Performance Analysis And Improvement Of Automobile Exhaust Muffler

It is an important topic to design a muffler with high performance and low pressure loss in the field of automobile noise control.But the traditional design of muffler were carried out according to the size and recommended parameters by the experienced designer and the transmission loss was used as the acoustic performance evaluation index.To a certain extent,this method can obtain the acoustic performance of the muffler,but it can't get the actual attenuation effect after coupling the muffler and the engine.Because the transmission loss depends only on the muffler structure itself,other than the acoustic characteristics of the sound source and the end of the pipe.In addition,when the muffler acoustic performance is poor,the optimization design of structural parameters are carried out separately.This optimization method fails to consider not only the mutual influence of the various parameters,but also the overall performance of the muffler.In order to make a reasonable improvement of a certain automobile muffler and obtain its actual acoustic and aerodynamic performance,first of all,the simulation model is built based on the GT-Power software.Then the insertion loss and pressure lost are analyzed based on the fact that the outlet pressure,flow rate,temperature and other related physical quantities are defined as the boundary conditions.The results show that: In the range of 1000-2500 r/min,the insertion loss of the muffler has not met the requirement,especially at the common speed 2500 r/min,the simulation value and the target value have the biggest difference and the noise elimination effect is poor.With the increase of speed,the pressure loss of the muffler is increasing,but it is far smaller than the target value of 0.20 bar,so the aerodynamic performance is good.Secondly,conducting the 1/3 octave analysis of the tail pipe noise at the speed whose insertion loss is low to determine the distribution of main noise frequency range,which indicates the direction for the subsequent optimization.On this basis,the connection pipe diameter between main and auxiliary silencer,perforation diameter and the length of tail pipe are selected as optimization parameters and the effect of the three factors on the tail pipe noise and pressure loss are discussed separately.The results show that the tail pipe noise decreases with the connecting pipe diameter decreases but the pressure loss is opposite;Both the pressure loss and tail pipe noise will increase with the diameter of perforation increases but not significantly;Increasing the length of tail pipe can reduce the tail pipe noise and has little influence on the pressure loss.Finally,the muffler has been improved based on the DOE method,results shows that the insertion loss not only increases from 19 d B to 30 d B at the common speed,meeting the requirement of the technical standards of automobile exhaust muffler,but also increases at the whole speed range;while the pressure loss increases from the original 0.10 bar to 0.13 bar,the change is small and far below the maximum limit value of the 0.20 bar,thus the comprehensive performance of the muffler has been significantly improved.