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EasyJet May Trial Hydrogen Fuel Cells For Taxiing (thestack.com)

Posted by timothy on from the why-not-tugboats? dept.

An anonymous reader writes: Low-cost airline easyJet is discussing plans to install hydrogen batteries as part of a proposed zero emission fuel system, which would power its aircraft during taxiing. The budget service revealed designs for a hybrid plane this week, and said that it would begin trialling the technology later this year. The system will involve embedding a hydrogen fuel cell on board the aeroplanes, with the energy captured from the brakes on landing able to power the jet on the ground. As the only waste product from a hydrogen cell would be fresh, clean water, Ian Davies, head of engineering at easyJet, also suggested that this could be used to refill the planes' water systems during the flight, providing a water source for passengers to drink and for flushing toilets.

12 of 150 comments (clear)

  1. So Much LUDD.. by Anonymous Coward · · Score: 3, Insightful

    Five comments in, and the signal-to-LUDD ratio from the Luddites has already dragged the conversation so far below the noise floor that it's not even a conversation anymore, just LUDD LUDD LUDD.

    Guess what? Internal combustion engines of any kind will, at some point in the future, become non-viable. We'll have to come up with alternatives or lose much of our transporation capabilities. What they're doing here doesn't have anything to do with propulsion during flight, but at least someone is trying to think outside the proverbial box.

  2. All for free!!!! by OzPeter · · Score: 5, Interesting

    The system will involve embedding a hydrogen fuel cell on board the aeroplanes, with the energy captured from the brakes on landing able to power the jet on the ground. This technique is similar to the high-end kinetic energy recovery systems (KERS) used in Formula One cars, which store recovered energy to later use for acceleration.

    TFA mentions harvesting the braking energy as being similar to KERS used in Formula 1. But no mention is made of the additional mass or equipment (unsprung at that) that would be needed to be added to the landing gear in order to harvest that energy. Such equipment needing to be robust and large enough to capture a worthwhile amount of energy in the 10 seconds of braking that a plane experiences when landing. For the rest of the 99.9999% of the flight this is dead weight that the plane has to burn fuel in order to carry it around.

    So color me surprised if anyone really thinks that is practical. (let alone the bizarre notion that the recovered energy could somehow be funneled into a hydrogen based fuel cell - super cap yes! fuel cell ? are you kidding me?)

    It would probably make more sense to assign a tractor to drag each aircraft from the gate to the start of the runway rather than use the planes fuel to taxi around.

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    1. Re:All for free!!!! by gweilo8888 · · Score: 5, Insightful

      What he said. This is buzzword-salad hype from EasyJet to get some free advertising from the media. Nothing more, nothing less.

    2. Re:All for free!!!! by dj245 · · Score: 3, Interesting

      The system will involve embedding a hydrogen fuel cell on board the aeroplanes, with the energy captured from the brakes on landing able to power the jet on the ground. This technique is similar to the high-end kinetic energy recovery systems (KERS) used in Formula One cars, which store recovered energy to later use for acceleration.

      TFA mentions harvesting the braking energy as being similar to KERS used in Formula 1. But no mention is made of the additional mass or equipment (unsprung at that) that would be needed to be added to the landing gear in order to harvest that energy. Such equipment needing to be robust and large enough to capture a worthwhile amount of energy in the 10 seconds of braking that a plane experiences when landing. For the rest of the 99.9999% of the flight this is dead weight that the plane has to burn fuel in order to carry it around.

      So color me surprised if anyone really thinks that is practical. (let alone the bizarre notion that the recovered energy could somehow be funneled into a hydrogen based fuel cell - super cap yes! fuel cell ? are you kidding me?)

      It would probably make more sense to assign a tractor to drag each aircraft from the gate to the start of the runway rather than use the planes fuel to taxi around.

      Not to mention that you can't start a gas turbine and immediately subject it to full load. It needs several minutes to heat up, bring the oil to operating temperature, and get any temporary "bow" out of the turbine rotor. Going from idle to full power (as in every takeoff ever) on a warm engine is somewhat detrimental to the engine since it results in huge temperature differentials. The engine is designed to handle this, but shortening the taxi/idle time is not a good idea and probably is outside of the turbine manufacturer's original design intentions.

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    3. Re:All for free!!!! by yodleboy · · Score: 4, Interesting

      "It would probably make more sense to assign a tractor to drag each aircraft from the gate to the start of the runway rather than use the planes fuel to taxi around."

      I was thinking the same thing... wouldn't it make sense to use autonomous tugs powered fuel cell, then tug the planes to the end of the taxiway? most of the tugs i've seen require manual connect/disconnect, so you'd have to automate that. unhook at end of taxi way, and pilot moves onto runway under own power, since you don't want anything else on an active runway. robo-tug heads back to terminal and to next assigned gate.

      I just figured out the fatal flaw... pilot and ground crew unions would never allow it...

    4. Re:All for free!!!! by Solandri · · Score: 4, Interesting

      For the rest of the 99.9999% of the flight this is dead weight that the plane has to burn fuel in order to carry it around.

      If I remember right, if a stewardess loses a sugar packet in some crevice of an airliner, the extra weight (4 grams) will cause an additional half liter of fuel burn in a year.

      It would probably make more sense to assign a tractor to drag each aircraft from the gate to the start of the runway rather than use the planes fuel to taxi around.

