本研究針對一部單缸四閥四行程125c.c.機車引擎(在此稱為原廠引擎)，使用商用套裝計算流體力學(Computational Fluid Dynamics, CFD)軟體CONVERGE，對汽缸內未噴油燃燒之流場進行計算模擬，探討節氣門開度與引擎轉速對汽缸內流場的影響，並計算容積效率、缸內平均壓力與溫度、紊流動能及滾轉比的變化。以面平均渦度滾轉比、體平均循環渦度滾轉比等數值來呈現缸內滾轉運動的量化強度。不同汽門開度及轉速會使缸內流場模態隨著曲軸角度改變，而使得缸內氣流滾轉強度有所差異。容積效率、循環紊流動能、體平均循環渦度滾轉比、餘隙(squish)是判斷氣流品質與油氣混合良窳的主要物理參數。固定節氣門開度於100%，引擎轉速7000RPM，探討更改燃燒室幾何形狀與尺寸時，以上四種主要物理參數的改變，綜合比較其相關性，判斷較佳之燃燒室設計幾何。更改的燃燒室幾何包括：穹頂傾斜角、活塞頂部形狀(中央球形、偏置球型、偏置槽型、淺碟型以及拱型(I))與餘隙。過去研究顯示，缸內氣流滾轉比改變會影響紊流強度以及油氣於渦流中的停駐時間，進而影響油氣混和的品質，最終會影響引擎之燃燒效率與污染物排放濃度。在進行引擎燃燒室設計時，必須同時考慮容積效率、循環紊流動能、體平均循環渦度滾轉比與餘隙。本研究發現循環紊流動能與體平均循環渦度滾轉比有相似的變化趨勢，但體平均循環渦度滾轉比可以呈現較明顯的特徵。因此，若容積效率與餘隙能控制在合理的數值時，缸內氣流滾體平均循環渦度滾轉可以作為設計較佳燃燒室幾何時的主要參數。

The in-cylinder flow characteristics of a single-cylinder, four-stroke motorcycle engine, which would affect the mixing and combustion performance were studied. A commercial engine with a displacement of 125cc was used as the benckmakr which was hereafdter called the “original engine.” Analyzed by the commercial computational fluid dynamic (CFD) software (Converge), the in-cylinder flow characteristics, such as the flow evolution patterns, turbulence kineytic energy (TKE), tumble ratio, were obtained. The effects of the parameters induced by the geometric arrangement of the engine combustion chamber, such as the volumetric efficiency and squish, were specifically studied. The angle of pent roof and the shape of the piston head which may significantly affect the in-cylinder flow characteristics were varied to examine the optimized designs for the combustion chamber. The engine spped and throttle opening were varied for the cases of study. The results showed that the pent roof angle at 22o to 23o may induce largest TKE and tumble ratio. The “original engne” had a pent roof angle of 22.9o which fell within the range of optimation design. A piston head with a slight concave or a slight convex of special designed geometries could increase tumble ratio up to about 10%. The variations of TKE and tumble ratio were almost unchanged under the conditions with and without installing the throttle value.

[1] Mayer, H., “Air Pollution in Cities,” Atmospheric Environment, Vol. 33, October 1999, pp. 4029-4036.
[2] Heywood, J. B., Internal Combustion Engine Fundamentals, McGraw-Hill, New York, 1988.
[3] Heywood, J. B., “Fluid Motion within the Cylinder of Internal Combustion Engines”－The 1986 Freeman Scholar Lecture, Journal of Fluids Engineering, Transactions of the ASME, Vol. 109, No. 1, 1987, pp. 3-35.
[4] Tennekes, H., and Lumley, J. L., A First Course in Turbulence, MIT Press, London, 1972.
[5] Wilson, N. D., Watkins, A. J., and Dopson, C., “Asymmetric Valve Strategies and Their Effect on Combustion,” Journal of Engines, Vol. 102, 1993, pp. 1081-1092. Also in SAE Transactions SAE 930821.
[6] Kent, J. C., Mikulec, A., Rimal, L., Adamczyk, A. A., Mueller, S. R., Stein, R. A., and Warren, C. C., “Observations on the Effects of Intake-Generated Swirl and Tumble on Combustion Duration,” Journal of Engines, Vol. 98, 1989, pp. 2042-203. Also in SAE Transactions SAE 892096.
