Designing commercial aircraft to use Liquid Hydrogen (LH~2~) is one of very few ways to substantially diminish life-cycle CO~2~ emissions from aviation. The merits of hydrogen as an aviation fuel have long been recognized. However, apart from very short-range applications, its integration into commercial aircraft is only viable when it is liquefied, due to the heavy weight and large volume of the tanks needed to store hydrogen as a compressed gas. The handling of cryogenic fuels adds complexity to aircraft and engine systems and operations, but cryogenic fuels also present opportunities since their heat-sink capabilities can be used to increase the efficiency of future propulsion systems.

Earlier design studies for LH~2~-fuelled aircraft at NASA and at Lockheed in the 1970s, by Tupolev in the 1980s and by Airbus in late 1990s, made steps towards establishing its operational feasibility. Interest in these studies diminished when oil prices fell and the cost of LH~2~ was deemed prohibitive. More affordable alternative fuels, including Liquid Natural Gas (LNG), were then considered. However, recent developments including the rapidly-falling cost of electricity generated from renewable sources, and the imperative to reduce CO~2~ emissions to tackle the anthropogenic impacts on climate, mean that the adoption of a ‘hydrogen economy’ could soon be realized and the economic case for hydrogen-fuelled aircraft is steadily improving. Further factors now favouring hydrogen are ongoing improvements in engine and aircraft performance, reducing fuel burn, and the potential of hydrogen to significantly reduce NO~x~ emissions and eliminating unburned hydrocarbon, soot and carbon monoxide emissions.

The European Commission recognising the potential benefits afforded by LH~2~ propulsion solutions by funding the Horizon 2020 project entitled ENABLing CryogEnic Hydrogen-Based CO~2~-free Air Transport: ENABLEH2. Coordinated by Cranfield University, this 3-year project, which commenced in September 2018, involves partners from Chalmers Tekniska Hoegskola, GKN Aerospace Sweden, Heathrow Airport Limited, London South Bank University, SAFRAN SA, and ARTTIC.

Part of the project includes the Technology Evaluator – Work Package 1 (WP1) – with the ultimate goal of a critical technology appraisal using the Techno-economic Environmental Risk Assessment (TERA) evaluation platform. This includes the estimation of life-cycle CO~2~ emissions and operating costs for a range of fuel price and emissions taxation scenarios.

The intermediate objectives set, involve the down-selection of aircraft concepts for both Short-to-Medium Range (SMR) and Long-Range (LR) operations, declaration of reference aircraft powered by JET A-1 / Drop-in Biofuel / Liquid Natural Gas (LNG) only, and technology and scenario evaluation studies on optimally-sized SMR and LR concepts for comparison with the reference aircraft designs.

This paper provides an overview of the scope and objectives of WP1 and describes the work completed to date. Justifications for the Top-Level Aircraft Requirements (TLARs) are given and flight profiles for the SMR and LR aircraft block operations adopted in ENABLEH2 are described. The SMR and LR aircraft are specified with design ranges of 3000 nmi and 7500 nmi and respectively seat 200 passengers (single class) and 414 passengers (two classes). Details of year-2050 comparative reference Jet A-1 aircraft are also presented.

The LH~2~ aircraft down-selection process and its outcomes are discussed. This study was undertaken in two phases with the first considering 30 potential airframe architectures (i.e. fuselage/wing/fuel-tank combinations) and 21 propulsion-system arrangements. The second phase featured the final down-selections from a short-list of nine integrated design concepts ranked according to 34 criteria, covering operating cost, passenger appeal, noise and safety. Upon completion of the process, four concepts, two SMR and two LR, were selected for more detailed aircraft sizing and optimisation. For each application, one more-radical ‘Max Synergy’ design was selected, aiming to maximise the overall aircraft block energetic efficiency through close integration of the airframe, fuel tanks and propulsion systems. The other two designs were classified as ‘Lower Risk’ since they retained conventional tube-and-wing morphology and located the LH~2~ fuel tanks above the fuselage.


Synergistic Technology Combinations for Future Commercial Aircraft Using Liquid Hydrogen

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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