GDI Engine – Design by Thermal Assessment

As the loading capabilities of modern IC engines are increasing, more heat is being produced per engine volume unit. Consequentially the thermal and mechanical load of the material also increases rapidly. From the heat transfer perspective, it is of interest to reduce the heat losses in the engine in an attempt to achieve higher mechanical efficiency. One of the most important fields related to this objective is reliable, comprehensive and complete engine thermal analysis.CFD simulation is already an established approach in engine development, especially in the component design phase. Combustion modeling has an important role in predicting the conversion from chemical to mechanical and thermal energy. On the thermal analysis side, finite element methods are conventionally used for the thermal analysis of the solid structure and stress analysis. On the CFD side also a coolant flow analysis has to be considered to contribute to the structure thermal conditions. Each of the analysis is conventionally done by separate software packages. By online coupling of both, the best engine structure temperature prediction can be expected. The present study uses a novel approach of using multi-material heat transfer analysis for the prediction of temperature distribution in the solid structure of a passenger car four cylinder GDI engine. This is an alternative method to the conventional fluidsolid (CFD-FEA) coupling method. This approach represents the simulation of the heat transfer within the GDI engine structure and its parts by considering the solid and fluid parts of the engine as a multi-domain. Heat exchange is determined by considering the complete engine cycle on the gas side. This includes induction, compression and expansion stroke. With this method the three domains approach is reduced to only two CFD domains where the finite element (FEA) tool is no longer required. The CFD tool AVL FIRE is used instead and the simulation workflow is significantly simplified. Better temperature prediction is achieved due to heat data exchange in every iteration step of the simulation instead of only between CFD-FEA coupling loops. A nucleate boiling effect on the water side as well as the contact resistance effect in the solid part are considered. At the end the simulation results are successfully validated against measured thermos-couples temperatures.