Dr Agrawal (right) and graduate students examine the noise sponge
Fri 10 May 2012 – A breakthrough technology to reduce aircraft engine noise at source has been developed and patented by an engineering professor from the University of Alabama. So far, noise reduction has been addressed after the fact – suppressing the noise outside the engine after the combustion process takes place. Dr Ajay Agrawal has come up with a sponge-like material that eliminates the noise at source, during the combustion process. The challenge of cutting the sound level during the process is that combustion happens at extremely high temperatures and pressure. Most materials cannot withstand such conditions but Agrawal says he and his team have found a suitable porous material.
The porous inert material, or foam, is a composite made of hafnium carbide and silicon carbide that can withstand intense levels of heat and pressure. The material is placed directly into the flame and acts like a sponge for the noise. Due to its high permeability, the foam allows gases to easily flow so combustion is not interrupted, yet is much quieter. The foam surrounds the flame, cuts the noise and eliminates the potential for engine instability.
By reducing the noise at source, it minimises the need for expensive modifications to exhaust equipment and allows for cost-efficient retrofitting of existing systems.
Agrawal says the application of the technology extends beyond jet engines to any industrial devices using combustion.
“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,” he explained.
The patent is based on Agrawal’s jet engine combustion work with Ultramet Corp and funded by the US Navy.
University of Alabama - Research
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