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單缸二行程引擎排氣管設計對引擎性能與排氣噪音之影響

The Effects of Exhaust System Design on the Performance and the Exhaust Noise for Single Cylinder Two Stroke Engines

摘要


本文主要是進行引擎在穩定運轉時的性能與排氣噪音計算,以探討各種不同排氣管設計對單缸二行程機車引擎性能與噪音的影響。二行程引擎的排氣管設計對性能的影響很大,通常機車排氣管都是由數個膨脹室與連通管所組成,而膨脹室與連通管的數目與排列方式並無一定規則可循。本文則探討膨脹室大小與連通管的數目、直徑、長度等設計參數對引擎性能與排氣噪音的影響。在本文中以WAVE軟體來模擬在整個引擎循環中,氣缸與進排氣管內的壓力與流量變化,並以此來計算排氣管出口外的總噪音量及噪音頻譜分佈。由於眞實排氣管是由數個膨脹室及連通管所組成,其中並包含觸媒轉化器,構造相當複雜,本文中將排氣管切割成幾個主要的氣室與連通管,再將各氣室細分成數個小氣室來分析。本文中先比較不同轉速下計算與量測的引擎整體性能,然後以原來的排氣管設計為基準,在不改變外型的前提下,改變排氣管內部膨脹室與連通管的數目與排列方式,並比較各種設計對引擎性能與排氣噪音的影響。結果發現,在不降低引擎性能而又能減少排氣噪音,最佳的方式是減少連通管的有效流道面積,如減少管數或管徑,然後是增加膨脹室二與膨脹室三的體積,其他的方法不是沒有效果就是會影響引擎性能。

關鍵字

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並列摘要


The noise radiated from the tail pipe plays an important role in the total noise emitted for small two stroke engines. The exhaust pipes of two stroke engines are usually of complicated geometry. They are composed of several short straight pipes and expansion chambers. Studies in the past have shown that the design of the exhaust pipe has significant influence on the engine characteristics. In this paper, engine cycle calculations were carried out with WAVE to study the effect of exhaust pipe design on the engine performance and the exhaust noise. A commercial 50 c.c., crankcase-scavenged type, single cylinder two stroke engine was used in this study. The arrangements of pipes and chambers were varied, and in each configuration, the diameter and the length of pipes and the volume of chambers were also varied to study the effect of these design parameters on the engine characteristics. Engine testing were also conducted for several configurations and the pressure variations in the exhaust pipe were recorded to verify the calculated data. Results of comparisons show that the predicted engine performance matched the measured data reasonably well. As for the effect of design parameters, results-of calculations show that the diameter of the connecting tubes is the most significant one in determining the exhaust noise, and the volume of the chamber is also a significant factor in this study.

並列關鍵字

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