Non-Restricted Muffler Design and Acoustic Performance Analysis

A muffler is a component of exhaust system of an automotive used to attenuate engine noise to surrounding. Muffler is a necessary because the sound pressure coming from the combustion in piston of the engine would generate extremely loud noise, if sent directly to the atmosphere. There are mainly two techniques to dampen the noise; reflection and absorption. In reflective mufflers the sound wave reflection principle is used to create a maximum amount of destructive interferences. In absorptive mufflers the principles of sound absorption is used to dampen noise by use of sound absorbing materials in it. In this work a non-restricted mufller is designed with sideways resonating chambers while there is no restriction to gas flows. This type of designs can increase the engine performance since there is no back pressure but reduces noise attenuation. The performance is determined numerically by method of Transmission loss. Transmission Loss in muffler describes the acoustic performance of a muffler. The higher Transmission loss in a muffler design indicates better noise cancellation. Transmission loss at different frequencies of a muffler can be calculated as by taking the logarithmic ratio of input power to output power respectively. In this experiment a non-restricted muffler is designed and performance is analysed numerically using finite element methods. The above CAE-image shows propagation of sound pressure level in the muffler design at 1250Hz. The maximum sound pressure area is plotted in red while minimum sound pressure is plotted with blue colour.