A Novel Experimental Approach to Increase Shell Stiffness of Double Layered Critically Shaped Automotive Muffler for Optimizing Shell Radiation Noise in a Cost Effective Way

Short development cycles, less packaging space and stringent noise emission rules have increased the need of CAE usage and first time right design approach. Engine exhaust noise is the main contributor of automotive noise when vehicle speed is low to moderate. Exhaust noise contains tailpipe noise and shell radiation noise. As vehicle speed increases, contribution of flow noise and tire noise is comparatively at higher side. The cold end development engineer is responsible to design a muffler to meet tailpipe and shell radiation noise targets. Muffler shell stiffness is a key characteristic for deciding shell radiation noise. High intensity pulses of exhaust gas passes through the exhaust pipe and hits cold end from inside which causes shell vibration and respectively shell noise. There are several conventional methods available to improve shell stiffness, but all of them are not applicable for ‘double layered critically shaped mufflers’ and all of them are not cost-effective. The purpose of this study is to review all traditional countermeasures, to propose and validate new cost-effective techniques to maximize shell stiffness of critically shaped muffler. The muffler boxes of turbocharged and non-turbocharged engines ranging from 1.4 to 1.6L engine volume were considered for investigation. Several trails have been taken for increasing muffler stiffness and the most effective methods are presented here. The use of impact hammer test is done for measuring muffler shell stiffness. At initial stages muffler shell was having 350 Hz natural frequency; with the use of new techniques, we observed that natural frequency of shell can be improved up to 500 Hz. From several experimental studies it has been found that proposed countermeasures are helpful to increase average natural frequency of muffler by 130 to 170 Hz and reducing shell noise by 4-6 dB (A) across all vehicle operating range. Proposed methods are simple, cost-effective and easy to apply in manufacturing.