FLOW AND ACOUSTIC ANALYSIS OF TWO-WHEELER MUFFLER

Abstract

Muffler manufacturers are being confronted with the problem of designing mufflers with low restriction as well as low radiated exhaust noise. Increased competition and stricter regulation norms have intensified the need for development of an efficient muffler. The traditional “build & test” procedure which is time consuming and expensive, can nowadays be assisted by simulation models which are able to predict the performance of several different muffling systems in a short time, thus saving time and resources. Generally, mufflers should be designed to satisfy the two requirements. One is high noise attenuation performance, which is a fundamental requirement of a muffler. An exhaust muffler should muffle the frequency range of interest, especially the low frequency range, because it is well known that most of the noise is limited to the engine rotational frequency and its first few orders & the second is minimum back pressure, the extra static pressure exerted by the muffler on the engine through restriction in the flow of exhaust gases. This needs to be kept to a minimum, because a large back pressure will result in reduction of volumetric efficiency and the specific fuel consumption rate. These two important design requirements for a muffler are often contradictory. The purpose of this work is to investigate the flow and acoustic performance of a 100 cc two wheeler muffler. The computational fluid dynamic (CFD) analysis is done to predict the flow performance by finding the flow parameters, pressure and velocity. When it comes to acoustical performance, there are several parameters that describes the characteristics of a muffler, the transmission Loss (TL) is the most popular amongst them because of the reason that it is a property of the muffler only and it doesn’t depend upon the sound source. It can also be useful, to check the validity of a mathematical model. For acoustic analysis, the transmission loss of the present muffler was predicted using commercial software package. At first the design was investigated for single expansion chamber, by doing harmonic acoustic analysis and the validation is made with the analytical results. Then the validated procedure is adopted for the concept muffler and results are compared with the experimental results. Comparing measured and FEA results allowed assessment of the accuracy and reliability of the simulation.