      That actually brings up another problem with the idea. The point of moving around under your own power while on the ground is so that any immediate problem with the engines or fuel reveals itself during taxi when you are nice and safe on the ground. Not when you are 10,000 ft in the air hurtling at 400 mph.

      I'll also add that the energy from combining hydrogen and oxygen to form 1 liter of water releases 237.14 kJ/mole (Gibbs free energy). 1 mole of water is about 18 grams, so 1 liter of water is formed for every 13.15 MJ released this way. An A320 has a maximum landing weight of 66 tons, so figure it's about 60 tons in regular service with a full load. Stopping from a landing speed of 135 knots, that's 252.5 MJ of kinetic energy. Enough to convert just 19 liters of water into hydrogen and oxygen at 100% efficiency. However, some of that kinetic energy is shed by the spoilers and thrust reversers, not the brakes. Frankly I'm not even sure that's worth the extra weight of machinery to recover.

      Summing all this up, the maximum energy you can recover from braking an A320 at landing is equivalent to 5.5 kg of aviation fuel (46 MJ/kg). At a (realistic) 25% conversion efficiency for the fuel, and (optimistic) 60% conversion efficiency for the electrolysis and 70% efficiency for the hydrogen fuel cell (42% overall), this device will basically be reducing your fuel requirement by about 9.24 kg (11.5 liters). Every 8 grams the device weighs more than that will result in an extra liter of fuel burn per year than just carrying around the extra fuel.

  3. Motors in wheels as part of the package ... hmm by enjar · · Score: 3, Insightful

    Not mentioned in the blurb is that this also includes putting motors in the plane's wheels and adding controller hardware. That's going to add on weight to the plane, as I can imagine a set of electric motors (and associated gear trains, etc) that can move a plane that weighs something like 100,000-150,000 lbs are exactly "light". Plus there is the difficulty of packing it all into the landing gear, where there's not exactly a lot of room. You could do a hydraulic drive of some sort, but then you have the pump and motor sitting somewhere, too, plus the weight of the hydraulic fluid.

    Less sexy would be to develop a tug that could not only push the plane back, but also perform taxi duties. You could have that thing run on batteries, fuel cells, etc -- and you don't have to fly it everywhere with you.

    1. Re:Motors in wheels as part of the package ... hmm by brambus · · Score: 5, Informative

      Less sexy would be to develop a tug that could not only push the plane back, but also perform taxi duties.

      This is already done. The pushback tugs are also used for repositioning aircraft between gates and/or hangars. There are many reasons why aircraft start their engines at the gate. This serves primarily as a checkout of the aircraft systems. If an engine behaves oddly, or has trouble starting, pulling back into a gate is simple. Doing it at the runway would be a lot more complicated, as it would require a full back-taxi, which on congested airports is already a major PITA. In addition, many of the internal systems such as flight control hydraulics are powered by the engines, so for example you won't have all flight controls fully functional (meaning, you can't perform a F/CTL check) and you can't fully extend flaps for takeoff unless you have at least one of the engine-driven pumps running. Secondly, the air conditioning packs inside the cabin are engine-powered and they take a lot of juice as well as compressed air (or you'd have to carry a sizable battery just to keep them running for the 20-30 minutes on the ground). On very long taxis to takeoff or after landing, many aircraft already do reduced-engine taxi. 747s routinely shut down 1 or 2 engines right after landing. Twins routinely do single-engine taxi. When there is a long queue for takeoff, similarly, engines get shut down. But doing the whole taxi completely shut down and only starting once close to lining up would probably result in tons of operational complications and possibly safety issues.

    2. Re:Motors in wheels as part of the package ... hmm by enjar · · Score: 3, Interesting

      Right. What I was getting at is that the blurb and accompanying article seems to almost imply that through some magic and a fuel cell the plane could move itself without some means of motive power. Currently this comes from the jet engine and that's it (barring, of course, external sources like a tug). Adding that motive power would add weight. Other non-sexy things might include some sort of chain embedded in the taxi way that could grab onto the front wheel of the plane, similar to the systems that bring a car through a car wash. The tug could get the plane out to this system and pull it along until it got to where it needed to go. Given that this is a system that would be in one place, and likely using electric power, you could generate those electrons in whatever eco-friendly way you wanted. Of course, this also hand-waves about a billion engineering difficulties away, as well -- chain strength, debris getting in, weather, etc. And then you could use the hand waving to extend the idea to use a catapult system to launch your commercial jet, just like an aircraft carrier ... which is happening with electricity nowadays ... just scale it up, that's easy, right?

      Your point about operating temperature is also a good one. Given that you want the engine making the most power at takeoff, running up a cold engine may not be a fantastic idea. I'm guessing for this use case of frequent short flights that this airline has, the engine is likely up to operating temperature more quickly. For long haul flights, time on the ground will shrink and be dominated by flight time.

  4. Re:fresh clean water? by fhage · · Score: 5, Funny

    You'd also need special humans for it. Pure H20 cannot be consumed by humans [...]

    Life Hack: Pure H2O becomes safe to drink by adding a sticker that says; "Gluten Free".

    I tried it and it totally works!

  5. Re:fresh clean water? by MightyYar · · Score: 3, Insightful

    You would need so little salt to treat the water that the tank would be insignificant in mass compared to the fuel cell equipment, or even the other food service equipment on board.

    This idea has many, many problems with it - but "pure H2O" is not one of them.

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  6. Re:fresh clean water? by PPH · · Score: 4, Funny

    Pure H20 cannot be consumed by humans.

    Flint Michigan public utilities, plz go.

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