Thermal structure of the blue whirl

Abstract

The blue whirl is a recently discovered regime of the fire whirl that burns without any visible soot, even while burning liquid fuels directly. This flame evolves naturally from a traditional fire whirl in a fixed-frame self-entraining fire whirl experimental setup. Here, detailed thermal measurements of the flame structure performed using thermocouples and thin-filament pyrometry are presented. Thermocouple measurements reveal a peak temperature of ∼2000 K, and 2-D temperature distributions from pyrometry measurements suggest that most of the combustion occurs in the relatively small, visibly bright, blue vortex ring. Different liquid hydrocarbon fuels such as heptane, iso-octane and cyclohexane consistently formed the blue whirl with similar thermal structures, indicating that blue whirl formation is independent of fuel type, and also that the transition from a fire whirl to a blue whirl may be influenced by vortex breakdown.