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Combustion is one of the main research areas of internal combustion engines. To reduce the air pollution from internal combustion engines, it is required to increase combustion efficiency. In this study, effects of air/fuel ratio were investigated numerically. An axisymmetrical internal combustion engine was modeled in order to simulate in-cylinder engine flow and combustion. Two dimensional transient continuity, momentum, turbulence, energy and combustion equations were solved. k-e turbulence model was employed. Fuel mass fraction transport equation was used for modeling of the combustion. For this purpose a computational fluid dynamics code was developed by using finite volume method with using FORTRAN programming code. The moving mesh was utilized to simulate the piston motion. The code developed simulates four strokes of engine continuously. In the case of laminar flow combustion, Arrhenius type combustion equations were employed. In the case of turbulent flow combustion eddy break-up model was employed

Tek silindirli buji ateşlemeli bir motorda, akış hareketi ve yanma karakteristiğini görselleştirmek amacıyla sayısal bir çalışma gerçekleştirilmiştir. Star CD/es-ice tarafından sağlanan RANS (Reynolds Ortalamalı NavierStokes) ve tümleşik alev modeli (Coherent Flame Model - CFM) modelleri kullanılarak benzinli bir motor modelinde tüm motor strokları incelenmiştir. Sıkıştırma oranının 8:1 ve motor hızının 1200 dev/dak. olduğu bir motor simüle edilmiştir. Yakıt olarak C8H18 (n-izooktan) kullanılmıştır. Sayısal simülasyonlarda, türbülanslı akış hareketini modellemek için AngelBelger duvar fonksiyonları ile beraber k-ε RNG türbülans modeli seçilmiştir. Simülasyonlar boyunca statik ateşleme avansı 20 KMA olacak şekilde belirlenmiştir. Tüm stroklarda silindir içi akış hareketi incelenmiştir. Özellikle, egzoz valfinin henüz açtığı zamanda bazı sayısal anormallik içeren durumlar fark edilmiştir. Küçük egzoz valfi açıklıklarında meydana gelen bu anormallikler, silindir ve egzoz portu arasındaki sıcaklık ve basınç farklarından kaynaklanmaktadır. HAD sonuçları kapsamında sıcaklık dağılımı, hız profilleri, yanmış/yanmamış yakıt konsantrasyonları verilmiştir. Egzoz stroğunda elde edilen Courant ve Mach sayıları detaylı bir şekilde incelenmiştir. Ayrıca, silindir içi basınç, sıcaklık ve ısı yayılım oranı gibi glabal motor parametreleri çizilmiştir. Özetle, CFM yanma modelinin kullanıldığı bu çalışmada alev ilerleme hızının beklenen değerlerden yüksek olduğu görülmüştür. Bu nedenle, silindir içinde elde edilen basınç ve sıcaklık değerleri deneysel verilerden daha yüksek olarak elde edilmiştir, In this study, a computer simulation was performed, to visualize fluid flow and combustion characteristics of a single cylinder spark ignition engine. The complete engine cycle process (inlet, compression, expansion and exhaust strokes) in gasoline engine model was investigated using RANS (Reynolds Averaged Navier-Stokes) and CFM (Coherent Flame Model) approaches offered by Star-CD/es-ice. Simulations were done for the compression ratio 8:1 and 1200 rpm engine speed. C8H18 (iso-octane) was used as the engine fuel. In the numerical simulations to model turbulent flow field, k - ε RNG turbulence model was selected with Angelberger wall functions. Static spark advance was set at 20 CA bTDC during the simulations. Fluid flow in the cylinder was observed during all the engine strokes. Especially, just before the exhaust valve open, some numerical abnormal situations were detected. It was observed that the pressure and temperature gradients between cylinder and exhaust port caused these abnormalities at small exhaust valve lifts. Temperature distribution, velocity profiles, burnt-unburnt fuel concentrations were obtained. Courant and Mach numbers were investigated in details at the exhaust stroke. Also global engine parameters such as in cylinder pressure, temperature and heat release rates were plotted. It was observed that CFM combustion model predicts faster flame propagation speed compared to experimental ones. Due to that higher temperature and peak pressure values were obtained in the numerical simulations

The flow and heat transfer in partially heated and partially cooled cavities were numerically analyzed. Using the control volume approach, a computer program based on SIMPLE algorithm was developed. A square enclosure with variable size heater and cooler on the vertical walls was considered. Computations were carried out to investigate the effects of heater and cooler size on the heat transfer rate. It was observed that for a given cooler size, the mean Nusselt number decreases with increasing heater size. On the other hand, for a given heater size, the mean Nusselt number increases with increasing cooler size. For all Rayleigh numbers considered, the same behavior was observed.

