LIQUID HYDROGEN POWERED AIRCRAFT – THE SHAPE OF THINGS TO COME?
Liquid Hydrogen (LH2) has the potential to completely decarbonise civil aviation, writes Cranfield University’s Dr Bobby Sethi.
At the moment this is a minority view within the industry, mainly due to the much higher cost associated with the infrastructure required.
But as soon as conventional fuel prices, emission taxation scenarios, and the sheer necessity of transformation are taken into account, the cost of transition is going to look remarkably modest for such a fundamental, long-term solution.
Flightpath 2050 very ambitiously targets 75% CO2 and 90% NOx emissions reductions, relative to year 2000.
It is unlikely that these targets will be met with carbon containing fuels, despite large research efforts on advanced, disruptive, airframe and propulsion technologies (including turbo/hybrid electric propulsion), even when coupled with improved asset and lifecycle management procedures.
Even if we were able to meet these targets, this would not be sufficient in the longer term for a fully sustainable future for civil aviation.
ENABLEH2 (ENABLing CryogEnic Hydrogen-Based CO2-free Air Transport) is a recently launched €4 million European H2020 project which aims to revitalise enthusiasm for LH2 research for civil aviation, demonstrate the feasibility of switching to hydrogen, and the need for more R&D into advanced airframes, propulsion systems and air transport operations as part of an LH2 future.
Combined, these technologies can more than meet the ambitious long-term environmental and sustainability targets for civil aviation.
ENABLEH2 is being led by Cranfield University and other partners include Chalmers University (Chalmers), London South Bank University (LSBU), Heathrow Airport, GKN Aerospace Safran, the European Hydrogen Association (EHA) and Arttic.
The civil aviation industry is beginning to seriously consider the LH2 model – demonstrated by the involvement in the project’s advisory board from Abengoa, Airbus, Air Liquide, Dassault, Gexcon, GKN Aerospace Services Limited, IATA, ICAO, International Airlines Group, Mitsubishi Power Systems, MTU Aero, Reaction Engines, Rolls-Royce, Safran, Siemens and Total.
Any sustainable alternatives face some serious technical challenges. Currently the weight of batteries and other electrical components make it unlikely that purely electric aircraft will be usable for anything other than short-haul flights with a limited payload.
By contrast, LH2 is a formidable means of absorbing excess heat, and so able to reduce the weight of electrical systems and heat exchangers needed – making it possible to enable advanced propulsion technologies.
The research on fuel system heat management in ENABLEH2 is being led by Chalmers and GKN.
Relative to the standard Jet-A1 kerosene fuel, hydrogen is more flammable. This means there can be ‘lean’ combustion producing ultra-low NOx emissions.
As part of ENABLEH2, Cranfield and Safran are developing this approach through hydrogen micromix combustion technologies using the University’s unique pebble bed heater and altitude relight facilities to replicate cruise and high altitude conditions.
ENABLEH2 technologies will be evaluated and analysed for different forms of modern aircraft type making use of turbo-electric propulsion systems, looking at energy efficiency and life cycle CO2 and what this means in cost terms for airlines, taking in to account the range of likely scenarios for fuel prices and the potential for emissions taxation.
This task is being led by Safran with input from all the partners, including up to date information on large scale sustainable production of hydrogen from EHA.
ENABLEH2 is also tackling key challenges and skepticism associated with the introduction of LH2 for civil aviation – i.e. safety, infrastructure development, economic sustainability and community acceptance.
It’s been over 80 years since the Hindenburg disaster, but that tragic event is still intrinsically linked to the public perception and understanding of hydrogen safety.
Fatally, the Hindenburg airship used cotton balloons to store the gas; now, and for many years, hydrogen has been used safely via stainless steel storage vessels (including hydrogen-powered London buses).
Unlike kerosene, if there was ever a spill, LH2 quickly vaporises and disperses, without the same kind of contamination and threat to health of airport staff.
LSBU is working with Heathrow to test the possible risks and scenarios and will deliver a comprehensive safety audit characterising and mitigating hazards to support integration and acceptance of LH2 at aircraft, operational and airport level.
The ENABLEH2 (www.enableh2.eu) project is receiving funding from the European Union’s Horizon 2020 research and innovation programme.
• Dr Bobby Sethi is a lecturer in the Centre for Propulsion Engineering at Cranfield University (www.cranfield.ac.uk) in the UK and lead researcher on the EU project.