Challenged
Pattern Altitude
"So far, noise reduction has been addressed after-the-fact, suppressing the noise outside the engine after the combustion process takes place. Agrawal’s technology eliminates the noise at the source, during the combustion process."
http://uanews.ua.edu/2012/04/ua-engineering-professor-quiets-combustion-with-patented-noise-sponge/
http://uanews.ua.edu/2012/04/ua-engineering-professor-quiets-combustion-with-patented-noise-sponge/