隨著科技發展和環保意識的抬頭，人們對於引擎性能及汙染排放的要求也越來越高；許多學者指出，「汽油缸內直接噴射式」(Gasoline Direct Injection,GDI)引擎可以達到降低油耗，提高效率且降低污染等優點。其中層狀燃燒為GDI引擎低油耗之關鍵，透過特殊設計，GDI引擎能讓油氣聚集於火星塞區域，如此即可在整體空燃比極高的狀況下燃燒，以此降低油耗。而實驗上難以觀測缸內氣體運動的情形，因此本論文使用ANSYS FLUENT軟體來模擬缸內流場；延續並改進盧裕翔[1]的研究成果 ，首先利用ANSYS GEOMETRY對廠商給予的引擎幾何模型進行修改，接著使用ANSYS MESH來對已完成的幾何模型劃分網格，最後進入ANSYS FLEUNT來設定數值模型和初始及邊界條件並開始模擬，模擬時先以冷流場來檢驗模型的可靠性，接著驗證模擬與實驗結果吻合後，便依據實驗所給予的操作條件，針對GDI引擎的均質模式進行模擬，觀測均質模式在各個時刻的油氣分布，並探討其燃燒行為，最後在該轉速下，以紊流動能做為參考，開始分析不同噴油正時間對缸內油汽分布之影響，設計出油汽分布最利於燃燒的層狀系統。

With the development of science and technology and the rise of environmental awareness, 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 ANSYS FLUENT to simulate the in-cylinder flow field. Continuing and improving the results of the literature[1], we first use ANSYS GEOMETRY modify the engine geometry given by the vendor, then use ANSYS MESH to divide the completed geometric model into grid, and finally enter ANSYS FLEUNT to set the numerical model and initial and boundary conditions, Then start the simulation. The simulation will be applied on cold flow field to check the energy conservation and continues law, then check the simulation results if it is in accordance to the experimental results. According to the operating conditions given by the experiment, we simulate homogeneous combustion mode of the GDI engine. Finally, we try different injection time to design the best stratified combustion system.

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