直通式消音器之性能分析

Abstract

車輛用排氣系統消音器在排氣背壓及消音能力兩項指標上通常無法同時達到最佳狀態，而直通式消音器對於汽機車引擎可使之排氣較順暢，但消音的能力較弱。對此，某公司設計出新型直通式消音器，來提升直通式消音器的消音能力。本文之研究目的為針對同樣大小共鳴箱，但內管設計不同之無槽孔膨脹管式消音器、延伸管式消音器，以及有槽孔同心管式消音器、新型直通式消音器四種直通式消音器進行壓力及消音能力的分析，並得知新型直通式消音器的特性。 在壓力分析方面，研究方法為使用有限元素軟體中之計算流體力學模式進行內部壓力分佈模擬，藉以分析消音器所造成之排氣背壓。在消音能力分析方面，研究方法為使用平面波傳輸矩陣法來模擬傳輸損失，並量測消音器的噪音減量，經由上述兩實驗比較出新型直通式消音器的特性後，再由介入損失的實驗量測新型直通式消音器的實際消音效果。 壓力模擬結果顯示有槽孔之同心管式消音器及新型直通式消音器內部壓力會大於無槽孔之膨脹管式消音器及延伸管式消音器，其中新型直通式消音器內部的壓力為最大。消音能力分析方面，結果顯示新型直通式消音器在低頻時之消音能力為最佳，而介入損失實驗結果顯示新型直通式消音器可有效降低引擎在低頻的噪音峰值。 經由本文之研究，可得知直通式消音器若要提升消音能力，仍需犧牲部份直通式消音器低排氣背壓這項能力。而新型直通式消音器之排氣背壓雖較其他三者為高，但消音能力也為最佳，且其搭配實際引擎排氣系統時相當適合。

Traditional straight through muffler can make engine exhaust smooth, but usually it cannot reduce noise to a satisfied level. A new straight through muffler has been designed to solve this problem. In this study, four kinds of straight through muffler including an expansion chamber muffler, an extended tube expansion chamber muffler, a concentric muffler, and a new straight through muffler, will be analyzed and compared their exhaust back pressure and performance of reducing noise. In this study a software called ANSYS was used to simulate the pressure in mufflers. For the performance of reducing noise, plane wave transfer matrix method was used to simulate the transmission loss of mufflers, and also to measure the noise reduction of mufflers. Finally, the insertion loss of new straight through muffler with a real engine was obtained by experiments. The result of pressure simulation shows that the back pressure in new straight through muffler is higher than that of others. And the result of noise reduction experiments shows that the new straight through muffler can reduce more noise than others, especially in low frequencies. Also the result of insertion loss experiments shows that the new straight through muffler can reduce the low frequency noise of an engine exhaust system effectively. Although the pressure in a new straight through muffler is higher than that of others, but the performance of noise reduction of a new straight through muffler is better than that of others, and it is applicable in the vehicle’s engine directly.