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

[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. © 2023 Press of Tsinghua University. All rights reserved.