A Comparison of the Blow-Off Behaviour of Swirl-Stabilized Premixed, Non-Premixed and Spray Flames
A Comparison of the Blow-Off Behaviour of Swirl-Stabilized Premixed, Non-Premixed and Spray Flames
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DOI：
10.1007/s10494-013-9470-z
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发表时间：
2013-09-01
影响因子：
2.4
通讯作者：
Mastorakos, Epaminondas
中科院分区：
文献类型：
--
作者：
Cavaliere, Davide E.;Kariuki, James;Mastorakos, Epaminondas
使用 OH* 化学发光和 OH-PLIF 在 5 kHz 下操作，在接近吹出极限和消光瞬态期间，对稳定在方形外壳中的轴对称钝体上的受限短湍流旋流预混和非预混甲烷和庚烷喷雾火焰进行了检查。通过比较同一基本空气动力场中不同规范类型的火焰，可以深入了解相对的吹灭行为。已经检查了火焰结构是否越来越接近吹灭的条件。可以看到，在稳定燃烧条件下，预混合火焰从圆柱形发生变化，火焰刷在接近吹灭的条件下关闭穿过流动。 PLIF图像显示，对于气态非预混火焰，随着接近吹灭条件，沿着火焰片出现孔洞的频率增加，而对于喷射火焰，这种趋势不太明显。非预混合和喷射火焰显示出随机发生的升空，这是局部灭绝的进一步证据。平均升空高度随着燃料喷射速度的增加而增加，并随着空气速度的增加而减少，并且在吹灭条件之前接近零（即火焰实际上附着），尽管随着接近熄灭，火焰片中明显有更多的孔。结果发现，当用特征流动时间 d/U (b)（d 是钝体直径，U (b) 是体积速度）标准化时，喷吹事件的平均持续时间在 9-38 范围内，其中喷雾火焰熄灭持续的时间比气态火焰短。最后，发现基于 Damkohler 数的相关性以合理的精度破坏了所有火焰的吹出速度数据。结果可以帮助开发先进的湍流燃烧模型。
Confined short turbulent swirling premixed and non-premixed methane and heptane spray flames stabilized on an axisymmetric bluff body in a square enclosure have been examined close to the blow-off limit and during the extinction transient with OH* chemiluminescence and OH-PLIF operated at 5 kHz. The comparison of flames of different canonical types in the same basic aerodynamic field allows insights on the relative blow-off behaviour. The flame structure has been examined for conditions increasingly closer to blow-off. The premixed flame was seen to change from a cylindrical shape at stable burning condtions, with the flame brush closing across the flow at conditions close to blow-off. The PLIF images show that for the gaseous non-premixed flame, holes appear along the flame sheet with increasing frequency as the blow-off condition is approached, while the trend is less obvious for the spray flame. Non-premixed and spray flames showed randomly-occurring lift-off, which is further evidence of localised extinction. The mean lift-off height increased with increasing fuel jet velocity and decreased with increasing air velocity and approaches zero (i.e. the flame is virtually attached) just before the blow-off condition, despite the fact that more holes were evident in the flame sheet as extinction was approached. It was found that the average duration of the blow-off event, when normalised with the characteristic flow time d/U (b) (d being the bluff-body diameter and U (b) the bulk velocity) was in the range 9-38 with the spray flame extinction lasting a shorter time than the gaseous flames. Finally, it was found that correlations based on a Damkohler number collapse the blow-off velocity data for all flames with reasonable accuracy. The results can help the development of advanced turbulent combustion models.