Periodic Reporting for period 3 - ENABLEH2 (ENABLing cryogEnic Hydrogen based CO2 free air transport (ENABLEH2))
Reporting period: 2021-09-01 to 2022-11-30
ENABLEH2 has provided thought leadership through revitalising enthusiasm in LH2 research for civil aviation to exploit the fuel’s unique environmental benefits. This was achieved by maturing key technologies to achieve zero mission-level CO2 and ultra-low NOx emissions, demonstrating safety and long-term sustainability that will not be possible with other fuels i.e. Jet A-1, LNG or Sustainable Aviation Fuels (SAF).
Key technologies researched include hydrogen micromix combustion and fuel system heat management.
Jet A-1 has relatively narrow combustion flammability limits which presents several challenges for low NOx combustion technologies. H2 has much wider flammability limits enabling leaner (lower flame temperature) combustion. The molecular diffusivity and high flame speed of H2 also offer good mixing and lower residence times, so significant reductions in NOx are possible. Micromix (diffusion) combustion enables superior fuel and air mixing without the risk of auto-ignition and flashback from premixing. Ultra-low NOx H2 micromix combustion technology was advanced through a combination of numerical and experimental research on injector arrays, full annular combustor segments and altitude-relight studies.
LH2 fuel tanks, fuel system design and integration and more efficient disruptive propulsion technologies enabled by the heat sink potential of LH2 were investigated. The project also matured technologies for compressor integrated cooling, intercooling, turbine rear structure integrated cooling, and heat exchangers to preheat hydrogen.
Models were developed to evaluate LH2-fuelled aircraft with respect to energy efficiency, emissions, life cycle CO2 and operating costs. The benefits and economic viability of LH2 were quantified relative to best-case scenario projections for Jet A-1, biofuels and LNG.
ENABLEH2 has generated best-practice safety guidelines for LH2 at aircraft, airport and operational levels and has also delivered comprehensive roadmaps for the introduction of LH2.
To maximise the technical rigour and impact of the project, ENABLEH2 developed an active Industry Advisory Board comprising key civil aviation stakeholders including aircraft and propulsion system OEMs, airlines, energy and other industry organisations. IAB members included: Abengoa, ACI, Airbus, Air Liquide, ATI (FlyZero), Clean Sky 2 JU, Dassault Aviation, EASA, easyJet, Gexcon, IAG, HyEnergy, IATA, ICAO, IMI, Infosys, Lufthansa Technik, MHPS, MOOG, MTU, Reaction Engines, Rolls-Royce, Siemens and Total.
Key technologies researched include hydrogen micromix combustion and fuel system heat management.
Jet A-1 has relatively narrow combustion flammability limits which presents several challenges for low NOx combustion technologies. H2 has much wider flammability limits enabling leaner (lower flame temperature) combustion. The molecular diffusivity and high flame speed of H2 also offer good mixing and lower residence times, so significant reductions in NOx are possible. Micromix (diffusion) combustion enables superior fuel and air mixing without the risk of auto-ignition and flashback from premixing. Ultra-low NOx H2 micromix combustion technology was advanced through a combination of numerical and experimental research on injector arrays, full annular combustor segments and altitude-relight studies.
LH2 fuel tanks, fuel system design and integration and more efficient disruptive propulsion technologies enabled by the heat sink potential of LH2 were investigated. The project also matured technologies for compressor integrated cooling, intercooling, turbine rear structure integrated cooling, and heat exchangers to preheat hydrogen.
Models were developed to evaluate LH2-fuelled aircraft with respect to energy efficiency, emissions, life cycle CO2 and operating costs. The benefits and economic viability of LH2 were quantified relative to best-case scenario projections for Jet A-1, biofuels and LNG.
ENABLEH2 has generated best-practice safety guidelines for LH2 at aircraft, airport and operational levels and has also delivered comprehensive roadmaps for the introduction of LH2.
