In this study, a muffler fitted to 2600cc-level agricultural machinery engines was removed and replaced with an exhaust after-treatment system to satisfy the tier-3 regulations for gas emissions. An analytical method was applied to assess whether the after-treatment system offers a noise reduction effect equivalent to that of the replaced muffler. While a desirable noise effect was displayed at 5 Hz because of a dramatic increase in transmission loss, overall performance was inferior to that of other exhaust after-treatment models. Comparison of average noise effects revealed that the DOC-DPF-SCR-AOC model showed the best performance. In a 1/3 octave analysis, the muffler and the DOC-DPF-SCR-AOC model were compared and it was found that the noise performance of the DOC-DPF-SCR-AOC model was better by, on average, 60% from 0 to 300 Hz, and 65% from 0 to 1,000 Hz, than the muffler.

muffler, noise, octave, sound power level, transmission loss, white noise.