Berlin 2005 – wissenschaftliches Programm

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AK: Akustik

AK 5: Thermo- und Strömungsakustik (Sitzungsorganisation: Martin Ochmann und Rafael Piscoya, Berlin)

AK 5.8: Hauptvortrag

Dienstag, 8. März 2005, 16:00–16:30, TU EB222

Measurement and simulation of the acoustical impedance of an internal combustion engine exhaust. — •Rene Boonen and Paul Sas — KULeuven, Faculty of Engineering, Dept. Mechanical Engineering, PMA, Celestijnenlaan 300B, B-3001 Leuven, Belgium

In this investigation, the acoustical impedance of an internal combustion engine is measured and simulated. The measurements are based on the two microphone transfer function method, which is described in the standard ISO/FDIS 10543-2. The method uses the transfer function between two microphones positioned on a waveguide connected to the impedance to be measured. Some improvements are proposed to this procedure, concerning the calibration of the measurement setup. New corrections are proposed to eliminate the speed of sound, the microphone locations and the the deviation between the microphone responses.

The method is applied to measure the acoustical impedance of an engine. The reflection coefficient at the engine exhaust is measured. From the reflection coefficient, the acoustical impedance is determined. To prevent the engine to disturb the reflection coefficient during the measurements, the engine is run with an electric motor and the intake is sealed.

The simulations are carried out using electrical analog circuits. The circuits are built by analyzing the engine parts contributing to the acoustical impedance. The electrical analog components are determined using the geometrical data of the engine and the exhaust manifold. The simulation results correlate well with the measured impedances . Also, some special cases are simulated, to determine the engine components which contribute primarily to the acoustical impedance.