Investigations on the influences of fuel mixture influencing parameters on the 3-D cylinder flow field of an internal combustion engine

In the last years manufacturers of engines have begun to place a large amount of effort in the direction of reducing emission and increasing power density of engines. Therefore, in modern diesel engines the compression ratio is rising, the inlet pressure is boosted via turbo charging, common-rail-injection systems enable multiple injections with injection pressures up to 3000 bar, and the peak pressure of the combustion is higher. These measures are not only decreasing the emissions and fuel consumption of the engine but are also increasing the pressure and thermal loads on the engine components. Heavy duty diesel engine cylinder head cracking is one of the main problems which affect engine durability. With the increasing requirements for better engine performance, less exhaust emission and lower fuel consumption, increased combustion pressure and elevated temperature make the engine cylinder head to be the most complicated and critical part for the engine design. In recent years more and more deviations between predicted and measured life cycles were reported at FEV GmbH. Newly developed engine cylinder heads failed much earlier at the test bench than calculated during the thermo-mechanical fatigue (TMF) analysis on the computer. The reason for the deviation between simulation and measurement might be that the models used for modeling the physical engines behavior are outdated, as perhaps they were not adjusted adequately to the changed demands of modern Diesel engines. The damage to the company caused by these cylinder head failures is reason enough to improve current simulation methodology. Therefore, three starting points were spotted: 1. prediction of the gas-side heat transfer; 2. prediction of the water-side heat transfer; 3. material data for TMF analysis. The target of this thesis is to re-engineer the current method of gas-side heat transfer prediction. This thesis work deals with the Computational Fluid Dynamics (CFD) simulations of the fuel injection and combustion parameters. In more detail this topic is about the investigation of the changing of the cylinder flow field under the variation of different fuel mixture influencing parameters During the course of this thesis work, effects of a variety of engine operating parameter on a 7.5 liter, six cylinder DI diesel heavy-duty truck prototype engine were investigated. A highlight of the work was that 3D CFD and DoE were used together for these investigations. The simulation software packages used in this thesis work are STAR-CD (for gas exchange) and KIVA (for combustion) that are available at FEV. The DoE modeling and analysis was carried out using PROCAL, a tool developed by FEV. The parameters, whose influences on fuel mixture influencing parameters on the 3D cylinder flow field were researched, are: Begin of injection (BOI) Air-fuel ratio – Lambda, λ Boost pressure Injection pressure Concluding the CFD work, an averaging procedure of the CFD model results was developed. The averaged heat transfer coefficient and gas temperature values were calculated for all simulations. Then, the heat transfer coefficient and temperature values of these points were taken and modeled in PROcal. With modeling process, mathematical representation of selected points was formed. Heat transfer coefficient and temperature values at each point were derived as a function of injection timing, lambda, boost pressure and injection pressure. As an output, a data base from DoE analyses will be built up. With the help of this data base the heat transfer and thermal stresses in future customer engines can be estimated in an early stage of development without a CFD simulation.