Bjorn’s Corner: The challenges of hydrogen. Part 17. Hydrogen airliner program

By Bjorn Fehrm

December 11, 2020, ©. Leeham News: We use this Corner to define the time table for our hydrogen airliner program and for what areas we need to conduct risk-reducing research before we embark on an actual design.

As we said in last week’s Corner, we aim to develop a hydrogen airliner for the heart of the domestic market after the COVID-19 Pandemic. It’s a 160 to 180 seat single-aisle turbofan driven airliner, using liquid hydrogen as the fuel.

Figure 1. Airbus ZEROe hydrogen-fueled airliner concepts. Source: Airbus.

A 160 to 180 seat hydrogen airliner

We know from the last Corner, our aircraft will use a classical tube with wings and a classical empennage. The engines will be turbofans, one on each wing. They will be hydrogen-fueled using an evolutionary development of the engines used today on the Airbus A320neo and Boeing 737 MAX.

Entry into service of the aircraft is targeted for 2035, the timetable of the Airbus hydrogen airliner. We spend the time until a program launch decision must be made by 2027 to do risk-reducing research for the most challenging areas of the project.

Areas covered in our risk-reducing research programs

There are several areas where we need to increase our knowledge before embarking on a design of a hydrogen airliner:

  • The highest priority is liquid hydrogen tank designs. The LH2 tank is the most challenging area for a hydrogen airliner. It needs ultra-efficient isolation for the -253°C cryogenic storage of LH2. Shall we make it as a vacuum flask design with additional polyurethane isolation (in case of a flask puncture) or a one-wall design with thicker polyurethane isolation?
  • Do we design with one big tank placed at the rear or two smaller tanks, preferably placed on both sides of the center of gravity? What are the effects on the cabin?
  • We need research on hydrogen fuel and leak detection components. Although the space launcher industry has developed suitable components, these need adaptations for longer-term use in an airliner environment.
  • We shall start an engine hydrogen conversion program together with an engine OEM. The risk reduction phase can use an existing engine from the A320neo/737 MAX that is converted to hydrogen. The work will center around combustor design and the heat exchanger we need to turn the liquid hydrogen to gas before entering the engine.
  • We shall hook up with a fuel cell manufacturer to develop a 1MW fuel cell to replace the APU function. It shall allow operation on the ground and during flight so we can use a more electrical aircraft architecture.
  • We start a ground operation program together with airport authorities that defines storage, liquefaction, and tanking facilities. Technology from the launcher industry is essential for the program. Practical tanking trails with dummy aircraft shall finish the program where different safety scenarios are simulated.
  • Together with our regulator, we shall start a safety program, where different safety scenarios are defined and simulated. From these, we shall research how the worst scenarios can be handled and mitigated. An example of a follow-on program is how to evacuate passengers during a hydrogen leak with both freeze and heat damage risks. We also need to understand how to fight such events. What equipment and methods are required. Must the airport fire brigades have different fire engines? Must aircraft safety rules be changed?

In the next Corners, we go through these areas and discuss the challenges, research activities and possible solutions.

22 Comments on “Bjorn’s Corner: The challenges of hydrogen. Part 17. Hydrogen airliner program

  1. Hello,

    Interesting article as usual. Could you rationalize the 1MW power class Fuel Cell for APU replacement. This power rating seems pretty big in order to supply non propulsive e-systems only (for a 160-180 PAX aircraft) ?

    • Hi Marsupio,

      it depends on how ambitious “more electric” we want the aircraft to be. Ideally, the engines can skip the auxiliary gearbox which is an unreliability source and degrades engine performance through loading of the spools. We also want to skip a bleed system.

      So we need electrical power for: normal consumers, ECS, brakes, de-icing of wings/tailplanes, engine start, and replacement of hydraulic pumps. Electric redundancy comes through spool-mounted starter generators but ideally, they are just backup as their use degrades engine efficiency.

