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Acoustic Field Analysis and Noise Reduction for Straight Exhaust Pipe

An exhaust pipe which connects with an internal combustion engine periodically produces a number of shock waves inside the pipe. The shock wave will result in wave diffraction around the pipe exit and expansion wave reflection inside the exhaust pipe when it leaves the exhaust pipe, and thus generates noise radiation downstream of the pipe exit. This study aims to explore methods of tailpipe noise reduction. Several experiments have been conducted. For sound pressure measurements, we used a B & K 4190 microphone (B & K Inc.) and a B & K 3550 spectrum analyzer to gauge noise levels at 25 cm and 50 cm distances from the pipe exit, with every inclination angle of 15° from the pipe centerline. We installed a layer of fiberglass in the designed muffler using alternate airspace dimensions to reduce noise. A simplified straight pipe with and without our designed muffler is studied first to understand the difference in emitted noise. Furthermore, a commercial exhaust pipe with our designed muffler is tested for proving the effectiveness of the proposed muffler. The noise reduction of the proposed muffler for the commercial exhaust pipe ranges from 0.84-1.95 dB (A), 0.74-2.94 dB (A) and 0.84-1.98 dB (A) at an engine speed of 3,000 rpm, 4,000 rpm and 5,000 rpm, respectively, at a distance of 0.5 m.