Noise emission of combustion engines is a major development concern. The engine internal excitations are minimised; the combustion process is tuned, tight tolerances are applied to machining, alignment and balancing of parts, vibration dampers are applied to pulleys and the modes of the rotating parts are optimised. The engine structure is also optimised by stiffening the main structure, careful design of component mounting interfaces, damping treatment to surfaces, close shields, etc. When optimising the engine structure, effectively, the transfer between the internal excitation forces and the sound pressure around the engine in (semi-)free field is minimised. This paper will concentrate on exposed surface optimisation. A new artificial excitation measurement technique is presented to identify the noise contribution of exposed surface parts to the noise emission.
