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首页> 外文期刊>Combustion Science and Technology >CHARACTERIZATION OF THE LOCAL FLAME STRUCTURE AND THE FLAME SURFACE DENSITY FOR FREELY PROPAGATING PREMIXED FLAMES AT VARIOUS LEWIS NUMBERS
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CHARACTERIZATION OF THE LOCAL FLAME STRUCTURE AND THE FLAME SURFACE DENSITY FOR FREELY PROPAGATING PREMIXED FLAMES AT VARIOUS LEWIS NUMBERS

机译：自由传播各种路易斯数的预混合火焰的局部火焰结构和火焰表面密度的表征

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摘要

The local flame structure and the flame surface density for freely propagating premixed turbulent flames are measured by laser sheet tomography and image processing techniques. Different fuel/air mixtures (methane, propane, and hydrogen) have been successively spark-ignited at atmospheric pressure in order to evaluate the influence of thermodiffusive effects characterized by the Lewis number, at quasi-constant ratio μ′/S_L~0. From the instantaneous flame front positions and the mono-dimensional mean progress variable distribution, spatial statistics including the turbulent flame brush, the mean orientation factors, and the components of the normal vector to the flame front have been characterized and compared with numerical and experimental results available in the literature. The temporal evolution of the flame surface density was also determined by several approaches and analyzed in terms of maximum flame surface density evolution and location of maximum flame surface density. It clearly appears that the maximum flame surface density decreases as the flame propagates and remains independent of the Lewis number in the space. The influence of the turbulence level μ′/S_L~0 on the maximum flame surface density is also presented and compared with various results available in the literature. The peak location is a little less than the symmetrical value = 0.5, and increases slightly as the flame propagates. An estimation of the Bray number, N_B, which characterizes the nature of the diffusion by turbulence (gradient or counter-gradient), is also proposed in order to characterize the turbulent flux of (or Σ).
机译：自由传播的预混湍流火焰的局部火焰结构和火焰表面密度通过激光断层扫描和图像处理技术进行测量。不同的燃料/空气混合物（甲烷，丙烷和氢气）已在大气压下连续火花点火，以便在近似恒定比率μ'/ S_L〜0下评估以Lewis数为特征的热扩散效应的影响。从瞬时火焰前沿位置和一维平均进度变量分布，表征了包括湍流火焰刷，平均取向因子和火焰前沿法向矢量分量在内的空间统计量，并将其与数值和实验结果进行了比较在文献中可用。火焰表面密度的时间演变也通过几种方法确定，并根据最大火焰表面密度的演变和最大火焰表面密度的位置进行了分析。显然，最大火焰表面密度随着火焰的传播而降低，并且保持独立于空间中的路易斯数。还提出了湍流度μ'/ S_L〜0对最大火焰表面密度的影响，并将其与文献中可获得的各种结果进行了比较。峰值位置略小于对称值 = 0.5，并且随着火焰的传播而略有增加。为了表征（或Σ）的湍流，还提出了对布雷数N_B的估计，该估计通过湍流（梯度或反梯度）来表征扩散的性质。

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