New "blue whirl" fire tornados spin up a cleaner burn

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Researchers have discovered a new type of fire tornado they call a "blue whirl", which burns cleaner and more efficiently than its yellow counterparts(Credit: University of Maryland)

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Harnessing the power of fire has served humanity well for thousands of years, but fire tornadoes are harder to tame. Now a team at the University of Maryland has discovered a new type of fire tornado they've dubbed "blue whirls", which produce a cleaner burn and could be harnessed to reduce carbon emissions and burn away oil spills with fewer airborne pollutants.

"A fire tornado has long been seen as this incredibly scary, destructive thing," says Michael Gollner, co-author of the study. "But, like electricity, can you harness it for good? If we can understand it, then maybe we can control and use it. This is the first time fire whirls have been studied for their practical applications."

Looking at the well-known yellow fire whirls, the team's goal was to investigate how the these burn fuel on the surface of water. In the process, they discovered blue whirls, a previously unobserved type of fire tornado that burns more efficiently and more stably while producing much lower emissions than their turbulent yellow counterparts.

"Blue whirls evolve from traditional yellow fire whirls," says Elaine Oran, co-author of the paper. "The yellow color is due to radiating soot particles, which form when there is not enough oxygen to burn the fuel completely. Blue in the whirl indicates there is enough oxygen for complete combustion, which means less or no soot, and is therefore a cleaner burn."

This efficiency could see blue whirls being employed on the site of ocean oil spills, where cleanup efforts sometimes involve corralling the crude oil into a thick layer that is then burned, producing clouds of toxic smoke. With the ability of the blue whirls to burn the oil more completely, the amount of pollutants that are released into the air and water would be reduced. The main hurdle to that process, the team says, is scaling up the blue whirl from the small lab-made versions.

"Fire whirls are more efficient than other forms of combustion because they produce drastically increased heating to the surface of fuels, allowing them to burn faster and more completely," says Gollner. "In our experiments over water, we've seen how the circulation fire whirls generate also helps to pull in fuels. If we can achieve a state akin to the blue whirl at larger scale, we can further reduce airborne emissions for a much cleaner means of spill cleanup."

In addition to improving fuel efficiency and environmental cleanup, blue whirls may also find use as a platform for studying vortices in the lab, and how a vortex can break down in fluid mechanics.

"A fire whirl is usually turbulent, but this blue whirl is very quiet and stable without visible or audible signs of turbulence," said Huahua Xiao, assistant research scientist in the Clark School's Department of Aerospace Engineering and corresponding author of the paper. "It's really a very exciting discovery that offers important possibilities both within and outside of the research lab."

The research appeared in the journal Proceedings of the National Academy of Sciences (PNAS) and the new blue whirls can be seen in action in the video below.

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