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Interactions for flames in a coaxial flow with a stagnation point

机译：具有停滞点的同轴流中火焰的相互作用

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摘要

The possible burning structures existing in two co-flowing combustible mixtures with different compositions, and their implications to the field of turbulent combustion are examined in this study. A coaxial burner with a quartz plate was used to experimentally investigate the flames of methane/air and propane/air mixtures propagating in a coaxial flow impinging onto a stagnation surface. The possible burning structures were observed to be: (1) a single-flame (a lean or rich premixed flame); (2) a double-flame (two lean or rich premixed flames, or a rich premixed flame and a diffusion flame); and (3) a triple-flame (a rich premixed flame, a diffusion flame and a lean premixed flame). An inner (or outer) mixture, far beyond the flammability limit, can still burn if a stronger outer (or inner) flame supports it. The extinction limit of the top part of the inner hat-shaped premixed flame is nearly independent of the burning intensity of the outer flame. It was found that the inner flame has a wider flammable region than the outer flame, and that the latter has a narrower flashback region than the former. Both propane and methane flames may exhibit flame-front instability, although the former displays much more clearly than the latter. Cellular and polyhedral instabilities can exist individually or appear simultaneously in the inner flame. However, only polyhedral (stripped-pattern) instability was observed in the outer flame. Finally, the experiments were analyzed theoretically using a simple geometrical model incorporated with the numerical simulations. The predicted shapes and locations of the flames are in good agreement with the experimental observations qualitatively.
机译：在这项研究中，研究了两种不同成分的并流可燃混合物中可能存在的燃烧结构，及其对湍流燃烧领域的影响。使用带有石英板的同轴燃烧器来实验研究甲烷/空气和丙烷/空气混合物的火焰，它们在同轴流中传播并撞击到停滞表面。观察到可能的燃烧结构为：（1）单火焰（稀薄或浓的预混火焰）； （2）双重火焰（两个稀薄或浓的预混火焰，或浓的预混火焰和扩散火焰）； （3）三重火焰（浓预混火焰，扩散火焰和稀薄预混火焰）。如果内部（或外部）混合物有较强的外部（或内部）火焰支持，则其内部（或外部）混合物仍会燃烧，远远超过可燃极限。内帽形预混火焰顶部的消光极限几乎与外火焰的燃烧强度无关。发现内部火焰的可燃区域比外部火焰的可燃区域宽，而外部火焰的回火区域比外部火焰窄。丙烷和甲烷火焰都可能显示火焰前缘不稳定性，尽管前者比后者更清晰。细胞和多面体不稳定性可以单独存在，也可以同时出现在内部火焰中。但是，在外部火焰中仅观察到多面体（条纹状）不稳定性。最后，使用结合了数值模拟的简单几何模型从理论上对实验进行了分析。火焰的预测形状和位置在质量上与实验观察非常吻合。

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