Quasi-steady combustion of normal-alkane droplets supported by Cool-Flame chemistry near diffusive extinction
Quasi-steady combustion of normal-alkane droplets supported by Cool-Flame chemistry near diffusive extinction
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DOI：
10.1080/13647830.2019.1588380
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发表时间：
2019-03
影响因子：
1.3
通讯作者：
F. Williams;V. Nayagam
中科院分区：
文献类型：
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作者：
F. Williams;V. Nayagam
两个稳态化学动力学近似被引入到最新的圣地亚哥正庚烷机理的明显最相关的五个冷火焰步骤中，并由第六步骤补充，该第六步骤被选择用于捕获热火焰化学对该机理中的冷火焰的影响，为了获得一个有效的四步化学动力学描述，以解决正构烷烃液滴在低级-负温度系数（NTC）范围的温度部分，在那里观察到冷火焰熄灭发生。并行的经典活化能渐近（AEA）分析的部分燃烧制度，伴随着一个分布式反应的近似描述的发展，然后追求作出预测的燃烧过程中，占大刘易斯数的燃料和中间物种的第一次。的预测进行了比较，在国际空间站（ISS）进行的液滴燃烧实验的结果，理论和实验之间的合理协议，并指出一些需要未来的改进率参数的值。此外，该理论首次预测了正构烷烃液滴燃烧的极限氧指数（LOI），例如，对于在正常室温下在氧-氮混合物中燃烧的庚烷，在环境大气中相应的氧摩尔分数约为0.10，低于该氧摩尔分数不能发生冷火焰支持的燃烧。
Two steady-state chemical-kinetic approximations are introduced into the apparently most relevant five cool-flame steps of the latest San Diego mechanism for n-heptane, supplemented by a sixth step chosen to capture the influence of hot-flame chemistry on the cool flame in that mechanism, in order to obtain an effectively four-step chemical-kinetic description for addressing quasi-steady combustion of normal-alkane droplets in the lower-temperature part of the negative-temperature-coefficient (NTC) range, where cool-flame extinction is observed to occur. A development paralleling the classical activation-energy-asymptotic (AEA) analysis of the partial-burning regime, accompanied by an approximate description of a distributed reaction, is then pursued to make predictions of the combustion process, accounting for the large Lewis numbers of the fuel and intermediate species for the first time. The predictions are compared with results of droplet-combustion experiments performed in the International Space Station (ISS), showing reasonable agreement between theory and experiment and pointing to some needed future improvements in values of rate parameters. In addition, the theory predicts, for the first time, a limiting oxygen index (LOI) for droplet combustion of normal alkanes, giving, for example, for heptane burning in oxygen-nitrogen mixtures at normal room temperature, a corresponding oxygen mole fraction on the order of 0.10 in the ambient atmosphere, below which cool-flame-supported combustion cannot occur.