Study On Acoustic Simulation Method And Design Technology Of Internal Combustion Engine Exhaust System

Insertion loss is the most effective criterion for the acoustic performance evaluation of a given muffler. In order to calculate the insertion loss, three parameters, namely source impedance of I.C. engine exhaust noise, four-pole parameters of exhaust system and radiation impedance of tail pipe need to be obtained. This thesis introduced the research situation and methods of I.C. engine exhaust noise source impedance, compared several major multi-load methods and discussed their relevant advantages and disadvantages. The proposed maximum sound power method obtained all positive real parts of source impedance, which had actual physical meanings. A linear source radiation noise model with known parameters was introduced in order to check the accuracy and sensitivity to the input errors of various methods. It was found that the present modified multi-load method is better than the conventional four-load method presented by Prasad and the refined multi-load method proposed by Jang and Ih regarding the accuracy and sensitivity to input errors. A major factor that affects the accuracy of the results is the selection of loads in addition to the difference between various multi-load methods employed in the source impedance evaluation. As for a certain multi-load method used to calculate the source impedance, correct results may be obtained by employing some loads, while a great deviation to the true value may be caused by employing some other loads. Therefore, the selection method of loads was studied and verified, and also the effects of loads number on the calculated results were analyzed in this thesis.In order to achieve the systematic and visual calculations for the exhaust system acoustical performance, the present thesis conducted the interface design by using GUI features via MATLAB platform. The designed interface is user-friendly, simple to use, and adhering to humanization ideas, which greatly simplified the programming and data input and output works in the acoustic calculations, and improved the efficiency of calculations and the accuracy of results, also saved a lot of post-processing time.Various methods were employed in the source impedance calculations of I.C. engine exhaust noise, and then the calculated results by using various methods were compared and analyzed. The effects of engine speeds and loads on the source impedance were studied in this thesis. The calculation methods of insertion loss and exhaust radiated noise were introduced, and then insertion loss and exhaust radiated noise were calculated and analyzed for a simple expansion chamber muffler. The calculated results by using various methods are in good agreement with each other, demonstrated that the calculations of source characteristics, insertion loss and exhaust radiated noise were correct.