Towards the distributed burning regime in turbulent premixed flames
Towards the distributed burning regime in turbulent premixed flames
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DOI：
10.1017/jfm.2019.316
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发表时间：
2018-06
影响因子：
3.7
通讯作者：
A. Aspden;M. Day;J. Bell
中科院分区：
文献类型：
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作者：
A. Aspden;M. Day;J. Bell
典型的统计稳定，统计平面湍流火焰的三维数值模拟已被用来在试图产生分布燃烧贫甲烷和氢气火焰。在整个火焰中的扩散意味着需要非常大的Karlovitz数;即使在研究的湍流的极端水平（高达8767的Karlovitz数），分布燃烧也仅在氢的情况下实现。在这种情况下，发现湍流在视觉上将反应区加宽了大约一个数量级，并且没有观察到热扩散效应（通常存在于贫氢火焰中）。在预热区，物种的组成有很大的不同，从一维火焰的基础上的一些不同的传输模型（混合物平均，单位刘易斯数和湍流涡粘度模型）。这种行为是湍流主导非统一刘易斯数物种传输的一个特征，而这种明显的限制又归因于膨胀及其对湍流的影响。峰值局部反应速率被发现是较低的分布的情况下比在较低的Karlovitz的情况下，但高于层流火焰，这是由于从修改后的燃料温度分布，结果从湍流混合占主导地位的低刘易斯数热扩散效应所产生的影响。最后，在可实现的条件下，实现分布式燃烧的方法进行了讨论，增加实现分布式燃烧的可能性的因素是较高的压力，较低的当量比，较高的刘易斯数和较低的反应物温度。
Three-dimensional numerical simulations of canonical statistically steady, statistically planar turbulent flames have been used in an attempt to produce distributed burning in lean methane and hydrogen flames. Dilatation across the flame means that extremely large Karlovitz numbers are required; even at the extreme levels of turbulence studied (up to a Karlovitz number of 8767) distributed burning was only achieved in the hydrogen case. In this case, turbulence was found to broaden the reaction zone visually by around an order of magnitude, and thermodiffusive effects (typically present for lean hydrogen flames) were not observed. In the preheat zone, the species compositions differ considerably from those of one-dimensional flames based a number of different transport models (mixture averaged, unity Lewis number and a turbulent eddy viscosity model). The behaviour is a characteristic of turbulence dominating non-unity Lewis number species transport, and the distinct limit is again attributed to dilatation and its effect on the turbulence. Peak local reaction rates are found to be lower in the distributed case than in the lower Karlovitz cases but higher than in the laminar flame, which is attributed to effects that arise from the modified fuel-temperature distribution that results from turbulent mixing dominating low Lewis number thermodiffusive effects. Finally, approaches to achieve distributed burning at realisable conditions are discussed; factors that increase the likelihood of realising distributed burning are higher pressure, lower equivalence ratio, higher Lewis number and lower reactant temperature.