Extreme role of preferential diffusion in turbulent flame propagation
Extreme role of preferential diffusion in turbulent flame propagation
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DOI：
10.1016/j.combustflame.2017.09.036
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发表时间：
2018-02
影响因子：
4.4
通讯作者：
Sheng Yang;A. Saha;W. Liang;Fujia Wu;C. Law
中科院分区：
文献类型：
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作者：
Sheng Yang;A. Saha;W. Liang;Fujia Wu;C. Law
在这篇文章中，我们论证了分子扩散在湍流火焰的结构和传播中的重要作用。我们首先证明了浓度接近或超过常规可燃极限的混合物可以在湍流中强烈燃烧，前提是混合物的控制分子质量扩散系数超过其热扩散系数，即混合物的Lewis数(Le)小于1。在这种情况下，相关的湍流火焰速度可能比相应的层流火焰速度大几个数量级，火焰表面具有独特的指状结构。此外，这种促进效应对于 -1混合物是完全反转的，导致湍流对其燃烧强度的名义上的增强作用实际上减弱了。从力学上讲，这种相反的效应是优先扩散和构成湍流火焰结构的褶皱小火焰片之间耦合的结果。
In this paper we demonstrate the essential role of molecular diffusion in the structure and propagation of turbulent flames. We first show that mixtures whose concentrations are near or beyond the conventional flammability limits can be rendered to burn strongly in turbulence, provided the controlling molecular mass diffusivity of the mixture exceeds its thermal diffusivity, namely the mixture Lewis number (Le) is less than unity. The associated turbulent flame speeds in such cases can be orders of magnitude greater than the corresponding laminar flame speeds, with distinctive finger-shape structures on the flame surfaces. Furthermore, this facilitation effect is completely flipped forLe> 1 mixtures, leading to actual weakening of the nominally enhancing effect of turbulence on their burning intensity. Mechanistically, such opposite effects are consequences of the coupling between preferential diffusion and the wrinkled laminar flamelets constituting the turbulent flame structure.