汽油缸內直接噴射(Gasoline Direct Injection, GDI) 引擎可以在低轉速低負載的操作點下，以層狀燃燒模式(Stratified Mode Operation) 運轉。利用氣缸內整體油氣稀薄，但在部分位置有較濃的燃油分佈的方式達到稀薄燃燒(Lean Combustion)，以獲得低油耗並且降低廢氣排放量。若是太早噴油，則可能造成過於均勻卻稀薄的油氣分佈，進而導致燃燒不穩定，而若是太晚噴油，則可能導致燃油沒有足夠的時間氣化或是油氣過度集中在火星塞周遭而無法順利燃燒。本論文運用Ansys Fluent 模擬目標缸內直噴汽油引擎的層狀模式，延續文獻[1] 的模型，探討低轉速(1500rpm)、低負載(Part Load) 的條件下，噴油正時對於缸內流場運動、油滴蒸發以及油氣分佈所造成的影響。並尋找在該操作點下能在點火正時達成適合燃燒的層狀環境的噴油正時區間。由於在實驗中僅能通過調整噴油壓力來控制燃油進入汽缸後的運動行為以及霧化行為，因此本模擬藉由調整燃油液滴的尺寸來使模擬更貼進實驗。並且通過對比汽缸內部溫度分佈與燃油分佈圖來預測是否會在點火正時之前就發生早燃的現象，最終模擬結果顯示當噴油正時介於58◦BTDC76◦BTDC 時，在點火正時火星塞周遭能形成當量濃度的油氣，且缸內分佈當量濃度燃油的位置的溫度在汽油自燃溫度的範圍外。依據此項模擬結果的噴油區間來進行實驗，比對在不同噴油正時下的燃燒行為表現。最終實驗結果顯示，在噴油正時介於54◦BTDC 到72◦BTDC 之間的燃油效率最佳。

With the development of science and technology and the rise of environmentalawareness, people request more and more on the engine performance and pollution emissions. Many scholars pointed out that the use of“gasoline direct injection technology”(Gasoline Direct Injection, GDI) will meet the demands of less fuel consumption, Improve the thermal efficiency and reduce the pollution and so on. Therefore, this paper aims to analyze the fluid motion inside GDI engine by means of numerical simulation, making it possible to find out the way to improve the GDI engine.
GDI technology can reduce the fuel consumption because it can form a thin layer of gasoline in the combustion chamber, the key to the design of thin layered combustion system is the use of different fuel injection timing, so that mixed oil and air distribution layer rather than homogeneous Distribution, if the oil is concentrated in the vicinity of the plug, and other areas of chamber is relatively thin, that can be in the case of a very high overall air-fuel ratio, resulting in sufficient torque, in order to obtain lower fuel consumption. However, the chamber of the internal combustion engine is very complex and difficult to observe. Therefore, this paper uses sc ANSYS FLUENT to simulate the in-cylinder flow field. literature [1] use sc ANSYS GEOMETRY modify the engine geometry given by the vendor, then use sc ANSYS MESH to divide the completed geometric model into grid, and finally enter sc ANSYS FLEUNT to set the numerical model and initial and boundary conditions, Then start the simulation. And find the best timing of injection to make the engine work in stratified charge.

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