The acoustic prediction of internal combustion engine exhaust systems is one of several important aspects needed to meet customer expectations and legislation targets. One dimensional flow duct acoustic simulation tools are already used for the prediction of the exhaust and intake orifice noise at the early stages of the engine development process. For the development of these kinds of prediction tools, experimental flow duct acoustic investigations are needed for better understanding of the acoustic behaviour of the flow ducts and for verification of the acoustic models. Flow duct acoustic measurement techniques and their application for investigating acoustic flow duct properties and verifying prediction models are described in this work. These include acoustical one-port and two-port measurements performed at zero and mean flow conditions for the evaluation of flow duct acoustic properties such as reflection coefficient, transmission loss and attenuation. From these studies it has been found that transmission loss alone is not always sufficient to verify acoustic wave transfer models. Acoustical quarter wave resonators are applied for reproducing resonant frequencies due to extended pipes into chambers. The influence of flow on these resonances has been investigated experimentally. Furthermore, the application of acoustical Helmholtz resonator models is discussed to account for some experimentally identified resonance frequencies.
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