Investigation on the Effect of Design Feature on Acoustic Performance of Exhaust Muffler for Vehicle 2022-28-0488

Primarily, Acoustic performance of muffler are evaluated by insertion loss (IL) and backpressure/restriction. Where Insertion loss is mainly depends upon proper selection of muffler volume, which is proportional to Engine Swept volume, along with internal design configuration, which drives the acoustic principle. Same time, meeting the vehicle level pass by noise (PBN) value as per regulatory norms and system level backpressure as per engine specification sheet are the key evaluating criteria of any good exhaust system. Here, a new Reactive/Reflective type muffler of tiny size have been designed for heavy commercial vehicle application, which is unique in shape and innovative to meet desire performance. In this design, mainly sudden expansion, sudden contraction, flow through perforation and bell-mouth flow phenomenon are used. The performance of this tiny muffler are optimized using multilevel design of experiments (DoE) by the measurement of pass by noise (PBN) and near exhaust noise (NEN) level and Backpressure of exhaust system along with predictive design calculation. The primary objective of this research is to investigate the effect of four design factors namely perforation percentage, perforation hole diameter, baffle thickness and baffle position on both acoustic performance and backpressure. The other objective is to do the comparative assessment between tiny size reactive muffler and existing 3-chamber hybrid or combination type muffler in holistic approach on typical heavy commercial truck. This comprehensive study reveals the importance of perforation baffle feature (preformation percentage, Perforation-hole diameter, baffle thickness) and baffler positioning in two chamber muffler to tradeoff between Noise (PBN & NEN) and Backpressure. Even though, the new muffler is meeting the regulatory norms but acoustic performance is marginally inferior to available hybrid type muffler. The predictive insertion loss value found matching with 98% accuracy. Further, the new muffler found very much cost effective, lighter weight and ease package-able/manufacture-able than existing one.