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Hydrogen vs. Battery
- Thread starter siry
- Start date
That's a piece of it. I think a bigger piece is it keeps their paradigm intact - you have to take the car to a station to fuel it, where fuel comes from the big energy company, who controls distribution, etc. They keep their collective monopoly and continue to set prices and reap profits.
EVs shatter that paradigm...
As a car fuel future of H2 does not look good. But hydrogen economy is not dead yet. It would give storage capacity for solar energy. Airplane powered with H2 fuel cells would have very long range.
Half an hour charge time for 400 mile battery is possible, perhaps even 15 min. But not much shorter. Only way to charge as fast or faster than refuel is battery swap. Are people willing to pay for it? Depends on price. That depends on price of battery. When EVs become common (more that 10% of traffic), there will be enough users for swap station.
Toroidion is planning to demonstrate battery swap in Le Mans 24 h race next year. I cannot find any new info, so they have run out of money or they are going to surprise everybody in Le Mans.
JRP3
Hyperactive Member
You assume that is necessary, but it's not. 15 minutes after 400 miles is simply not an issue for 99.99% of all people, the 0.01% who can't deal with it will just have to ... deal with it.
Maybe. The hydrogen itself has about three times the energy density of typical liquid fuels, and the fuel cells are likely around fifty percent more efficient than the turbines.
But you have to balance the entire system, not just the fuel. The tanks to contain hydrogen at high pressures are much, much heavier than the equivalent fuel tanks, and putting them into the wings of a traditional airliner won't be practical since they really need to be cylindrical to handle the pressure.
The fuel cells and electric motors will weigh as lot more than turbines of equivalent power/thrust basis, too.
It might happen at some point in the future, but it's certainly not a given and there are a lot of technical challenges to overcome before it becomes a reality or challenges the well established paradigm.
Electrification of aircraft is already happening though, in small ways. The 787 eliminated the engine bleed air systems and replaced them entirely with electric, including a dedicated compressor for cabin air and HVAC and electric start for the engines. I think you're going to see that trend expand, and in the near future airliners with slightly bigger battery packs and front axle wheel motors will be able to push themselves back and taxi without the engines, and regenerate some of the energy lost during the landing roll. As the motors get better, they'll replace or supplement the brakes on the main gear, too - greatly reducing tire wear since the wheels can be spun up to speed before they hit the ground.
Of course airplane would use liquid H2. Motors developed for airplanes have already high power/mass. Already better than turbines at small plane with sort range: Lilium Superconducting motors are much smaller. Cooling those is very easy, when you have LH2.
Perhaps fuel cells are problem now, probably not long. Long distance jet needs kerosene 40% of takeoff mass. So there is lot of room for improvement.
Acceleration from 0 to 60 mph in less than 10 s is completely unnecessary. Nobody needs it.
In future I drive to charging station with two choices 20 $ + 30 min for supercharging or 40 $ + 2 minutes battery swap. Often I would select cheaper option, but not always. Note that swap would give fully charged battery, 30 min charging probably not. I believe many would take faster choice. To make system practical there needs to be lot of cars with swapable and leased battery. Swap station is more expensive than charger, so it needs lot of customers. So this does not happen next year.
My purpose was not to claim that Lilium uses superconducting motors (I don't believe they do). I wrote that too quickly.
Liquid hydrogen may be possible as an aviation fuel, but the energy density is still not great. Kerosene has around 10.5 kWh per liter, while liquid hydrogen has around 2.35 kWh per liter. That means that with liquid hydrogen, the fuel tanks need to have a volume that's over four times bigger for the same amount of energy. With a larger aircraft, more mass is added to the structure and the air resistance increases. On top of that, you can fill kerosene into pretty much any structural cavity, without much fuss. With liquid hydrogen, you need a lot of insulation, and you need to be pretty careful in how you design the aircraft to avoid temperature differentials. Large temperature variations can cause metal fatigue over time. To have the least amount of insulation relative to storage volume, spherical or cylindrical tanks are best. (Though you can have other shapes, at the cost of added insulation.)
Another consideration is that while kerosene is relatively inflammable, hydrogen is both quite easily ignited *and* it can detonate quite easily. The safety considerations alone can stop hydrogen-powered passenger aircraft from becoming a reality for years or even decades.
I read the above with a bit of incredulity.
Right now, i'm imagining an airplane, flying at an altitude of 25,000 ft, with giant tanks of hydrogen pressurized to 700 atmospheres at the surface, becoming an amazing fireball.
The pressure at the surface is 1 atmosphere, the hydrogen tanks are pressurized to 700 atmospheres
at 25,000 ft the exterior pressure is 0.37 atm so now your H2 tanks are at ~1,891 atmospheres, if not leaking, then seriously distending prior to expolding H2 gas
Not 1891 atmospheres; 700.63 atmospheres...
Anyway, the only feasible way to use hydrogen is to use liquid hydrogen. This can be kept at something like 1 atmosphere.
you ARE aware I hope that liquid H2 is at 20 degrees kelvin, -253 degrees C, or 20 degrees ABOVE absolute zero, -273.
things get brittle at those tempuratures
We did use liquid Nitrogen at work, giant cylindrical, slowly out gassing cylinders and it was only -193 degress C and a LOT "hotter" than liquid H2
the exterior atmospheric pressure at 25,000ft is 0.37 atmospheres.
If you keep the interior of the airplane at sea level pressure, maybe.
If you don't pressurize the exteriot of the tanks, they have only 0.37 atm pressing in, so the relative pressure differential would the divided by 0.37 or an equivalent pressure of 1,891:1 intsead of 700:1 because the equivalent pressure is (700/0.37):1 or 1,891:1, PLUS the H2 is at 20 degrees kelvin, a "bit of a difficulty", or it's a gas
No, the effective tank pressure is the internal pressure minus the external pressure, so at sea level it's 701 atm - 1 atm = 700 atm, while in space it's 701 atm - 0 atm = 701 atm. And 100 meters under the ocean it's 701 atm - 11 atm = 690 atm.
JRP3
Hyperactive Member
Another reason it will never happen. To be financially viable it would need to be on constant use, not sitting around waiting for the occasional swap. It's too expensive and too cumbersome to have fully charged packs sitting around waiting for swaps, not to mention the pack degradation from sitting fully charged.
i shall take your answer under advisement, and ask my engineer friends, some whom work for NASA, if i am incorrect.
If so, i apologize, but i need confirmation from other engineers
JohnSnowNW
Active Member
As an aerospace engineer, his answer is correct. Your statement about what the ratio of the interior pressure to the exterior pressure becomes is also correct, but the assumption that this means a massive increase in the loading of the structure is incorrect.
If you think about it, if the ratio were driving the load, it'd make it almost impossible to contain anything in outer space, since that ratio will approach infinity for even low pressures like our normal sea level atmosphere when compared to near perfect vacuum.
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