Locally resonant stop band acoustic metamaterial muffler with tuned resonance frequency range

Exhaust noise and pollution are the main environmental drawbacks of internal combustion engines. Although humans may seem to have become accustomed to noise, but they are continuously exposed to its risks. This paper aims to investigate exhaust noise and provide an improved design for the construction of muffler internal baffles. In this regard, locally resonant acoustic metamaterial baffles (AMB) were shown to be promising in the sense of transmission loss at desired high, medium and low-frequency domains. Hence, in terms of acoustic performance, a specific frequency range was targeted to be influenced by the changes made in the design of AMB resonators. To better characterize the AMBs, the arrangement and number of baffles were studied using resonators with different natural frequencies. Results were compared to those related to an empty cylindrical muffler model and previous studies. Findings indicate that the AMBs clearly enhance the muffler transmission loss to values up to 85 dB and that not only resonator dimensions, but also spacing of the baffles play an important role in the improvement of the transmission loss. Finally, to evaluate the real operational performance of the muffler, important factors such as flow and pressure drop are also considered and highly reasonable results are obtained.