Computerunterstützte Auslegung eines Brennstoffzellen-Batterie-Hybridsystems für die Bordstromversorgung

摘要

This thesis is concerned with developing a methodology for the further development of afuel cell system for mobile applications. This methodology was subsequently applied to anexisting 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 threetopics: 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 combinedwith experimental studies. A model for the dynamic simulation of the fuel processingsystem 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 dynamicsimulations, various models for porous bodies were examined and experimentally validatedusing transient simulations. The start-up process of the package was optimized by utilizing thevalidated model and an enhancement of the two-dimensional package model. For the threedimensionaloptimization of the packages, an optimized meshing methodology was developedto reduce the computation time of the simulations.The overarching objective of developing a holistic methodology for optimizing the system wasaccomplished in this thesis. The methodology was applied to the further development of a fuelcell 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 andair, 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 timeincreased to 30 minutes in the three-dimensional simulation. This shows that the componentsmust be optimized three-dimensionally. For the enhancement to a hybrid system, an activehybrid circuit was used to adapt the power output of the fuel cell and in order to react tovarying power demand profiles. In cases where the fuel cell can be heated with waste heat fromthe application, the efficiency of the hybrid system for the power demand profile increases from25.3 % to 28.1 %. Starting the reformer electrically by an integrated heating element was demonstratedsuccessfully. The process of pre-heating and supplying steam with the integratedheating element alone was concluded within 30 minutes.This methodology is a starting point for future developments of compact and efficient systems