Extinguishing fire using sound

Fire is a huge concern in the process industries with major accidents serving as a reminder of the devastation it can cause.

However, despite the severity of the threat, no new methods for extinguishing or manipulating fire have been developed.

Now American researchers at the Defence Advanced Research Projects Agency (DARPA) believe they have come up with a new solution.

In 2008, DARPA launched the Instant Fire Suppression (IFS) project to develop a fundamental understanding of fire with the aim of transforming approaches to firefighting.

Traditional fire-suppression technologies focus largely on disrupting the chemical reactions involved in combustion.

However, from a physics perspective, flames are cold plasmas. DARPA theorised that by using physics techniques rather than combustion chemistry, it might be possible to manipulate and extinguish flames.

One of the technologies explored was a flame-suppression system that used a handheld electrode to suppress small methane gas and liquid fuel fires.

Researchers also evaluated the use of acoustic fields to suppress flames. In the video below, a flame is extinguished by an acoustic field generated by speakers on either side of the pool of fuel.

Two dynamics are at play in this approach. First, the acoustic field increases the air velocity. As the velocity goes up, the flame boundary layer, where combustion occurs, thins, making it easier to disrupt the flame.

Second, by disturbing the pool surface, the acoustic field leads to higher fuel vaporisation, which widens the flame, but also drops the overall flame temperature.

Commenting on the impact of the IFS project, Matthew Goodman, DARPA programme manager, 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.”