Acoustics Performance Optimization Of The Exhaust System For A New Car Model

Exhaust system,which is one of important parts of internal combustion engine and connected to the exhaust valve of the combustion engine,plays a key role of exhausting the burned gases successfully and reducing the noise of flowing fluid which caused by the piston and the engine valve.Further more,the acoustic performance of the muffler dictated the acoustic performance and the NVH performance of the vehicle.This paper's research is based on the engineering project,which targets to develop a wanted exhaust system of the passenger car.After testing the idling noise at the tail piple of the original plan,the test results show that the original plan have a dissatisfied accousitc performance at the low frequence.The acoustic model of the engine-exhaust system was established,and the accuracy of the model was calibrated based on the data of the engine pedestal.Then,the transmission loss of the front muffler and the rear muffler was calculated,and results show that the main reason of the dissatisfied accousitc performance at the low frequence of the original plan was that the transmission loss of the front muffler was too low at the low frequence.the back pressure of the original plan was calculated,and results show that back pressure of the original plan was unseasonable.At the base of the analysis results of the original plan's low accousitc performance,the optimized case was proposed,and the comparison of the transmission loss of the front muffler and the rear muffler between the original plan and the optimized case was calculated and the comparison of noise at the tail piple,at the condition of the third gear and whole throttle accelerating.the results show that the transmission loss of the front muffler and the rear muffler of the optimized case was higher than the original plan.The Computational Fluid Dynamics model of the exhaust system was established,and and the comparison of the pressure distribution and the velocity distribution of the front muffler and the rear muffler between the original plan and the optimized case was calculated.the results show that the pressure distribution and the velocity distribution of the front muffler the optimized case was higher than the original plan.A vehicle experiment has tested tail pipe noise of the original plan and the optimized case both at the idle speed and third gear and whole throttle accelerating,and the experimental results show that the optimized case has greater degree of improvement compared with the original plan,which meets the technical requirements.