Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

ZEROe: Hydrogen-hybrid aircraft concept

airbus.com

Post reply on HN
Print view View original

21–30 of 111 posts

Re: ZEROe: Hydrogen-hybrid aircraft concept

#21

Post by Robotbeat »

Hypx wrote: post #3
jeffreyrogers wrote: post #2

Interesting that this doesn't primarily use fuel cells[0] (which is what hydrogen-electric aviation usually proposes to use), but directly combusts the hydrogen to run a traditional jet engine. There was a Soviet Union airliner that did this, so it definitely works, although I'm skeptical that hydrogen makes sense as an aviation fuel because jet fuel is much more convenient (easier to transport, store, and handle, an…

Fuel cells are too heavy, at least for the time being. Other than biofuels or synfuels, there's basically no alternatives. Aviation companies will have to pick one of those fuels.

Fuel cells are better because they don't emit directly. Turns out high altitude water vapor is itself a powerful greenhouse gas. At least with fuel cells, you could collect the water and dispense it periodically as a liquid at lower altitudes. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200...

But actually, batteries are better than people think. 1000km battery-electric range is feasible with current chemistries, and ~3000-5000km is feasible with metal-anode, maybe lithium-sulfur or other advanced chemistries plus extremely high performance structures and aerodynamics. Lithium-air batteries with these improvements could enable >10,000km flights.

Re: ZEROe: Hydrogen-hybrid aircraft concept

#23

Post by skykooler »

Robotbeat wrote: post #20

Not as helpful for reducing effective emissions as you might think. High altitude water vapor is just as big of a problem as CO2 as the lifetime of water vapor in the stratosphere is measured in years, not days or hours like it is in the lower troposphere. Water vapor is, after all, a much stronger greenhouse gas than CO2, it's just that normally its lifetime in the atmosphere is so short so as not to matter. So unle…

Keep in mind however that all hydrocarbon fuels, kerosene included, turn into both CO2 and water.

Re: ZEROe: Hydrogen-hybrid aircraft concept

#24

Post by DesiLurker »

Robotbeat wrote: post #21
Hypx wrote: post #3

Earlier quoted context omitted.

Fuel cells are too heavy, at least for the time being. Other than biofuels or synfuels, there's basically no alternatives. Aviation companies will have to pick one of those fuels.

Fuel cells are better because they don't emit directly. Turns out high altitude water vapor is itself a powerful greenhouse gas. At least with fuel cells, you could collect the water and dispense it periodically as a liquid at lower altitudes. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200... But actually, batteries are better than people think. 1000km battery-electric range is feasible with current che…

but wont this just create another problem, the mass for the 'spent' hydrogen would be 9 times more than original because of Oxygen being much weightier (atomic mass: 16). so your fuel tank would basically get 9 times heavier. that will negate any benefit you get from higher energy density. also it may create storage problems because now you have to provision another tank for water storage.

I think they'll just handwave it and release it periodically.

Re: ZEROe: Hydrogen-hybrid aircraft concept

#25

Post by Hypx »

Robotbeat wrote: post #21
Hypx wrote: post #3

Earlier quoted context omitted.

Fuel cells are too heavy, at least for the time being. Other than biofuels or synfuels, there's basically no alternatives. Aviation companies will have to pick one of those fuels.

Fuel cells are better because they don't emit directly. Turns out high altitude water vapor is itself a powerful greenhouse gas. At least with fuel cells, you could collect the water and dispense it periodically as a liquid at lower altitudes. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200... But actually, batteries are better than people think. 1000km battery-electric range is feasible with current che…

H2O as an emission lasts for days, not centuries. It shouldn’t be that big of a deal.

You do realize a fuel cell is a hydrogen-air battery? If you’re going to bring up metal-air batteries, you might as well skip to the end and try to figure out fuel cells.

Re: ZEROe: Hydrogen-hybrid aircraft concept

#26

Post by Hypx »

DesiLurker wrote: post #24
Robotbeat wrote: post #21

Earlier quoted context omitted.

Fuel cells are better because they don't emit directly. Turns out high altitude water vapor is itself a powerful greenhouse gas. At least with fuel cells, you could collect the water and dispense it periodically as a liquid at lower altitudes. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200... But actually, batteries are better than people think. 1000km battery-electric range is feasible with current che…

but wont this just create another problem, the mass for the 'spent' hydrogen would be 9 times more than original because of Oxygen being much weightier (atomic mass: 16). so your fuel tank would basically get 9 times heavier. that will negate any benefit you get from higher energy density. also it may create storage problems because now you have to provision another tank for water storage. I think they'll just handwa…

Metal-air cells have the same problem. That’s why they were briefly considered for airplanes, and then abandoned once they realized that problem.

