Research of Engine Exhaust Muffler Based on Finite Element Analysis of Acoustic and Unsteady Viscous Flow

The muffler is the main component to deal with the exhaust noise of an engine. Based on the designed bench, the spectral characteristics of the exhaust noise before and after installing the muffler are analyzed and compared to the expected NR curve, to find the bad frequency bands of the muffler performance. According to the theory of the fluid mechanics and the acoustics, based on the finite element analysis, the performances of a complex muffler in the unsteady viscous flow state are analyzed, including the pressure field, the temperature field, the flow regeneration noise field and the major frequency band of the regeneration noise, meanwhile, the transfer loss in the steady-state and the acoustic-mode of the air is obtained. It is shown that the flow regeneration noise is the major factor to deteriorate the high-frequency muffler performance. Based on the numerical model analysis of the muffler, the relation between the structure characteristic of its simple cavity and its muffler performance is obtained, and the special perforated structure of the muffler can be improved and the sound-absorbing materials are also selected. Through testing of the bench, the insert losses of the original and improved mufflers are obtained, which shows that the above analysis is reliable.