Parametric studies on muffler internal geometry related to sound transmission loss and pressure drop

Abstract

Muffler is a device to attenuate noise generated in the exhaust gas. Based on the current noise regulation, automotive manufacturer was forced to improve the muffler performances. Parametric approached was used to improve the existing muffler performances rather than designing a new muffler. The research aim was to investigate the effect of main muffler internal geometry towards STL and PD across the muffler. A comprehensive parametric study was conducted to analyse the effect of muffler internal geometry towards its performance. Two mufflers were selected in this research work; one simple expansion chamber and the other was a complex muffler 1.6 litre natural aspirated engine. Both mufflers performances were measured experimentally using impedance tube and SuperFlow bench machine. The simple expansion chamber was used to validate the proposed concept of 1D model generated by Ricardo WAVE meanwhile, the complex muffler was used for comprehensive parametric studies to investigate the effect of internal muffler geometry towards STL and PD using the 1D model. Four parameters were examined, namely main shell volume, pipe diameter, perforated baffle and perforated pipe. The effect of internal geometry was analysed from the parametric studies. When the muffler volume was increased, the average STL was increased and the PD was reduced, respectively. When the diameter of the pipe was increased, the average STL and PD were dropped. The perforated on baffle showed less effect on average STL where it can increase by a maximum of 1 dB. However, the PD showed a reduction trends as the perforated on baffle was increased. The perforated on pipe shows major effect at 600 Hz only and PD reduced as the perforated on pipe was increased. From the parametric studies, the STL was mostly affected by the muffler main volume while PD was affected by the pipe diameter. In order to minimise the PD, the perforated was introduced to the muffler design. Adding a resonator and increasing the baffle spacing help to improve the muffler performances. As a result, the complex muffler was successfully optimised with an increase in average STL by 3.59% and maintained the PD.