Experimental Study of the Effects of Initial Ullage Height and Water Layer Thickness on Crude Oil Boilover Characteristics

In crude oil storage tank fires, large amounts of firefighting water are used, which may trigger boilover. Variations in oil level affect ullage height, while firefighting water injection alters the water layer thickness, with both processes influencing boilover behavior. This study conducts boilover experiments with 3 types of crude oil to investigate the effects of ullage height and water layer thickness. The results show that the water-cooling effect delays boilover onset time, suppresses intensity, and reduces the mass burning rate, with Jidong crude showing the highest reduction (19.2%). However, the water-cooling effect has a limit, and its influence weakens when the water layer thickness exceeds 6 cm. Ullage height affects flame behavior. A moderate increase enhances combustion and shortens boilover onset time, while further increases cause self-extinction. The oil-water interface temperature varies nonlinearly between approximately 100 and 120 degrees C with changing ullage height. The variation trends of hot wave propagation rate with water layer thickness and ullage height are consistent with those of the burning rate, and correlation equations between them are established. Additionally, the study shows that light crude oil exhibits a later boilover onset with a longer duration and experiences 2 similar to 3 distinct boilover events, whereas high-viscosity Jidong crude oil undergoes a single short and intense boilover.