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Startling discovery aboard the ISS may lead to cleaner ignition in cars

Astronaut Tom Marshburn works on Combustion Integrated Rack. Photo Credit: NASA

A surprising discovery aboard the International Space Station may have a very practical—and timely—benefit on Earth: cleaner-burning and more efficient cars. The team, led by Dr. Forman Williams of the University of California, discovered a cool-burning flame when heptane fuel was ignited as part of the Flame Extinguishment Experiment (FLEX). The FLEX was designed to test how to extinguish flames in microgravity. Dr. Williams works out of San Diego. The FLEX experiments are operated by remote control from the John Glenn Research Center in Cleveland, Ohio. The results were analyzed by scientists at Cornell, NASA, Princeton, UC Davis, UC San Diego, the University of Connecticut, and the University of South Carolina.

Astronaut Mike Fincke with the Combustion Integrated Rack facility in the Destiny module of the ISS. Photo Credit: NASA

Astronaut Mike Fincke with the Combustion Integrated Rack facility in the Destiny module of the ISS. Photo Credit: NASA

“We observed something that we didn’t think could exist,” Williams said. After the heptane fuel was ignited, the flames burned for a time, then cooled and appeared to be extinguished. But then sensors showed that it was still burning, but invisibly and at temperatures of 500K to 800K. As a point of comparison, on Earth normal visible flames burn at 1500K to 2000K.

“That’s right—they seemed to be burning without flames,” Williams said. “At first we didn’t believe it ourselves.”

The experiments was conducted in several environments, including air similar to Earth’s atmosphere, as well as atmospheres diluted with nitrogen, carbon dioxide, and helium.

“Their chemistry is completely different,” Williams said. “Normal flames produce soot, CO2 and water. Cool flames produce carbon monoxide and formaldehyde.” Those toxic chemicals burned off. “In microgravity, flames burn differently—they form little spheres,” Williams said.

The reason flames form little spheres in space is because they lack buoyancy. On Earth, the heat from a flame rises, and cool air rushes in from underneath. In such an environment, there’s no time for the complex chemical reactions to form which allow cool flames to burn. In space, though, the situation is different. Rather than rushing about to consume oxygen, a flame in space simply burns quietly and allows to oxygen to come to it. Without buoyancy, the chemical reactions that form cool flames have time to collect. The cool flames can burn for many minutes.

A burning droplet of heptane fuel aboard the International Space Station continued to burn after the visible flame was extinguished. Photo Credit: NASA

A burning droplet of heptane fuel aboard the International Space Station continued to burn after the visible flame was extinguished. Photo Credit: NASA

According to Williams, “There are practical implications of these results. For instance, they could lead to cleaner auto ignitions.”

Williams is referring to homogeneous charge compression ignition (HCCI), which would not use a spark, but a compression of fuel and oxidizer in the chamber.

“The chemistry of HCCI involves cool flame chemistry. The extra control we get from steady-state burning on the ISS will give us more accurate chemistry values for this type of research.”

NASA is now planning a new series of experiments to investigate this new phenomenon. Tentatively the new experiments are called the Cool Flame Investigation. The results of the experiment were published in June in the journal Microgravity Science and Technology. The Combustion Integrated Rack is located in the Destiny module of the International Space Station.

 

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Collin R. Skocik has been captivated by space flight since the maiden flight of space shuttle Columbia in April of 1981. He frequently attends events hosted by the Astronaut Scholarship Foundation, and has met many astronauts in his experiences at Kennedy Space Center. He is a prolific author of science fiction as well as science and space-related articles. In addition to the Voyage Into the Unknown series, he has also written the short story collection The Future Lives!, the science fiction novel Dreams of the Stars, and the disaster novel The Sunburst Fire. His first print sale was Asteroid Eternia in Encounters magazine. When he is not writing, he provides closed-captioning for the hearing impaired. He lives in Atlantic Beach, Florida.

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