      • Hi Bjorn,

        thank you for answering my comment. I confirm that for the entire scope of e-systems you are mentioning, the final bill is not 1MW (for a 160-180 PAX aircraft). It is more than half of that (which is still however a challenge for a “APU like” Fuel Cell subsystem). If you are interested I can give you the power budget details for each e-system you mentioned.

        • I think Bjorn is following the design guidelines established broadly for the more-electric aircraft, which gave 1 MW as a goal to be met. That’s not to say 1 MW is required for every aircraft, or at all times.

          The 787 already has in excess of 1 MW in total capacity. The expectation is that this will grow over time, for all aircraft.

          For smaller aircraft, the APU size can be reduced if there is redundancy in the engine generators. But another goal is to reduce those over time, if one or more fuel cell APU’s can be shown to be practical and reliable.

        • Thanks Marsupio,

          please do. The more electric 787, which is about three times such an aircraft in size and capacity has an onboard system of 1450kVA. But it also has gearbox and APU driven hydraulic pumps, supplying power to all the movables (including spoilers, flaps, landing gear operation) and no start-generators on the engines that need energy. If you have de-icing, fast movements of all control surfaces including gear, flaps, and fast engine accelerations (where the starter generators aid the engine’s transients) due to bad weather Go Around, you can’t skimp on the capacity of the electrical system. Please give the power budget for a worst-case like the one described. I think we come close to 1 MW as you need margins.

          • How about 2x of Hyzon’s 400KW Fuel Cell? Use their prelim data to have something to start with? At the current pace of innovation, we’re likely looking at a much lighter and more reliable Fuel Cell in 2035. Which means you’ll probably want that Fuel Cell to do as much as possible, maybe even look at redundancy to allow it to perform more tasks with less backup?

  2. I think requirements for double walled tubes in the aircraft and the intertube cavity vented to ambient. I can see special requirements on fuel boost pumps prohibiting the open versions in cansters where fuel do the motor cooling and lubrication even though there are hydrogen cooled generators in the nuclear industry. The engine gbx driven fuel pumps will see different new requirements to avoid pump wheel bursts as the low operating teperatures makes non destructive testing for minute defects harder. Fuel-Oil coolers will look different as you don’t want liquid hydrogen into the engine oil system, engine combustion sections will be different to avoid very hot zones producing NOX, preservation fluids will be different for the fuel system. PWA mentioned that you want to redesign the engines to use the LH2 cooling capabilies and the certification requirements that those performance enhancing systems will impose.

    • Since piping LH2 requires insulated lines which would be heavy and volumetrically wasteful, to use LH2 for engine cooling, the tanks would have to be close to the engines, not the configuration that BF posited.

      • Yes, there might be tube requirements for both vacuum insulation and drain purge cavity hence 3-walled tubes with spiral spacers in between. Peco tubes and other tube specialists migh do extremenly well. The complex tube unions might be 3D printed in Ti alloys like the GE9X Fuel/oil cooler that normally are massive amounts of thin walled tubes brazed that now are replaced with 3D printed equivalent. Similar for valves, pumps housings with impellers and check valves that connects to these complex tubes are made possible with 3D metal vaccum print. Fuel nozzles ae already 3D metal printed.
        We don’t know how expensive these tube system components will be, just very expensive to buy and repair.
        The fuel dump valve and procedures must be defined where 10-35 ton of liquid hydrogen gets dumped into the atmosphere and gasify before rising fast. Procedureas around all airports need to be decied where aircraft can dump LH2 in emergencies.
        How tanks will be integrated into the fuselage might copy the liquid rocket standards but with increased insulation and damage tolerance, if placed closed to c.g. and in the pathway of engine debries new requirements for engine bursts might be added with lower allowed disc stresses, more frequent removals, clean and NDT before relube, moment weight, position optimization and reinstalltion.

      • The engine burns H2 so the distance wouldn’t be from the tanks. And those pipes needs to be isolated anyway to not have air condensate to LO2. Bigger problem is more the shock cooling when the engine is started. Or restarted in the air, or ice forming after landing.

