An entirely new class of fire, spherical cool diffusion flames, appropriately referred to as “cool flames,” has been documented by a collaborative team of researchers from Washington University in St. Louis, the University of Maryland and the University of California, San Diego.
Creating this unique fire required an equally unique laboratory: the microgravity environment of space.
These dim, quiet flames were documented aboard the International Space Station.
“The Space Station is a lab like no other,” said Richard Axelbaum, the Stifel & Quinette Jens Professor of Environmental Engineering Science in Washington University’s Department of Energy, Environmental & Chemical Engineering in the McKelvey School of Engineering.
“Being able to perform experiments in microgravity allowed us to observe a flame that just would not exist on Earth. This type of discovery is what makes the Space Station so invaluable to scientific exploration.”
The discovery, itself, transforms researchers’ understanding of what fire can be and what fire can do, said lead researcher Peter Sunderland, a professor at the University of Maryland. “The goal of our research is to understand the particular processes ongoing in spherical cool diffusion flames. If we can understand and model how they work, then we might be able to harness cool flames to design a new class of clean combustion engines.”
First observed during an experiment burning a fuel droplet aboard the International Space Station (ISS) in 2012, the cool flames appeared only briefly before the liquid fuel was depleted. The sighting catalyzed an emerging, rapidly growing field in combustion research.
The flames are also somewhat mysterious: As recently as 10 years ago, cool flames had only been theoretically predicted.
In these new experiments, cool spherical gaseous flames were observed for the first time. Cool flames burn at extremely low temperatures and are nearly invisible. For comparison, a natural gas flame on a conventional stove top can burn at around 3100 degrees Fahrenheit/1700 Centigrade; a typical cool flame hovers around 950 degrees Fahrenheit/500 Centigrade.
“Little is known about combustion chemistry at these low temperatures,” Sunderland explained. “Part of what we’re learning is how much we didn’t know.”
The project to understand cool flames is one of two that Axelbaum is involved with on the International Space Station. He leads the other project, also a collaboration with Sunderland, working to design soot-free flames.