A team of scientists at the University of Maryland has discovered a beautiful, swirling flame phenomenon, the ‘blue whirl,’ which evolves from a fire whirl (fire tornado) and burns with nearly soot-free combustion. The discovery could lead to beneficial new approaches for reducing carbon emissions and improving oil spill cleanup.
Front view of structure of a blue whirl generated over water. The structure mainly consists of a blue region and a violet region. A reflection of the blue whirl in the water can be seen in the lower part of the image. Image credit: Huahua Xiao et al.
“Blue whirls evolve from traditional yellow fire whirls,” said co-author Prof. Elaine Oran, from the Department of Aerospace Engineering at the University of Maryland.
“The yellow color is due to radiating soot particles, which form when there is not enough oxygen to burn the fuel completely.”
A blue whirl is smaller, very stable, and burns completely blue as a hydrocarbon flame, indicating soot-free burning.
The combination of fast mixing, intense swirl, and the water–surface boundary creates the conditions leading to nearly soot-free combustion.
Prof. Oran and colleagues set out to investigate the combustion and burning dynamics of fire whirls on water.
What the scientists discovered was a novel, blue flame that they say could help meet the growing worldwide demand for high-efficiency, low-emission combustion.
“A fire tornado has long been seen as this incredibly scary, destructive thing,” said co-author Dr. Michael Gollner, from the Department of Fire Protection Engineering at the University of Maryland.
“But, like electricity, can you harness it for good? If we can understand it, then maybe we can control and use it.”
Some oil spill remediation techniques include corralling up the crude oil to create a thick layer on the water surface that can be burned in place, but the resulting combustion is smoky and incomplete.
However, blue whirls could improve remediation-by-combustion approaches by burning the oil layer with increased efficiency, reducing harmful emissions into the atmosphere around it and the ocean beneath it.
“In our experiments over water, we’ve seen how the circulation fire whirls generate also helps to pull in fuels,” Dr. Gollner said.
“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.”
“A fire whirl is usually turbulent, but this blue whirl is very quiet and stable without visible or audible signs of turbulence,” said lead author Dr. Huahua Xiao, from the Department of Aerospace Engineering at the University of Maryland.
“It’s really a very exciting discovery that offers important possibilities both within and outside of the research lab.”
The team’s results appear in the Proceedings of the National Academy of Sciences.
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Huahua Xiao et al. From fire whirls to blue whirls and combustion with reduced pollution. PNAS, published online August 4, 2016; doi: 10.1073/pnas.1605860113
