Acoustic Field Analysis and Noise Reduction for Straight Exhaust Pipe

Shen-Min Liang ； Kai-Hsiang Ku

《應用聲學與振動學刊》 5卷1期 (2013/06) Pp. 31-41

https://doi.org/10.6282/JASV.2013.5.1.04

摘要

連接著內燃機的排氣管會有許多周期性震波排出。當震波離開管口時，會在管口處發生震波的繞射與反射的現象，因而造成排氣管口下游的噪音產生。本研究主要是針對降低排氣下游的尾流的噪音，因而設計出排氣管尾部消音器，以進行減低噪音。為此，本研究執行數個減低噪音的實驗，使用B & K公司的麥克風（B & K 4190）及頻譜分析儀（B & K 3550）來量測距離排氣管出口25 cm與50 cm之噪音量，量測位置在由排氣管中心軸起算，每隔15度角量測一次。並對本文設計之消音器內裝設有消音棉（玻璃纖維）及不同空氣層（airspace）厚度之消音效果做量測。研究發現2 mm厚空氣層有較佳減噪效果。並以一商用排氣管作為測驗，進行原地噪音量測，結果顯示：當尾管加裝消音棉與空氣層（airspace）時會比原先商用排氣管的噪音量下降。在距離排氣尾管管口50 cm時，引擎轉速為3,000轉，減噪量為0.8-1.9 dB (A)；在引擎轉速為4,000轉，減噪量為0.8-2.9 dB (A)；在引擎轉速為5,000轉，減噪量為0.8-2.0 dB (A)。

關鍵字

排氣管 ； 降低噪音 ； 玻璃纖維 ； 聲壓位準 ； 消音器

並列摘要

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.

並列關鍵字

Exhaust Pipe ； Noise Reduction ； Fiber Glass ； Sound Pressure Level ； Muffler