3 ms·

Yeah, as always, they forget to mention volumetric energy density. Big red flag. There's some concepts that may work around that, like a blended-wing design. A

by audunw 5y ago

Yeah, as always, they forget to mention volumetric energy density. Big red flag. There's some concepts that may work around that, like a blended-wing design. Airbus seems to think it's viable. https://www.airbus.com/en/innovation/zero-emission/hydrogen/zeroe https://www.airbus.com/en/innovation/zero-emission/hydrogen/... Also, a hydrogen fuel cell based plane could be designed to fly much more efficiently than a regular turbofan plane. For instance, something like the Maxwell X-57 where you have very thin, low-drag wings, and use small electric propellers to provide the extra lift needed during take-off and landing. Electric propulsion enables new designs that wasn't possible with turbofans, and I'm sure electric planes will end up looking quite different from todays planes. But it'll take a couple of decades to figure it out.

bell-cot 5y ago
From some quick searches, it sounds like modern jet engines are up to ~40% energy efficient, measuring kerosene ==> thrust. I'll guess that production-aircraft-grade hydrogen fuel cells won't get past 85% efficient (hydrogen ==> electricity). Then you have the inefficiencies of the electric motor, and the propeller. Maybe 60% total efficiency could be achieved? (So 1.5x the current-generation commercial jet engine efficiency.) My point: Your "much more efficient" looks correct, as language to use among informed engineers. But risky to use around managers, customers, etc. - who'll quickly develop fantasies of around-the-world jumbo jet flights, powered by the hydrogen tank in their carry-on duffel bag.
- xoa 5y ago
  I don't agree. Yeah there are definitely a multitude of factors at play. But overall electric is definitely more efficient, reliable, and opens up a range of new designs. That's a very important part of the picture in general because it's part of why electric aircraft may start becoming viable earlier than would be indicated by the abysmal energy density of storage. Electric motors can be extremely efficient at their optimal load [0], that's not really a limiting factor. They're also much simpler and more reliable with excellent performance per volume themselves. But one of the biggest advantages GP was getting at is plumbing. Moving fuel around an aircraft is non-trivial and heavy. It's just not feasible to slap a dozen engines of various sizes on each wing. Running a power line to an electric motor is a lot more doable to put it mildly. That has massive implications for aircraft design and opens up a lot of further more efficient wing designs for example. Long haul aircraft will definitely be last if ever (it's perfectly possible to make green synthetic hydrocarbon fuel directly from atmospheric CO2 which in turn is carbon neutral, for niche applications where it's worth it we can move from fossil fuels without moving from hydrocarbons). For short/medium haul though the volumetric energy density of hydrocarbons doesn't necessarily need to be remotely matched. Although all that said, I don't think hydrogen is going to play a role there long term anymore than I think it will anywhere else. Batteries have the ceiling and have too many network effects at this point, and syngas is close to as green as hydrogen (more non-global warming pollutants in use) while being what we're already use to working with. Only place I really see hydrogen having a niche is space, but even there it's not clear the ISP advantages will ultimately be worth it vs the vastly easier to store/refuel methane. ---- 0: https://new.abb.com/news/detail/1789/ABB-motor-sets-world-record-in-energy-efficiency-saves-half-a-million-dollars https://new.abb.com/news/detail/1789/ABB-motor-sets-world-re...
- krisoft 5y ago
  > I'll guess that production-aircraft-grade hydrogen fuel cells won't get past 85% efficient (hydrogen ==> electricity). Why would you convert the hydrogen to electricity instead of burning it in the jet engine?
  - AbrahamParangi 5y ago
    Burning it in our nitrogen- rich atmosphere creates NOx which is bad
  - bell-cot 5y ago
    Because the efficiency of hydrogen-burning jet engines is not substantially better than that of kerosene-burning jet engines? Vs. a fuel cell/motor/propeller system could be much more efficient?
- LargoLasskhyfv 5y ago
  Have you taken https://www.airbus.com/en/newsroom/stories/2021-03-cryogenics-and-superconductivity-for-aircraft-explained https://www.airbus.com/en/newsroom/stories/2021-03-cryogenic... into account? And maybe even https://en.wikipedia.org/wiki/Slush_hydrogen https://en.wikipedia.org/wiki/Slush_hydrogen ?

by audunw 5y ago

bell-cot 5y ago

From some quick searches, it sounds like modern jet engines are up to ~40% energy efficient, measuring kerosene ==> thrust. I'll guess that production-aircraft-grade hydrogen fuel cells won't get past 85% efficient (hydrogen ==> electricity). Then you have the inefficiencies of the electric motor, and the propeller. Maybe 60% total efficiency could be achieved? (So 1.5x the current-generation commercial jet engine efficiency.) My point: Your "much more efficient" looks correct, as language to use among informed engineers. But risky to use around managers, customers, etc. - who'll quickly develop fantasies of around-the-world jumbo jet flights, powered by the hydrogen tank in their carry-on duffel bag.

xoa 5y ago
I don't agree. Yeah there are definitely a multitude of factors at play. But overall electric is definitely more efficient, reliable, and opens up a range of new designs. That's a very important part of the picture in general because it's part of why electric aircraft may start becoming viable earlier than would be indicated by the abysmal energy density of storage. Electric motors can be extremely efficient at their optimal load [0], that's not really a limiting factor. They're also much simpler and more reliable with excellent performance per volume themselves. But one of the biggest advantages GP was getting at is plumbing. Moving fuel around an aircraft is non-trivial and heavy. It's just not feasible to slap a dozen engines of various sizes on each wing. Running a power line to an electric motor is a lot more doable to put it mildly. That has massive implications for aircraft design and opens up a lot of further more efficient wing designs for example. Long haul aircraft will definitely be last if ever (it's perfectly possible to make green synthetic hydrocarbon fuel directly from atmospheric CO2 which in turn is carbon neutral, for niche applications where it's worth it we can move from fossil fuels without moving from hydrocarbons). For short/medium haul though the volumetric energy density of hydrocarbons doesn't necessarily need to be remotely matched. Although all that said, I don't think hydrogen is going to play a role there long term anymore than I think it will anywhere else. Batteries have the ceiling and have too many network effects at this point, and syngas is close to as green as hydrogen (more non-global warming pollutants in use) while being what we're already use to working with. Only place I really see hydrogen having a niche is space, but even there it's not clear the ISP advantages will ultimately be worth it vs the vastly easier to store/refuel methane. ---- 0: https://new.abb.com/news/detail/1789/ABB-motor-sets-world-record-in-energy-efficiency-saves-half-a-million-dollars https://new.abb.com/news/detail/1789/ABB-motor-sets-world-re...
krisoft 5y ago
> I'll guess that production-aircraft-grade hydrogen fuel cells won't get past 85% efficient (hydrogen ==> electricity). Why would you convert the hydrogen to electricity instead of burning it in the jet engine?
- AbrahamParangi 5y ago
  Burning it in our nitrogen- rich atmosphere creates NOx which is bad
- bell-cot 5y ago
  Because the efficiency of hydrogen-burning jet engines is not substantially better than that of kerosene-burning jet engines? Vs. a fuel cell/motor/propeller system could be much more efficient?
LargoLasskhyfv 5y ago
Have you taken https://www.airbus.com/en/newsroom/stories/2021-03-cryogenics-and-superconductivity-for-aircraft-explained https://www.airbus.com/en/newsroom/stories/2021-03-cryogenic... into account? And maybe even https://en.wikipedia.org/wiki/Slush_hydrogen https://en.wikipedia.org/wiki/Slush_hydrogen ?