Computerunterstützte Auslegung eines Brennstoffzellen-Batterie-Hybridsystems für die Bordstromversorgung

This thesis is concerned with developing a methodology for the further development of a fuel cell system for mobile applications. This methodology was subsequently applied to an existing fuel cell system which is based on a high-temperature polymer electrolyte fuel cell (HT-PEFC) and fuel processing through diesel reforming. The methodology focused on three topics: starting up the system, hybridizing the system, and packaging the fuel processing system. A compact and flow-optimized system design is crucial for packaging. In the methodological approach, calculation methods with various levels of detail were combined with experimental studies. A model for the dynamic simulation of the fuel processing system was compiled to permit a coupled consideration of the issues of start-up and hybridization. In order to optimize the start-up process through spatially resolved fluid dynamic simulations, various models for porous bodies were examined and experimentally validated using transient simulations. The start-up process of the package was optimized by utilizing the validated model and an enhancement of the two-dimensional package model. For the threedimensional optimization of the packages, an optimized meshing methodology was developed to reduce the computation time of the simulations. The overarching objective of developing a holistic methodology for optimizing the system was accomplished in this thesis. The methodology was applied to the further development of a fuel cell system which uses diesel reforming. In addition to the development of the methodology, this approach resulted in further key insights. By pre-heating the reformer through steam and air, the two-dimensional simulations reduced the pre-heating time from 22 minutes to 9.5 minutes. By taking the pipework into consideration in package 6, however, the pre-heating time increased to 30 minutes in the three-dimensional simulation. This shows that the components must be optimized three-dimensionally. For the enhancement to a hybrid system, an active hybrid circuit was used to adapt the power output of the fuel cell and in order to react to varying power demand profiles. In cases where the fuel cell can be heated with waste heat from the application, the efficiency of the hybrid system for the power demand profile increases from 25.3 % to 28.1 %. Starting the reformer electrically by an integrated heating element was demonstrated successfully. The process of pre-heating and supplying steam with the integrated heating element alone was concluded within 30 minutes. This methodology is a starting point for future developments of compact and efficient systems