PERFORMANCE ANALYSIS OF EVOLUTIONARY HYDROGEN-POWERED AIRCRAFT
EXECUTIVE SUMMARY
Aviation is a hard-to-decarbonize sector of the transport industry due to the stringent mass and volume requirements for aviation fuel. The high energy content of liquid jet fuel, both per unit mass (specific energy) and per unit volume (energy density), makes it difficult to replace. Significant emphasis has been placed on drop-in Sustainable Aviation Fuels (SAFs) to reduce emissions without sacrificing aircraft performance. But SAFs emit carbon dioxide (CO2) when combusted (carbon capture during production reduces life-cycle emissions) and their uptake has fallen short of expectations due to their high cost, limited supply, and concerns about the land-use impacts of biofuels.
Interest is growing in hydrogen, particularly liquid hydrogen (LH2), as a potential alternative to SAFs. LH2 emits no CO2 during combustion and can be produced with near-zero carbon emissions if made using renewable electricity (“green hydrogen”). However, its low energy density and heavy cryogenic tank requirements incur performance penalties when compared to Jet A-powered aircraft.
This study explores the potential performance characteristics, fuel-related costs and emissions, and replaceable fossil fuel market of LH2-powered aircraft entering service in 2035. In keeping with aviation’s conservative approach to new aircraft design, only evolutionary advances in design parameters that are feasible by 2035 are considered. Two LH2 combustion designs are assessed: a smaller turboprop aircraft targeting the regional market, and a narrow-body turbofan aircraft suitable for short and medium-haul flights. These designs are benchmarked against the ATR 72 and the Airbus A320neo, respectively.
Both hydrogen-powered designs will require an elongated fuselage to accommodate LH2 storage behind the passenger cabin. Gravimetric indices (GI), which denote the ratio of the fuel mass to the mass of the full fuel system including the cryogenic tank, are investigated, at values between 0.2 and 0.35. Seating pitch (SP) values of 29 and 30 inches, mimicking the seating density of low-cost and regular airliners, are used. The potential market coverage of LH2-powered aircraft families, which include variants of the baseline design with different ranges and passenger capacities, are analyzed as well.
Overall, we find that LH2-powered aircraft entering service in 2035 could contribute to aviation’s 2050 climate goals but with performance penalties relative to fossil-fuel aircraft. Compared to fossil-fuel aircraft, LH2-powered aircraft will be heavier, with an increased maximum takeoff mass (MTOM), and less efficient, with a higher energy requirement per revenue-passenger-kilometer (MJ/RPK). They will also have a shorter range than fossil-fuel aircraft. Nevertheless, we estimate that evolutionary LH2-powered narrow-body aircraft could transport 165 passengers up to 3,400 km and LH2-powered turboprop aircraft could transport 70 passengers up to 1,400 km. Together, they could service about one-third (31 to 38%) of all passenger aviation traffic, as measured by revenue passenger kilometers (RPKs). This represents 57% to 71% of all RPKs serviced by narrow-body aircraft and 89% to 97% of all RPKs serviced by turboprops. Aircraft with lighter fuel systems (GI of 0.35) and tighter seating density (seating pitch of 29 inches) would provide larger market coverage.
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