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This seems like more organic chemistry research, not a giant breakthrough. Still, we need sustainable fuels in aviation for the foreseeable future. Given the ph

This seems like more organic chemistry research, not a giant breakthrough. Still, we need sustainable fuels in aviation for the foreseeable future. Given the physics of flight on this planet, batteries just won’t cut it. Unfortunately even with a 100% renewable fuel, you still have additional greenhouse effect from the condensation trails. I doubt there’s a reasonable way to capture jet exhaust, and even if it did it would increase the weight of the aircraft. So basically, the future is steampunk dirigibles, and don’t let anyone tell ya different.

dataflow 4y ago
I almost didn't believe you that the effect of contrails could be that large, but I searched and it sounds crazy: https://e360.yale.edu/features/how-airplane-contrails-are-helping-make-the-planet-warmer https://e360.yale.edu/features/how-airplane-contrails-are-he...
- edrxty 4y ago
  For what it's worth, contrails only form when conditions are right at certain altitudes, so if we had renewable fuels we could theoretically move aircraft outside the contrail altitude window. It would piss off controllers and burn slightly more fuel sometimes but it could be done.
  - twoslide 4y ago
    I believe it's not actually contrails specifically but rather the effects of releasing exhaust (CO2) at a high altitude (which would happen whether the contrails form or not).
    - masklinn 4y ago
      I’m not sure what you’re talking about, but the thread and article are about contrails, specifically.
    - someweirdperson 4y ago
      CO2 is just the basic evil everyone talks about. Water is a lot more evil (much broader range of wave lengths of light absorbed than the comparatively tiny range of CO2), if it is in the air. Water changes it behavior depending on the relative amount in the air. A sufficiently high amount will act on visible light (contrails, clouds, fog, ...), but even in its "transparent" form it messes with wave lengths outside of the visible range. Contrails are created by local changes of temperature at the wing tips (turning the invisible water into visible, temporarily) and by adding water as part of the exhaust. Burning CxHy leaves some H2O, visible or not. I would have guessed that the visible form is contributing more to cooling than the (probably more common) invisble form. Possibly a matter of when they turn invisible, which might be more likely in the morning than at night (those produced during one day staying visible during the night helping with heating but vanishing next day, not helping with cooling). Modelling water properly is quite surely complicated, with bigger effects than CO2. Not only for contrails.
      - sokoloff 4y ago
        Contrails are ice from water in the exhaust, unrelated to the wingtips. You will sometimes see vortices at high angles of attack on takeoff or landing, but those don’t turn into contrails.
      - ouid 4y ago
        labster 4y ago
        It’s true, though. Water causes roughly 30°C of global warming. We can’t get much if any more from water vapor, but there are several positive and negative feedbacks from clouds that are quite interesting. High clouds are ice, which allow transmission of visible light, but absorb in the infrared. Water is to rain as CO2 is to glucose.
  - ZeroGravitas 4y ago
    This became a minor fake controversy recently when Google changed their carbon footprint measures on flight to stop estimating these non carbon effects. The reason they did so was they were just using a rule of thumb that applies to all flights and they want to be able to encourage airlines to adopt the known practices that can avoid these extra emissions (shifting time of flights is the big one I think). There's no standard yet for estimating them though, but they are working on one: https://airqualitynews.com/2022/09/01/is-google-airbrushing-emissions-data-to-boost-sales/ https://airqualitynews.com/2022/09/01/is-google-airbrushing-...
- abazeeeeeee 4y ago
- jl6 4y ago
  I guess it’s unintuitive because the contrails only last a few hours, so how could they have any long term effect? But aviation is continuous, so they get replaced quickly, so there’s probably a constant contribution to warming. I’m not sure how the contrail effect interacts with Earth’s increasing cloudiness.
