Numerical investigation of in cylinder flow structure for TLM16V185 heavy duty diesel

As environmental problems caused by internal combustion engines becomes (ICE) more severe, emission regulations and fuel consumption values becomes more restrictive. Therefore, engine manufacturers are being forced to improve much better engines that they manufacture in terms of both emissions and fuel consumption rates. In order to achieve improvements that mentioned above, first thing that should be investigated is combustion chamber of the engines. Because parameters of combustion chamber: injection, injection type, injection start, injection duration, combustion chamber shape directly effects the fuel consumption and emission rates. Combustion chamber investigation starts with air motion during intake and compression processes. Because nearly end of the compression stroke turbulent kinetic energy (TKE) and swirl or tumble flow of air and spray interaction is dramatically important for the success of spray tip penetration, combustion and emission rates. For this reason in this thesis air motion in diesel engine was investigated. Flow structures in cylinder starts to generated mostly during the admission stroke, and evolve under the influence of volume reduction during the compression stroke. Two general kinds of flow structures are generated during air admission: swirl motion that corresponds to a coherent rotating motion of the fluid around the cylinder axis; and the other one is tumble motion, that corresponds to coherent fluid motion taking place parallel to the cylinder axis. While tumble motion is broken down into turbulence during the compression stroke, swirl motion survives compression and results in global flow structures when fuel is injected. As a consequence, generation of tumble motion is important in spark ignition engines to ensure good propagation of the flame front, while swirl motion is the flow structure that can be used to influence combustion in diesel engines. In terms of combustion chamber types, there are two basic categories designs. First one is direct injection engine (DI), which have a single open combustion chamber into on where fuel is injected directly. Second one is indirect injection engine (IDI), where the chamber is divided into two regions and the fuel injected into the "prechamber" or "swirlchamber" which is connected to main chamber via nozzle or orifice. Fluid flow in an internal combustion engine presents one of the most challenging fluid Dynamics problems to model. It is because the flow is associated with large density variations. Further, the fluid motion inside combustion chamber is turbulent, unsteady, cyclic and nonstationary both spatially and time dependently. Until recently there are a few experimental methods to investigate air flow inside combustion chamber: LDA (Laser Dopppler Anemometer), PIV (Particle Image Velocimeter) and HWA (Hot Wire Anemometer) are those methods. Problem with these methods are they are expensive, for every design changing it should be tested again. Also it's difficult to examine the entire flow region inside the combustion chamber. Moreover especially for LDA and HWA, they are intrusive methods that probably effect flow inside. For all those reasons engine manufacturers started to seek for new methods and with the help of improvements of computer technologies and turbulence models Computational fluid dynamics has been looked more preferable. However it doesn't mean that experimental methods are not used anymore on the contrary they have been still used for validations of CFD results. Computational fluid dynamics techniques are very functional tools for geometry design and examination of complex engine geometries. In spite of the fact that the most of the present CFD investigations are on steady flows, there is growing interest in unsteady flow computations. With the aid of modern computers can solve numerically the equations of fluid dynamics. Computational fluid dynamics are developed with the combinations of techniques and subroutines. There have been numerous computational studies about in-cylinder flow especially with the dedicated CFD softwares for in-cylinder flow. Since CFD is a most challenging area in computational studies, a few commercial programs have been developed, such as KIVA, Star-CD, AVL-FIRE, Converge. Recent researches show that these softwares give satisfactory results. Until recently in cylinder flow researches carried out both experimentally and numerically. In most of these studies it is widely proven that CFD solutions give satisfactory results compared to experimental works. Recent reseaches show that Piston top surface modification, injector pressure and arrangements that can change swirl flow has tremendous effect on flow structure and this also effects on fuel economy. In this thesis, in-cylinder cold flow analysis carried out for TLM16V185 type (which is being used on DE24000 type locomotives) heavy duty diesel engine's combustion chamber. In this study design including intake-exhaust ports and valves, time dependent cold flow study carried out by using STAR-CD software. STAR-CD uses finite volume for modeling in flow characteristics of the engine's combustion chamber. In this thesis, for preprocessing three dimensional part body of flow volume and meshing cold flow analysis examined. Combustion chamber of TLM16V185 is old-fashioned precombustion chamber type. So this engine uses pintle type injectors rather than using common rail type injectors. On the other side by using pintle injectors, TLM16V185 engines are not sensitive against contaminated fuels. Therefore this kind of engines are still desirable in military and railway applications. Turbulence modeling is important in diesel engines. Since turbulence directly affects spray, mixing and combustion in engine, adequate prediction of turbulence behavior is necessary for understanding these phenomena correctly in order to improve engine performance and emissions. Until now there are so many turbulence models released like k-ε, k-ω, LES, etc. Researces shows that RNG k-ε is the turbulence model to predict swirl flow and emission rate. Therefore in this study, we chosed RNG k-ε model. In the first step of this study CAD model of cylinder head, piston, valves and cylinder liner. All of these parts assembled with correct measurements. Then with the reverse model technique that we used in Solidworks, we got the flow field intake and exhaust ports included. Than this new CAD model converted to parasolid format to be able to used for CFD software STAR-CD. Before importing geometry for meshing, firstly geometry surface tolerance is readjusted by Prosurf which is submodule of STAR. With the help of STAR-CCM surface meshing was prepared. In es-ICE; ports valves and piston surfaces were defined and piston and valve motions entered. After 2D template of meshing, complete 3D hexahedral meshing created in es-ICE. STAR-CD uses pressure correction based PISO algorithm. For the momentum and turbulence equations Monotonic Advection and Reconstruction Scheme (MARS) was used. For time step 0.1⁰ CA was selected. Cold flow analsis from intake of air to end of compression carried out. Results show that during the end of stroke and start of the injection (-26° TDC) swirl and turbulent kinetic energy is not high enough to create succesful spray air mixture. This situation also explains why the soot and HC emissions are high in this engine. In the next step mass consumption and pressure–CA relation in-cylinder will be validated by datas that we obtained from thhe test cell of TÜLOMSAS.