Damköhler number effects on soot formation and growth in turbulent nonpremixed flames
Damköhler number effects on soot formation and growth in turbulent nonpremixed flames
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Damköhler 数对湍流非预混火焰中烟灰形成和生长的影响
DOI：
10.1016/j.proci.2014.05.084
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发表时间：
2013
影响因子：
1.5
通讯作者：
H. Pitsch
中科院分区：
文献类型：
--
作者：
A. Attili;F. Bisetti;M. Mueller;H. Pitsch
本文通过大尺度直接数值模拟方法研究了三种不同Damköhler数、雷诺数为15，000的三维正庚烷/空气射流火焰中Damköhler数对湍流非预混碳烟生成火焰的影响。一个减少的化学机制，其中包括烟尘前体萘，和高阶矩量法。在最高的Damköhler数，局部消光是可以忽略不计的，而火焰孔观察到的两个最低Damköhler数的情况下。与温度和燃料氧化化学控制的其他物种相比，萘被发现受到达姆科勒数的影响更显着。因此，总的碳烟质量分数减少了一个数量级以上的四倍减少的达姆克勒数。相反，在三种情况下，碳烟颗粒的总体数密度大致相同，但其在混合分数空间中的分布是不同的。总烟尘质量增长率被发现是成比例的Damköhler数。在两个最低Da数的情况下，观察到穿过火焰的烟灰泄漏。利用拉格朗日统计，得出的结论是，烟灰泄漏是由于补丁的烟灰，通过火焰孔穿过化学计量表面。这些结果显示了湍流混合在控制湍流火焰中碳烟动力学中的主导作用。
The effect of Damköhler number on turbulent nonpremixed sooting flames is investigated via large scale direct numerical simulation in three-dimensionaln-heptane/air jet flames at a jet Reynolds number of 15,000 and at three different Damköhler numbers. A reduced chemical mechanism, which includes the soot precursor naphthalene, and a high-order method of moments are employed. At the highest Damköhler number, local extinction is negligible, while flames holes are observed in the two lowest Damköhler number cases. Compared to temperature and other species controlled by fuel oxidation chemistry, naphthalene is found to be affected more significantly by the Damköhler number. Consequently, the overall soot mass fraction decreases by more than one order of magnitude for a fourfold decrease of the Damköhler number. On the contrary, the overall number density of soot particles is approximately the same, but its distribution in mixture fraction space is different in the three cases. The total soot mass growth rate is found to be proportional to the Damköhler number. In the two lowest Da number cases, soot leakage across the flame is observed. Leveraging Lagrangian statistics, it is concluded that soot leakage is due to patches of soot that cross the stoichiometric surface through flame holes. These results show the leading order effects of turbulent mixing in controlling the dynamics of soot in turbulent flames.