3 ms·

> Hydrogen has 3x the energy density of kerosene, what is called "aviation fuel". You are confusing "specific energy" (energy/mass) with "energy density" (ene

by danans 5y ago

> Hydrogen has 3x the energy density of kerosene, what is called "aviation fuel". You are confusing "specific energy" (energy/mass) with "energy density" (energy/volume). Hydrogen has 3x the specific energy of kerosene, but 1/4 the energy density at the same pressure.

ncmncm 5y ago
For aviation, specific energy, or mass-energy density, wins. Lofted volume is cheap, lofted weight is dear.
- danans 5y ago
  You still need to compress and contain hydrogen to get an amount of energy practicable for flight. Hydrogen, even when compressed to 700 bar only provides 1.4kWh/L [1]. Kerosene provides 10kWh/L. A 747 uses 36k liters (36 cubic meters) kerosene for a 10 hour flight, or 360MWh. [2] With 700bar H2, that amount of energy requires 260k liters (260 cubic meters), not counting the thicker storage vessel needed. 260 cubic meters seems tractable (assuming you can safely loft 700 bar hydrogen), although still takes an order of magnitude more space than kerosene. Since we know how to safely loft syn fuels, and we have a fleet of aircraft that can use them, it might make more sense to go that route. It would also allow blending into the existing jet fuel supply infrastructure along with kerosene and biofuels. 1. https://www.energy.gov/eere/fuelcells/physical-hydrogen-storage https://www.energy.gov/eere/fuelcells/physical-hydrogen-stor... 2. https://science.howstuffworks.com/transport/flight/modern/question192.htm https://science.howstuffworks.com/transport/flight/modern/qu...
  - ncmncm 5y ago
    Nobody would even consider lofting compressed hydrogen, under any circumstances. It is actively misleading, even dishonest, to bring it up. The topic here is LH2, liquified hydrogen.
    - danans 5y ago
      LH2 energy density is still only 2.3kWh/L, 1/4 of kerosene or synfuel. It also needs to be kept at -253C. > Nobody would even consider lofting compressed hydrogen The HY4 prototype aircraft uses hydrogen compressed to 350 bar: https://www.compositesworld.com/amp/news/hydrogen-fuel-cell-powered-hy4-aircraft-takes-flight https://www.compositesworld.com/amp/news/hydrogen-fuel-cell-...
      - ncmncm 5y ago
        The heading of the linked article reads "MAHEPA consortium demonstrates feasibility and advances toward liquid hydrogen tanks" Again, volumetric density is of little consequence for aviation. See above. You are visibly reaching. Why reach?
        danans 5y ago
        I'm "provoking" the question of synthetic aviation fuel versus hydrogen, which is hardly settled, and hardly provocative.
        ncmncm 5y ago
        You are repeatedly throwing up known irrelevancies. Hydrogen, by the way, is also synthetic, and also fuel, and also usable for aviation. Thus, "synthetic LH2 aviation fuel". So, no, you are apparently trying, instead, to promote synthetic or mined kerosene, and doing it by trying to distract attention from its most appealing alternative. Ineptly. We know that mined kerosene will become increasingly expensive, relative to synthesized hydrogen, as electric power cost declines. Synthetic kerosene might become cheaper than mined, or anyway than mined-plus-carbon-taxes. It will certainly never be cheaper than hydrogen, which is an essential ingredient. Will synthetic kerosene be able to compete with the radically better value proposition of LH2 fuel? Only insofar as synthetic kerosene helps to preserve the capital value of existing airframes. But airframes have to be replaced anyway as they age out.
        5y ago

by danans 5y ago

ncmncm 5y ago

For aviation, specific energy, or mass-energy density, wins. Lofted volume is cheap, lofted weight is dear.

danans 5y ago
You still need to compress and contain hydrogen to get an amount of energy practicable for flight. Hydrogen, even when compressed to 700 bar only provides 1.4kWh/L [1]. Kerosene provides 10kWh/L. A 747 uses 36k liters (36 cubic meters) kerosene for a 10 hour flight, or 360MWh. [2] With 700bar H2, that amount of energy requires 260k liters (260 cubic meters), not counting the thicker storage vessel needed. 260 cubic meters seems tractable (assuming you can safely loft 700 bar hydrogen), although still takes an order of magnitude more space than kerosene. Since we know how to safely loft syn fuels, and we have a fleet of aircraft that can use them, it might make more sense to go that route. It would also allow blending into the existing jet fuel supply infrastructure along with kerosene and biofuels. 1. https://www.energy.gov/eere/fuelcells/physical-hydrogen-storage https://www.energy.gov/eere/fuelcells/physical-hydrogen-stor... 2. https://science.howstuffworks.com/transport/flight/modern/question192.htm https://science.howstuffworks.com/transport/flight/modern/qu...
- ncmncm 5y ago
  Nobody would even consider lofting compressed hydrogen, under any circumstances. It is actively misleading, even dishonest, to bring it up. The topic here is LH2, liquified hydrogen.
  - danans 5y ago
    LH2 energy density is still only 2.3kWh/L, 1/4 of kerosene or synfuel. It also needs to be kept at -253C. > Nobody would even consider lofting compressed hydrogen The HY4 prototype aircraft uses hydrogen compressed to 350 bar: https://www.compositesworld.com/amp/news/hydrogen-fuel-cell-powered-hy4-aircraft-takes-flight https://www.compositesworld.com/amp/news/hydrogen-fuel-cell-...
    - ncmncm 5y ago
      The heading of the linked article reads "MAHEPA consortium demonstrates feasibility and advances toward liquid hydrogen tanks" Again, volumetric density is of little consequence for aviation. See above. You are visibly reaching. Why reach?
      - danans 5y ago
        I'm "provoking" the question of synthetic aviation fuel versus hydrogen, which is hardly settled, and hardly provocative.
        ncmncm 5y ago
        You are repeatedly throwing up known irrelevancies. Hydrogen, by the way, is also synthetic, and also fuel, and also usable for aviation. Thus, "synthetic LH2 aviation fuel". So, no, you are apparently trying, instead, to promote synthetic or mined kerosene, and doing it by trying to distract attention from its most appealing alternative. Ineptly. We know that mined kerosene will become increasingly expensive, relative to synthesized hydrogen, as electric power cost declines. Synthetic kerosene might become cheaper than mined, or anyway than mined-plus-carbon-taxes. It will certainly never be cheaper than hydrogen, which is an essential ingredient. Will synthetic kerosene be able to compete with the radically better value proposition of LH2 fuel? Only insofar as synthetic kerosene helps to preserve the capital value of existing airframes. But airframes have to be replaced anyway as they age out.
        5y ago