引擎缸壁溫度的均勻度取決於汽缸水套的幾何形狀與流場狀態，而入水口、出水口與墊片開口的位置對溫度均勻分佈的影響更為深鉅。因此，本研究利用商業套裝計算流體力學(computational fluid dynamics, CFD)軟體STAR-CD，針對一部四行程單缸水冷式引擎之散熱機構，進行模擬計算並結合實驗的方式，改良汽缸水套的設計，以提升其散熱效果。設計過程先以數值計算的方式，對原始汽缸水套進行模擬，藉由數值計算所得的熱對流係數並配合實驗量測的溫度，求得模擬穩態的缸壁局部熱通量之方法與得知水套欲修改的方向。為了解決原始汽缸流場的混亂狀態，起初在汽缸頭水套內設置檔板，並修改墊片的開口位置，由模擬計算結果得知，在汽缸壁周圍平均溫度與溫度均勻度皆改善了不少，之後在汽缸體的入水口處設置檔板，發現其散熱效果更佳。這使用實驗量得的缸壁溫度配合CFD方法計算缸壁的局部熱通量，由改良後的模擬計算與實驗結果證明，此種方法對於預先得知汽缸體的熱傳分佈狀況明顯有效果。改良後的汽缸壁周圍平均溫度改善率最高為10.2%，而汽缸壁的溫度均勻改善率最高為72.4%。另外，經各項修正後，引擎扭力、馬力、油耗等等性能並未下降。

A methodology is developed to improve the heat dissipation performance of a single-cylinder, four-stroke-cycle, water-cooled engine by employing the experimental method in conjunction with the numerical simulation technique. At first, the commercial code, STAR-CD, is employed to calculate the velocity distributions of the water flow in the water jacket surrounding the engine cylinder and cylinder head based on the situation of non-combusting engine operation. By using a empirical formula the heat transfer coefficient distributions on the engine cylinder and the cylinder head are obtained. The real temperature distributions around the engine cylinder and the cylinder head are measured experimentally by attaching 40 T-type thermocouples with 250 μm bead diameter to circumferential positions of the engine cylinder and cylinder head. The measured temperature data and the calculated heat-transfer coefficients are used to compute the local heat flux by using the fundamental conduction heat transfer formula. With the distributions of heat flux, the STAR-CD is employed to calculate the flow field and the temperature distributions of the fluids and the cylinder walls. The calculated wall temperatures are compared with the measured temperatures. If the differences between the calculated and the measured temperatures are beyond a prescribed threshold, the wall temperatures are modified and are used to calculate new heat flux distributions. Final convergence is attained when the prescribed threshold is satisfied. The converged temperature distributions are then assumed to be the designed temperatures. With the developed method, the improvement on the temperature distributions around the engine is performed by modifying the flow channel geometry of the water jacket. Totally 21 modifications are proposed. After tedious operations of the developed methodology, an optimized design is finally obtained. The new water jacket design can provide much better heat transfer and temperature distributions according to the computation results. The new design is mockup and the temperature distributions are experimentally measured. The computed temperatures are in good agreement with the experimental results. The circumferentially averaged temperature and the maximum temperature difference around the cylinder are lowered by about 10% and 72%, respectively without scarification of engine horsepower and torque output.

[1] Aoyagi, Y., Takenaka, Y., Niino, S., Watanabe, A. and Joko, I., “Numerical Simulation and Experimental Observation of Coolant Flow Around Cylinder Liners in V-8 Engine,” Journal of Engines, SAE Transactions, Vol. 97, 1988, pp. 141-150, SAE 880109.
[2] Harashina, K., Murata, K., and Satoh, H., “A New Cylinder Cooling System Using Oil,” Journal of Engines, SAE Transactions-Section 3, Vol. 104, 1995, pp. 1846-1850, SAE 951796.
[3] 李進修, 王漢英, 汽機車引擎設計與分析技術, 國立清華大學出版社, 2005.
[4] Boeman, G. and Nishiwaki, K., “Internal-Combustion Engine Heat Transfer,” Progress in Energy and Combustion Science, Vol. 13, No. 1, 1987, pp. 1-46.
[5] Alkidas, A. C., Puzinauskas, P. V., and Peterson, R. C., “Combustion and Heat Transfer Studies in a Spark-Ignited Multivalve Optical Engine,” Journal of Engines, SAE Transactions-Section 3, Part 1, Vol. 99, 1990, pp. 817-830, SAE 900353.
[6] Chen, C. and Veshagh, A., “A One-Dimensional Model for In-Cylinder Heat Convection Based on the Boundary Layer Theory,” Journal of Engines, SAE Transactions-Section 3, Vol. 101, 1992, pp. 1776-1792, SAE 921733.
[7] Jennings, M. J. and Morel, T., “A Computational Study of Wall Temperature Effects on Engine Heat Transfer,” Journal of Engines, SAE Transactions-Section 3, Vol. 100, 1991, pp. 641-656, SAE 910459.
[8] Li, C. H., “Thermal and Mechanical Behavior of an L-4 Engine,” Journal of Engines, SAE Transactions, Vol. 97, 1988, pp. 1318-1331, SAE 881149.
[9] Abraham, J., Ramoth, D. and Manniato, J., “3D Steady-State Wall Heat Fluxes and Thermal Analysis of a Stratifird-Charge Rotary Engine,” Journal of Engines, SAE Transactions-Section 3, Vol. 100, 1991, pp. 1214-1226, SAE 910706.

