Project on_Analysis and design of a semi-active muffler
SYNOPSIS
Project on - Analysis and design of a semi-active muffler. (COMSOL)
Abstract:-
In this work, a flow reversal resonator fitted with a short-circuit duct connecting the inlet and outlet is analysed and used as a tuneable muffler element, aimed to be used use in a semi-active muffler on an IC-engine. The work done can be divided into 3 main parts.
1), a study of what type of valve that could be used to change the acoustical properties of the short-circuit duct.
2), Design of a flow reversal resonator with a controllable valve as the short-circuit.
3), experimental validation in a flow acoustic test rig.
The flow reversal resonator with a controllable valve as short-circuit is successfully validated to work as tuneable muffler element during laboratory conditions. The same valve concept is simulated in a full scale concept but not validated experimentally on a running IC-engine.
The theory used to describe the acoustics of a flow duct element is also presented together with three simulation techniques and the two microphone technique used to determine the acoustic properties of the investigated flow reversal resonator.
Background:-
In flow duct applications, such as e.g. IC-engine exhaust systems on cars and trucks, high sound pressure levels are a common problem. The sound is usually attenuated with a muffler in which two different types of silencing elements is used, reflective and resistive. Resistive elements are elements where the acoustic energy is dissipated as heat, such material is e.g. mineral wool and perforated plates. Reflective elements attenuate the sound by destructive interference between sound waves travelling in different directions. Some examples of these are area discontinuities and resonators like the quarter wave resonator and the Helmholtz resonator. Depending of the geometry, the reflective elements will have one or more eigen-frequencies with maximum attenuation. In this work, a reflective type of muffler, the flow reversal resonator, has been studied and modified to act as a semi-active muffler.
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