DARPA has figured out how to suppress flame using nothing but sound.
Back in 2008, the Defense Advanced Research Projects Agency (DARPA) decided that somebody should really work on improving a hundred year-old theory regarding how we might control fire using sound. Now, almost four years on, the agency has just about cracked it - its scientists have managed to extinguish a flame using nothing but sound.
In the attached video, we see a speaker-bound flame flicker, reignite, and then die under the pressure of some relatively quiet noises. While the technology still has a long way to go - with the eventual aim being fire suppression devices for use in places like aeroplane cockpits and ship holds - the achievement remains noteworthy.
How does this work, then? There are two main techniques at work in the video. The first is that the sound buzzing around the flame is increasing the air's velocity by just enough to thin the flame boundary (the area of the flame in which combustion occurs). At the same time, the sound waves are disturbing the flame's fuel source to the point where its speed of vaporization is increasing. This cools and spreads the fuel, disturbing the flame at the same time as shortening its brief life. The sound doesn't need to be loud to achieve this (hence why your lighter stays alive at concerts); rather, it just needs to be tailored.
"We have shown that the physics of combustion still has surprises in store for us," said DARPA manager Matthew Goodman. "Perhaps these results will spur new ideas and applications in combustion research."
Happily, this isn't the end of the road for DARPA's investigations into sound-powered fire suppression. Bolstered by its success, the agency now hopes to realize its goal of inventing a practical and worthwhile application for this kind of technology. In its current form, the technology might be at its most useful in environments where fuel-based fires are particularly problematic. But who knows where this could go? Should we take bets on how long will it take someone to mod it so that it yells "Fus Roh Dah!" when you switch it on? Here's hoping this makes it that far.