Anyone living near an airport will tell you that combustion engines can be pretty noisy things. The combustion process in jet and other industrial engines can generate sound waves so powerful they can cause intense pulsations that can shake the engine and accelerate mechanical failure. Using a sponge-like material, researchers at the University of Alabama have managed to significantly quiet combustion at the source, providing the potential to make work environments safer, extend the life of valuable equipment, and maybe let those living near an airport sleep a little easier.

Because most materials can’t withstand the extreme temperatures and pressures present at the point of combustion, current approaches to reducing the noise of combustion engines focus on suppressing the noise outside the engine after combustion has taken place. However, the material employed by University of Alabama engineering professor Dr. Ajay K. Agrawal is able to tolerate the conditions of jet engine combustion, making it possible to eliminate the noise at the source.

The composite material is a porous inert material made of hafnium carbide and silicon carbide. Its ability to withstand intense temperature and pressure levels allows it to be placed surround the flame and act as a sponge for the noise before it can escape. The high permeability of the material allows gases to easily flow, so it cuts the noise without interfering with the combustion process.

“Experimenting with combustion can be quite noisy and unstable, shaking the whole building, but when you put the foam in place, you can talk to the person next to you. It’s a night and day difference,” Agrawal said.

By reducing the noise at the source, the material allows bulky and expensive noise dampening equipment on exhaust systems to be minimized. And the ability to retrofit the material to existing systems makes it easy and cheap to install. In addition to jet engines, the technology could also cut noise in gas turbines, burners, furnaces, power generators and other industrial combustion devices.

Agrawal was recently granted a patent for the technology based on his work on jet engine combustion with Ultramet Corp., which was funded by the U.S. Navy.

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