Sound Absorbing Material: Study of Acoustic Properties and its effect on Exhaust Muffler Noise and Performance

Paper #:
  • 2018-01-0143

  • 2018-04-03
With increasing market competition in low cost and mid-range vehicles, it’s important to delight the customer with value for money in terms of better NVH and higher fuel efficiency. Exhaust system plays an important role in noise attenuation and has to be worked upon for the better NVH characteristics without affecting engine performance. This can be achieved using Absorptive/Hybrid mufflers. Glass-wool’s effectiveness is governed by its physical and mechanical properties; this paper focuses on the sensitivity analysis of above properties using CAE for improving the acoustic simulation and its correlation with Testing and subsequently establishing process for acoustical development of mufflers.The study of Porous material in an acoustic field is based on Biot theory. Biot parameters (porosity, flow resistivity, tortuosity, viscous characteristic length, and thermal characteristic length) and Sound absorption coefficient for different sound absorbing materials which are commonly used in the hybrid mufflers were tested and eventually a material database was generated. Sensitivity analysis using 1D and 3D simulation software was done to understand the contribution of each Biot parameter on overall acoustics of a muffler. Output of this sensitivity analysis was used to predict accurately the transmission loss of a muffler. Simultaneously, backpressure and Tail pipe noise were also checked for engine performance. Thus a standard process was established for development of an efficient hybrid muffler for initial stages of vehicle design. CAE simulation process was established and a guideline for selection of glass wool depending on type of application and frequency range of interest was defined. Also a complete sound absorbing material database was generated through extensive testing for future model developments. The process will help the designers for specifying correct porous material properties to the material supplier for ensuring better sound quality. Thus reducing prototyping cost, time and testing efforts.
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