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ENABLing cryogEnic Hydrogen based CO2 free air transport (ENABLEH2)

Periodic Reporting for period 1 - ENABLEH2 (ENABLing cryogEnic Hydrogen based CO2 free air transport (ENABLEH2))

Reporting period: 2018-09-01 to 2020-02-29

Liquid Hydrogen (LH2) has the potential to completely decarbonise civil aviation. At the moment this is a minority view within the industry, mainly due to the anticipated higher costs. But considering heightened environmental awareness emisions taxation scenarios, and the sheer necessity of transformation, the cost of transition will be relatively 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 will be extremely challenging to meet these targets with carbon based fuels, despite large research efforts on disruptive airframe and propulsion technologies, even when coupled with improved asset and lifecycle management procedures. Even if we were able to meet these targets, this would not be sufficient for a fully sustainable future for civil aviation, particularly considering the rate at which other sectors are decarbonising. The unique environmental benefits of LH2 for aviation must exploited, with the transition starting as soon as possible. ENABLEH2 is providing thought leadership through revitalising enthusiasm in LH2 research for civil aviation by maturing key technologies to achieve zero mission-level CO2 and ultra-low NOx emissions, with long term safety and sustainability.

Key technologies being studied are:

1. H2 Micromix combustion
Jet A-1 has relatively narrow combustion flammability limits which presents several challenges for low NOx combustion technologies. H2 is a promising fuel as it has much wider flammability limits enabling leaner (lower flame temperature) combustion. Additionally, the molecular diffusivity and high flame speed of H2 offer good mixing and lower residence times, therefore significant reductions in NOx are possible. Micromix (diffusion) combustion enables superior fuel and air mixing without the risks of auto-ignition and flashback associated with premixing. The improved mixing reduces local high flame temperature regions, leading to ultra-low NOx emissions. Within WP3, ultra-low NOx H2 Micromix combustion technology is being matured through a combination of numerical and experimental research comprising injector array, full annular combustor segment and altitude-relight studies.

2. Fuel system heat management
In order to exploit the formidable heat sink potential of LH2, to enable more-efficient disruptive propulsion technologies, WP2 is maturing technologies for compressor integrated cooling, intercooling and variable cooling concepts, fuel pumps, heat exchangers, turbines for expander cycles and cryogenic cooling for electric systems for turboelectric distributed propulsion. WP1 is maturing LH2 fuel tank design and integration.

In WP1, a suite of models is being developed to evaluate LH2-fuelled aircraft with respect to energy efficiency, emissions, life cycle CO2 and costs, for potential fuel price and emissions taxation scenarios. The benefits and economic viability of LH2 will be quantified relative to best-case scenario projections for Jet A-1, Biofuels and LNG. WP4 is generating best-practice safety guidelines for LH2 at aircraft, airport and operational level. WP5 will deliver comprehensive roadmaps for the introduction of LH2.

In order to maximise the technical rigour and impact of the project, ENABLEH2 also has a highly active Industry Advisory Board (IAB). The IAB comprises key civil aviation stakeholders including aircraft and propulsion system OEMs, airlines, energy and industry organisations. IAB members include Airbus, Rolls-Royce, MTU, Safran, GKN, IAG, Lufthansa Technik, IATA, ICAO, Reaction Engines, Dassault Aviation, Infosys, Air Liquide, Total, Gexcon, Siemens, Abengoa, MHPS and the Clean Sky 2 JU.
Key achievements to date:

WP1 has reviewed developments in H2 production and infrastructure and made projections for the long-term costs of alternative fuels. Four LH2 aircraft configurations have been selected for detailed studies (one “more conventional” and one “maximum synergy” configuration each for a typical short-medium range and long range mission). These concepts were down-selected from several aircraft configurations via a rigorous quality function deployment exercise. Assessments of reference aircraft utilising Jet A-1, biofuels and LNG is almost complete.
WP2 has developed tools for the conceptual design and performance analysis of fuel system components. The design of the rig to investigate the potential of core flow cooling with cryogenic H2 has been completed and parts are being manufactured. The down-selection and design of preferred heat management systems and fuel tanks is also underway.
Within WP3, comprehensive CFD-based studies (comprising design space exploration, emissions and thermoacoustic assessments) have been completed and have highlighted limitations, uncertainties and significant discrepancies between H2 and air mixing and combustion models of 3 state-of-the-art commercial combustion CFD codes. These models will be further evaluated, validated and calibrated based on the results obtained from the experiments. The design and commissioning of the rigs are underway.
In WP4 a review of aeronautic and H2 industry safety synergies, conflicts and knowledge gaps, and preliminary hazard analyses of laboratory and aircraft systems has been completed. A safety management plan has been issued. Experimental studies are currently underway. The safety of LH2 at airports, has been assessed via a Preliminary Hazard Analysis workshop held at Heathrow.
As part of WP5, a dedicated project website and community management tool have been set up to engage with the IAB members in a formal capacity. Twelve key technology research strands have been identified for the introduction of LH2 for civil aviation as part of a preliminary roadmapping exercise.
Key deliverables expected by the end of the project:

1. Compressor integrated cooling, intercooling and variable cooling (TRL 4)
2. Fuel tank and fuel system model (TRL 2)
3. Ultra-low NOx annular micromix combustor segment design (TRL 3/4)
4. Verified aircraft, propulsion system, emissions and life cycle numerical models (TRL 2)
5. Quantified Technoeconomic Environmental Risk Assessments (TERA) at mission level
6. A comprehensive safety audit, characterizing and mitigating hazards in order to support integration and acceptance of LH2 at aircraft, airport and operational level
7. Life cycle costs and CO2 emissions relative to best case scenario projections for Jet-A1, bio-fuels and LNG for different fuel price and emissions taxation scenarios
8. Roadmaps for maturing the technologies to TRL 6 by 2030 – 2035 and also for the gradual introduction of LH2 for civil aviation including airport infrastructure development

Key impact indicators to date:

ENABLEH2 is developing technologies which will make a substantial contribution to meeting the ambitious environmental targets for civil aviation. By complementing research in other sectors the project will support transition towards a H2 economy. ENABLEH2 is revitalising enthusiasm in LH2 for civil aviation by engaging with key aviation stakeholders through the CMT, alleviating public perception safety concerns and demonstrating the long-term environmental and economic case for LH2. There have been dedicated sessions for ENABLEH2 in several international conferences. The project has featured in the ICAO 2019 Environmental Report, The Times, and Airport World Magazine.
Examples of LH2-fueled aircraft concepts being modelled in WP1
Examples of LH2-fueled aircraft concepts being modelled in WP1
Fuel heat management system-potential exploitation of LH2 as a heat sink