Analysis of a Gas Turbine Enhanced Fuel Cell Powertrain for Future Aircraft

In this work, we present a novel idea of an SOFC combined with a gas turbine as the main powertrain of an aircraft. Contrary to similar, existing ideas, a pre-burner instead of a post-burner is used to heat up the gases before the fuel cell together with a hot air feedback. This allows for an autonomous start-up, the complete avoidance of air/air heat exchangers, which reduces weight and flow losses, and the use of high pressures, which is favorable for the operation of the SOFC. The investigations of this work are based on a dynamic Modelica model using components of the ThermoFluidStream (TFS) library, developed by the German Aerospace Center (DLR) with a custom fuel cell model following the TFS approach. To analyze the propulsion system, a preliminary control scheme is developed to perform simulations of an exemplary, regional aircraft over a whole mission while considering the different flight phases. First, a baseline case is simulated to investigate whether the system can be operated, also from the control perspective, and whether the performance is sufficient for the application in an aircraft. The results reveal that the system with the preliminary control loop achieves overall system efficiencies of up to 77% during the cruise phase. Second, simulations with different take-off temperatures and altitudes are carried out showing that the system runs robustly under more extreme conditions. These results show that the proposed architecture is very promising for aircraft applications.