APU Silencing Technology Development

Auxiliary power units (APU) offer potential to improve operational efficiency and provide significant tactical advantage for surveillance missions conducted from land vehicle platforms. Current installations have resulted in higher than acceptable noise levels, adversely impacting the ability to perform a"silent"watch. In particular, noise created by the combustion process presents a problem due to its relatively low frequency. Low frequency noise propagates efficiently through the atmosphere resulting in audible detectability at unacceptable range. Low frequency noise can be reduced using passive silencing techniques, but these devices are typically large and heavy and present objectionable integration burdens. This effort outlines activities to establish feasibility and preliminary design of an active exhaust silencer for use with an APU. The desired outcome is a compact and lightweight solution capable of reducing exterior noise to levels that enable inaudible operation at a range of 20 meters. The considerable challenge of achieving a durable solution for creating anti-noise will be addressed through a parallel path approach, with one path focused on innovative integration of COTS technology and the other focused on development of a novel noise source able to directly withstand the extreme exhaust environment.