[7] Endres, H., Neuber, H.-J, and Wurms, R., “Influence of Swirl and Tumble on Economy and Emissions of Multi Valve SI Engines,” Journal of Engines, Vol. 101, 1992, pp. 942-953. Also in SAE Transactions SAE 920516.
[8] Omorl, S., Iwachido, K., Motomochi, M., and Hirako, O.,“Effect of Intake Port Flow Pattern on the In-Cylinder Tumbling Air Flow in Multi-Valve SI Engines,” Journal of Engines, Vol. 100, 1991, pp. 729-740. Also in SAE Transactions SAE 910477.
[9] Ekchian, A., and Hoult, D. P., “Flow Visualization Study of the Intake Process of an Internal Combustion Engine,” Journal of Engines, Vol. 88, 1979, pp. 383-400. Also in SAE Transactions SAE 790095.
[10] Rask, R. B., “Laser Doppler Anemometer Measurements in an Internal Combustion Engine,” Journal of Engines, Vol. 88, 1979, pp. 371-382. Also in SAE Transactions SAE 790094.
[11] Gharakhani, A., and Ghoniem, A. F., “3D Vortex Simulation of Intake Flow in a Port-Cylinder with a Valve Seat and a Moving Piston,” Journal of Engines, Vol. 105, 1996, pp. 1627-1639. Also in SAE Transactions SAE 9961195.
[12] Richter, M., Axelsson, B., Aldén, M., Josefsson, G., Carlsson, L-O., Dahlberg, M., Nisbet, J., and Simonsen, H. “Investigation of the Fuel Distribution and the In-cylinder Flow Field in a Stratified Charge Engine Using Laser Techniques and Comparison with CFD-Modelling,” Journal of Fuels and Lubricants, Vol. 108, 1999, pp. 1652-1663. Also in SAE Transactions SAE 1999-01-3540.
[13] Zolver, M., Klahr, D., and Torres, A., “An Unstructured Parallel Solver for Engine Intake and Combustion Stroke Simulation,” Journal of Engines, Vol. 111, 2002, pp. 1919-1929. Also in SAE Transactions SAE 2002-01-1120.
[14] Versteeg, H.K. and Malalasekera, W., An Introduction to Computational Fluid Dynamic-The FiniteVolume Method, Addison Wesley Longman Limited, New York, 1995.
[15] Kihyung, L., Choongsik, B., and Kernyong, K., “The Effects of Tumble and Swirl Flows on Flame Propagation in a Four-Valve S.I. Engine,” Applied Thermal Engineering, Vol. 27, 2007, pp. 2122-2130.
[16] Surenda, G., Klunal, A., Vamshi, K., and Cho, S., “Steady and Transient CFD Approach for Port Optimization,” Journal of Engines. Also in SAE Transactions SAE 2008-01-1430.
[17] Rakopoulos, C., Kosmadakis, G., and Pariotis, E., “Investigation of Piston Bowl Geometry and Speed Effects in a Motored HSDI Diesel Engine Using a CFD Against a Quasi-Dimensional Model,” Energy Conversion and Management, Vol. 51, 2010, pp. 470-484.
[18] 張小燕：「一款汽油機的性能提升研究」，CDAJ-China中國用戶論文集，長安汽車工程研究院，重慶，四川，中國，2004。
[19] 林冠旭：「增強內燃機缸內氣流滾轉運動的方法與診測：計算模擬與PIV實驗量測」，機械工程技術研究所碩士論文，國立台灣科技大學，台北，臺灣，中華民國，2006。
[20] 林聖諺：「以計算模擬與 PIV量測方法探討二閥引擎的缸內流場」，機械工程技術研究所碩士論文，國立台灣科技大學，台北，臺灣，中華民國，2015。
[21] 陳威元：「引擎球形燃燒室幾何形狀最適化研究」，機械工程技術研究所碩士論文，國立台灣科技大學，台北，臺灣，中華民國，2016。
[22] 王品翰：「機車單缸引擎燃燒室最適化設計」，機械工程技術研究所碩士論文，國立台灣科技大學，台北，臺灣，中華民國，2017。
[23] 陳韋霖：「機車引擎燃燒室屋脊型穹頂幾何形狀最適化設計」，機械工程技術研究所碩士論文，國立台灣科技大學，台北，臺灣，中華民國，2017。