Abstract Internal structure of extremely turbulent flames is investigated experimentally using simultaneous planar laser-induced fluorescence of formaldehyde molecule and hydroxyl radical as well as stereoscopic particle image velocimetry. The mean bulk flow velocity is changed from 5 to 35 m/s. The fuel-air equivalence ratio is 0.7 for all tested conditions. Three different turbulence generating mechanisms leading to a wide range of turbulence intensity with the corresponding Reynolds and Karlovitz numbers ranging from 19 to 2729 and 0.3 to 76.0, respectively, are examined. Preheat and reaction zone thicknesses for the tested flames are calculated and compared with those of the laminar flame to quantify deviation from flamelet behavior. It is shown that the preheat and reaction zone thicknesses increase to values that are about 6.2 and 3.9 times the laminar flame counterparts, respectively. While broadening of the preheat zone is reported in the literature, broadening of the reaction zone for a relatively large diameter Bunsen burner is reported for the first time in this study. The broadening of the reaction zones is related to non-flamelet behavior of the tested flames, and a parameter proposed earlier by the authors is used to quantify this non-flamelet behavior. Swirling strength contours are overlaid on the cold reactants and preheat zones to study the reason for the reported broadening. The results show that positive correlations exist between the preheat/reaction zone thicknesses and the mean value of eddy swirling strength inside the reactants and preheat zone. These correlations as well as the estimated turbulent kinetic energy of these eddies suggest that energetic eddies may potentially penetrate into the preheat and reaction zones causing broadening of these zones.

中文翻译：

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非火焰湍流预混燃烧中的厚反应区

摘要 利用甲醛分子和羟基自由基的同步平面激光诱导荧光以及立体粒子图像测速法，对极度湍流火焰的内部结构进行了实验研究。平均体积流速从 5 变为 35 m/s。对于所有测试条件，燃料空气当量比为 0.7。研究了三种不同的湍流产生机制，它们导致了大范围的湍流强度，相应的雷诺数和卡洛维茨数分别从 19 到 2729 和 0.3 到 76.0 不等。计算测试火焰的预热和反应区厚度，并与层流火焰进行比较，以量化与小火焰行为的偏差。结果表明，预热区和反应区厚度增加到大约 6.2 和 3 的值。分别是层流火焰对应物的 9 倍。虽然文献中报道了预热区的加宽，但本研究首次报道了相对大直径本生灯的反应区的加宽。反应区的加宽与测试火焰的非火焰行为有关，作者早先提出的参数用于量化这种非火焰行为。涡流强度等高线覆盖在冷反应物和预热区上，以研究所报告的变宽的原因。结果表明，预热/反应区厚度与反应物和预热区内涡旋强度的平均值之间存在正相关关系。