IC-engine acoustic source characterization in-situ with capsule tube method

Typically, a component level approach is used in control of internal combustion engine (IC-engine) exhaust noise. This has enabled the development of new, cost-efficient silencers, for example. However, prediction of sound emission from a tailpipe or insertion loss of a silencer requires a more extensive, system level approach. Therefore, valid IC-engine source characteristics and a valid model of the whole transmission path are needed. When characterizing an IC-engine as a source with the commonly used in-duct multi-load method, the requirements for load impedance variation must be fulfilled. It is fairly easy to vary the load in automotive cases, whereas new methods must be developed for large IC-engines, used e.g. in power plants. In this study, the source data determination process is investigated in detail, a novel "capsule tube method" is developed further and used for experimental acoustic source data determination of medium speed IC-engine exhaust system in harsh environment. With suitable filtration and statistical outlier rejection methods presented in this paper, the source data of a test IC-engine exhaust system was derived with success.