The study of acoustics of muffler with multiple chambers by experiment and the finite element simulation

• Main Authors: Tsai-Jay Hung, 洪才傑
• Other Authors: James Shih-Shyn Wu
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/72236355905422680396

碩士 === 國立中興大學 === 機械工程學系所 === 103 === Although the muffler is not designed to serve all primary exhaust functions in the combustion engine, it is a necessary part. After the fuel burns in the engine, the waste gas generated is exhausted in a waved state at high speed and high pressure, which makes extremely loud noise. Generally, an exhaust system includes a series of in- and out-pipes and a chamber with a larger volume. The fiberglass attached to the pipe inner wall can effectively decrease some of the sound pressure of the waste gas. However, the structure of the chamber may cause a harmonic motion to produce the function of destructive interference to decrease the wave energy and descend noises in different levels. The study of the relation between mufflers and noise can make design work on the exhaust system a significant research topic. Bafflers are one of the most commonly used silencers used in mufflers. When mufflers install with baffles, the sound waves travel through the chamber will be changed. The location of the baffles may change the length of sub-chambers formed in the chamber and fits a specific sound wave with the length of a sub-chamber, it becomes a good device obtains the purpose of increasing the transmission loss for a specific frequency of sound waves. In the beginning of this study, the acoustic transfer within the cavity is learned by using plain wave theory. With the experiment results, the transmission loss is evaluated and compared by four pole method. The experiments concern mufflers with the solid and the perforated pipes, environment temperature, and multi-chambers. Moreover, simulation with the finite element models is also used to compare results from experiments. More studies on the finite element models concerning with the pipes, bafflers and environmental temperatures have done to understand the characteristics of different muffler designs. It is concluded that mufflers with perforated pipes provide better quieting effect, and bafflers must be placed uniformly in the chamber which can benefit the multiplication of Helmholtz resonance. The best frequency and its transmission loss can also be evaluated on chambers with minimum length.