Numerical Investigation of Back Pressure and Acoustic Attenuation Performance of Two and Three Chamber Exhaust Muffler

Two and Three chamber expansion muffler are commonly used in light category vehicle for meeting the noise level legislature requirement. The Helmholtz resonator and expansion chamber are used in exhaust muffler to attenuate the noise in low and middle frequency range. In this work, the effect of expansion chamber size on back pressure is determined using CFD and the same geometry were used to study the acoustic attenuation performance using FEA in the frequency range of 0 to 3000 Hz. Regarding the size of individual expansion chamber there is about 17% increase and decrease in size from base model geometry were considered for performance comparison in both two and three chamber type of muffler. It is found that minimum back pressure of about 241 Pa is observed for 2 chamber base model (2C-B) with slightly higher turbulent kinetic energy value of 77.53 J/Kg. The sound pressure level (SPL) at outlet pipe is less for 3 chamber mufflers and the obtained value is less than 120 dB for most of the frequency range of 0 Hz to 3000 Hz. Similarly transmission loss (TL) is higher for 3 chamber mufflers and the value remains same for 0 to 1600 Hz frequency range and peak fluctuation occurs at higher frequency. The obtained results shows that 3C-A model is having higher noise attenuation performance with back pressure value within acceptable limit.