- themitigating 4y ago
  I want to also say I didn't believe them but because I thought he was referring to the conspiracy theory not the actual water vapor trails
  - ghastmaster 4y ago
    "Chem trails" is the terminology usually associated with the conspiracy theories.
Schroedingersat 4y ago
> I doubt there’s a reasonable way to capture jet exhaust, and even if it did it would increase the weight of the aircraft. Just taking it with you is a non-starter. If your fuel is mostly carbon by weight, then the CO2 will weigh 2-3x as much. At that point batteries are starting to look appealing by comparison. There are battery techs with around 400Wh/kg and various almost-working ideas in the 500-600 region. Once you run 11000Wh/kg hydrocarbons through a turbine at 30% and carry the 2 Oxygen atoms for every C you might only be getting 1000Wh per kg of exhaust you carry.
- myblake 4y ago
  Does commercial aviation carry an oxidizer though? I thought jets were air breathing.
  - londons_explore 4y ago
    OP's point is that if they wanted to capture the exhaust, then they would be carrying the oxidizer...
  - Schroedingersat 4y ago
    You are correct. I was speaking of the exhaust which is oxidised (that is, after all why you burn the fuel). If you wanted to do CCS on a jet the H2O can be vented, but the CO2 (which you have to carry to your destination) weighs 44/12 times the carbon in the fuel (which is a large portion of the fuel mass -- abput 3/4ths iirc).
shawnb576 4y ago
I think the hydrogen-electric [1] development is more promising here because it has the potential to deliver long haul flights with no emissions or contrails. While H2 isn't great for decarbonization at scale, in specific industries like aviation it might be applicable assuming it's made cleanly. [1] https://www.zeroavia.com/ https://www.zeroavia.com/
- Teknoman117 4y ago
  What's the justification to expect that 25-50% of human climate impact will be from aviation by 2050? Growing population? Lower cost of access to flight? Other industries decarbonizing and causing aviation impact to just be a larger fraction of overall impact?
  - jabl 4y ago
    IIRC it's a combination of air travel continuing to expand at the roughly 2.5% yearly rate it has been doing for the past decades, and other sectors of the economy successfully decarbonizing.
- kwhitefoot 4y ago
  Isn't a contrail a condensation trail? In a hydrogen fuel cell the waste product is H2O so surely there is a contrail.
  - cesaref 4y ago
    I believe contrail formation requires nucleation sites, which is normally provided by soot particles from the burning fuel.
    - kwhitefoot 4y ago
      Good point, thanks.
    - labster 4y ago
      It doesn’t in a really moist layer. Ice condensation nuclei are relatively rare (thus the silver nitride seeding idea), so a lot of times ice clouds form when a parcel of air gets supersaturated. This is pretty common.
DrewADesign 4y ago
I'm not a subject matter expert, but think much of the value stems from lignin being so abundant because it's a byproduct of paper making rather than some advancement in chemistry, itself.
deleted 4y ago
[deleted]
abazeeeeeee 4y ago
- once_inc 4y ago
  Wh-Whut? Is that supposed to be six contrails?
danhor 4y ago
There are indications that SAF burn cleaner and thus produce less than half the contrails: https://www.nasa.gov/press-release/nasa-dlr-study-finds-sustainable-aviation-fuel-can-reduce-contrails https://www.nasa.gov/press-release/nasa-dlr-study-finds-sust... and lowers the effeet on global warming.
- labster 4y ago
  This should be the top reply to me. Cool research. I wouldn’t have thought about it (though I did worse in my atmospheric chemistry class than anything else I studied in atmospheric science, so not surprising).
ZeroGravitas 4y ago
Batteries make sense for shorter flight today and will slowly increase their range, future plane designs will likely use hydrogen fuel cells, but yes, for existing planes and the next couple of decades the industry is looking at a range of Sustainable ways to make e-kerosene to burn in existing engines, several of which are at pilot (no pun intended) stages.

