Analysis For The Exhaust Noise Characteristics Of An Internal Combustion Engine And Acoustical Source Impedance Calculation

A muffler is a device for reducing the amount of noise emitted by the exhaust of an internal combustion engine.But the exhaust system,as well as reducing noise,can have a beneficial effect on the performance of an engine,particularly when muffler with complex structure is used.Since the back pressure,flow rate and other parameters are essential for engine exhaust system design.Firstly,this article does one-dimensional simulation with GT-Power software and coupling simulation with Fluent and GT-Power for a gasoline engine and exhaust system coupling model.Based on the result of comparison,this paper puts forward some suggestions in the aspects of the two methods in the hope that they would be of some help to exhaust system design.By studying on the effect of turbocharger system for the engine exhaust noise,this paper analyzes turbocharging effect on exhaust noise characteristics.This text also summaries the engine noise variation law under transient conditions,by combining features of speed governing and load bearing.Insertion loss can be obtained by two different methods.One is direct measurement method,the other is indirect measurement method,which needs to know the source characteristics.In order to get precise reflection coefficients,it is necessary to select correctly theoretical model of sound radiation.By comparing Levine-Schwinger model and Munt model,it finds Munt theory is much more practical and accurate.The input data are usually contaminated by measurement error in the actual measurements.This paper has studied the effects of the input errors on the results numerically,and then proposes its own method about acoustical impedance calculation.In contrast with other methods,the new method ensures the acoustic resistance is always positive and can be used to predict radiated noise successfully.It is noted that,frequently,only a set of open pipes is used when applying the multiload method to the internal combustion engine sources.A set of pipe lengths,which cause the calculated results to be least sensitive to the input data error,can be found when using open pipe loads.The present work is intended to produce guidelines for preparing an appropriate load set in order to obtain accurate source properties.Also the guideline can be used to optimize the source characteristics calculated.With GT-Power acoustic impedance modules,an investigation is underway to find out how acoustical resistance and reactance change between naturally aspirated and turbocharging system.Because principles GT-Power and the suggested method used are quitely different,this text explains the distinction between results acquired from these two methods.The effects of engine speed and load to source characteristics are studied,showing it depend on air intake to a certain degree.Finally,the insertion loss is predicted.Regarding the merits and demerits of two methods,this text makes a complete diagnosis of respective result.