrm{CH}_{3} \dot{\mathrm{O}}_{2} \rightarrow \mathrm{HNO}+\mathrm{CH}_{3} \mathrm{O}_{2} \mathrm{H}$ 影响相对较小。

Abstract

Understanding the low-temperature chemistry of ammonia（NH₃）and its interaction with hydrocarbon chemistry is a significant challenge in the kinetics of ammonia blended fuel combustion，especially with the grow-ing interest in novel combustion concepts and the increasing use of NH₃ as an energy carrier.Carbon-nitrogen（C -N）interactions play an important role in the combustion characteristic of NH₃ blends with hydrocarbon fuels.In this work，the kinetics of two possible C-N interaction reactions， H -atom abstractions from NH₃ and aminoxyl radical (H₂NO) by methylperoxy radical $\left({\mathrm{C}\mathrm{H}}_{3}{\dot{\mathrm{O}}}_{2}\right)$，is investigated.These reaction pathways show some sensitiv--ity to the low-temperature ignition of NH₃/CH₄.However，they have not been considered in any combustion kinetic models so far.Due to the intrinsic multi-reference nature of their transition states，the energy barriers for the two reactions are determined using the CASPT2/aug-cc-pVTZ method with the active space of（7e，7o），and CASPT2/cc-pVDZ method with the active space of (14e,12o)，respectively，based on the optimized geometries and rovibrational properties obtained at M06-2X/6-311＋＋G（d，p）level of theory.The rate constants for the two reac-tions in the temperature range 298.15-2000 K are calculated by using transition state theory.By incorporating these two reaction pathways with our calculated rate constants into a NH₃/CH₄ kinetic model，the predicted low-temperature ignition delay times（IDT）of NH₃/CH₄ mixtures become noticeably shorter.

关键词

氨 / 甲基过氧自由基 / 燃烧反应动力学 / 氢提取反应 / 多参考态

Key words

ammonia / $\mathrm{CH}_{3} \dot{\mathrm{O}}_{2}$ / combustion reaction kinetics / H -atom abstraction / multi-reference

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基金资助

国家自然科学基金国际合作项目(W2411043)