CHARACTERIZATION OF RASPING NOISE IN AUTOMOTIVE ENGINE EXHAUST DUCTS

Abstract This paper presents an experimental study of a non-linear acoustic phenomenon resulting in the generation of a large high component in the automotive engine exhaust system. This phenomenon may occur when an engine is submitted to an abrupt acceleration. The perceived noise, known as “rasping noise” has a metallic and strident tone. The results of frequency and wavelet analysis of the tailpipe noise are presented. Both of them show that a high-frequency component is instantaneously generated at a critical engine speed. An efficient criterion based on multiresolution wavelet analysis is proposed in order to detect the rasping occurrence and quantify the rate of high-frequency component in the tailpipe noise. The obtained results are well correlated with subjective analysis. The analysis of the internal pressure along the exhaust pipe shows that the rasping noise is generated in the intermediate tube and that the acoustic pressure measured at the exit of the manifold does not contain any high-frequency component. The authors favour the hypothesis of non-linear coupling between resonance modes which explains the sensitivity of the rasping noise generation to the slope of the acceleration.