April 2, 2011— -- Researchers have shown that they can put out a fire by zapping it with electricity -- pointing an electrical wand at a flame and applying a current.
But it's too early to replace a firefighter's hose or an office sprinkler system with a zapping wand.
"It's still very much premature to say how this could affect firefighters in the field," said Ludovico Cademartiri of George Whitesides's research group at Harvard University, who presented his findings this week at a meeting of the American Chemical Society in Anaheim, Calif.
Previous experiments have shown that applying a constant electric field created small effects on flames, but Cademartiri's work used an oscillating electric field to greater effect.
"When you start using oscillating fields there are new mechanisms that come into play and these mechanisms lead to much stronger effects on flames -- effects that are so strong as to have been shown to suppress fires," Cademartiri said.
The team reported that when they placed an insulated wire at the base of a thin, 19-inch flame and applied about 600 watts of power -- similar to a medium -- sized microwave oven, the flame went out.
Why this happened is still a bit of a mystery. Cademartiri emphasized the complexity of flames, saying no single principle could explain why the flame goes out. However, one key principle may be that the electric field moves charged particles inside the flame in such a way that the flame sort of blows itself out from within.
"This is quite different from blowing air on the flame," Cademartiri said. "When you blow on the flame, you generate flow outside the flame and you push air into this flame. In our case, we generate this flow within the flame."
This flow may be strong enough to separate the flame from its fuel source, which may be why the flame goes out. During experiments, the researchers found that the smokier the fire, the bigger the effect.
One application of key interest is extinguishing cockpit fires, he said. Fires in enclosed spaces like cockpits or ships are a key interest of DARPA, who funded the research as part of a search for new technologies to suppress or control fires. Small cockpit fires may also be better suited to this technology than larger fires. Cademartiri notes that a fire spread over a pool of oil, for example, would probably not be a good candidate for extinguishing with the new approach.
Electric Fields Help Reduce Soot Formation, Pollutant Emissions
The team is now in the process of determining how the electric field works with different sized flames to determine what kind of applications might exist for such a technique.
Derek Dunn-Rankin of the University of California, Irvine, who works with NASA to study the effects of flames in electric fields in microgravity, doubts this technique will be used to put out large fires. His team has concluded from their own experiments that "it will not be possible to ever usefully extinguish flames of significant size," he said, because flames naturally have few charged particles to be moved by the electric field.
The exciting part of Cademartiri's experiments is to show that an electric field can influence a flame from a distance without moving parts. But large-scale firefighting is another matter.
Still, there are many reasons to pursue such studies, he said. Electric fields can help reduce soot formation and pollutant emissions from flames.