Abstract: Abstract: The spread experiment of unignited n-heptane and the combustion experiment of ignited n-heptane were carried out on the sand substrate to study the influence of sand particle size on the spread and combustion characteristics of n-heptane. The spreading distance, flame front and burning rate were analyzed, and the influence of heat transfer process on the characteristics of flowing fire was explored. The results show that because the adsorption capacity of sand decreases with the increase of sand particle size, the spreading distance and speed of unignited n-heptane in the spreading stage increase with the increase of sand particle size, and are smaller than those of no-sand working conditions. With the increase of sand particle size, during the stable combustion flame front of ignited n-heptane first increases and then decreases, and the stable combustion rate first decreases and then increases. The heat transfer analysis shows that when the sand particle size increases from 0.25 mm to 4 mm, the reduction of heat conduction feedback is the main reason for the reduction of the combustion rate; and when the sand particle size is further increased to 8 mm, the heat radiation feedback increases, leading to an increase in the burning rate. Finally, it is concluded that the adsorption capacity of sand is the main factor that affects the spreading stage, the thermal feedback is the main factor that affects the stable combustion stage, and the 0.25 mm fine sand is more suitable for blocking and extinguishing the flowing fire.

Key words: Key words: spill fire, spreading distance, flame front, combustion rate, thermal feedback