Conditions for Formation of the Blue Whirl

The blue whirl is a regime of the fire whirl with peak temperatures around 2000 K, and burns a variety of liquid hydrocarbons directly with little visible soot. Here, the conditions required for blue whirl formation are investigated in a fixed-frame self-entraining fire whirl setup. The parameters governing the fire whirl regime are buoyancy (determined by Q ̇, heat release rate from combustion) and level of swirl (determined by Γ, circulation due to entrainment). The two parameters are coupled in a self-entraining configuration, causing only certain regimes of the fire whirl to stably form. Q ̇ is controlled over a wide range of values by adjusting the fuel supply rate, and the resulting inlet velocities into the fire whirl enclosure are measured using a hot-wire anemometer. A graph of Q ̇ vs. Γ for the different regimes shows that stable blue whirl formation occurs in a narrow region close to the extinction limit found in literature. Two scaling approaches are outlined to predict the formation conditions for different enclosure sizes, and further understand the physical processes controlling blue whirl formation. The scaling approach shows that the blue whirl occurs in a circulation-dominated flow field.