An experimental study of the blue whirl: Effect of fuel surface diameter

Author：Xiao, H. H., Chen, Z. X., Li, X., Wang, X. H.

Journal：Combustion and Flame

DOI:  10.1016/j.combustflame.2024.113322

Keywords: Blue whirl, Fuel surface diameter, Burning rate, Flame width, Flame precession, precessing vortex core, fire whirls, oh-asterisk, combustion, flame, temperature, Thermodynamics, Energy & Fuels, Engineering

Abstract: 

Diameter of liquid fuel surface is generally an important factor for pool fires. This work studies the effect of diameter of liquid fuel surface on the flame dynamics of the blue whirl formed on a concaved smooth metal surface with a 10-degree inclination. The results show that diameter of liquid fuel surface has a significant influence on the formation and evolution of the blue whirl. When the fuel surface diameter is in the range of 25 mm < d < 50 mm, a stable blue whirl can be formed. When d >= 50 mm, the blue whirl becomes unstable, that is a yellow whirling flame is generated in the center region of the envelope of the blue whirl, forming a transitional state. As the fuel surface diameter increases, both the circulation and flame width of the blue whirl show a nearlinear growth. The liftoff height of the flame edge in the stable state of blue whirl varies linearly with fuel diameter, while remaining almost constant in the transitional state. Whereas the flame precession frequency of blue whirl increases linearly with the increase of circulation, the precession radius keeps nearly constant. The mass burning rate per unit area of the blue whirl decreases with increasing the fuel surface diameter. A radiative heat transfer model for the blue whirl is established based on radiation theory, and the modified burning rate expressions for the stable and transitional states of the blue whirl are obtained using the model and experimental measurements. Further scaling laws, based on dimensional analysis, are proposed for predicting the flame geometric features and flame precession frequency of the blue whirl. This work provides experiments of the flame dynamics at various fuel surface diameters and insights into the physics of the blue whirl.