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Vickrin t1_iy5ewxj wrote

Reply to comment by A40 in 'Landmark achievement': Rolls-Royce and easyJet hail successful hydrogen jet engine test by Wagamaga

Hydrogen is not energy dense, it would require extremely high pressure storage which is heavy as hell and expensive.

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A40 t1_iy5fzn0 wrote

Diesel has an energy density of 45.5 megajoules per kilogram (MJ/kg), slightly lower than gasoline, which has an energy density of 45.8 MJ/kg. By contrast, hydrogen has an energy density of approximately 120 MJ/kg, almost three times more than diesel or gasoline. What this really means is that 1 kg of hydrogen, used in a fuel cell to power an electric motor, contains approximately the same energy as a gallon of diesel (rmi.org). site

As for storage weight: train, locomotive. Expensive: probably, until it's a mature industry.

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Vickrin t1_iy5hgyq wrote

1kg of diesel can sit in a metal tank, at room temperature, no pressure needed.

Do you know how much space 1kg of hydrogen takes up?

Liquid hydrogen needs to be stored at -250c at 1 bar or more of pressure. This requires high strength storage. This means your 1kg of hydrogen ends up actually weighing a hell of a lot more than 1kg. Keeping it cool also requires energy which means you get even less out of your hydrogen fuel.

Sure you could store it as a gas but that would require 350-700 bar of pressure which requires even MORE expensive storage.

It's not as simple as the raw maths.

Can you imagine the damage if a train derailed with high pressure hydrogen tanks? Diesel doesn't explode and neither does electricity.

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A40 t1_iy5nvj8 wrote

Thanks for the info!

So a hydrogen jet engine is... less than useless?

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Vickrin t1_iy5ohqn wrote

Exploring the concept is never wasted, people might learn something.

Putting a hydrogen engine in an aircraft is not going to be a viable option for the forseeable future.

Aircraft are probably one of the hardest things to move to a green fuel source.

Batteries are also awful when it comes to aircraft.

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Xe6s2 t1_iy5r1zo wrote

Plus hydrogen leaks the most out of all fuels. Magnetic bottles would work better imo.

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Funktron3000 t1_iy6tud0 wrote

What if we just used it at lower pressures and filled blimps with it?

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lestofante t1_iy7knjd wrote

Not really, Remeber, the most powerful rocket are hydrogen+oxigen.
The bigger the amount you want to store, the less is the coat of the container, as container weight grow as square(perimeter), while volume contained grow as cube.
A hydrogen train make a lot of sense and they have been already successful experimented, but will never take off until cost of diesel is cheaper.

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AzzaClazza t1_iy7zccq wrote

1kg of liquid hydrogen takes up 14L of volume, plus the tank itself.

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Vickrin t1_iy98rkb wrote

And a tank that can hold hydrogen weighs a lot

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