Abstract
Due to the increasing demand for higher specific engine power and better overall efficiency some engine components require special attention during the development process as they have to be designed much closer to their mechanical limits. One of these components is the cylinder head, which thereby becomes more and more critical in terms of high-cycle fatigue (HCF) and thermo-mechanical fatigue (TMF) behaviour. To counter the challenges of cutting edge engine design new simulation approaches are necessary. The objective of this study is to investigate a new highly efficient simulation methodology which is capable of delivering accurate results within a shortened development time.
In the context of this paper on one hand a new simulation approach for the derivation of structural heat transfer boundary conditions for diesel engines from 3-D computational fluid dynamics (CFD) analysis is presented. Based on this approach a thermal analysis database was created, which allows its users to derive reliable gas side boundary conditions right in the early development phase of a new project. On the other hand, a new geometry optimizer based on a parameterized cylinder head computer aided design (CAD) model is introduced. With the aid of the optimizer a pre-optimized cylinder head geometry in terms of thermo-mechanical fatigue design can be identified at the beginning of a new project. For the validation of the new methodology numerous comparisons between simulation results and test bench measurement have been carried out.
The result of the introduced process is a maximization of accuracy and effectiveness in virtual engine development. With the methodology presented cylinder heads can be designed in a highly reliable way even for very tough loading scenarios and the virtual development time and costs can be reduced significantly. The key factor therefore is a new pre-optimization model linked with a newly developed thermal engine database and a geometry optimizer. The application of the proposed method is presented on the example of different high end cast iron diesel engine cylinder heads with a specific power up to 100 kW/L and a peak firing pressure of 250 bar.
KEYWORDS – cylinder head, combustion analysis, heat transfer, high cycle fatigue, thermo mechanical fatigue, structural optimization