Improving the performance of internal combustion engines is one of the major concerns of researchers. Experimental studies are more expensive than computational studies. Also using computational techniques allows one to obtain all the required data for the cylinder, some of which could not be measured. In this study, an axisymmetric homogeneous charged spark ignition engine was modeled. Fluid motion and combustion process were investigated numerically. Turbulent flow conditions were considered. Standard k- ε turbulence model for fluid flow and eddy break-up model for turbulent combustion were utilized. The effects of valve angle on the fluid flow and combustion are analyzed for constant air/fuel and compression ratios. It is found that, velocities and strength of tumble increases in-cylinder flow and due to increase in turbulence strength, the flame propagation is faster for small valve angles., {"references":["A. D. Gosman, A. Melling, J. H. Whitelaw, P. Watkins, \"Axisymmetric\nflow in a motored reciprocating engine,\" Heat and Fluid Flow IMechE,\nvol. 8 n.1, pp. 21-31, 1978.","A. D. Gosman, R. J. R. Johns, \"Computer analysis of fuel-air mixing in\ndirect-injection engines,\" SAE Transactions, 800091, pp. 581-596, 1980.","D. C. Haworth, S. H. El Tahry, \"Probability density function approach\nfor multidimensional turbulent flow calculations with application to incylinder\nflows in reciprocating engine,\" AIAA Journal, vol. 29, n. 2, pp.\n208-218, 1991.","D. C. Haworth, S. H. El Tahry, M. S. Huebler, S. Chang,\n\"Multidimensional port-and-cylinder flow calculations for two-and fourvalve-\nper-cylinder engines: influence of intake configuration on flow\nstructure,\" SAE Transactions, 900257, pp. 647-678, 1990.","J. A. Naser, A. D. Gosman, \"Flow prediction in an axisymetric inlet\nvalve/port assembly using variants of k-╬Á,\" Proc. Instn. Mech. Engrs.,\nvol. 209, pp. 57-69, 1995.","A. D. Gosman, P. S. Harvey, \"Computer analysis of fuel-air mixing in an\naxisymmetric D. I. diesel,\" SAE Transactions, 820036, pp. 121-141,\n1982.","B. Ahmadi-Befrui, A. D. Gosman, F. C. Lockwood, A. P. Watkins,\n\"Multidimensional calculation of combustion in an idealised\nhomogeneous charge engine: a progress report,\" SAE Transactions,\n810151, pp. 636-651, 1981.","B. Ahmadi-Befrui, A. D. Gosman, \"Assesment of variants of the k-╬Á\nturbulence model for engine flow applications,\" International Journal\nfor Numerical Methods in Fluids, vol. 9, n.9, pp. 1073-1086, 1989.","S. Sugiura, T. Yamada, T. Inoue, K. Morinishi, N. Satofuka, \"Numerical\nanalysis of flow in the induction system of an international combustion\nengine - multi-dimensional calculation using a new method of lines,\"\nSAE Transactions, 900255, pp. 618-628, 1990.\n[10] K. Naitoh, H. Fujii, T. Urushihara, Y. Takagi, K. Kuwahara, \"Numerical\nsimulation of the detailed flow in engine ports and cylinders,\" SAE\nTransactions, 900256, pp. 629-646, 1990.\n[11] A. Chen, K. C. Lee, M. Yianneskis, \"Velocity characteristics of steady\nflow through a straight generic inlet port,\" International Journal for\nNumerical Methods in Fluids, vol. 21, pp. 571-590, 1995.\n[12] A. P. Watkins, S-P Li, R. S. Cant, \"Premixed combustion modeling for\nspark-ignition engine applications,\" SAE Transactions, 961190, 1996.\n[13] J. Ranasinghe, S. Cant, \"A turbulent combustion model for a stratified\ncharged, spark ignited internal combustion engine,\" SAE Transactions,\n2000-01-0275, pp. 336-346, 2000.\n[14] S. Jakirlic, C. Tropea, I. Hadzic, H. Pascal, K. Hanjalic, \"Computational\nstudy of joint effects of shear, compression and swirl on flow and\nturbulence in a valveless piston-cylinder assembly,\" SAE Transactions,\n2001-01-1236, pp. 1402-1439, 2001.\n[15] I. Celik, I. Yavuz, A. Simirnov, \"Large eddy simulations of in-cylinder\nturbulence for international combustion engines: a review,\" Int. J.\nEngine Res., vol. 2, n. 2, pp. 119-148, 2001.\n[16] F. Payri, J. Benajes, X. Margot, A. Gil, \"CFD modeling of the incylinder\nflow in direct-injection diesel engines,\" Computers & Fluids,\nvol. 33, pp. 995-1021, 2004.\n[17] B. E. Launder, D. B. Spalding, \"The numerical computation of turbulent\nflows,\" Comput. Meth. APPl. Mech. And Engng., vol. 3, pp. 269-289,\n1974.\n[18] H. K. Versteeg, W. Malalasekera, An Introduction to Computational\nFluid Dynamics: The Finite Volume Method, Prentice Hall, England,\n1995, pp. 1-246.\n[19] S. V. Patankar, Numerical Heat Transfer and Fluid Flow, Hemisphere\nPublishing Corp., New York, USA, 1980, pp. 1-183."]}