Flame behavior of horizontal propane jet fire in a pit

doi:10.11949/0438-1157.20211425

Abstract

Abstract:

A small-scale experimental device of jet fire in a pit was built, and experimental simulation was conducted to study the flame characteristics of horizontal propane jet fire caused by the leakage of pipeline buried underground. The flame is restricted by the side wall of the pit, first hits the tunnel and then develops upward along the side wall to form a vertical flame. The experimental results show that the flame length first increases and then decreases as the leakage mass flow rate increases, while the flame width continuously increases. In addition, vortex pairs, indicated by a pair of counter-rotating flames, were observed to appear on both lateral sides of the flame under critical conditions. In order to explore the formation mechanism of vortex pairs, the instability of flame flow field is further studied by numerical simulation.

Key words: pit, jet flame, flame length, flame width, instability, safety

摘要：

通过搭建坑道限制条件下小尺寸喷射火实验装置，模拟研究埋地管道泄漏场景中引发的水平喷射火火焰特性。火焰受坑道侧壁的限制，先撞击坑道而后沿着侧壁向上发展形成垂直火焰。实验结果表明，随着泄漏质量流量的增加，火焰长度先增加后减小，而火焰宽度不断增加。同时发现，在一定条件下火焰两侧会出现涡旋对，形成一对反向旋转的火焰，为了探究其形成原因及产生条件，结合数值模拟手段进一步研究了火焰流场不稳定性。

关键词: 坑道, 喷射火, 火焰长度, 火焰宽度, 不稳定性, 安全

CLC Number:

X 931

Mengya ZHOU, Kuibin ZHOU, Chao WANG, Mengyuan HUANG, Yifan WANG, Juncheng JIANG. Flame behavior of horizontal propane jet fire in a pit[J]. CIESC Journal, 2022, 73(2): 960-971.

周梦雅, 周魁斌, 王朝, 黄梦源, 王一凡, 蒋军成. 坑道限制条件下水平丙烷喷射火火焰行为研究[J]. 化工学报, 2022, 73(2): 960-971.

Figures/Tables 22

Fig.1 Schematic diagram of experimental device

Table 1 Experimental test conditions

d/mm	m_c/(g/s)	V/(m/s)	U/d
2.0	0.03~0.37	5~63	29.00
2.3	0.03~0.37	3~48	25.22
3.2	0.03~0.37	2~25	18.125

Fig.2 Flame geometry of jet fire in a pit

Fig.3 Test repeatability of jet fire in a pit justified by the time profiles

Fig.4 3D geometric model of simulation

Table 2 Number of computational grids for three different grid systems

Case	网格总数	网格平均质量	最大扭曲度
1	152451	0.83462	0.83
2	325001	0.83480	0.82
3	435349	0.83513	0.82

Fig.5 Comparison of simulation results of different grid numbers

Table 3 Initial conditions of simulation

工况	V/(m/s)	m_c/(g/s)	Re
1	8	0.12	2.2×10³
2	12	0.18	4.9×10³
3	16	0.24	8.7×10³
4	18	027	1.1×10⁴
5	20	0.31	1.4×10⁴

Fig.6 Comparison of instantaneous flame shape between experiment and simulation (mc = 0.12 g/s)

Fig.7 Comparison of flame length and flame width between experiment and simulation (d=3.2 mm)

Fig.8 Variation of flame length with mass flow rate under different nozzle diameters

Table 4 Critical Reynolds number of flow state

d/mm	层流阶段-过渡阶段			过渡阶段-完全湍流阶段
d/mm	m_c/(g/s)	V/(m/s)	Re	m_c/(g/s)	V/(m/s)	Re
2.0	0.12	19.57	8544	0.20	34.36	14758
2.3	0.12	16.05	8443	0.20	25.98	14184
3.2	0.16	12.22	8389	0.28	21.38	14499

Fig.9 Variation of dimensionless flame length with Froude number at nozzle exit

Fig.10 Variation of flame width with mass flow rate under different nozzle diameters

Fig.11 Variation of dimensionless flame width with Froude number at nozzle exit

Fig.12 Flame evolution process of special fire behavior （d = 3.2 mm, mc = 0.12 g/s）

Fig.13 Variation of flame shape with mass flow under different nozzle diameters

Fig.14 Evolution frequency of special fire behavior (d =3.2 mm)

Fig.15 Variation of temperature and velocity within 5 seconds along the X direction when mc=0.12 g/s

Fig.16 Variation of temperature and velocity with distance along the centerline of wall (or Y axis)

Fig.17 R-T instability in the flow field (mc = 0.12 g/s)

Fig.18 Variation of buoyancy and Richardson number with mass flow rate

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