A series of experiments on the International Space Station resulted in the discovery of a new type of cool burning flame.
Harnessing the chemistry of this kind of flame could lead to better internal combustion engines in cars. The prospects for cleaner engines are exciting, researchers say.
A team of international researchers, led by Forman Williams, a professor of mechanical and aerospace engineering at the University of California, San Diego, conducted the experiments. They ignited heptane fuel to see if the flames would self-extinguish, as they do on earth. And at first, it looked like they did. The researchers couldn't see the flames. But the sensors gauged that the heptane was still burning invisible flames.
"We observed something that we didn't think could exist," said Williams. The findings were published in the journal Microgravity Science and Technology. The researchers express hope that the new kind of flame could be used to develop homogenous-charge compression ignition in car engines, or engines that burn fuel at lower temperatures, thus releasing less soot, nitric oxide, nitrogen dioxide and other pollutants.
The experiments produced the cool flames in atmospheres similar to that of earth and areas with nitrogen, carbon dioxide and helium. The products of the combustion include carbon monoxide and formaldehyde, which then burn off.
Researchers think that the reason they produced the reaction in space is because it requires elementary chemicals that do not have enough time on earth to react fully. When droplets of heptane fuel burn in earth's atmosphere, the amount of time the gas surrounds the droplets is limited by buoyancy. But there's no buoyancy in a microgravity environment, so the gas surrounds the droplets for a long enough time in space to allow the reaction to complete.
How do researchers plan on bringing this reaction home? They require the perfect mixture of fuels. In response to the challenge, NASA is setting up experiments called "Cool Flame Investigation" to try to figure out how to produce the flame on earth and then, hopefully, how to use the application for cleaner engines.
This recent study was conducted on the ISS because the parameters required a microgravity environment and adequate time to produce the cool flame reactions. Williams and colleagues used a device on the ISS called the Multiuser Droplet Combustion Apparatus that ignites droplets of fuel in varying atmospheric conditions.
Sensory and video cameras send the data back to NASA's John Glenn Research Center in Cleveland, where the experiments are controlled by remote. Experiments like this, conducted on the ISS and controlled from afar, allow us to understand processes that just don't happen on earth, says Williams.
