Life cycle assessment for sustainable regional air transport with alternative powertrains

• Lebenszyklusanalyse für nachhaltigen regionalen Luftverkehr mit alternativen Antrieben

Lückhof, Jan-Marcus; Stumpf, Eike (Thesis advisor); Hornung, Mirko (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

Following the serious warnings concerning climate change raised in particular by recent IPCC reports, efforts are increasingly being made to find and implement solutions across industry and society. It has become evident, that energy-intensive and weight-sensitive sectors, such as aviation, are especially difficult to decarbonize. Consequently, in contrast to other industries and modes of transport, the entire sector is still powered by conventional fossil fuels. As options to change that, alternative energy carriers are being discussed which can potentially be produced and supplied with net-zero emissions, namely electricity, hydrogen, biofuels and Power-to-X fuels. For the first two, major modifications concerning the aircraft’s powertrain architecture are required, while the latter two can be designed as drop-in fuels. This thesis investigates the aforementioned pathways to decarbonization with respect to the entire life cycle of the aircraft (cradle-to-grave) as well as the life cycle of the energy carrier. The latter is subdivided into the production and transportation of each form of energy (well-to-tank) and its final use in the aircraft (tank-to-wake). In order to analyse the tank-to-wake process along with all relevant parameters such as mass, volume and efficiency of each powertrain architecture, a flexible algorithm for preliminary aircraft design has been drafted and implemented in Matlab/Simulink. As use cases, aircraft in the 4-PAX class and 19-PAX class are modelled. For a meaningful comparison of the investigated options, five key performance indicators are analysed: technical feasibility, environmental impact, costs, fresh water demand and land use. It is shown, that battery-electric aircraft are not technically suited for passenger transport due to current battery technology. Hybrids (parallel and series) could potentially reduce fuel flow by up to 12% in the 4-PAX class but are highly dependent on the corresponding conventional engine characteristics. The use of biofuels can reduce life cycle emissions by 26% to 91%, depending on the feedstock. However, due to low current production capacities, an increase in ticket prices of 24% is calculated. More importantly, up to 50% of the world’s farmland would be required for feedstock cultivation, to satisfy the current demand for aviation grade jet fuel. Power-to-X fuels promise ecological advantages if produced with electrolysis which in turn is powered with an electricity mix below 284 g CO2,eq/kWh. Prices are highly uncertain, due to a lack of large scale production, however a carbon tax in the order of 380 €/t would be necessary to make them economically competitive. Green hydrogen is found to potentially decrease emissions by up to80%. This scenario assumes the use of a fuel cell. Although less efficient, direct burn of hydrogen in a turbine shows emission savings of up to 30%. Since most technology options have key components in common (e.g. development of reliable electric motors, production of green hydrogen), a parallel approach of multiple pathways is advisable.