The aviation sector is responsible for 2-3% of all anthropogenic carbon emissions and 12% of transport-related emissions. In order to address this problem, the European Comission devised the “Flight Path 2050” reduction targets: 75% CO2 reduction per passenger kilometer relative to the capabilities of typical new aircraft in 2000, as well as 90% NOx and 65% perceived noise reduction. Considering the increasing amount of air travel, these goals are unlikely to be reached by evolutionary improvements of existing aviation technology and, in fact, the overall carbon emissions are predicted to increase further in the years to come.

As an alternative to hydrocarbon fuels (directly correlated with CO2 emissions), one solution is the use of hydrogen as fuel. Compared to kerosene, hydrogen has three times higher gravimetric energy density (33.3 kWh/kg); nevertheless, its volumetric energy density is four times lower than hydrocarbons, which gives some difficulties regarding the integration of the tanks into the aircraft. Besides, once hydrogen is used as a fuel, it can be used either into a gas turbine or to generate electricity using a fuel cell (e.g., PEMFC). In this work, a mathematical optimisation approach is used to evaluate the feasibility of a hybrid hydrogen-powered aircraft retrofit. The propulsion systems include hydrogen fuelled gas turbine propulsion, hydrogen fuel cell electric propulsion (which can be coupled with lithium-ion batteries), as well as the current technology used, kerosene fuelled gas turbine propulsion.

This study aimed at identifying potential alternatives to classical aircraft design. The problem was tackled using a mathematical optimisation approach, considering aircraft design specifications and aerodynamics as model constraints, with the objective of identifying the most promising aircraft configurations. In the near future, we envisage to further develop the model to consider the different flight phases as well as to estimate the carbon emissions integrating a life cycle assessment of each technology.