To maximise the technical rigour and impact of the project, ENABLEH2 developed an active Industry Advisory Board comprising key civil aviation stakeholders including aircraft and propulsion system OEMs, airlines, energy and other industry organisations. IAB members included: Abengoa, ACI, Airbus, Air Liquide, ATI (FlyZero), Clean Sky 2 JU, Dassault Aviation, EASA, easyJet, Gexcon, IAG, HyEnergy, IATA, ICAO, IMI, Infosys, Lufthansa Technik, MHPS, MOOG, MTU, Reaction Engines, Rolls-Royce, Siemens and Total.
For low NOx H2-micromix combustion systems, ENABLEH2 has:
• Established best practices for numerical simulations
• Assessed the impact of injector design parameters on flame interactions and NOx
• Demonstrated a hybrid manufacturing approach for intricate designs of fuel injectors
• Assessed performance and emissions in a high pressure and temperature combustion rig
• Demonstrated that low momentum flux ratio injector designs deliver the lowest NOx
• Demonstrated that they have lower risk of low frequency thermoacoustic instabilities than Jet A-1/SAF fuelled low NOx combustion systems, and that higher frequency modes may be relatively easily mitigated
• Demonstrated that altitude relight may be easier relative to Jet A-1 fuelled combustion systems
• Derived a reduced order NOx emissions prediction correlation for aircraft mission-level assessments including aircraft trajectory and engine cycle optimisation
• Estimated that LH2-fuelled aircraft may deliver 40-60% reductions in mission NOx relative to their Jet A-1/SAF counterparts.
The studies on H2 fuel system thermal management have concluded that:
• High heat transfer rates are possible using existing surfaces in the engine to preheat the fuel. However their limited area restricts the amount of heat transferred and gives little benefit to engine performance.
• The integration of compact heat exchangers in the core gas path is cumbersome. Low pressure losses can be achieved, but variable geometry (e.g. variable bleed valves) may be necessary for off-design operation.
• Intercooling alone results in a fuel burn benefit and NOx reductions of up to 30%. However, combining intercooling and recuperation would yield greater benefits and merits further investigation.
The technology evaluation studies have concluded that:
• To expedite H2-fuelled aircraft entry into service, several innovation waves will be necessary. The primary objectives of the first innovation wave should be to mature the key technologies, demonstrating safety and establishing certification rules. Subsequent innovation waves may then focus on further improving efficiency and reducing emissions e.g. by exploiting the heat sink potential of LH2 to enable advanced disruptive technologies like turboelectric distributed propulsion.
• Y2050 LH2-fuelled aircraft should deliver significantly lower mission NOx emissions than those fuelled by Jet A-1 or SAF.
• Due to a much higher exhaust water content, hydrogen-fuelled engines are likely to produce contrails at lower altitudes. However due to the absence of soot particles, contrails may be less persistent and will have lower global warming characteristics. Furthermore contrails generated from hydrogen-fuelled engines may be completely mitigated by appropriate mission trajectory management for contrail avoidance. Although this may mean flying at sub-optimal fuel burn cruise altitudes this will not come at the expense of generating CO2.
• Higher fuel costs and CO2 emissions charges in Y2050 are found to be partly offset by improvements in aircraft and propulsion system efficiencies and the studies have shown that LH2 aircraft may be cost competitive with alternative fuels in the long term.
A comprehensive review of aeronautic and H2 safety synergies, conflicts and knowledge gaps, and preliminary hazard analyses of laboratory and aircraft systems was completed. A safety management plan has been issued. Experimental studies have been undertaken to determine flammability limits and burning velocities over a range of temperatures and pressures. For both early introduction and significant fleet penetration of H2 aircraft, detailed risk and mitigation plans have been issued for varying airport infrastructural and operational requirements.
ENABLEH2 has delivered a comprehensive roadmap with thirteen key technology research strands that need to be addressed to expedite entry into service of LH2-fuelled aircraft.