[10] Chiodi, M. and Bargende, M., “Improvement of Engine Heat-Transfer Calculation in the three-Dimensional Simulation Using a Phenomenological Heat-Transfer Model,” Journal of Engines, SAE Transactions-Section 3, Vol. 110, 2001, pp. 2291-2303, SAE 2001-01-3601.
[11] Kleemann, A. P., Menegazzi, P., and Henriot, S., “Numerical Study Knock for SI Engine by Thermally Coupling Combustion Chamber and Cooling Circuit Simulation,” Journal of Engines, SAE Transactions-Section 3, Vol. 112, 2003, pp. 821-831, SAE 2003-01-0563.
[12] Miyairi, Y., “Computer Smulation of an LHR Di Diesel Engine,” Journal of Engines, SAE Transactions-Section 3, Vol. 97, 1988, pp. 282-293, SAE 880187.
[13] Bohac, S. V., Barker, D. M., and Assanis, D. N., “ A Global Model for Steady State and Transient S.I. Engine Heat Transfer Studies,” Journal of Engines, SAE Transactions-Section 3, Vol. 105, 1996, pp. 196-214, SAE 960073.
[14] Fiveland, S. B. and Assanis, D. N., “A Four-Stroke Homogeneous Charge Compression Ignition Engine Simulation for Combustion and Performance Studies,” Journal of Engines, SAE Transactions-Section 3, Vol. 109, 2000, pp. 452-468, SAE 2000-01-0332.
[15] Shiozawa, T., Nakanishi, A., Ozawa, T., and Oki, T., “Thermal Air Flow Analysis of an Automotive Headlamp-The PIV Measurement and the CFD Simulation by Using a Skeleton Model,” Journal of Passenger Cars: Mechanical Systems, SAE Transactions-Section 6, Vol. 109, 2000, pp. 1098-1104, SAE 2000-01-0802.
[16] Launder, B. E. and Spalding, D. B., Lectures in Mathematical Models of Turbulence, London , New York: Academic Press, 1972.
[17] Mitty, T. J., Jameson, A., and Baker, T. J., “Solution of Three-Dimensional Supersonic Flowfields via Adapting Unstructured Meshes,” Computer and Fluids, Vol. 22, No. 2/3, 1993, pp. 271-282.

[18] Pirzadeh, S., “Structured Background Grids for Generation of Unstructured Grids by Advancing-Front Method,” AIAA Journal, Vol. 31, No. 2, 1993. pp.257-265.
[19] Warsi, Z. U. A., “Conservation Form of the Navier-Stokes Equations in General Nonsteady Coordinates,” AIAA Journal, Vol. 19, No. 2, 1981, pp. 240-242.
[20] Versteeg, H. K. and Malalasekera, W., An Introduction to Computational Fluid Dynamics-The Finite Volume Method, Harlow, Essex, England: Longman, 1995.
[21] Patankar, S. V. and Spalding, D. B., “A Calculation Procedure for Heat, Mass and Momentum Transfer in Three-Dimensional,” Int. J. Heat mass Transfer, Vol. 15, No. 10, 1972, pp. 1787-1806.
[22] Jayatilleka, C. L., “The Influence of Prandtl Number and Surface Roughness on the Resistance of the Laminar Sub-Layer to Momentum and Heat Transfer,” Progress in Heat and Mass Transfer, Vol. 1, Pergamon Press Inc., 1969, pp. 193-329.