Transient Analysis of a Solid Oxide Fuel Cell/ Gas Turbine Hybrid System for Distributed Electric Propulsion

Gas turbine technology for aerospace applications are approaching limits in efficiency gains as increases in efficiency today occurs in very small increments. One limitation in conventional gas turbine technology is the combustion process, which destroys most of the exergy in the cycle. To address this limitation in a traditional Brayton power cycle, a hybrid system which is integrated with Solid Oxide Fuel Cell (SOFC) and gas turbine is developed. Hybrid systems involving fuel cells have better efficiencies than conventional power generation systems. Power generation systems with improved performance from low fuel utilizations and low maintenance costs are possible. The combination of a SOFC fuel cell with a gas turbine has shown higher efficiencies than conventional gas turbine systems due to the reduction of exergy destruction in the heat addition process. A one-dimensional dynamic model of a Solid Oxide Fuel Cell (SOFC) integrated with a gas turbine model to develop an efficient electrical power generation system for aviation applications is investigated. The SOFC - Combustor concept model was developed based on first principles with detailed modeling of the internal steam reformer, electrochemical and thermodynamics analysis is included. Initially, a detailed investigation of internal steam reformer kinetics is presented. The overall purpose of this thesis is to analyze the performance of the hybrid SOFC-GT system for both on-design and off-design operation in an aerospace application. Transient analysis is performed to understand the uncertainties in the SOFC temperatures and hybrid system; control and stability with sudden transient iii changes of the system (rapid throttle changes, environment changes like climb). Finally, SOFC model integrated with a compressor and turbine model and investigation on the overall performance of the innovative hybrid thermodynamic cycle is presented. The SOFC hybrid system has a lower power density at sea level compared to a turbo-generator, but in a typical commercial flight the SOFC hybrid system outperforms the turbo-generator in both endurance and power-to-weight ratio at cruising altitude