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 combustion engine considered as a noise source. It is shown that, although extremely severe conditions exist (high sound pressure level, high temperatures, turbulent how, etc.), a linear theory can predict the noise level at the output of the exhaust systems with a surprisingly good accuracy 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 linearity hypothesis is achieved and the predicted exhaust noise level is compared with experimental results in the case of a tube and in the case of a silencer composed of three expansion chambers.