NASA Creates Cool Flames on the International Space Station: Great Balls of Fire! (Video)

Fire is one of the most useful tools known to man. While a flickering flame on Earth looks like a teardrop, though, in microgravity it forms a ball, or sphere. Now, NASA has studied fire in space a bit further--and has made some surprising findings.

Fire is difficult to understand. In an ordinary candle flame, for example, thousands of chemical reactions take place. Hydrocarbon molecules from the candle's wick are vaporized and cracked apart by heat. They then combine with oxygen to produce light, heat, CO2 and water. Some of the hydrocarbon fragments form ring-shaped molecules called polycyclic aromatic hydrocarbons and eventually become soot. This soot can either burn or drift away as smoke.

Microgravity is a whole other ball game for fire. Unlike on Earth, flame balls that form in microgravity let the oxygen come to them rather than expanding greedily. Fuel and oxygen combine in a narrow zone on the surface of the sphere rather than completely through the flame. Yet scientists witnessed an interesting phenomenon during a recent experiment.

The researchers aboard the International Space Station (ISS) were conducting an experiment called "FLEX" in an attempt to learn how to put out fires in microgravity. During the course of the study, they found that small droplets of heptane were burning inside the FLEX combustion chamber. These flames went out, as they were supposed to. Yet the droplets of fuel somehow, some way, continued to burn.

"That's righ-t-they seemed to be burning without flames," said Forman A. Williams, a professor of physics at UC San Diego, in a news release. "At first we didn't believe it ourselves."

In fact, these spheres weren't even burning at high temperatures. Normal fire burns at temperatures between 1500K and 2000K. While the heptane flame balls started out in this category, though, cool flames eventually took over. Burning between 500K and 800K, cool flames have a completely different chemistry. They produce monoxide and formaldehyde instead of soot, CO2 and water.

So what exactly was happening? The flames were probably still there-j-ust too faint to see. Similar cool fires have been produced on Earth, but they flicker out almost immediately. Yet the spheres on the ISS burned for minutes.

The cool flames aren't just an interesting phenomenon, though. They could potentially be used for cleaner auto ignitions. In fact, automakers have been working on the idea of homogenous charge compression ignition (HCCI) for years. During HCCI, a gentler, less polluting combustion process occurs throughout the chamber rather than one spark in the automobile chamber.

While it'll take some time to find out how to sustain this reaction on Earth, though, the new findings could eventually lead to cleaner cars.

Want to see the flames for yourself? Check out the video below, courtesy of YouTube and NASA.