Cycle-Level Performance Analysis of a Hydrogen fuelled Hybrid SOFC–Turbofan Engine

Abstract

Aviation is responsible for a significant share of global greenhouse gas emissions and remains one of the more challenging industries to transition to carbon-neutral operation. Research into alternative fuels and reductions in fuel consumption is therefore critical. This thesis investigates the extent to which integrating a hydrogen-fuelled Solid Oxide Fuel Cell into a CFM56-5B1 turbofan can reduce the Thrust Specific Fuel Consumption during cruise conditions. The SOFC was modelled as a 0D electrochemical component developed in OpenMDAO and integrated into pyCycle for cycle-level steady-state analysis. To assess feasibility, four heat exchanger placements were evaluated across a range of Bypass Ratio (BPR) and Jet Velocity Ratio (JVR) values. Maintaining the BPR and JVR equal to those of the baseline hydrogen-fuelled CFM56-5B1 yielded fuel consumption reductions of 12.2-16.2%, depending on heat exchanger placement. Allowing both parameters to vary produced reductions of up to 27.6% relative to the hydrogen-fuelled baseline. Total engine efficiency increased from approximately 33% for the baseline to approximately 43% for the most efficient hybrid configuration. The inter-turbine heat exchanger placement was found to be thermodynamically optimal, while positioning the heat exchanger downstream of the cathode exhaust achieved the second-highest efficiency with potential benefits in terms of system weight and compactness. The maximum power output of the fuel cell stack is fundamentally limited by the available cooling capacity of the cathode airflow in this type of SOFC integrated type. Several hybrid architectures also operated at lower combustion chamber temperatures than the baseline engine, offering the additional benefit of reduced NOx emissions.