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by Christopher Surgenor (GreenAir Online) If deployed to their maximum potential, liquid hydrogen-powered aircraft could enable aviation emissions to be capped at 2035 levels, although a 6-12% reduction in CO2e emissions relative to projected 2050 levels is more realistic, finds an ICCT study. However, such aircraft, assuming they enter service by 2035 as targeted by Airbus, are likely to come with performance penalties and much higher fuel costs relative to fossil-fuel aircraft. In 2020, Airbus unveiled three concept hybrid-hydrogen aircraft: two powered by turbofan and turboprop engines and the other a revolutionary blended design with turbofan engines. The new study focuses on the smaller turboprop aircraft targeting the regional market and a narrow-body turbofan aircraft suitable for short and medium haul flights, benchmarked against the ATR 72-600 and Airbus A320neo respectively. Together, the two liquid hydrogen powered aircraft could service 31-38% of all passenger traffic, as measured by RPKs. Another ICCT study just published concludes environmental constraints are likely to severely limit the market for supersonic aircraft.

A significant challenge for hydrogen-powered aircraft design is fuel storage as hydrogen stores 2.8 times the energy on a per unit basis than fossil Jet A. However, its volumetric energy density is significantly lower than that of Jet A and for sufficient hydrogen to be carried in an aircraft, its density needs to be increased. This is achieved by storing gaseous hydrogen (GH2) at high pressure, or by liquefying it and storing the liquid hydrogen (LH2) at very low temperatures. Producing the energy of a unit volume of Jet A requires seven times that volume of compressed GH2 and four times that volume of LH2, so making the latter a superior option from the perspective of improving the payload capacity and range of potential aircraft designs.

The hydrogen study notes that compared to fossil-fuel aircraft, LH2-powered aircraft will still be heavier, less efficient as they have a higher energy requirement per revenue passenger km (RPK) and also have a shorter range.

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To make green LH2 cost-competitive with fossil jet fuel, ICCT says taxes will need to be levied on CO2 emissions, with a carbon price of around $250/tonne CO2e needed in 2025 for cost parity in the United States, falling to $100 in 2050. Europe, where renewable hydrogen is expected to be more expensive, may require a higher carbon price.

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The study, led by Dr Jayant Mukhopadhaya, calls for supportive government policies if LH2-powered aircraft are to succeed, to include carbon pricing, low-carbon fuel standards or alternative fuel mandates to bridge the cost gap with fossil fuel, together with life-cycle accounting to ensure aviation has access to the cleanest sources of hydrogen.

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Meanwhile, a joint study by ICCT and MIT’s Laboratory for Aviation and the Environment (LAE) has found that both ‘low-boom’ designs and ultralow cost sustainable aviation fuels will be needed for a sizeable supersonic aircraft market to develop.   READ MORE

UK FlyZero project concludes liquid hydrogen is the optimum fuel for zero-carbon flight by 2050 (GreenAir Online)

HydrogenOne Capital Growth plc and Safran announce a joint investment in UK flight innovator Cranfield Aerospace (HydrogenOne/Safran)