Experimental study of lean flammability limits of methane/hydrogen/air mixtures in tubes of different diameters
Experimental study of lean flammability limits of methane/hydrogen/air mixtures in tubes of different diameters
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DOI：
10.1016/j.expthermflusci.2009.10.027
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发表时间：
2010-04
影响因子：
3.2
通讯作者：
Y. Shoshin;L. D. Goey
中科院分区：
文献类型：
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作者：
Y. Shoshin;L. D. Goey
对甲烷/氢气/空气混合物在内径为6.0、8.9、12.3、18.4、25.2、35.0和50.2mm的管道中传播的贫燃极限火焰进行了实验研究。火焰从管的开口底端向上传播到封闭的上端。燃料气体中的氢含量在0- 40mol%的范围内变化。贫油可燃极限已经确定，火焰形状记录和火焰传播的可见速度测量。在直径为8.9-18.4mm的管道中，所观察到的极限火焰多为封闭形状，可表征为扭曲或球形火焰球。氢含量较高的混合物在较宽的管径范围内形成较小、较均匀的火焰球。当燃气中氢含量大于等于20%时，最大直径（35.0 mm和50.2 mm ID）管中的极限火焰与管直径相比较小，尺寸为“透镜”形。“常规”前开式倾斜极限火焰仅在最小直径（6.0 mm和8.9 mm）和最大直径（35.0和50.2 mm ID）下观察到，并且仅在甲烷/空气和（90%CH4 + 10%H2）/空气混合物下观察到，除了6 mm ID管中所有极限火焰都具有前开式。在所有的实验中，除了在8.9mm ID管中的甲烷/空气和（90%CH4 + 10%H2）/空气混合物中的贫极限火焰，以及在6.0mm ID管中的所有极限火焰之外，可见火焰速度非常弱地依赖于燃料气体中的氢含量，并且接近或低于上升热泡速度的理论估计。这一观察结果表明，浮力是决定所研究的极限火焰的可见火焰速度的主要因素，除了最后提到的。对于内径在18.4-50.2mm范围内的甲烷/空气和（90%CH_4 + 10%H_2）/空气混合物，观察到贫燃极限值随管径减小而减小。这种效应是由于在较窄的管道中，对于类似于上升气泡的火焰，优先扩散和火焰拉伸的综合效应更强。
Lean limit flames in methane/hydrogen/air mixtures propagating in tubes of internal diameters (ID) of 6.0, 8.9, 12.3, 18.4, 25.2, 35.0, and 50.2mm have been experimentally studied. The flames propagated upward from the open bottom end of the tube to the closed upper end. The content of hydrogen in the fuel gas has been varied in the range 0–40mol%. Lean flammability limits have been determined; flame shapes recorded and the visible speed of flame propagation measured. Most of the observed limit flames in tubes with diameters in the range of 8.9–18.4mm had enclosed shape, and could be characterized as distorted or spherical flame balls. The tendency was observed for mixtures with higher hydrogen content to form smaller size, more uniform flame balls in a wider range of tube diameters. At hydrogen content of 20% or more in the fuel gas, limit flames in largest diameters (35.0mm and 50.2mm ID) tubes had small, compared to the tube diameter, size and were “lens”-shaped. “Regular” open-front lean limit flames were observed only for the smallest diameters (6.0mm and 8.9mm) and largest diameters (35.0 and 50.2mm ID), and only for methane/air and (90% CH4+10% H2)/air mixtures, except for 6mm ID tube in which all limit flames had open front. In all experiments, except for the lean limit flames in methane/air and (90% CH4+10% H2)/air mixtures in the 8.9mm ID tube, and all limit flames in 6.0mm ID tube, visible flame speeds very weakly depended on the hydrogen content in the fuel gas and were close to- or below the theoretical estimate of the speed of a rising hot bubble. This observation suggests that the buoyancy is the major factor which determines the visible flame speed for studied limit flames, except that last mentioned. A decrease of the lean flammability limit value with decreasing the tube diameter was observed for methane/air and (90% CH4+10% H2)/air mixtures for tubes having internal diameters in the range of 18.4–50.2mm. This effect has been attributed to the stronger combined effect of the preferential diffusion and flame stretch in narrower tubes for flames which resemble rising bubble.