Local flame structure and turbulent burning velocity by joint PLIF imaging
Local flame structure and turbulent burning velocity by joint PLIF imaging
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DOI：
10.1016/j.proci.2010.06.087
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
Kazuhiro Yamamoto;Shinji Isii;M. Ohnishi
中科院分区：
文献类型：
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作者：
Kazuhiro Yamamoto;Shinji Isii;M. Ohnishi
在这项研究中，我们通过联合PLIF成像，同时使用HCHO/OH-PLIF和正交的OH-PLIF测量来研究局部火焰结构。在考虑火焰起皱程度的基础上，从二维图像中获得了三维火焰表面积。我们使用旋风-喷射燃烧室建立了丙烷/空气混合物在较宽的湍流范围内的湍流预混火焰，覆盖了燃烧图上的火焰区和薄反应区区域。结果表明，随着燃烧室出口平均速度的增加，火焰结构更加复杂，出现多个小火焰。接近整体消光时，反应区的氢氧化峰浓度几乎为零，而预热区的甲醛浓度仍保持不变。结果，热释放率大幅降低，导致局部消光。由平均火焰形状决定的湍流燃烧速度随湍流的增大而增大，在薄反应区观察到弯曲效应。另一方面，与火焰周长不同，火焰表面积是线性增加的。由于皱纹火焰中的湍流燃烧速度用经典公式可以很好地预测，弯曲现象可以用局部燃烧速度的降低来解释。因此，在我们测量的框架内，即使在薄反应区区域，火焰面方法仍然有效。
In this study, we have examined local flame structure by joint PLIF imaging, using simultaneous HCHO/OH-PLIF and orthogonal OH-PLIF measurements. By considering the degree of flame wrinkling, three-dimensional flame surface area is obtained from 2D images. We have used a cyclone–jet combustor to establish turbulent premixed flames for propane/air mixtures in a wide range of turbulence, covering the flamelet regime and thin-reaction-zones regime on combustion diagram. Results show that as the mean velocity at the combustor exit is increased, more complex flame structure is observed with multiple flamelets. Near the global extinction, peak OH concentration in reaction zone becomes almost zero whereas HCHO concentration in preheat zone still remains. As a result, the large reduction of heat release rate occurs, resulting in local extinction. The turbulent burning velocity determined by the mean flame shape is increased with turbulence, and the bending effect is observed in thin-reaction-zones regime. On the other hand, different from the flame perimeter, the flame surface area is linearly increased. Since the turbulent burning velocity is well predicted by the classical formula in wrinkled flames, the bending is explained by the reduction of local burning velocity. Thus, within the frame work in our measurement, the flamelet approach could be still valid even in the thin-reaction-zones regime.