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Perforated ducts are present in most designs of exhaust mufflers, due to their convenient sound attenuation properties. While suitable tools are available for the estimation of this attenuation, accounting for the influence on attenuation of the perforated ducts for different arrangements, a similar tool but related to the back-pressure generated by mufflers containing perforated ducts is not available. In this paper, the basis for such a tool are set by defining a suitable characterisation of perforated pipes that may allow for the consideration of the influence of a particular perforated duct on the back pressure generated by a given muffler. The results obtained have been validated in a particularly simple case, and the results confirm the feasibility of the proposed methodology, while suggesting possible future improvements.

The use of computer calculation tools in order to reduce the cost of the development of optimized exhaust systems has turned out to be a generalized industrial practice. Therefore, considerable efforts are devoted to the development of suitable calculation tools, which are representative of the real phenomena taking place in the exhaust systems. In the present paper, the results of the application of a hybrid linear/nonlinear calculation method to the prediction of the exhaust noise radiated by I.C. engines are presented. First, a brief description of the method is given. Then, comparison is shown between the results of the calculation and experimental measurements, both for in-duct pressure and for noise radiated. The agreement obtained indicates that this method may be used as a design tool in the frame of the new methodologies presently arising in exhaust system development.