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.

Sustainability has become an increasingly important issue, and several different governments around the world have been working towards more environmentally friendly approaches throughout different industries. This has led to measures such as the European Green Deal, which aims to make Europe climate neutral by 2050. For the aircraft industry, however, this goal creates a so-called circular causality problem. This is because there may be limited investment in increasing production of alternative energy sources due to the limited availability of aircraft that use them. On the other hand airlines may hesitate due to the limited availability of fuel to buy such aircraft. In order to solve this problem, the carbon neutral ready aircraft has been proposed. The carbon neutral ready aircraft is designed such that it initially is powered by fossil fuels and can then be converted to be powered by a carbon neutral energy source. The carbon neutral energy source that is chosen for this aircraft design is synthetic kerosene. The carbon neutral aircraft has a high wing configuration with a high aspect ratio wing. To cope with the large span of the aircraft it was decided to give the aircraft the ability of the wing tips to be folded up. Furthermore, the wing has support struts which connect the wing to the lower part of the fuselage. The propulsion system of the aircraft has two novel features: two wing mounted ultra high bypass ratio turbofan engines and an electrically powered ducted fan, which ingests the boundary layer at the aft of the fuselage. An additional five-gear configuration was chosen for the landing gear to provide the aircraft with stable ground operations while not creating a need for a fairing which interferes with the boundary layer being ingested by the aft ducted fan. Carrying out the design of this aircraft shows that the aircraft is financially feasible and performs as well as the baseline A320 aircraft in terms of payload and range, while allowing sustainability goals such as the European Grean Deal to be met. The aircraft has a 17 % emission reduction compared to the A320neo, while still employing fossil fuel based kerosene. Furthermore, at least 90% by mass of the primary structure of the aircraft is recyclable. From the recommendations however, it is clear that a lot still needs to be done before the carbon neutral aircraft can enter into service in 2030.