Simulation Of Acoustic And Fluid Dynamic Performance Of Reactive Exhaust Mufflers

Exhaust muffler is playing the most important role in reducing the exhaust noise,which contributes the most in the engine noise of automobiles. At present, acousticperformance and fluid dynamic performance are considered as the two key factors in theevaluation of mufflers. The former performance shows the ability of reducing noiseswhile the latter performance indicates the level of backpressure produced by mufflers.Thus a general analysis of the muffler’s performance is quite necessary.In this thesis, a comprehensive study of the muffler’s acoustic and fluid dynamicperformance was conducted. Transmission loss and pressure loss of certain mufflerswere computed specifically.Firstly, the transmission loss of three groups of imperforate muffler components andfour groups of perforated muffler components was computed, and the influences ofseveral factors to the transmission loss were also analyzed. Results show that theacoustic performance of imperforate muffler components is strongly associated withtheir structure parameters, such as expansion ratio and location of outlet pipe. And forthe perforated muffler components, in addiction to corresponding structure parameters,factors like porosity also affect their transmission loss significantly. Particularly, forcomponents having two or more inlets, the location of all the inlets also impacts theacoustic performance remarkably.Next, the pressure loss of all the muffler components was computed, along with theanalysis of inner fluid distribution. Results indicate that the pressure loss of allcomponents increases when the airflow at the inlet accelerates. For specific mufflercomponents, the pressure loss of mufflers having insertion tubes is lower than that ofsimple expansion chambers with the same velocity of the airflow at the inlet, while thepressure loss of simple expansion chambers is lower than that of mufflers having sidetubes or multiple outlets. For perforated muffler components, the pressure loss is verylow when the perforated structure is used as a resonator, while the pressure loss is muchhigher when the perforated structure is used as a channel for the airflow.Finally, models of a certain complicated exhaust muffler were established, whichwas used in heavy-duty trucks. Transmission loss and pressure loss of this muffler werecomputed. Improved mufflers were designed according to results derived from formercomputation. It shows that, compared with the original muffler, the transmission loss of improved mufflers has increased and, meanwhile, the pressure loss of improvedmufflers has decreased.