Fire spread characteristics of kerosene-wetted loess under inclined base conditions

Liquid fuel leakage on sloped porous media, such as loess, is a common hazard in oil storage, transportation, and the chemical industry in the loess-covered areas of China. On inclined terrain, the gravity effect changes the seepage and the heat and mass transfer of liquid fuel inside the porous medium, which accelerates fire spread and expands the thermal influence range. Most existing studies on liquid fuel fire spread over porous media adopt quartz sand as the research medium, while the pore structure, permeability, and adsorption characteristics of natural loess are obviously different from those of quartz sand; therefore, the existing conclusions cannot be directly applied to loess fire scenarios. In addition, the coupling mechanism between base inclination angle and ignition position on fire spread behavior has not been systematically clarified. It is therefore of practical significance to explore the fire spread rules of kerosene-infiltrated loess under different inclination conditions, which can provide theoretical support for fire prevention, risk assessment, and emergency disposal in loess areas.

In this work, a self-designed experimental platform with an adjustable inclination angle was adopted to carry out a series of fire spread experiments. Dry loess with a particle size range of 0.116–3.675 mm was paved evenly in the experimental tank to form a uniform porous medium bed. Kerosene was injected slowly into the loess bed in multiple small doses until the medium reached full saturation. Seven working conditions with equivalent inclination angles of −9°, −6°, −3°, 0°, 3°, 6°, and 9° were set by combining different base angles and ignition positions. Anhydrous ethanol was used as the ignition source in the designated ignition area to initiate combustion, and the total duration of fire spread was set to 20 min. A high-definition camera with a frame rate of 50 frames per second was arranged 100 cm away from the experimental platform to record the evolution of flame morphology and the spread process. Meanwhile, 12 K-type armored thermocouples with a probe diameter of 0.5 mm were arranged in a 6 × 2 array to synchronously measure the temperature distribution on the surface and inside the loess bed along the axial direction. All flame characteristics, spread velocity, and temperature data were collected and analyzed quantitatively.

The experimental results revealed that the coupling effect of inclination angle and ignition position exerted a prominent influence on flame structure and propagation. Under the same inclination angle, the flame height and propagation distance of lower-end ignition were greater than those of upper-end ignition. For the upward fire spread on positive inclination bases, the height of the yellow flame zone increased with the rise of inclination angle; for the downward fire spread on negative inclination bases, the height of the yellow flame zone gradually decreased as the inclination angle increased. The flame spread at a constant velocity under all working conditions, and the spread velocity rose monotonically with the increase of inclination angle. The velocity of upward spread was obviously higher than that of downward spread under the same absolute inclination value. When the flame front arrived at the measuring points, an obvious layered heat transfer feature was observed: the surface heating rate of loess was far higher than the internal heating rate. Compared with the horizontal base, the inclined base presented a lower steady combustion temperature, a shorter time to reach thermal stability, and a larger internal temperature gradient inside the loess bed.

The base inclination angle changes the fuel seepage path and the intensity of heat feedback through gravity, and further regulates flame morphology, spread velocity, and the internal temperature field of the loess bed. The layered heat transfer characteristics of the loess bed are determined by differences in heat transfer mechanisms between the surface and the internal porous structure. The results clarify the mechanisms by which inclination angle and ignition position influence fire spread in kerosene-wetted loess. These findings can provide guidance for the design of fire isolation zones, the development of emergency response plans, and the optimization of firefighting strategies in sloped loess terrains. They also lay a foundation for further study on the evolution of fire hazards associated with liquid fuel leakage on loess substrates.