Linear acoustic simulation and experimental characterisation of a modular automotive muffler

Abstract

Development schedules and acoustic performance criteria for automotive mufflers require ever-increasing understanding of the flow phenomena inside the muffler. The ability to predict the effect of changes to the muffler layout quickly and accurately is needed. One option is to use a linear acoustic (frequency domain) approach to simulate the different parts of the muffler. This has the advantage of being extremely quick compared to both non-linear (time domain) simulation methods and experimental techniques. In order to test this approach a modular version of a production automotive muffler consisting of multiple chambers, perforated baffles and pipes with perforated sections is used. The arrangement of the muffler can be changed in terms of porosity of perforated sections, positions of baffles and lengths of pipes. A linear acoustic computer simulation is then used to predict the transmission loss of different configurations of this modular muffler. All parts of the muffler are modelled using fundamental linear acoustic elements such as pipes and quarter wave resonators. The perforated sections are modelled using lumped impedance elements based on theoretical models for the flow through the holes. Measurements of the transmission loss of two different configurations of the modular muffler are used to validate the simulation models. These measurements are done using cold flow on a test bench using the two microphone method.