Sound transmission loss of particulate filter of exhaust system by homogenization method

Abstract

Diesel or gasoline particulate filters are included in almost all vehicles to clean emission gas from internal combustion engines. On the other hand, a new regulation for vehicle noise emission has been into operation, and noise from exhaust system must be reduced. Although mufflers with expansion chambers and sound-absorbing material are mainly applied to reduce noise emission, diesel or gasoline particulate filter can reduce noise transmitted through the filter. In this study, sound transmission loss of diesel or gasoline particulate filter is measured and some amount of sound transmission loss is found to be obtained. Then, we propose a method to predict sound transmission loss of diesel and gasoline particulate filters from a microstructure model of ceramic porous material that is applied for filters. Homogenization method for sound-absorbing poroelastic material based on the asymptotic expansion approach is applied in this study. This method was proposed by one of the authors of this study. Microscopic structure images are obtained by scanning electron microscope, and the size of pores are identified by image analysis. Homogenized properties, such as equivalent density and bulk modulus are calculated by performing microscopic analysis with unit cell finite element model. Finally, sound transmission loss is obtained by macroscopic calculation with homogenized properties. Numerical sound transmission loss agrees well with sound transmission loss measured by acoustic tube and simplified exhaust system.

Keywords

• diesel particulate filter
• gasoline particulate filter
• sound transmission loss
• exhaust noise
• exhaust muffler
• homogenization method
• microscopic structure