Visualization experimental research of oil gas vapor cloud deflagration in large-scale unconfined space
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摘要: 为探究大尺度开敞空间油气爆燃动态发展过程，利用自行设计并搭建的大尺度开敞空间油气爆燃模拟实验条件测试系统，通过可视化监测手段及对压力与火焰信号的采集获得了油气爆燃过程中关键参数的变化规律。结果表明：在不同的初始油气浓度下引燃预混油气混合物将形成三类主要的燃烧模式；油气浓度接近爆炸极限范围内时火焰主要分布于台架的内场、点火面后方及正上方，根据动态超压时序发展曲线可将爆燃过程划分为3个子阶段；爆燃火焰传播速度呈波动性下降趋势，并可与超压发展阶段相互耦合；随着初始油气浓度的增加，超压峰值呈现出先减后增的趋势，形成峰值耗时则呈现相反规律；爆燃火焰的温度梯度与火焰行进方向相关，火焰峰面温度梯度通常小于尾端火焰；爆燃辐射峰值形成时间与火焰强度相比具有一定的延时性，爆燃传播末期更易于形成高强度辐射。Abstract: An oil-gas deflagration simulation experimental condition system in the large-scale unconfined space was independently designed and built against the theoretical requirements for safety monitoring and controlling of oil-gas mixture explosions in large-scale unconfined spaces. To begin with, pressure and flame signals, variations in global temperature and radiation indicators in various areas of the system were accurately collected through sensors, thermal imagers and radiometers. Also, high-speed cameras were adopted to capture the dynamic development of flames during deflagration, acquiring specific behavior characteristics of flame shape. The results show that the oil-gas combustion modes in the unconfined space can be divided into fireless gas cloud firing, oil-gas combustion with open flame, and oil-gas deflagration with compression wave, according to the differences in initial oil-gas concentration. To be specific, the flame generated from oil-gas deflagration is in the mirror-image shape of “L”, which can be found in the infield of the bench as well as behind and right above the ignition surface. Moreover, several peaks can be found in the dynamic overpressure sequence development curve. Based on the peak type, the whole deflagration process can be partitioned into stable spread, flame bleeding, and burning collapse. Specifically, the high-intensity area of deflagration flame could be primarily observed at the 1/3 to 2/3 of the bench, with the peak reaching up to 4816.03 mV. It can be observed that the flame is principally presented in blue and orange, and the flame speed is downward in fluctuation along with the deflagration process. It can also be coupled with the overpressure development stage. After that, the overpressure peak is presented in a trend of first decreasing and then increasing along with the increase in the initial oil-gas concentration, whereas time consumed in peak forming is displayed in an opposite law. Note that both can fitted using the cubic polynomial. Besides, temperature gradient of deflagration flames is associated with the flame heading, and the temperature gradient of the flame front surface is typically smaller than that of the tail flame. What’s more, the formation time of radiation peak of deflagration has a certain delay in comparison to the flame intensity, causing that high-intensity radiation can be easily formed at the end of deflagration spreading. To sum up, key parameter supports and theoretical bases are provided for the online monitoring and explosion suppression of oil gas cloud deflagration in the large-scale unconfined space, presenting a significance in guiding the research and development of explosion suppression equipment.
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图 6 典型开敞空间油气爆燃进程
Figure 6. Deflagration process of gasoline in typical unconfined space
图 9 爆燃内场不同峰值对应时刻的火焰形态
Figure 9. Internal flame morphology corresponding to different peak values
图 11 爆燃外场不同峰值对应时刻的火焰形态
Figure 11. External flame morphology corresponding to different peak values
图 13 爆燃高位不同峰值对应时刻的火焰形态
Figure 13. High ground flame morphology corresponding to different peak values
图 14 不同油气浓度下超压峰值和到达峰值耗时分布
Figure 14. Overpressure peaks & time to reach peaks under different concentrations
图 15 火焰传播速度（2 L,
$\varphi$ =1.34%）Figure 15. Flame propagation velocity (2 L,
$\varphi$ =1.34%)
图 16 三个时刻点对应火焰传播形态
Figure 16. Three moments corresponding to the flame propagation pattern
图 17 火焰强度发展过程（2 L,
$\varphi$ =1.34%）Figure 17. Flame intensity-time profiles during deflagration (2L,
$\varphi$ =1.34%)
图 20 油气爆燃过程温度分布（2 L,
$\varphi$ =1.34%）Figure 20. Distribution of temperature during deflagration process (2 L,
$\varphi$ =1.34%)
图 21 油气爆燃辐射发展过程（2 L，
$\varphi$ =1.34%）Figure 21. Development of inradiation during deflagraion process (2 L,
$\varphi$ =1.34%)
图 22 三个时刻对应火焰传播形态
Figure 22. Three moments correspond to the flame propagation pattern
表 1 爆燃内场超压参数特征
Table 1. Internal overpressure parameter characteristics during deflagration
采集点 初始油量/L φ/% 点火电压/V Δpmax/kPa tr/s Emax/(kPa2·s−1) 1 2 1.34（16℃） 15 1.275 0.876 23.560 2 1.447 1.178 2.092 3 0.215 1.496 0.221 4 0.083 2.817 0.008 注：Δpmax为最大爆燃超压峰值，tr为到达爆燃峰值的用时. 
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表 2 爆燃外场超压参数特征
Table 2. External overpressure parameter characteristics during deflagration
采集点 初始油量/L φ/% 点火电压/V Δpmax/kPa tr/s Emax/(kPa2·s−1) 1 2 1.34（16℃） 15 0.155 1.495 0.039 2 0.112 1.151 0.075 3 0.641 0.717 3.699 4 0.313 0.725 0.233
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表 3 爆燃高位超压参数特征
Table 3. High ground overpressure parameter characteristics during deflagration
采集点 初始油量/L φ/% 点火电压/V Δpmax/kPa tr/s Emax/(kPa2·s−1) 1 2 1.34（16℃） 15 1.123 1.193 1.057 2 0.996 1.166 4.636 3 0.701 1.138 0.432 4 2.262 1.695 3.896
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表 4 不同油气浓度下超压峰值和到达峰值耗时分布
Table 4. Overpressure peaks & time to reach peaks under different concentrations
油料体积/L φ/% 点火电压/V Δpmax/kPa tr/s Emax/(kPa2·s−1) 1.5 1.15% 15 1.202 1.183 1.221 2 1.34% 1.447 1.178 2.092 2.5 1.68% 2.895 0.935 8.964 3 1.97% 1.246 1.054 1.469 3.5 2.36% 0.591 1.125 0.310
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表 5 不同初始油气浓度下火焰颜色特征
Table 5. The flame color under different concentrations
油气体积/L φ/% 点火电压/V 火焰传播特征 1.5 1.15 15 蓝色锋面+内部斜上方45°橙色蘑菇状火焰 2.0 1.34 淡蓝色锋面+内部斜上方45°橙色蘑菇状火焰 2.5 1.68 亮蓝色（高亮） 3.0 1.97 蓝绿色（高亮） 3.5 2.36 橙色（高亮）
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