With the increase of low frequency noise importance engine exhaust noise has been discussed more and more in the industry, especially for large engine manufacturers. For both maritime and power plant businesses, strict noise regulations are often applied to protect the neighbourhood's living comfort. Thus, it is important for the engine manufacturer to understand the engine exhaust noise features, its impact to the surroundings and the way of reliably measuring and informing to customer the engine exhaust noise level. Wärtsilä studied on large engine exhaust gas noise more than a decade ago and a relatively reliable in-duct exhaust noise measurement system has been realised and used for years. Lately in cooperation with VTT, even more knowhow and confidence has been built on this subject. An entire exhaust pipeline system in Wärtsilä Vaasa factory was modelled and the exhaust noise propagation in the pipeline was calculated. From both simulation and measurement, the challenges and uncertainties of in-duct exhaust noise quantification were revealed. The exhaust pipeline geometry and the exhaust gas temperature influence on the noise level were investigated. This paper will start from the correlation of exhaust noise and environmental noise in real life and mainly discuss on the in-duct noise propagation features and measurement techniques in practice. The absence of a worldwide guideline for large engine in-duct exhaust noise measurement is addressed and the important factors for achieving reliable exhaust noise information are explained in detail.
