A four‑year, international programme led by Rolls‑Royce and easyJet to demonstrate hydrogen as a viable aviation fuel has culminated in a world-first achievement in a modern aero engine running on 100 per cent hydrogen at full take-off power, proving the potential of hydrogen to play a transformative role in future zero-carbon aviation.

HYEST (Hydrogen Engine System Technologies) is a major research initiative to develop liquid-hydrogen combustors for commercial aviation. Aimed at enabling zero-carbon, hydrogen-powered flights, it focuses on overcoming extreme heat and fuel reactivity by creating advanced fuel spray nozzles and subsystem architectures.

At the end of April, the companies tested a modified Rolls-Royce Pearl 15 aircraft engine, demonstrating that a modern jet engine, scalable to power a narrowbody aircraft, can safely operate on gaseous hydrogen across a fully simulated flight cycle, including start-up, take-off, cruise and landing.

The programme followed an incremental, technology-led approach to prove the fundamental technologies. Progressing from early engine testing at Boscombe Down in the UK in 2022, the technology was scaled and further developed through a UK and European programme of component and system rig tests, including the development of a full-scale hydrogen test facility, before moving to full integration into a hydrogen fuelled demonstrator engine. Earlier modifications also focused on adapting the engine to replace traditional jet fuel with hydrogen while considering both carbon and non-CO2 impacts through an expansive combustion programme.

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