Numerical investigation of flow and combustion in a spark ignition engine cylinder

NUMERICAL INVESTIGATION OF FLOW AND COMBUSTION IN ASPARK IGNITION ENGINE CYLINDER(Ph.D. Dissertation)Nureddin DİNLERGAZİ UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYSeptember 2006ABSTRACTIn-cylinder flow and combustion are important subjects on internal combustionengines. In this study, fluid flow and combustion in a spark ignition engine werenumerically investigated. For this purpose a computational fluid dynamics codewas developed. For turbulent flows, k-ε turbulence model was used. Thecomputer code was developed step by step. First, laminar and turbulent flows ina pipe were investigated. Next, flow in pipes with fins attached on internal facewas considered. Effects of fins on fluid flow and heat transfer were investigated.A low-Reynolds number turbulence model was developed. Using the codedeveloped sudden expansion flow was investigated. After coordinatetransformation, piston motion was given, and then motion of fluid in cylinderinvestigated. Finally, combustion models added to the code. Arrhenius typeequations were used for laminar conditions combustion, eddy break-up modelwas used for turbulent combustion.In results, effects of engine speed, compression ratio, valve angle on flowmotion, and effect of excess air ratio on combustion in laminar and turbulentflow conditions were analyzed. Increasing compression ratio, magnitude ofvortices in the cylinder increases with increasing compression ratio. When fuel-air mixture enters the cylinder nearly horizontal, higher velocities occurred inthe cylinder. For this reason, homogenity of mixture increases. One of theparameters that effect combustion duration is excess air ratio. Increasing excessair ratio, decreases the combustion temperature and increases combustionduration time.For laminar and turbulent flow conditions all over the cycle was investigated.Graphs of in-cylinder pressure vs. crank angle, in-cylinder pressure vs. cylindervolume, change of mass fraction ratio, combustion products fraction ratio,burned mass fraction ratio and in-cylinder mean temperature vs. crank anglewere also given.Science Code : 914.1.038Key Words : internal combustion engine, flow modeling,combustion modeling, k-ε turbulence modelPage Number : 323Adviser : Prof. Dr .Nuri YÜCEL