Airbus has great marketing
ZEROe: Hydrogen-hybrid aircraft concept
31–40 of 111 posts
Re: ZEROe: Hydrogen-hybrid aircraft concept
#32Not 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…
> 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.
On Table 1 of your study, it’s measuring residence time of stratospheric water vapor in days. How are you getting years from that?
Re: ZEROe: Hydrogen-hybrid aircraft concept
#33Earlier quoted context omitted.
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 (…
> It lasts for days in the lower troposphere but years in the stratosphere
I addressed this in my other reply. Table 1 of the study you cited stated that the residence time of stratospheric water vapor is measured in days. I'm not seeing a lifetime of years in that study.
> however lithium-air is much more energy dense (volumetrically)
Maybe. Lithium-air absorbs oxygen when it is operating. Not sure how to calculated this though.
Re: ZEROe: Hydrogen-hybrid aircraft concept
#34Not 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…
> 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. On Table 1 of your study, it’s measuring residence time of stratospheric water vapor in days. How are you getting years from that?
The article doesn't mention the water vapor lifetime in stratosphere... But they do mention that cryoplanes should not fly close to tropopause, for the fear of water vapor escaping to stratosphere.
Re: ZEROe: Hydrogen-hybrid aircraft concept
#35Earlier quoted context omitted.
> It's not any inherently greener then synthetic hydrocarbon production, which can be produced from atmospheric carbon for zero net carbon impact As I understand it, the production of complex hydrocarbons that can be used as a replacement for jet fuel is even more inefficient when compared to the production of hydrogen, as many of the known processes that start from CO2 actually use hydrogen in the process. So, altho…
> As I understand it, the production of complex hydrocarbons that can be used as a replacement for jet fuel is even more inefficient when compared to the production of hydrogen, as many of the known processes that start from CO2 actually use hydrogen in the process. Sure. Here's the thing though: we can efficiently store those complex hydrocarbons. We can't efficiently store hydrogen. It destroys containers, and can…
The idea here is to do basically a cryoplane. Hydrogen can be generated on demand for the planes to refuel and can be stored highly compressed for that particular use case. We're not talking about using it for GA or cars.
As for volume - there's a reason why they call them cryoplanes ;) From Airbus - Liquid hydrogen is used as fuel for combustion with oxygen.
Re: ZEROe: Hydrogen-hybrid aircraft concept
#36Earlier quoted context omitted.
This is a simplification, think about this: You can manufacture hydrogen anywhere as long as you have water, an electrolyzer, and a power source. Oil can only be pumped out of the ground in certain places, water is technically _much_ more abundant everywhere. Hydrogen storage tech has improved in the last twenty years. It's becoming affordable and "as safe" to store hydrogen at fuel densities similar to that of petro…
> It's becoming affordable and "as safe" to store hydrogen at fuel densities similar to that of petroleum based fuels. Have we solved hydrogen embrittlement issues? What about hydrogen leaking out of containers?
Hydrogen leaking is an issue for longer term storage, not particularly an issue for liquid hydrogen that is going to run an airplane for a very specific number of hours.
Re: ZEROe: Hydrogen-hybrid aircraft concept
#37Earlier quoted context omitted.
> 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. On Table 1 of your study, it’s measuring residence time of stratospheric water vapor in days. How are you getting years from that?
The article doesn't mention the water vapor lifetime in stratosphere... But they do mention that cryoplanes should not fly close to tropopause, for the fear of water vapor escaping to stratosphere.
It states:
> f Residence time = accumulated H2O divided by emitted H2O (days). Corresponding values for the stratosphere only are given in parenthesis.
That seems like it is in days. Unless there's something that I missed, I'm not seeing the part that claims water vapor lasts for years in the stratosphere.
Re: ZEROe: Hydrogen-hybrid aircraft concept
#38I'll admit I really don't get the fascination with hydrogen as an energy storage medium. It has to be manufactured, so how green it is depends on whatever the power input is coming from. It's not any inherently greener then synthetic hydrocarbon production, which can be produced from atmospheric carbon for zero net carbon impact, and of course has no sulfur or aromatics. It also works fine with existing engineering.…
> It's not any inherently greener then synthetic hydrocarbon production, which can be produced from atmospheric carbon for zero net carbon impact As I understand it, the production of complex hydrocarbons that can be used as a replacement for jet fuel is even more inefficient when compared to the production of hydrogen, as many of the known processes that start from CO2 actually use hydrogen in the process. So, altho…
> start from CO2
Why would that route even be taken though? Biofuel for jet engines is proven technology in limited use for many years now. Let plants deal with the CO2, since they're good at it, then process the resultant vegetable oils to produce a suitable diesel or jet fuel.
Re: ZEROe: Hydrogen-hybrid aircraft concept
#39Earlier quoted context omitted.
> It's becoming affordable and "as safe" to store hydrogen at fuel densities similar to that of petroleum based fuels. Have we solved hydrogen embrittlement issues? What about hydrogen leaking out of containers?
Hydrogen leaking is an issue for longer term storage, not particularly an issue for liquid hydrogen that is going to run an airplane for a very specific number of hours.
> for a very specific number of hours
Unless you plan on throwing away the planes after one or two flights, those tanks will be filled with hydrogen for tens of thousands of hours over their lifespan. Perhaps they have light weight alloys that can cope with this though, I'm no metallurgist..
Re: ZEROe: Hydrogen-hybrid aircraft concept
#40Earlier quoted context omitted.
> It's not any inherently greener then synthetic hydrocarbon production, which can be produced from atmospheric carbon for zero net carbon impact As I understand it, the production of complex hydrocarbons that can be used as a replacement for jet fuel is even more inefficient when compared to the production of hydrogen, as many of the known processes that start from CO2 actually use hydrogen in the process. So, altho…
> start from CO2 Why would that route even be taken though? Biofuel for jet engines is proven technology in limited use for many years now. Let plants deal with the CO2, since they're good at it, then process the resultant vegetable oils to produce a suitable diesel or jet fuel. https://en.wikipedia.org/wiki/Aviation_biofuel
> Let plants deal with the CO2, since they're good at it
They aren't good with it at all. Convert CO2 slowly, take space to do that, take other resources like fertilizers, require some shielding from pests and herbs, can produce massive fires... They have advantages, but it's not a silver bullet, especially when you're in a hurry.