An experimental study of co-axial tailpipe mufflers for internal combustion engines

The design and construction of an apparatus for the investigation of the acoustical effects of radial temperature gradients on the performance of internal combustion engine exhaust elements is presented. An exhaust system with variable elements and a flanged termination into anechoic space is acoustically excited in the frequency range of 500 Hz to 5000 Hz in the presence of a radially decreasing temperature gradient with no bulk gas flow. Sound pressures are recorded in the anechoic space, and insertion losses determined. The acoustic pressures in the outer tube of co-axial tube resonator tailpipes are mapped under uniform temperature conditions. The performance evaluation of co-axial tube resonators indicates that radial temperature gradients have a significant effect on the performance of some acoustical exhaust elements; up to approximately 20 dB more insertion loss at some frequencies with temperature gradients present compared to a uniform temperature condition for a two-hole co-axial tube resonator.