A study on the effect of an acoustic valve in the exhaust silencer for noise reduction in automotive application

Customer preference towards quieter vehicles is ever-increasing. Exhaust tailpipe noise is one of the major contributors to in-cab noise and pass-by-noise of the vehicle. This research proposes a silencer with an integrated acoustic valve to reduce tailpipe noise, especially in the lower frequency range. Incident exhaust wave coming from the engine strikes the acoustic valve and generates reflected waves. Incident waves and reflected waves cancel out each other which results in energy loss of the exhaust gas. This loss of energy results in reduced noise at the exhaust tailpipe end. To evaluate the effectiveness of the proposed silencer with an acoustic valve, the Noise, vibration, and harshness (NVH) performance of the proposed silencer is compared with the existing silencer which is without an acoustic valve. A compressed natural gas (CNG) Bus powered by a six-in-line cylinder engine is chosen for the NVH trail. After NVH evaluation, it was found that when using the proposed silencer, third engine order noise and sixth engine order noise reduce substantially throughout the engine operating range. Further, noise at the exhaust tailpipe end reduces significantly throughout the engine operating range. Noise reduction at the exhaust tailpipe end leads to a considerable reduction in in-cab noise and pass-by-noise of the vehicle.