DETERMINATION OF THE ACOUSTICAL SOURCE CHARACTERISTICS OF AN INTERNAL-COMBUSTION ENGINE BY USING SEVERAL CALIBRATED LOADS

A least squares method is applied to characterize an internal combusti on engine considered as a noise source. It is shown that, although ext remely severe conditions exist (high sound pressure level, high temper atures, turbulent how, etc.), a linear theory can predict the noise le vel at the output of the exhaust systems with a surprisingly good accu racy when the transfer matrix is known. The measurements avoid the use of calibrated internal microphones; Only one external microphone and a set of calibrated loads are needed. An indirect validation of the li nearity hypothesis is achieved and the predicted exhaust noise level i s compared with experimental results in the case of a tube and in the case of a silencer composed of three expansion chambers.