Muffler Internal Geometry Parametric Study Related to Sound Transmission Loss and Pressure Drop

Abstract

A muffler is a device used to attenuate noise generated in an exhaust system. The current research objective is to study the changes in internal muffler geometry effect towards the sound transmission loss (STL) and pressure drop (PD). A complex muffler of 1.6L natural aspirated engine was chosen for this research work. The research tools used were Ricardo Wave Build and Wave Build 3D. The four focus parameters: main muffler volume, pipe diameter, porosity of the baffle and porosity of the inlet pipe. The effect of internal geometry was analysed from the parametric studies. When the muffler volume increased by 10%, the average STL increased by 1% and the PD reduced by 2% respectively. When the diameter of the pipe increased with fixed muffler volume, the average STL dropped by 9% and PD dropped by 30%. The perforated on baffle showed less effect on average STL which can increase by a maximum of 1 dB and PD showed an average reduction by 0.8% as the perforated on baffle increased. For the case of perforated on pipe, as perforated on pipe increase, STL improved less than 1dB and PD reduced by 7%. From the result of all parametric studies, the STL was mostly affected by the muffler main volume while PD was affected by the pipe diameter.