Testing issues with breakout noise of mufflers

There is an increasing need for lighter yet high performance mufflers for use in lightweight aircraft. As muffler shells become lighter, breakout noise or noise radiated by the muffler shell and end plates may dominate true exhaust system performance. The objective of this paper is to compare the sound power level from the outlet to the breakout sound power for a lightweight muffler. It is shown that the breakout sound power is on the same order of magnitude as and sometimes exceeds the transmitted sound power from the outlet. This influence is shown experimentally and via numerical analysis. It is also demonstrated that noise from the end plates, which are flat, can exceed that from the cylindrical shell for the same material thickness. At the conclusion of the paper, a design approach is discussed based on these results.