The Defense Advanced Research Projects Agency (DARPA) has taken a novel approach to combating fire — developing a bass cannon that can put out fires with pure sound.
A new video from the agency shows how to extinguish burning fuel by trapping it in an acoustic field generated by surrounding speakers. Officially referred to as “acoustic suppression of flame”, each speaker emits a low frequency to increase the rate of air velocity. By manipulating this, the origin of the fire’s combustion — the flame boundary layer — can be disrupted.
When the air velocity changes, the flame boundary layer — where combustion occurs — begins to thin. Not only this, but by disturbing the surface, the acoustic fields lead to higher fuel vaporizaton. This results in widening the flame, but more importantly, it brings down the overall temperature of a blaze.
In the video below, the demonstrators have shown that by using the correct bass frequencies, a flame can be extinguished quickly and effectively.
Remarking on the overall impact of the research, DARPA program manager Matthew Goodman said:
“We have shown that the physics of combustion still has surprises in store for us. Perhaps these results will spur new ideas and applications in combustion research.”
Traditionally, fire-suppression technologies focus on disrupting the chemical reactions that result in combustion. However, if you take a physics perspective on the make-up of flames, the phenomenon is cold plasma. DARPA theorized that by using techniques applied in physics rather than chemistry, it may be possible to extinguish flames without water or solution.
This kind of technology, once developed further, could be applied to enclosed spaces — such as military ship holds, ground vehicles or aircraft cockpits. Blazes in these kinds of areas can cause extreme damage, and traditional methods to combat fire may not be easy to carry out. An example is the shipboard fire on the aircraft carrier USS George Washington in May 2008 which burned for 12 hours, causing an estimated $70 million in damage.
Image credit: DARPA