Dagaut Philippe, Dayma Guillaume
CNRS, Laboratoire de Combustion et Systèmes Réactifs, 1C, Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France.
J Phys Chem A. 2006 Jun 1;110(21):6608-16. doi: 10.1021/jp054535w.
The mutual sensitization of the oxidation of NO and a natural gas blend (methane-ethane 10:1) was studied experimentally in a fused silica jet-stirred reactor operating at 10 atm, over the temperature range 800-1160 K, from fuel-lean to fuel-rich conditions. Sonic quartz probe sampling followed by on-line FTIR analyses and off-line GC-TCD/FID analyses were used to measure the concentration profiles of the reactants, the stable intermediates, and the final products. A detailed chemical kinetic modeling of the present experiments was performed yielding an overall good agreement between the present data and this modeling. According to the proposed kinetic scheme, the mutual sensitization of the oxidation of this natural gas blend and NO proceeds through the NO to NO2 conversion by HO2, CH3O2, and C2H5O2. The detailed kinetic modeling showed that the conversion of NO to NO2 by CH3O2 and C2H5O2 is more important at low temperatures (ca. 820 K) than at higher temperatures where the reaction of NO with HO2 controls the NO to NO2 conversion. The production of OH resulting from the oxidation of NO by HO2, and the production of alkoxy radicals via RO2 + NO reactions promotes the oxidation of the fuel. A simplified reaction scheme was delineated: NO + HO2 --> NO2 + OH followed by OH + CH4 --> CH3 + H2O and OH + C2H6 --> C2H5 + H2O. At low-temperature, the reaction also proceeds via CH3 + O2 (+ M) --> CH3O2 (+ M); CH3O2 + NO --> CH3O + NO2 and C2H5 + O2 --> C2H5O2; C2H5O2 + NO --> C2H5O + NO2. At higher temperature, methoxy radicals are produced via the following mechanism: CH3 + NO2 --> CH3O + NO. The further reactions CH3O --> CH2O + H; CH2O + OH --> HCO + H2O; HCO + O2 --> HO2 + CO; and H + O2 + M --> HO2 + M complete the sequence. The proposed model indicates that the well-recognized difference of reactivity between methane and a natural gas blend is significantly reduced by addition of NO. The kinetic analyses indicate that in the NO-seeded conditions, the main production of OH proceeds via the same route, NO + HO2 --> NO2 + OH. Therefore, a significant reduction of the impact of the fuel composition on the kinetics of oxidation occurs.
在一个运行于10个大气压的熔融石英喷射搅拌反应器中，在800 - 1160 K的温度范围内，从贫燃料到富燃料条件下，对一氧化氮（NO）与天然气混合物（甲烷 - 乙烷比例为10:1）氧化反应的相互敏化作用进行了实验研究。采用声波石英探针采样，随后进行在线傅里叶变换红外光谱（FTIR）分析和离线气相色谱 - 热导检测器/氢火焰离子化检测器（GC - TCD/FID）分析，以测量反应物、稳定中间体和最终产物的浓度分布。对本实验进行了详细的化学动力学建模，使得本实验数据与该建模结果总体上吻合良好。根据所提出的动力学方案，这种天然气混合物与NO氧化反应的相互敏化作用是通过HO₂、CH₃O₂和C₂H₅O₂将NO转化为NO₂来进行的。详细的动力学建模表明，在低温（约820 K）下，CH₃O₂和C₂H₅O₂将NO转化为NO₂的反应比在高温下更重要，在高温下NO与HO₂的反应控制着NO向NO₂的转化。HO₂氧化NO产生OH，以及RO₂ + NO反应生成烷氧基自由基，促进了燃料的氧化。描绘了一个简化的反应方案：NO + HO₂ --> NO₂ + OH，接着是OH + CH₄ --> CH₃ + H₂O和OH + C₂H₆ --> C₂H₅ + H₂O。在低温下，反应还通过CH₃ + O₂(+ M) --> CH₃O₂(+ M)；CH₃O₂ + NO --> CH₃O + NO₂以及C₂H₅ + O₂ --> C₂H₅O₂；C₂H₅O₂ + NO --> C₂H₅O + NO₂进行。在较高温度下，甲氧基自由基通过以下机制产生：CH₃ + NO₂ --> CH₃O + NO。后续反应CH₃O --> CH₂O + H；CH₂O + OH --> HCO + H₂O；HCO + O₂ --> HO₂ + CO；以及H + O₂ + M --> HO₂ + M完成整个反应序列。所提出的模型表明通过添加NO，甲烷与天然气混合物之间公认的反应活性差异显著降低。动力学分析表明，在添加NO的条件下，OH的主要生成途径相同，即NO + HO₂ --> NO₂ + OH。因此，燃料组成对氧化动力学的影响显著降低。
