Flame geometric characteristics of large-scale pool fires under controlled wind conditions

Abstract

This paper presents an experimental study on the flame geometric characteristics of large-scale open pool fires under well-controlled wind conditions. Square fuel pools with combustion areas of 50 m2, 100 m2, 200 m2, 380 m2, and 400 m2 were used to burn RP-5 aviation fuel and diesel oil. A large-scale open jet wind tunnel generated a well-controlled and regulated horizontal wind field with wind speed (U) of up to 17 m/s. It was found that the evolution of large-scale pool fires under wind conditions involved four regimes, namely free vertical pool fire, tilted pool fire without flame drag, tilted pool fire with stable flame drag, and tilted pool fire close to the ground. The wind significantly affected the flame shape, the vortex structures, and the smoke layer characteristics around the flame. Five quantities of flame geometry were measured, including the flame base drag (ld), the flame length (L), the vertical flame height (H), and two flame tilt angles of θ1 (defined by the fuel pool center) and θ2 (defined by the flame base center). The critical wind speeds for flame base drag were obtained for the first time, and it showed a steady increase with the fuel pool size. With increasing U, the vertical flame height (H) decreased steadily, while the flame length (L) increased slightly, and the flame base drag (ld) and the flame tilt angles (θ1, θ2) increased steadily and leveled off for U>7–8 m/s. By introducing the buoyancy length scale and integrating the mixture fraction equation, the correlations for the five flame geometric characteristics were derived, which agreed well with the data of large-scale pool fires in this work and literature. The correlation for flame base drag also successfully predicted the critical wind speed for the occurrence of the flame drag.