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EasyJet May Trial Hydrogen Fuel Cells For Taxiing (thestack.com)
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.
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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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.
Pure H20 is so corrosive you need special tubing for it. You sure this is a great idea?
Yet another reason this is a really BAD idea...
1. Hydrogen is an explosive risk when stored
2. Storing quantities of hydrogen sufficient to power anything requires either pressurization, very cold temperatures or both and the equipment to do this is pretty heavy if you wish to avoid the problem #1
3. Industrial sources of Hydrogen cause a LOT of CO2 emissions or are environmentally very unfriendly.
4. Fuel cells are pretty inefficient, so it takes a lot of fuel and oxidizer to obtain a specific amount of work.
5. Utilizing electric power to taxi an aircraft with will require the redesign of a number of aircraft systems, many of which are critical to safety and are subject to very specific regulations. If you use electric motors in the wheels, they will need to not impact the success of the abort takeoff at max weight with no fire test, which I find unlikely. Plus these systems will add a lot of weight in wiring and control electronics, which is the absolute opposite direction you go for designing an efficient aircraft.
6. It will be expensive to operate. You will have multiple fuel types to load, more complex systems to maintain, a heaver aircraft and less useful load. Complexity breeds inefficiency and cost, weight just makes you burn more fuel.
7. H2O is corrosive...
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101