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In order to describe simultaneously the thermo-fluid dynamics and the acoustics of an Internal Combustion engine, a mathematical model and a computer program has been developed which integrate the Method of the Characteristics with the Acoustic. Transfer Matrix Method. The former method is currently used to model the fluid dynamics of Internal Combustion engines, whilst the latter allows the description of the acoustical behaviour of the intake and exhaust systems. The theory presented in the article integrates the two approaches, allowing the fluid-acoustics of the global system engine-silencers to be described, taking into account the mutual interactions. Preliminary investigations on a simplified system, constituted of a constant section duct, have demonstrated the consistency and validity of the model.

In recent years, car manufacturers have been shifting their efforts towards improving quality of interior noise, rather than simply reducing noise levels. One of the most important issues, which is today widely accepted, is that noise contains information. Slamming noise should warn us that doors are safely closed, control panel pushbutton “clicks” inform us about the correct turning on of devices, etc.. One of the acoustic researchers' task is therefore to modify the original noise to emphasize quality of information and to reduce annoying components. For these reasons, it is very important to affect noise timbre, by investigating the relationships between mechanical and acoustical parameters. In this paper we describe a workstation (which we have called N.O.T.E.: Noise Optimizator for Thermal Engine) for intake and exhaust system noise synthesis, that integrates an acoustical simulation code with a synthesizer.