Re: ZEROe: Hydrogen-hybrid aircraft concept

#27

Post by gus_massa »

kolinko wrote: post #18
mayama wrote: post #16

Earlier quoted context omitted.

> You can manufacture synthetic hydrocarbons anywhere so long as you have water, carbon dioxide You need coal or some biomass to manufacture synthetic hydrocarbons. And tail emission is still a concern.

You can extract carbon from atmosphere.

Organic reactions to produce complex molecules have an horrible efficiency. (For example, photosynthesis in plants has a 1% or 2% of efficiency.)

Perhaps the efficiency to produce methane is not so bad, but a chain with 6 or 7 carbons like gasoline is very complicated. It is not equivalent if they are aligned or they form a ramified structure like a tree, and it is very difficult to choose which one they will form unless you have a very complex process. There are some graphics in https://en.wikipedia.org/wiki/Octane_rating#Isooctane_as_a_r...

Re: ZEROe: Hydrogen-hybrid aircraft concept

#28

Post by Robotbeat »

Hypx wrote: post #25
Robotbeat wrote: post #21

Earlier quoted context omitted.

Fuel cells are better because they don't emit directly. Turns out high altitude water vapor is itself a powerful greenhouse gas. At least with fuel cells, you could collect the water and dispense it periodically as a liquid at lower altitudes. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200... But actually, batteries are better than people think. 1000km battery-electric range is feasible with current che…

H2O as an emission lasts for days, not centuries. It shouldn’t be that big of a deal. You do realize a fuel cell is a hydrogen-air battery? If you’re going to bring up metal-air batteries, you might as well skip to the end and try to figure out fuel cells.

It lasts for days in the lower troposphere but years in the stratosphere. And kg for kg, H2O is a much stronger Greenhouse gas than CO2, so the long-term averaged effect is on the same order as CO2 (maybe higher, depending on conditions).

And sure, I guess you could argue lithium-air is a type of fuel cell (or that hydrogen fuel cells are a kind of inefficient battery), however lithium-air is much more energy dense (volumetrically) than hydrogen-air and both the "fuel" and the "exhaust" are solid and stay in the battery, which has operational advantages. (Although to be completely fair, hydrogen fuel cells are high TRL whereas lithium-air is still lab scale at best.)

Re: ZEROe: Hydrogen-hybrid aircraft concept

#29

Post by Robotbeat »

DesiLurker wrote: post #24
Robotbeat wrote: post #21

Earlier quoted context omitted.

Fuel cells are better because they don't emit directly. Turns out high altitude water vapor is itself a powerful greenhouse gas. At least with fuel cells, you could collect the water and dispense it periodically as a liquid at lower altitudes. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200... But actually, batteries are better than people think. 1000km battery-electric range is feasible with current che…

but wont this just create another problem, the mass for the 'spent' hydrogen would be 9 times more than original because of Oxygen being much weightier (atomic mass: 16). so your fuel tank would basically get 9 times heavier. that will negate any benefit you get from higher energy density. also it may create storage problems because now you have to provision another tank for water storage. I think they'll just handwa…

Releasing it periodically can be done at a slightly lower altitude and in a liquid phase, both of which should significantly reduce impact.

Re: ZEROe: Hydrogen-hybrid aircraft concept

#30

Post by Robotbeat »

skykooler wrote: post #23
Robotbeat wrote: post #20

Not as helpful for reducing effective emissions as you might think. High altitude water vapor is just as big of a problem as CO2 as the lifetime of water vapor in the stratosphere is measured in years, not days or hours like it is in the lower troposphere. Water vapor is, after all, a much stronger greenhouse gas than CO2, it's just that normally its lifetime in the atmosphere is so short so as not to matter. So unle…

Keep in mind however that all hydrocarbon fuels, kerosene included, turn into both CO2 and water.

In some ways, direct CO2 capture combined with carbon monoxide fuel (if burned super cleanly) might actually be better than either kerosene or hydrogen for super high altitude flight. The years-long lifetime of air in the stratosphere is small compared to the normal lifetime of CO2 in the atmosphere, so on net would be much better than hydrogen fuel.
Post reply on HN