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 develop and demonstrate a prototype active noise cancellation (ANC) system on a representative 10 kW class APU in representative laboratory conditions. Development activities include controller and amplifier design and development as well integration and development activities of the mechanicla components of the system. Considerable durability testing, thermal performance characterization, and noise cancellation perfromance evaluation and tuning are included. Successful execution of this effort will result in an ANC system for engine exhaust that matures the technology to a TRL level of 5, enabling selection of a demonstration platform to further elevate technological maturity and TRL level.