Analysis of coupling effect between chambers of reactive muffler

Abstract

The efficient optimisation of the sound reduction performance of multi-chamber reactive mufflers has always been a challenging problem, not only because of the presence of multiple muffler units but also because of the complicated interactions between the chambers. Previous studies have shown that the interactions between chambers can significantly affect the performance of mufflers. To better understand the coupling mechanism between the chambers and thus provide guidance for the optimisation design of reactive mufflers, first, the sound propagation characteristics in (1) a muffler with two expansion chambers and (2) a muffler with a resonant chamber and an expansion chamber were solved using a two-dimensional (2D) axisymmetric analytical method, combined with a new analytical model of transmission loss (TL), by considering multiple acoustic modes in the mufflers. The influences of key structural parameters on the chamber-coupling effect of the mufflers were investigated. The results reveal that the noise reduction performance of the first chamber deteriorated while that of the second chamber was improved by the coupling effect. To further understand the coupling effect, the coupling mechanism was analysed using acoustic impedance transfer theory. Impedance-tube measurements were carried out to validate the proposed analytical model and inter-chamber coupling effect. Based on the results, the optimisation of a reactive muffler for a bulldozer was carried out. The results obtained by numerical analyses and experiment reveal that the noise attenuation characteristics of the optimised muffler are obviously better than those of the original muffler, and the average insertion loss (IL) increased by 8 dB.