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This paper presents a numerical study of reactive-type automotive mufflers. The main objective of the paper is to study the effects of various geometrical parameters on the muffler performance. Transmission losses (TL) are used to characterize the performance of the mufflers. Commercially available solver, ANSYS [1] is used to solve the muffler TL characteristics. The paper also summarizes the development of a general-purpose program capable of modeling complex muffler cavities using ANSYS parametric design language (APDL). APDL is a scripting language that is used to automate common tasks and build the model in terms of parameters. The program takes the key geometric parameters of the muffler as input variables and creates the muffler geometry, hexahedral-structured mesh, applies suitable boundary conditions, solves and then post-processes the results. The program provides good flexibility in creating complex (perforations) geometric models.

The air induction system of an automobile engine contributes to the noise level generated by a passenger car. The contribution is significant in the perception of vehicle noise quality. There is a great value in reducing and controlling passenger car air induction noise. Helmholtz resonators are widely used for noise reduction in vehicle induction and exhaust system. These resonators are usually mounted as side branch volumes to the main induction system, occupying larger space. The design presented here describes the use of compact inline Helmholtz resonator (Patent application no. 190/Bombay/98) for elimination of low frequency noise character in passenger car. Finite element model of the acoustic cavity of induction system along with the inline resonator is made. The transmission loss characteristics computed analytically correlates very well with the experimental transmission loss characteristics.

Measurement of sound intensity techniques has very good application in the source identification of a particular noise character. It has been applied effectively along with modal analysis and FE experimental excitation techniques to find out root cause of a particular noise character in small gasoline engine. A FEM shell model was used to make cylinder block and cylinder head model. FEM simulation was carried out which matched with experimental results. It helped to remove the noise character from engine. The other part of the paper describes the noise reduction of the crankcase cover used for the same motorcycle. It houses crankcase as well as two speed gearbox. The methodology involves very effective combination of experimental harmonic analysis, FE model with the shell element for the 3 piece crankcase cover, and experimental measurements. A particular sequence of this experimental techniques along with computer simulation techniques gives extremely good results.