Development of a Noise Prediction Technique for Designing a High-Performance Muffler of Motorcycle

Motorcycle exhaust mufflers are important devices which influence not only exhaust noise and engine performance but also appearance of motorcycle. Since the improvement of engine performance often contradicts the attenuation of exhaust noise in designing mufflers, it is necessary that both the exhaust noise and the engine performance are predicted simultaneously. Recently, unsteady-state one-dimensional computational fluid dynamics (1-D CFD) analysis is being applied to this problem. We have developed the technique to predict engine performance and exhaust pulsating sound by adopting unsteady-sate 1-D CFD analysis (here, we treat the exhaust pulsating sound which is a discrete frequency component of exhaust noise). In this paper, firstly, as a result of a preliminary study, it is shown that our prediction technique can predict the acoustic transmission loss of a muffler. Next, it is presented that the analytical result of pressure pulsation reasonably agrees with the experimental result in the exhaust system of a four-stroke engine. Finally, in order to predict the radiation field of exhaust pulsating sound precisely, the transfer function is investigated. As a result, it is found that our sound radiation model is almost appropriate.