“Noise sponge” cuts jet engine noise at the source of combustion


May 3, 2012

The "noise sponge" that can significantly reduce the noise of combustion in jet engines (Photo: Zach Riggins, University of Alabama)

The "noise sponge" that can significantly reduce the noise of combustion in jet engines (Photo: Zach Riggins, University of Alabama)

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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.

Source: University of Alabama

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

This «sounds» nice ! Love to see more information on the devices effect, if any, on combustion efficiency...


Please apply this invention to leaf-blowers and lawn-mowers, the much-hated devices which have destroyed the peace of suburbia! Cordless electric versions would cut down on noise too, but I fear that these will remain too expensive for several more years to replace the obnoxious combustion-powered models.


The rapid high turbulence flame propagation IS as noisy as anything.

I used to design really intense short combustion depth furnace burners.....

When it comes down to it, the sound of the combustion front, is basically all of the noise that comes out of a jet engine.

Mr Stiffy

I would be surprised if this produced a signifigant reduction in noise for jet engines since the volume required would surely be an issue (given it uses silicon carbide). I could see it having some use in a ballistic silencing device where there is a rise and fall in pressure where it could releive that power over time.

Charles Griffith


The noise I hear is the friction between the "still air" and the veryfast moving plume of burning gases exiting the engine, the speed diferential must be the major source of sound! A relation of mine working with Boeing created a method of reducing that friction by enveloping the Jet plume with LPG. The idea worked very well but Boeing decided that people would not like to ride in an airplane with 100ft long blue flames from every Jet orifice!

Mike MacDonald

This might also work to quiet down artillery and other noisy weapons. James Bond take note.

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