機車在台灣以及東南亞為最普遍使用之交通工具，而小c.c數的機車冷卻系統以氣冷式為主。機車引擎的散熱系統是直接影響引擎性能的因素，過高的溫度會使零件損壞，過低的溫度會使熱效率降低與油耗增加，故冷卻系統的設計成為很重要的關鍵。
本文建立光陽AFA9，163cc單缸氣冷引擎之冷卻通道外流場及引擎共軛熱傳分析模型。由於在高速運轉容易產生火星塞周圍的溫度過高，及汽缸頭與汽缸溫度分佈不均勻的問題，因此對高速運轉9000rpm進行模擬。為了改善火星塞周圍熱點溫度過高的問題，對導風罩上可能影響火星塞附近溫度的兩個特徵，分別為導風板及側凹板進行改良。首先對導風板高度進行改良，Case1為原始設計之導風板H=0mm，Case2到Case5分別為將導風板向缸頭上方提高H=5、10、15mm及移除導風板，對不同導風板高度搭配原始模型之側凹板寬度W=4.5cm進行外流場分析與共軛熱傳分析。再對側凹板寬度進行改良，Case1為原始設計之側凹板寬度W=4.5cm，Case2到Case4分別為將側凹板寬度W改成4cm、3cm和移除側凹板，對不同側凹板寬度搭配原始模型之導風板H=0mm進行外流場分析與共軛熱傳分析。從數值模擬結果與光陽公司提供之實驗數據互相對照，發現最大誤差約為9 %。此外，以3D列印之方式印製一可替換不同導風板高度與不同側凹板寬度的透明導風罩，藉以觀察流體流動狀況，再將所觀察之結果以影片方式呈現並與數值模擬之流場進行交互比對。
模擬結果顯示，在不同導風板高度的Case中，從降低火星塞周圍溫度為首要目的來說，Case1(原始模型H=0mm)與Case2(向缸頭上方提高H=5mm)對火星塞周圍溫度差異不大，但比其他Case來的低，而在Case5(無導風板)時溫度最高，散熱最差。再從溫度均勻性為次要目的來說，Case2整體溫差比Case1的溫差來的小，因此以Case2(向缸頭上方提高H=5mm)的設計最佳。
在不同側凹板寬度的Case中，從降低火星塞周圍溫度為首要目的來說，Case3(側凹板寬度W=3cm)在火星塞周圍平均溫度比其他Case來的低。再從溫度均勻性為次要目的來說，Case3的整體溫差也比其他Case來的好，因此以Case3(側凹板寬度W=3cm)的設計最佳。

In this study, a 3-D numerical air-cooling channel model of a 163c.c four stroke single cylinder scooter engine is established and evaluated through computational fluid dynamics(CFD) with a conjugated heat transfer scheme to show the temperature distribution of the engine. The flow field is also observed, and the correlation between the heat transfer performance and flow field is discussed. In order to observe the real flow field inside the engine shroud, we also establish a transparent engine shroud model through 3-D printer.
In view of the temperature around the spark plug hole is too high; thus, we try to improve the two features on the shroud, which are deflector and concave. We first improve the height of the deflector on the shroud. There are 5 cases in discussion. Then, we try to change the anther feature, width of the concave. There are 4 cases in discussion. The result shows the temperature around the spark plug hole and temperature differences on different fins. We find the optimal design of the air-cooling channel, which has the lowest temperature around the spark plug hole and better temperature difference on the fins.

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