REVIEW OF THEORETICAL AND EXPERIMENTAL ASPECTS OF ACOUSTICAL MODELING OF ENGINE EXHAUST SYSTEMS

In an internal combustion engine, the engine is the noise source and the exhaust pipe is the main transmitter of noise to the atmosphere. Mufflers are often used to reduce the engine noise radiated from the exhaust pipe. To optimize a muffler design, a series of experiments can be conducted using various mufflers installed in the exhaust system. For each exhaust system arrangement, the radiated sound pressure can be measured. However, this is not a very efficient approach and there is no guarantee that an optimum arrangement is attained. A second approach is to develop a scheme involving only a few measurements, which can be used to predict the radiated sound pressure at a specified distance from the open end of the exhaust pipe. In the research work reported here, the engine exhaust system was modeled as a lumped source-muffler-termination system. An expression for the predicted sound pressure level was derived in terms of the source and termination impedances, and the muffler geometry. The velocity source and monopole radiation models were used for the source and the open end of the exhaust pipe, respectively. Four-pole parameters were used to relate the acoustical properties at different cross sections of the muffler and the exhaust pipe.