高闪点液体燃料浸润多孔介质砂床火蔓延行为实验研究

Experimental study on the characteristics of fire spread on porous sand bed infiltrated by high flash point liquid fuel

为探究液体燃料(煤油和0#柴油)浸润多孔介质砂床(石英砂)表面火蔓延特征行为,开展了一系列不同颗粒粒径(0.428~4.500 mm)工况的燃烧测试,实验测量了燃料质量损失速率、砂床内部温度分布、砂床表面火蔓延速率等特征参数,分析了颗粒粒径对浸润燃烧场景下燃烧蔓延特性的影响机制。实验结果表明:在当前实验中,毛细管作用影响了燃烧反应进程的传热速率,较细颗粒砂床(直径0.428 mm)的传热速率快于较粗颗粒砂床(直径2.180 mm)。不同颗粒粒径工况下的质量损失速率的增长快慢存在差异,准稳定燃烧阶段质量损失速率的增长速率随颗粒粒径的增大而先减小后增大。在准稳定燃烧阶段中,随着颗粒粒径增大,煤油和0#柴油浸润石英砂床表面的平均火蔓延速率呈现出先减小后增大的趋势。在相同颗粒粒径条件下,0#柴油的平均火蔓延速率低于煤油。

[Objective]Previous studies on propagation-type combustion have yielded fruitful results.However,relatively few studies have investigated the characteristics of fire spread behavior of nonvolatile high flash point liquid fuel in porous media.[Methods]A series of combustion tests were performed on typical high flash point liquid fuels(kerosene,0#diesel)infiltrating quartz sand beds of various particle sizes.The average particle sizes of quartz sand under the designed experimental conditions were 0.428,0.715,1.200,2.180,3.675,and 4.500 mm.The fire spread was recorded using a high-definition video camera at 25 frames per second,with the camera positioned 100 cm away from the experimental tank.The mass loss rate was measured using an electronic balance with a 0.1 g accuracy,and the fire spread rate was determined from the flame front position data using MATLAB.A series of K-type armored thermocouples with a diameter of 0.5 mm were arranged on the side wall of the experimental tank to measure the temperature distribution in the quartz sand bed.[Results]The experimental results reveal that the heat transfer rate of a fine-grained sand bed(d=0.428 mm)is faster than that of a coarse-grained sand bed(d=2.180 mm)at the same depth.This difference can be attributed to the effect of capillary action on the mass transfer efficiency of the sand layer,which in turn affects the heat transfer rate during the combustion reaction process.Furthermore,a preheating zone of a certain length exists near the flame front,which is primarily dominated by heat conduction and has minimal effect on convection and radiation heat transfer.In the process of fire spreading on the quartz sand bed with liquid fuel,the mass loss rate increases over time.However,the growth rate of mass loss rate varies under different particle size conditions.In the quasi-stable combustion stage,the growth rate of mass loss rate initially decreases and then increases with increasing particle size.As the particle size increases,the average fire spreading rate of kerosene and 0#diesel on the surface of the quartz sand bed first decreases and then increases.Because of the relatively high flash point and viscosity of 0#diesel,its average fire spreading rate on the surface of the quartz sand bed is lower than that of kerosene.[Conclusions]This study analyzes the characteristics of fire spread on the surface of a typical porous sand bed infiltrated with high flash point liquid fuel and reveals the mechanism of the effect of particle size on the characteristics of fire spread to a certain extent.The research results provide references for the security protection and decontamination treatment of the fire spread problem when liquid fuel leaks into porous media.