Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/2259
標題: 單缸四行程引擎瞬時進氣流量之計算與量測
The Analysis and Measurement of the Instant Air Flow Rate at Single Cylinder 4-Stroke Engine
作者: 李維忠
W.Z.Lee
關鍵字: discharge coefficient;流量係數;instant flow;engine simulation;瞬時進氣流量;引擎模擬
出版社: 機械工程學系
摘要: 
空氣流經進氣閥門與閥座時會產生極大的速度梯度、剪力流層、分離流及迴流等複雜流場流動現象,將造成實際流動面積縮小,因而進氣閥的流量係數是關係整個四行程引擎容積效率的重要參數。過去有關進氣閥流量係數之研究,均僅進行靜態與擬動態的量測實驗,探討流量係數變化。與實際引擎運轉狀態下,將會有明顯的出入。本研究則是將針對實際引擎運轉狀態下,流經閥門處之瞬時質量流率及動態流量係數變化情形進行探討,深入了解引擎操作狀態。另外也將其結果代入一維非穩態的數值計算,做為發展初步數值引擎之用。
量測研究結果發現,各個轉速下,動態流量係數的變化範圍為0 ~ 0.3之間。在相同閥昇程下,閥門開啟與關閉階段的動態流量係數也明顯不同。各轉速下進氣閥的平均流量係數為0.12 ~ 0.25,與引擎轉速約成正變關係。
數值計算結果顯示,採用平均流量係數與動態流量係數進行數值計算,發現兩種不同定義的流量係數,對於整體計算結果沒有太大的影響。另外,各個轉速下,利用特徵線法所計算出的結果與實驗量測結果很接近。

Air flowing through the inlet valve would generate sharp velocity gradients, separations, and flow circulation. The flow pattern would in turn reduce the actual valve flow area . As a result, the discharge coefficient of inlet valve is the most important parameter for determining the breathing capacity of the four-stroke engine. A lot of work concerning the discharge coefficient has be done, but most of these studies are only based on static measurement or quasi-dynamic measurement.
The purpose of this study is to evaluate the instantaneous air flow rate and the dynamic discharge coefficient at a real four-stroke engine. It was found that the dynamic discharge coefficient is in the range of 0~0.3. Besides, the dynamic discharge coefficient in the opening period is different from that in the closing period under the same valve lift. The mean discharge coefficient is in the range of 0.12 ~ 0.25, approximately proportional to the engine speed.
The mean discharge coefficient is then used in a flow simulation calculation. It was found that the instantaneous inlet flow rate obtained with the dynamic discharge coefficient is close to that obtained with the mean discharge coefficient. Both are close to the measured flow rate.
URI: http://hdl.handle.net/11455/2259
Appears in Collections:機械工程學系所

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