Acoustical source characterization studies on a multi-cylinder engine exhaust system

It is well known that the characterization of the acoustic source in an exhaust muffler system is of utmost importance in the proper evaluation of the acoustic performance of the muffler. However, in the literature, there are very few experimental studies on source characterization of a multi-cylinder internal combustion engine. This paper describes the use of a transfer function method (with a random excitation source) for measurement of the internal source impedance of an eight-cylinder engine under running conditions. The results obtained agree well with those obtained by the standing wave method by earlier investigators. The studies include the effect on the measured internal source impedance caused by variation of engine speed and load. The source impedance results obtained for the engine in operation are compared with those for the engine not in operation. The use of these results in the overall modeling of the exhaust system is described in an accompanying paper.