Rapid acoustic assessment of exhaust systems during engine acceleration

Abstract

This study describes new computational and experimental procedures to evaluate the acoustic performance of exhaust systems under the practical operating conditions of a vehicle.  The aim was to facilitate rapid acoustic optimisation.

An advanced experimental technique has been developed which incorporates order analysis methods to acquire precise estimates of the forward and backward travelling complex wave amplitudes at appropriate positions along the exhaust system from the variable harmonic pressure data.  However, capturing such data at regular engine speed intervals requires reliable in-duct pressure records.  The contamination of the acoustic pressure field by flow-induced noise make this a formidable challenge.  Effective procedures are described to yield precise and reliable estimates of the acoustic performance of an exhaust system.  The advantages of the new transient approach (compared to existing procedures, based on constant engine speed conditions) in producing a comprehensive set of rapid results to assess the acoustic properties of a silencer component were demonstrated.

Corresponding predictions were calculated by adapting existing validated linear acoustic code (APEX) to follow the changing flow conditions during normal engine operation.  The new prediction code was applied to the design procedure of an exhaust system, illustrating the potential advantage of facilitating the rapid optimisation of the acoustic performance as opposed to a procedure based on tail-pipe orifice noise emission.

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