水冷式引擎是以流體由內而外的方式進行降溫，為使引擎能維持在適當的工作溫度，水套之設計十分重要，當水套幾何設計不佳時，容易造成流體流動不順，使得引擎內部產生局部熱點，為改善局部熱點問題，藉由調整汽缸與汽缸頭間墊片之開口分布，影響水套流場進而改善引擎內局部熱點，使引擎溫度場均勻且在良好的工作溫度下運轉，提高引擎熱機效率，避免機件熱膨脹變形導致損壞。本文建立400cc四行程單缸水冷引擎之水套分析模型及引擎共軛熱傳模型兩種模型，透過數值模擬分析水套內之流場及引擎溫度場之分佈，探討流場特性與熱傳之關係。為驗證數值模擬之精確性，由機車開發商提供引擎運轉時之實際溫度，將實驗點與模擬進行比對後，發現最大誤差約為20%。
本文將探討5種汽缸與汽缸頭間墊片不同開口數及開口分佈，Case1為開發商之原始設計， Case2將原始設計之開口順時針移往引擎內熱點，針對熱點進行冷卻，Case3開3個口，Case4開4個口，Case5開8個口，由數值結果可知，隨著開口數增加，流量隨之增加3~22%，而平均熱傳係數卻是降低3~17%，以此說明水套散熱能力與流量無直接關係，而是與流動分佈相關。
此外，本文以3D列印之方式印製一只透明之引擎水套，且自行製作汽缸與汽缸頭間之墊片，建立一套實驗系統，觀察流體在水套內之實際流動，將所觀察之結果以照片方式呈現並與數值模擬所得流場進行交互比對。

Water-cooled engine is cooled from inside to outside by the fluid, so that the engine can be maintained at the proper operating temperature. If the design of the water jacket is poor, it will be easy to make the local hot spots in the engine. Therefore, the design of the water jacket is very important. In this paper, author establishes 3D numerical model that is a 400c.c four strokes single cylinder water-cooled motorcycle engine and uses CFD simulations in conjugate heat transfer between all parts of the engine and water jacket to show the temperature of the engine Besides, author makes a transparent water jacket model by 3D printing and rearranged the hole on the gasket and observes the actual flow flied.

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