5 ms·

I am very skeptical they will be able to get the efficiency numbers to a place where it makes sense in the timeframes they're throwing around unless oil goes up

I am very skeptical they will be able to get the efficiency numbers to a place where it makes sense in the timeframes they're throwing around unless oil goes up like 4x in price. Storing hydrogen is really hard and the related tradeoffs are much tougher than with a room temp liquid hydrocarbon. I imagine burning it in turbines also comes with some new issues but I know less about that. I think it's a decent path forward if we can figure it out, and I imagine the engine related problems are likely much more surmountable than the storage issues. There's also the related fuel infra that will need to happen before this is viable. It's far away unless something truly drastic changes the calculus on fossil fuels. (which would be great)

upofadown 5y ago
>Storing hydrogen is really hard Wouldn't this just be a low pressure insulated tank? The temperature would self regulate as the liquid H2 boiled off.
- deepnotderp 5y ago
  There are also issues like hydrogen embrittlement, tiny cracks, etc. These are all solvable, but it's just expensive and hard.
  - ncmncm 5y ago
    Hydrogen embrittlement is a problem in high-pressure high-temperature tanks. When the pressure is low, nothing is being driven into the metal.
dehrmann 5y ago
I wonder if we'll just end up running jet engines on biodiesel for long-haul flights where batteries aren't viable.
- nradov 5y ago
  Yes this has already been tested in existing commercial turbine engines and works fine. It's safe and won't require any changes to aircraft or aviation infrastructure. The sticking point is the cost of manufacturing the fuel. It will only be economically viable with some major government intervention.
  - zardo 5y ago
    A sticking point for biofuels but in all likelihood one they share with hydrogen.
karmakurtisaani 5y ago
I don't think they burn the hydrogen at all. Rather, it's turned into water and free electrons by some chemical process whose details I totally forgot. One idea I've seen floating around would be having small scale nuclear plants near airports producing hydrogen from water and electricity (the reverse process of what happens in the plane turbines).
- ElectronCharge 5y ago
  You’re talking about fuel cells, which are only used with the smallest (prop) design. The two larger jets are intended to have hydrogen turbines, burning hydrogen and producing water. I love the idea of small modular reactors (SMRs) being used to produce the hydrogen from water. We also need a vast buildout of safe, clean, dependable modern nuclear reactors to provide the developing world with enough energy to make the demographic transition (via a higher standard of living) to better environmental practices.
ncmncm 5y ago
Storing hydrogen underground is, in fact, very easy and cheap. And, storing liquified hydrogen is likewise cheap. We can expect hydrogen to be produced on-site at large airports from power delivered over transmission lines, stockpiled against low-wind low-sun periods. Once hydrogen-fueled aircraft enter a particular air freight market, kerosene-fueled craft will be unable to compete, because with LH2's much better mass-energy density, the fuel mass dispensed with may be replaced with paying cargo. Furthermore, hydrogen fuel produced on-site electrically will be cheaper per unit joule than mined, refined, and transported kerosene. I am surprised to see designs with inboard LH2 tanks. I would expect to see LH2 tanks in wing nacelles, minimizing piping to engines.
- nradov 5y ago
  Producing hydrogen is not very energy efficient. Electric power would have to get much cheaper to make hydrogen cost competitive with fossil fuels. While hydrogen has sightly higher mass-energy density, the tankage is larger and more complex so the total mass savings is limited and there's a significant drag penalty.
  - credit_guy 5y ago
    > While hydrogen has sightly higher mass-energy density It’s not slightly, it’s three times as much, or more. Per wikipedia [1], Hydrogen has an energy density of 120 MJ/kg vs 43 MJ/kg for kerosene. That’s if you burn it outright. If you put Hydrogen in a fuel cell, and the output of the reaction is liquid water rather than water vapor, then the energy density is 142 MJ/kg. [1] https://en.wikipedia.org/wiki/Energy_density#In_chemical_reactions_(oxidation) https://en.wikipedia.org/wiki/Energy_density#In_chemical_rea...
    - iamthemonster 5y ago
      The mass density of hydrogen is very much negated by the fact that liquefied hydrogen needs to be in a 700 bar pressurised tank whereas kerosene is happy at atmospheric pressure. The more valid comparison is "hydrogen in a hydrogen pressure vessel" to "kerosene in a tank". I know cars are different, but the Toyota Mirai is actually heavier than the Tesla Model 3 even though it only needs a measly 5 kg of hydrogen to go as far as the Tesla.

