Analysis of chemical pathways and flame structure for n-dodecane/air turbulent premixed flames
Analysis of chemical pathways and flame structure for n-dodecane/air turbulent premixed flames
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DOI：
10.1016/j.combustflame.2019.05.026
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发表时间：
2019-09
影响因子：
4.4
通讯作者：
D. Dasgupta;Wenting Sun;M. Day;A. Aspden;T. Lieuwen
中科院分区：
文献类型：
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作者：
D. Dasgupta;Wenting Sun;M. Day;A. Aspden;T. Lieuwen
本文分析了十二烷-空气火焰的湍流化学相互作用，重点关注湍流火焰相对于其相应的层流火焰的火焰结构和燃料氧化途径的变化程度。这项工作基于 Aspden 等人的精益 (phi= 0.7)n-十二烷-空气火焰 DNS 数据库。 （2017）。在不同的湍流强度下检查释放热量和产生/消耗自由基的主要反应的相对作用，并与逆流火焰和完美搅拌反应器的拉伸火焰计算进行比较。这些结果表明，空间整合的化学路径对湍流强度相对不敏感，并且模仿拉伸火焰的行为。换句话说，给定反应对热量释放或自由基产生的贡献（整合到整个火焰中）对湍流不敏感。还进行了以火焰拓扑特征和温度为条件的局部分析。前一分析表明，较大的路径变化发生在火焰的正弯曲区域。最重要的是，它表明火焰的热结构发生了变化，因为随着卡洛维茨数的增加，低温（即低于 1200K）区域的峰值反应速率和热量释放向更高的温度转移。鉴于先前对较轻燃料（例如氢气）的研究显示出相反的行为，这一结果特别有趣。进行了各种具有改变的传输效应的拉伸、层流火焰计算以供参考。这些计算使用混合平均 andLe=1 传输模型，可以捕获层流火焰中随着拉伸增加而向更高温度的类似转变。然而，必须调整拉伸速率和传输值以不同地匹配热结构中的这些变化，具体取决于反应、物种和Ka值。这种效应对于低温物种尤其突出。因此，这些结果表明，火焰并不像之前所建议的那样简单地转变为具有高湍流强度的 aLe=1 热结构，而且改变的标量扩散率和拉伸效应之间存在相互作用。
This paper analyzes turbulence-chemistry interactions of ann-dodecane-air flame, focusing on the degree to which flame structure and fuel oxidation pathways change in turbulent flames relative to their corresponding laminar flames. This work is based on a lean (ϕ= 0.7)n-dodecane-air flame DNS database from Aspden et al. (2017). The relative roles of dominant reactions that release heat and produce/consume radicals are examined at various turbulence intensities and compared with stretched flame calculations from counterflow flames and perfectly stirred reactors. These results show that spatially integrated chemical pathways are relatively insensitive to turbulence intensity and mimic the behavior of stretched flames. In other words, the contribution of a given reaction to heat release or radical production, integrated over the entire flame, is insensitive to turbulence. Localized analysis conditioned on topological feature of the flame and on temperature is also performed. The former analysis reveals that larger alteration of pathways occurs in the positively-curved regions of the flame. Most significantly, it shows that the thermal structure of the flame is altered, as peak reaction rates and heat release in the low temperature (i.e., below 1200 K) region shift towardshighertemperatures with increases in Karlovitz number. This result is particularly interesting given that prior work with lighter fuels (e.g., hydrogen) showed the opposite behavior. Various stretched, laminar flame calculations with altered transport effects were performed for reference. These calculations, using mixture-averaged andLe= 1 transport model, can capture similar shifts towards higher temperatures in laminar flames with increasing stretch. However, the stretch rate and transport values must be tuned to match these shifts in thermal structure differently, depending upon reactions, species, andKavalue. This effect is particularly prominent for low temperature species. Thus, these results show that flames do not simply shift to aLe= 1 thermal structure with high turbulence intensity, as previously suggested, but there is interplay between altered scalar diffusivity and stretch effects.