Transient Analysis of an Innovative Cycle Integrating a SOFC and a Turbogenerator for Electric Propulsion

Abstract

Gas turbine technology for aerospace applications is approaching limits in efficiency gains as efficiency gains today occur 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 integrating a Solid Oxide Fuel Cell (SOFC) and gas turbine is developed. Hybrid systems involving fuel cells have better efficiencies than conventional power generation systems. The combination of a SOFC 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 SOFC is integrated in a SOFC-Combustor configuration with a gas turbine to develop efficient electrical power generation for aviation applications. The SOFC–Combustor configuration is an unique concept for reducing system weight, volume, complexity, and response time, which are important attributes for aerospace systems. SOFC-Combustor model was developed based on first principles with detailed modeling of the internal steam reformer, electrochemical and thermodynamics of the SOFC included. The overall purpose of this paper is to analyze the performance of the hybrid SOFC system for high altitude operation for both on-design and off-design operating conditions. Steady-state analysis for cruise condition performed to calculate the respective mission efficiencies. By determining the operating efficiencies of the system, gravimetric comparisons including fuel are performed for alternative power cycles for given flight durations. Transient analysis is performed to understand the behavior in the SOFC temperatures and hybrid system with sudden perturbations to the system (rapid throttle changes, environment changes).