Towards a kinetic understanding of the NOx promoting-effect on ignition of coalbed methane: A case study of methane/nitrogen dioxide mixtures
Towards a kinetic understanding of the NOx promoting-effect on ignition of coalbed methane: A case study of methane/nitrogen dioxide mixtures
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对 NOx 对煤层气着火的促进作用的动力学理解：甲烷/二氧化氮混合物的案例研究
DOI：
10.1016/j.fuel.2016.04.090
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发表时间：
2016-05
期刊：
影响因子：
7.4
通讯作者：
Huang Zuohua
中科院分区：
文献类型：
--
作者：
Deng Fuquan;Yang Feiyu;Zhang Peng;Pan Youshun;Bugler John;Curran Henry J.;Zhang Yingjia;Huang Zuohua
二氧化氮（NO2）是煤层气中的重要杂质，也是实际发动机NOx污染的主要成分。本文通过实验和动力学研究，研究了它对甲烷着火的促进作用。在激波管中测量了NO2/CH 4/O2/Ar混合气体的点火延迟时间，其中NO2：CH 4的混合比分别为30：70、50：50和70：30。实验涵盖了一系列的压力（1.2-10.0大气压）和温度（933-1961 K）。在所有压力下，NO2的加入均促进了甲烷的反应活性，降低了甲烷的反应活化能，且在最高压力和最低温度下，NO2浓度最高的混合物的反应活性最强.为了模拟实验测量，将五个文献NOx子机制与AramcoMech 1.3集成。模拟结果表明，对于低NOx浓度的混合气，五种模型的着火延迟时间与实验结果吻合较好。然而，对于高NOx含量的混合物，所有五种模型都不能再现实测数据，并且随着NO2浓度的增加，模型的不一致程度也增加。提出了一种更新的机制，根据修改的灵敏度和反应通量进行分析，以定量确定NO 2促进甲烷点火的化学原因。结果表明，在甲烷氧化点火初期，NO2的加入通过影响自由基池的结构，干扰了关键反应途径的分支比.提出了一个新的反应循环来解释添加NO2对甲烷着火的促进作用，该循环的反应顺序为：H3 + NO2惠CH 3 O + NO，CH 3 O惠CH 2 O+ H2 + M，NO2+惠NO+ O惠H，CH 4+ O惠H3 + H2O.
Nitrogen dioxide (NO 2) is an important impurity in coal-bed methane (CBM) and a dominant component of NO x pollution in practical engines. Its promoting effect on methane ignition has been studied in the current experimental and kinetic study. Ignition delay times of NO 2/CH 4/O 2/Ar mixtures, with blending ratios of NO 2: CH 4 of 30: 70, 50: 50 and 70: 30 for stoichiometric methane mixtures were measured in a shock tube. Experiments cover a range of pressures (1.2–10.0 atm) and temperatures (933–1961 K). Under all tested pressures, NO 2 addition promotes the reactivity of methane and reduces the global activation energy at all pressures, and these effects are most significant for the mixtures with highest NO 2 concentrations, at the highest pressures and at the lowest temperatures. To simulate the experimental measurements, five literature NO x sub-mechanisms were integrated with AramcoMech 1.3. The simulations demonstrate that, for the mixtures with low levels of NO x concentrations, the five models agree well with the experimental ignition delay times. For the mixtures with high NO x content, however, all five models are unable to reproduce the measured data, and the level of disagreement increases with increasing NO 2 concentration. An updated mechanism is proposed, based on modifications made as a result of sensitivity and reaction flux analyses performed to quantitatively determine the chemical reasons for NO 2 promoting methane ignition. The results indicate that, NO 2 addition perturbs the branching ratio of key reaction pathways by affecting the structure of the free radical pool at the initial ignition stage of methane oxidation. A new reaction cycle via the following sequence of reactions ĊH 3+ NO 2⇔ CH 3 O ̇+ NO, CH 3 O ̇+ M⇔ CH 2 O+ Ḣ+ M, NO 2+ Ḣ⇔ NO+ O ̇ H, and CH 4+ O ̇ H⇔ ĊH 3+ H 2 O is proposed to explain the observed effect of NO 2 addition on the promotion of methane ignition.
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