An Experimental Analysis of Vehicle Exhaust Noise Signals by Means of Order Tracking Approach

Exhaust noise represents one of the major noise sources in vehicles powered by internal combustion engine, and consequently an important noise pollution contributor in urban environment. Experimental measurements of exhaust noise emissions is often necessary for implementing a subsequent refinement process aimed to reduce noise levels, as established by the new EU Regulations, and to improve perceived sound quality. This work presents the results of an experimental campaign carried out on a gasoline passenger car in order to measure exhaust noise levels and analyze frequency spectra. Specifically, experimental tests were conducted by using a microphone located at a proper distance from the exhaust termination. Acquiring exhaust noise signal in engine rapid run up condition, a depth order tracking analysis has been performed. Different stationary operating conditions have been investigated, too. Of course, all the acquired signals have been triggered with the tachometer signal containing the information about the engine rotational speed. The analysis of the exhaust noise frequency content reveals a predominant noise emission at low frequency range up to 250 Hz, and a particular behavior of the engine orders peak values at some of the investigated operating conditions.