DARPA’s Instant Fire Suppression program has been looking into using sound waves to put out flames.
In this video, 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 vaporization, which widens the flame, but also drops the overall flame temperature. As the same amount of heat is spread over a larger area, combustion is disrupted.
I’m not sure if this has any real-world application, unless you can put a huge stereo around your house when it’s on fire (oh, I’d love to see that stereo!), but it’s pretty cool nonetheless. Having said that, it appears as though this could be useful in enclosed areas, and areas where you cannot throw water or chemicals around due to health or other issues.