Spring 2019 > Research Excellence

The Simply Gorgeous Blue Flame

Prof. Elaine ORAN, Glenn L. Martin Institute Professor and A. James Clark Distinguished Professor of Engineering, University of Maryland, and IAS Senior Visiting Fellow, likes to play with fire—not just the ordinary type of fire, but a tiny blue whirl.

\\ It leaves no waste, no pollutants, and could be a new and alternative tool for oil-spill cleanup.\\

It started when a friend of Oran’s sent her a video of a powerful vortex of swirling flames atop a pond of water on which alcohol had been spilled. Oran was completely captivated. “‘Let’s find some use for this thing!’ I told my research team, because little had been done on this kind of fire, and no one had suggested any applications.”

This “thing,” as Oran called it, is in fact the fire whirl, also commonly known as fire devil, fire tornado or firenado, named for its resemblance to a stack of long vertical “chimneys” spinning in a vortex. Fire whirls pick up “burning embers, ash, flaming-hot gases and flammable debris, creating a terrifying tower of flame that can extend hundreds of feet into the air.”1 According to Oran, despite lasting only a few minutes, a fire whirl is as powerful and devastating as a tornado.

Dragon Twist

“Smaller fires can often develop into fire whirls, ‘eating’ everything around them. Fire fighters usually end up running away from them because they are so fierce and difficult to put out.” In a recent talk, “The Beauty of Turbulence and Transitions in Reactive Flows,” jointly organized by the IAS and School of Engineering at HKUST, Oran showed the audience some drawings of the large fire whirl in the Great Kanto Earthquake (關東大地震) of 1923 that hit Tokyo, Japan. After an earthquake and tsunami ravaged the area, claiming many lives, a fire whirl, named the “dragon twist” by locals, further increased the death toll in the catastrophe. This fire whirl was one of the largest ever recorded.

“The high combustion efficiency of fire whirls implies a great potential for highly efficient and low-emission combustion. My colleague at the University of Maryland, Prof. Michael GOLLNER, and I kept asking ourselves: Can we put the destructive fire whirl to a constructive use, such as generating energy?” said Oran.

With funding from the US National Science Foundation, Oran, Gollner and Prof. XIAO Huahua (now at University of Science and Technology of China) and their team started investigating the combustion mechanism and dynamics of fire whirls by performing experiments on top of a round steel pan filled with water.

Unexpectedly, they found a new flame phenomenon—a blue whirl— several inches tall, that burned at an extremely high temperature yet amazingly quietly and cleanly, without any soot.

From Yellow to Blue

“Isn’t it gorgeous?” said Oran, whose eyes sparkled with excitement when a video of the blue whirl, captured by her team during an experiment, was shown at the IAS lecture. “If you put your hand right next to the blue whirl, you feel nothing, because there is no radiation. The top, however, can be a couple thousand degrees Kelvin.”

Oran and her team published a paper, From Fire Whirls to Blue Whirls and Combustion Without Pollution, in 2016, which described their discovery of the blue whirl and its potential use for the in situ burning of oil spills. The news went viral, and thousands of calls and media invitations for interviews flocked in.

The blue whirl, which evolves from a yellow fire whirl, is described in the research paper as a “small, intensely whirling blue flame.” Compared with a turbulent “pool fire” or a fire whirl, “the blue whirl shows no visible or aural signs of turbulence. A stable blue whirl is very quiet.”2 The team believes that an air-water-fuel boundary layer created under their experimental conditions contributed to the increased combustion efficiency of the fire whirls on water. The transition from yellow to blue is caused by the presence of enough oxygen for complete combustion. This kind of premixed flame limits soot formation in the vortex.

Burning for a Good Cause

“Fire has been no stranger to humans since the Stone Age, but nobody had ever seen the blue whirl before. It leaves no waste, no pollutants, and could be a new and alternative tool for oil-spill cleanup,” said Oran.

To understand what happens in the interior of the blue whirl, Oran and her team are now trying to simulate one through large-scale computations, and then use this information to produce even bigger whirls in the lab. “There is still much to be done in terms of understanding how they form and their inner structure. We need to probe the fluid dynamics and chemical reactions, look for the optimal conditions and try to replicate it at a larger scale,” added Oran. As Oran and her researchers noted in their paper, if the blue whirl could be harnessed and controlled, it could offer a new form of combustion with minimal emissions, improving the combustive remediation of oil spills (burning faster and more completely by sucking in the surrounding flames).

“We are entering a new stage in our research. There’s still a lot more to be found out,” Oran commented. 

Although many questions remain, one thing is for sure: the discovery of the blue whirl and its mechanisms has provided a solid groundwork for future research and development.

Evolution from a pool fire to a blue whirl over water in a swirl generator.
Photo: Huahua Xiao et al. PNAS doi:10.1073/pnas.1605860113

“Whirling Flames: How Fire Tornadoes Work,” Live Science, May 16, 2014, http://www.livescience.com/45676-what-is-a-firenado.html

Huahua Xiao, Michael J. Gollner, and Elaine S. Oran (2016). From fire whirls to blue whirls and combustion with reduced pollution, Proceedings of the National Academy of Sciences, 113(34) 9457-9462. Retrieved from http://www.pnas.org/content/early/2016/08/03/1605860113

Prof. Elaine Oran

Prof. Oran has been affiliated with the IAS since 2013. Her research achievements have been recognized by the American Physical Society, which awarded her the 2013 Fluid Dynamics Prize for her “seminal contributions to the understanding of reactive flows through computational simulations, especially the deflagration-to-detonation transition in gases and supernovae.”

Fascinated by science fiction, Oran was inspired to be a scientist at an early age. “My father was a bit shocked when I told him that I wanted to go to graduate school and study physics, which was beyond his understanding. He paused, looked aside, and then said to me, ‘I wish you good luck’,” Oran recalls.

After receiving her MPhil in Physics and PhD in Engineering and Applied Sciences from Yale University in 1968 and 1972 respectively, Oran became one of very few female scientists working in a male-dominated research environment at the US Naval Research Laboratory (NRL) in the Plasma Physics Division, and later in the Laboratory for Computational Physics. In 1988, her passion for fluid dynamics led her to become the NRL Senior Scientist for Reactive Flow Physics, responsible for theoretical and computational research on the fluid and molecular properties of complex dynamic systems.

Prof. Oran joined the faculty of the University of Maryland in 2013 as Glenn L. Martin Institute Professor of Engineering. She is also an Adjunct Professor of Aerospace Engineering at the University of Michigan and a Visiting Professor at the University of Leeds. Her research interests include reactive, compressible turbulent flows in high-speed engines and astrophysical scenarios. She is the author of over 300 refereed journal articles as well as many conference papers and presentations. She is also the co-author of the book Numerical Simulation of Reactive Flow.

Among many other prestigious awards, Oran was the recipient of the Achievement Award (2016) from the Society of Women Engineers, was inducted into the Women in Technology International Hall of Fame (2002) and received the Dryden Research Award from the American Institute of Aeronautics and Astronautics. She is a Member of the US National Academy of Engineering and a Fellow of the American Academy of Arts and Sciences. As a female engineer and scientist for almost half a century, she has one piece of advice for those, particularly female students, who would like to pursue a career in engineering or science:

“Go for it!”