• Established best practices for numerical simulations
• Assessed the impact of injector design parameters on flame interactions and NOx
• Demonstrated a hybrid manufacturing approach for intricate designs of fuel injectors
• Assessed performance and emissions in a high pressure and temperature combustion rig
• Demonstrated that low momentum flux ratio injector designs deliver the lowest NOx
• Demonstrated that they have lower risk of low frequency thermoacoustic instabilities than Jet A-1/SAF fuelled low NOx combustion systems, and that higher frequency modes may be relatively easily mitigated
• Demonstrated that altitude relight may be easier relative to Jet A-1 fuelled combustion systems
• Derived a reduced order NOx emissions prediction correlation for aircraft mission-level assessments including aircraft trajectory and engine cycle optimisation
• Estimated that LH2-fuelled aircraft may deliver 40-60% reductions in mission NOx relative to their Jet A-1/SAF counterparts.
The studies on H2 fuel system thermal management have concluded that:
• High heat transfer rates are possible using existing surfaces in the engine to preheat the fuel. However their limited area restricts the amount of heat transferred and gives little benefit to engine performance.
• The integration of compact heat exchangers in the core gas path is cumbersome. Low pressure losses can be achieved, but variable geometry (e.g. variable bleed valves) may be necessary for off-design operation.
• Intercooling alone results in a fuel burn benefit and NOx reductions of up to 30%. However, combining intercooling and recuperation would yield greater benefits and merits further investigation.
The technology evaluation studies have concluded that:
• To expedite H2-fuelled aircraft entry into service, several innovation waves will be necessary. The primary objectives of the first innovation wave should be to mature the key technologies, demonstrating safety and establishing certification rules. Subsequent innovation waves may then focus on further improving efficiency and reducing emissions e.g. by exploiting the heat sink potential of LH2 to enable advanced disruptive technologies like turboelectric distributed propulsion.
• Y2050 LH2-fuelled aircraft should deliver significantly lower mission NOx emissions than those fuelled by Jet A-1 or SAF.
• Due to a much higher exhaust water content, hydrogen-fuelled engines are likely to produce contrails at lower altitudes. However due to the absence of soot particles, contrails may be less persistent and will have lower global warming characteristics. Furthermore contrails generated from hydrogen-fuelled engines may be completely mitigated by appropriate mission trajectory management for contrail avoidance. Although this may mean flying at sub-optimal fuel burn cruise altitudes this will not come at the expense of generating CO2.
• Higher fuel costs and CO2 emissions charges in Y2050 are found to be partly offset by improvements in aircraft and propulsion system efficiencies and the studies have shown that LH2 aircraft may be cost competitive with alternative fuels in the long term.
A comprehensive review of aeronautic and H2 safety synergies, conflicts and knowledge gaps, and preliminary hazard analyses of laboratory and aircraft systems was completed. A safety management plan has been issued. Experimental studies have been undertaken to determine flammability limits and burning velocities over a range of temperatures and pressures. For both early introduction and significant fleet penetration of H2 aircraft, detailed risk and mitigation plans have been issued for varying airport infrastructural and operational requirements.
ENABLEH2 has delivered a comprehensive roadmap with thirteen key technology research strands that need to be addressed to expedite entry into service of LH2-fuelled aircraft.
ENABLEH2 is viewed by many key civil aviation stakeholders as one of the flagship projects that has helped revitalise enthusiasm in LH2-fuelled aircraft and related technologies. ENABLEH2 has helped advance low-NOx H2 micromix combustion (TRL 2/3), fuel system thermal management (TRL 2 – 4), H2 fuel tanks and fuel system models (TRL 2) and verified aircraft, propulsion system and life cycle numerical models (TRL 2). A comprehensive safety audit has been issued, characterizing and mitigating hazards to support integration and acceptance of LH2 at aircraft, airport and operational level. Roadmaps have also been issued for maturing the technologies to TRL 6 by 2030 – 2035.
ENABLEH2 partners have participated in numerous conferences/workshops/outreach initiatives. ENABLEH2 has also featured in major reports, EU brochures, press articles, videos and more. Details are available on the ENABLEH2 project website.
ENABLEH2 partners have participated in numerous conferences/workshops/outreach initiatives. ENABLEH2 has also featured in major reports, EU brochures, press articles, videos and more. Details are available on the ENABLEH2 project website.