Levitating ring flame’s burning secrets revealed

Researchers have revealed how burning fuel can form a blue whirl, a ghostly ring-shaped flame that unlike regular fire vortices produces almost no sound nor soot. The work could potentially allow more efficient combustion of mixed hydrocarbons from oil spills.

Fire whirls occur when the intense heat rising from a fire creates a tornado-like vortex that sucks in oxygen and flammable material from the surroundings, creating a plume of high-temperature flame that can reach kilometres into the air. ‘They have a lot stronger suction than normal fires and much higher burning rates, and all of this results in something that’s much more dangerous,’ explains aerospace engineer Joseph Chung of University of Maryland, US. A fire whirl ignited by the 1923 Great Kantō earthquake in Japan killed 38,000 people in 15 minutes.

In 2016, University of Maryland researchers led by Elaine Oran were investigating whether fire whirls’ high burning efficiency could be useful for cleaning oil spills, which are often ignited. While studying fire whirls on water in the laboratory, they found that the turbulent, noisy fire whirls could spontaneously transform into blue–violet, torch-shaped auras hovering just above the water. ‘They had no idea what they were looking at,’ explains Chung.