  3. The purpose of creating a hydrogen powered airliner is to reduce CO2 emissions. Since much of the energy (electricity) used to make H2 from H2O is lost from electrolysis, compression, transport, liquefaction and the H2 turbine is no more efficient than a petroleum turbine it is much ado about not so much.

    If we are to have any hope of substantially reducing CO2 emissions we (the whole world) must do the things that are most cost effective first.

    Coal burning still amounts roughly half of all CO2 emissions and it is especially bad because the amount of thermal energy released by burning per amount of CO2 is the worst of all the fossil fuels it; coal is basically just carbon with some polluting impurities. Petroleum is 2+ H atoms per carbon atoms and natural gas is 4 H per Carbon. The H burns to H2O.

    Better to put the world’ resources to the things that get the most bang for the buck. A methane powered airliner would have significantly lower CO2 than Petroleum and far less difficulty than H2.

    • Agreed.
      But I think Bjorn’s rationale is that, if mass production/distribution of LH2 is up and running for other transport modes — as is happening in several European countries — it’s then a natural next step to try to extend that to aviation. Remember that Greta’s uninformed mob have designated aviation as the root of all evil, so there has to be at least a token effort to show that the industry is also trying to migrate to LH2.
      After all, when did logic, reasoning and engineering arguments ever make an impression on an agitated mob with pitchforks?

      • The regular lower tech industry that emits the majority of CO2 are so politically connected and want the high tech aerospace to develop the technology first, then copy. Dan F. is right that coal is the “bad guy” and just replace it with Natural gas gives huge effect. The technology for compressed and Liquid natural gas is already available for heating, industry use, cars, trucks and gas turbines. The political will to enforce it onto its main industrial donors are limited. The techonolgy for heat pumps and air conditioning using 100-150m deep wells is well established and ready to expand if oil home heating is banned or heavily taxed.

        • Dont forget the ‘Tesla factor’, that company is now worth more than all the other western car companies put together-$600 bill. [Fiat Chrysler ($20 billion), Ford ($24 billion), Ferrari ($32 billion), General Motors ($36 billion), BMW ($41 billion), Honda ($46 billion) and Volkswagen ($74 billion).- according to Forbes]
          Plane makers know they need to ‘disrupt’ to keep their market values intact or even better ‘soar’

          So its Wall St they are wanting to please not Greta

          • I think as the regulations are issued it will be strict and it will be expensive to comply, still as Money is poured in, it will evolve just like the Toyota Murai. Toyota will not make any money until gen III of the Murai and they should be applauded for taking “the bleeding edge” on hydrogen cars.

          • Tesla is a good example of the difference between “value” and “price”…or, equivalently, “tangible worth” and “market capitalization”.
            The stock has a Price/Earnings (P/E) ratio of more than 1100, whereas normal S&P companies have P/E ratios below 25, and most solid tech companies have P/E ratios below 50. Tesla is the quintessential example of a hot-air stock, driven to bubble heights by (predominantly) millennial retail investors who haven’t a clue what a balance sheet is.
            Not a situation to be emulated by anyone with even half a cortex.

          • Apart from Musk himself at around 20% I think you find most of the rest of the stock is ‘institutions and hedge fund’ types and not small direct investors. Ill agree its a bubble stock but still was worth a lot for its size even before the 9x increase this year

  4. Hi Bjorn,
    Thanks for these set of very instructive details about the H2 aircraft. I would like to come back to the “Fuel Cell APU”. If we would like to remove unknowns, why we just don’t apply the same approach than the Engines and adapt a conventional fuel APU to burn Hydrogen? It is not as efficient as a Fuel Cell, but it is a well known technology, thus reducing risks and “unknowns”.
    There were some trials in the past with very old Turbine-APUs and worked very well.

    • Fuel Cells have been around for a long time, but their innovation has lately picked up pace significantly. Many Fuel Cells have 30,000hrs between major overhaul, which is afaik a useable service interval for aviation. They’ve been used in everything from space crafts to submarines, for critical functions. I see little reason why Airbus would de-risk to a turbine since Fuel Cells are already proven to be reliable enough in other very challenging environments.

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