upofadown 5y ago

>Storing hydrogen is really hard Wouldn't this just be a low pressure insulated tank? The temperature would self regulate as the liquid H2 boiled off.

deepnotderp 5y ago
There are also issues like hydrogen embrittlement, tiny cracks, etc. These are all solvable, but it's just expensive and hard.
- ncmncm 5y ago
  Hydrogen embrittlement is a problem in high-pressure high-temperature tanks. When the pressure is low, nothing is being driven into the metal.

dehrmann 5y ago

I wonder if we'll just end up running jet engines on biodiesel for long-haul flights where batteries aren't viable.

nradov 5y ago
Yes this has already been tested in existing commercial turbine engines and works fine. It's safe and won't require any changes to aircraft or aviation infrastructure. The sticking point is the cost of manufacturing the fuel. It will only be economically viable with some major government intervention.
- zardo 5y ago
  A sticking point for biofuels but in all likelihood one they share with hydrogen.

karmakurtisaani 5y ago

I don't think they burn the hydrogen at all. Rather, it's turned into water and free electrons by some chemical process whose details I totally forgot. One idea I've seen floating around would be having small scale nuclear plants near airports producing hydrogen from water and electricity (the reverse process of what happens in the plane turbines).

ElectronCharge 5y ago
You’re talking about fuel cells, which are only used with the smallest (prop) design. The two larger jets are intended to have hydrogen turbines, burning hydrogen and producing water. I love the idea of small modular reactors (SMRs) being used to produce the hydrogen from water. We also need a vast buildout of safe, clean, dependable modern nuclear reactors to provide the developing world with enough energy to make the demographic transition (via a higher standard of living) to better environmental practices.

ncmncm 5y ago

Storing hydrogen underground is, in fact, very easy and cheap. And, storing liquified hydrogen is likewise cheap. We can expect hydrogen to be produced on-site at large airports from power delivered over transmission lines, stockpiled against low-wind low-sun periods. Once hydrogen-fueled aircraft enter a particular air freight market, kerosene-fueled craft will be unable to compete, because with LH2's much better mass-energy density, the fuel mass dispensed with may be replaced with paying cargo. Furthermore, hydrogen fuel produced on-site electrically will be cheaper per unit joule than mined, refined, and transported kerosene. I am surprised to see designs with inboard LH2 tanks. I would expect to see LH2 tanks in wing nacelles, minimizing piping to engines.

nradov 5y ago
Producing hydrogen is not very energy efficient. Electric power would have to get much cheaper to make hydrogen cost competitive with fossil fuels. While hydrogen has sightly higher mass-energy density, the tankage is larger and more complex so the total mass savings is limited and there's a significant drag penalty.
- credit_guy 5y ago
  > While hydrogen has sightly higher mass-energy density It’s not slightly, it’s three times as much, or more. Per wikipedia [1], Hydrogen has an energy density of 120 MJ/kg vs 43 MJ/kg for kerosene. That’s if you burn it outright. If you put Hydrogen in a fuel cell, and the output of the reaction is liquid water rather than water vapor, then the energy density is 142 MJ/kg. [1] https://en.wikipedia.org/wiki/Energy_density#In_chemical_reactions_(oxidation) https://en.wikipedia.org/wiki/Energy_density#In_chemical_rea...
  - iamthemonster 5y ago
    The mass density of hydrogen is very much negated by the fact that liquefied hydrogen needs to be in a 700 bar pressurised tank whereas kerosene is happy at atmospheric pressure. The more valid comparison is "hydrogen in a hydrogen pressure vessel" to "kerosene in a tank". I know cars are different, but the Toyota Mirai is actually heavier than the Tesla Model 3 even though it only needs a measly 5 kg of hydrogen to go as far as the Tesla.