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Flamewars in SPAAACE: cooler fires hint at energy efficiency

Experiment aboard ISS shows we should all chill out for cleaner engines

Candle in the dark

Video A fire on the International Space Station (ISS) – intentional of course – has provided hints at the kinds of research needed to make engines on Earth cleaner and more fuel efficient. Surprisingly, the experiments turned up flames burning at lower temperatures than thought possible.

In the research, astronauts set fire to large droplets of a heptane-based fuel, in experiments designed to look at how differences in buoyancy affect how droplets burn. In the extremely low buoyancy of the ISS's microgravity environment, gases released by combustion hang around the droplet for longer than they do on Earth.

As a result, what the researchers observed was unexpected: long after someone watching the flame with the naked eye believed a droplet had burned out, sensors showed the heptane was still burning.

The burning of the heptane creates toxic compounds such as carbon monoxide and formaldehyde – but instead of being released (as they might be if the same experiment were conducted on Earth), on the ISS these compounds stayed in proximity of the flame and burned off.

As the University's release notes, the researchers, led by mechanical and aerospace engineering professor Forman Williams, “believe that the cool flames are the result of elementary chemical reactions that do not have the time to develop around burning fuel droplets on earth, where they can only exist for a very short period of time.”

Were a cool flame engine to be feasible on Earth, the researchers think they could get engines that emit less soot, less nitric oxide, and less nitrogen dioxide.

NASA likes the idea, and has proposed a Cool Flame Investigation series of experiments for 2015.

The experiments were conducted in the ISS's Multiuser Droplet Combustion Apparatus in the space station's Destiny module. ®

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