Research On Theacoustic Performance Of Engine Exhaust System Components

As vehicles become more and more important in people’s daily life, peoplebecome extremely critical about the performance of vehicles. The exhaust noise isone of the main part of the vehicle noise, and the exhaust system can significantlyaffect the exhaust noise if the contractures of its components change. Structure ofcatalytic converter carrier and tail pipe are of great importance to the acousticperformance of the exhaust system, but there is not enough research in this field. Tothrow light upon the relationship between the two components structure and theexhaust noise, these two components with different structure Parameters wereinvestigated through simulation and experiments. The simulation also took differentflow field Parameters into consideration.The main work includes both simulation and experiment Part. The simulation ismainly based on the three-dimensional modeling and CFD software Fluent. First thethree-dimensional model of the small pipe, which is the basic unit of catalyticconverter carrier, was built using UG. Then, based on the time domain CFD methodpulse method, the sound propagation model was built using Fluent. Soundpropagation performance of pipes with different cross-section, diameter and lengthwas simulated. By comparison between different models, the affect law of structureParameters to sound propagation performance was obtained. Based on this, theacoustic performance of small pipe-combinations was also investigated. Thetransmission loss experiment results consist with the simulation.Acoustic performance of tail pipes with different structure Parameters underdifferent flow field conditions was also investigated. Flow field model of the tail pipeincluding downstream flow was built. The acoustic model FW-H of fluent wasapplied in the research. And the downstream flow center and the acoustic pressure atcertain monitoring points in downstream flow were selected as assessment criteria.The effect of different structure Parameters including tail pipe length, diameter,section of the outlet, and the angel of the pipes’ flections were considered. The flowfield Parameters like the velocity, acceleration and the pressure pulsation also weretook into consideration to obtain their effect to tail pipe noise. Based on the simulation and experiment results, improved exhaust systemstructure for a1.8L engine was developed. The former exhaust system is notworkable as it gave out abnormal exhaust noise sound. Simulation and experimentswere carried through for the improved structure, and the result shows that theimprovement in structure can solve the abnormal exhaust noise problem and improvethe acoustic performance of the engine. This case shows that the simulation modeland research result above are applicable.