Reformierung von BtL-Kraftstoffen für die HT-PEFC in luftfahrttechnischen Systemen

The existing development trend towards „more electric aircraft” architectures means a steady growth in electrical power demand on board of aircrafts. For various reasons fuel cells may be ideally suited for covering the electrical power demand of future commercial aircraft. Fuel cells not only have a higher efficiency compared to the conventional gas turbine APU (auxiliary power unit), but they also do not generate any environmentally problematic NO$_{x}$ emissions. Furthermore, the potential utilization of the reaction product water promises a partially or fully independent freshwater supply. Apart from this, the low-oxygen exhaust air of the fuel cell systems is interesting for inerting the kerosene tanks. The fuel cell type HT-PEFC (high-temperature polymer electrolyte fuel cell) is particularly promising for the application as an APU in aviation. One of the most important advantages of the HT-PEFC over its long-standing low-temperature version is its high tolerance for carbon monoxide. This property simplifies the application of reformate gas as fuel and avoids a complicated hydrogen storage system. A very attractive reforming process for on-board hydrogen generation is provided by the method known as “autothermal reforming”. But the success of the reforming process depends not only on the reformer design and the reforming parameters, but also on the reforming properties of the hydrocarbon mixture. As opposed to mineral-oilbased fuels, synthetic Fischer–Tropsch kerosene (”XtL”) such as biogenic BtL (“biomass toliquid“) contains neither aromatic compounds nor sulfur, which is favourable for the reforming process. This dissertation connects to these topics. The principal aim was the assessment of the technical competitive potential of HT-PEFC systems applied as aircraft APUs. The resource base of the hydrogen required for the fuel cell operation and the way in which it was provided played a key role for the results. In the first place, experimental trials with 5 kWel class reformers were conducted to reveal the current development status of the auto thermal reforming and to obtain empirical findings for future development work. Sulfur-free hydro cracker kerosene and XtL kerosene were both used as fuels. Considering the encouraging trial results, autothermal reforming is a promising way to reliably provide mobile fuel cell systems with hydrogen in the longterm. The availability of XtL fuel can be a required criterion for this. In the second main part of this dissertation, the competitiveness of technically mature HTPEFCsystems was analysed in various future scenarios. The analysis is based on dynamic simulations of complete flight cycles of a more electric aircraft equipped with an HT-PEFCAPU. A more electric aircraft with a conventional gas turbine APU served as a reference. The major criteria for the evaluation were the primary energy demand and the greenhouse gas emissions. According to the simulation results, an HT-PEFC APU can be a serious alternative to the gas turbine APU as long as the power density can be increased relative to today. However, the technical obstacles for achieving competitiveness is significantly lower for reformate gas than for hydrogen