DARPA is showing off a new system that can put out flames using only sound. It’s part of the U.S. defense agency’s “Instant Fire Suppression” program.
The Defense Advanced Research Projects Agency (DARPA) has published the video alongside details of how the technique was achieved in their labs back in December 2011.
The team arranged two speakers either side of a liquid fuel flame to demonstrate how fire can be controlled by amping up an acoustic field. The sound increases air velocity, which then thins the area of the flame where combustion occurs, known as the flame boundary. Once the boundary area is thinned, the flame is easier to extinguish. At the same time, the acoustics are disturbing the pool of fuel and creating higher fuel vaporisation — this widens the flame, thinning it out so it is less concentrated and cool enough to extinguish.
Even better, the sound does not even need to be offensively loud to achieve any of this.
“We have shown that the physics of combustion still has surprises in store for us,” commented Darpa manager Matthew Goodman in a statement. “Perhaps these results will spur new ideas and applications in combustion research.”
Manipulating fire with sound is not a new trick. In the 1900s German physicist Heinrich Rubens demonstrated the technique using a length of pipe with holes punched along the top. One end was sealed off with a sound speaker attached, the other sealed off and fixed with a gas supply. After lighting the gas leaking from one of the holes and changing the sound frequency being emitted, the height of the flames could be manipulated.