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'Noise sponge' leads to quieter combustion

03 May 2012

A sponge-like material employed by a University of Alabama engineering professor can significantly quieten the noise of combustion, possibly making work environments safer and extending the life of equipment. The technology decreases the noise generated by combustion systems at the source by placing the sponge-like material directly in the flame.

Dr Ajay Agrawal (right) with graduate students Justin Williams (left) and Joseph Meadows (centre) examine the 'noise sponge'
Dr Ajay Agrawal (right) with graduate students Justin Williams (left) and Joseph Meadows (centre) examine the 'noise sponge'

The combustion process, especially that of a gas turbine, produces extremely high noise levels that can also affect the engine structure itself. Sound waves produced as a result of combustion can cause intense acoustic pulsations, which can result in mechanical failure.

So far, noise reduction has been addressed after-the-fact, suppressing the noise outside the engine after the combustion process takes place. University of Alabama professor of mechanical engineering, Dr Ajay Agrawal’s technology eliminates the noise at source - at the heart of the combustion process.

The challenge was to find a noise dampening material that would survive the extremely high temperatures and pressures of combustion. Most material cannot withstand such conditions; however, Dr Agrawal has found a porous material that can tolerate the conditions of jet engine combustion.

This porous inert material, or foam, is a composite of hafnium carbide and silicon carbide that can withstand intense levels of heat and pressure. The material is placed directly in the flame but, thanks to its high permeability, it allows gases to flow easily through its porous structure, so combustion is not affected.

“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,” says Dr Agrawal.

This technology reduces noise at its source, minimising the need for bulky and expensive modifications to exhaust equipment. It also increases the uniformity of the combustion and allows for retrofitting of existing systems, which is highly cost efficient. This technology will be useful in gas turbines, burners, furnaces, power generators and other industrial combustion-based devices.

Dr Agrawal was recently granted a patent for his combustion noise reduction technology. This patent is based on his work on jet engine combustion with Ultramet Corp., which was funded by the US Navy.

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