SILENCING TECHNIQUES

The author examines the problems of silencing techniques in relation to internal combustion engines. Two methods are discussed: the reactive system and the resistive system. Each system is described, the reactive type consisting of a set of acoustic filters, and the resistive system comprising porous packing material filling an annular chamber around a perforated or mesh tube: energy is removed from the vibrating gas by inertia and frictional resistance. The problems of counteracting aerodynamic noise are discussed, together with the significance of back pressure and silencer performance. Details are given of a method of analysing the noise output of the reactive type of silencer, which produces an "engine noise signature" in the form of a narrow band spectrum, plotted against wavelength; the wavelengths of the loudest constituents of the noise spectrum are apparent, and hence it is possible to determine the lengths of the annular chambers around the pipe intrusions needed to filter them out. The importance of ensuring that none of the pipe lengths is designed such that its fundamental frequency or any of its harmonics coincide with those of another pipe is emphasised. Influencing factors such as speed and temperature of the exhaust gas are considered. It is concluded that with future developments in car design related to fuel economy, clear exhaust gas, and low noise levels, the problems of aerodynamic noise will be stressed. /TRRL/

  • Corporate Authors:

    IPC Industrial Press Limited

    33-40 Bowling Green Lane
    London EC1R 0NE,   England 
  • Authors:
    • GARRETT, K
  • Publication Date: 1975-2

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Filing Info

  • Accession Number: 00126256
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Feb 19 1976 12:00AM