dataflow 4y ago

I almost didn't believe you that the effect of contrails could be that large, but I searched and it sounds crazy: https://e360.yale.edu/features/how-airplane-contrails-are-helping-make-the-planet-warmer https://e360.yale.edu/features/how-airplane-contrails-are-he...

edrxty 4y ago
For what it's worth, contrails only form when conditions are right at certain altitudes, so if we had renewable fuels we could theoretically move aircraft outside the contrail altitude window. It would piss off controllers and burn slightly more fuel sometimes but it could be done.
- twoslide 4y ago
  I believe it's not actually contrails specifically but rather the effects of releasing exhaust (CO2) at a high altitude (which would happen whether the contrails form or not).
  - masklinn 4y ago
    I’m not sure what you’re talking about, but the thread and article are about contrails, specifically.
  - someweirdperson 4y ago
    CO2 is just the basic evil everyone talks about. Water is a lot more evil (much broader range of wave lengths of light absorbed than the comparatively tiny range of CO2), if it is in the air. Water changes it behavior depending on the relative amount in the air. A sufficiently high amount will act on visible light (contrails, clouds, fog, ...), but even in its "transparent" form it messes with wave lengths outside of the visible range. Contrails are created by local changes of temperature at the wing tips (turning the invisible water into visible, temporarily) and by adding water as part of the exhaust. Burning CxHy leaves some H2O, visible or not. I would have guessed that the visible form is contributing more to cooling than the (probably more common) invisble form. Possibly a matter of when they turn invisible, which might be more likely in the morning than at night (those produced during one day staying visible during the night helping with heating but vanishing next day, not helping with cooling). Modelling water properly is quite surely complicated, with bigger effects than CO2. Not only for contrails.
    - sokoloff 4y ago
      Contrails are ice from water in the exhaust, unrelated to the wingtips. You will sometimes see vortices at high angles of attack on takeoff or landing, but those don’t turn into contrails.
    - ouid 4y ago
      - labster 4y ago
        It’s true, though. Water causes roughly 30°C of global warming. We can’t get much if any more from water vapor, but there are several positive and negative feedbacks from clouds that are quite interesting. High clouds are ice, which allow transmission of visible light, but absorb in the infrared. Water is to rain as CO2 is to glucose.
- ZeroGravitas 4y ago
  This became a minor fake controversy recently when Google changed their carbon footprint measures on flight to stop estimating these non carbon effects. The reason they did so was they were just using a rule of thumb that applies to all flights and they want to be able to encourage airlines to adopt the known practices that can avoid these extra emissions (shifting time of flights is the big one I think). There's no standard yet for estimating them though, but they are working on one: https://airqualitynews.com/2022/09/01/is-google-airbrushing-emissions-data-to-boost-sales/ https://airqualitynews.com/2022/09/01/is-google-airbrushing-...
abazeeeeeee 4y ago
jl6 4y ago
I guess it’s unintuitive because the contrails only last a few hours, so how could they have any long term effect? But aviation is continuous, so they get replaced quickly, so there’s probably a constant contribution to warming. I’m not sure how the contrail effect interacts with Earth’s increasing cloudiness.
themitigating 4y ago
I want to also say I didn't believe them but because I thought he was referring to the conspiracy theory not the actual water vapor trails
- ghastmaster 4y ago
  "Chem trails" is the terminology usually associated with the conspiracy theories.

Schroedingersat 4y ago

> I doubt there’s a reasonable way to capture jet exhaust, and even if it did it would increase the weight of the aircraft. Just taking it with you is a non-starter. If your fuel is mostly carbon by weight, then the CO2 will weigh 2-3x as much. At that point batteries are starting to look appealing by comparison. There are battery techs with around 400Wh/kg and various almost-working ideas in the 500-600 region. Once you run 11000Wh/kg hydrocarbons through a turbine at 30% and carry the 2 Oxygen atoms for every C you might only be getting 1000Wh per kg of exhaust you carry.

myblake 4y ago
Does commercial aviation carry an oxidizer though? I thought jets were air breathing.
- londons_explore 4y ago
  OP's point is that if they wanted to capture the exhaust, then they would be carrying the oxidizer...
- Schroedingersat 4y ago
  You are correct. I was speaking of the exhaust which is oxidised (that is, after all why you burn the fuel). If you wanted to do CCS on a jet the H2O can be vented, but the CO2 (which you have to carry to your destination) weighs 44/12 times the carbon in the fuel (which is a large portion of the fuel mass -- abput 3/4ths iirc).

shawnb576 4y ago

I think the hydrogen-electric [1] development is more promising here because it has the potential to deliver long haul flights with no emissions or contrails. While H2 isn't great for decarbonization at scale, in specific industries like aviation it might be applicable assuming it's made cleanly. [1] https://www.zeroavia.com/ https://www.zeroavia.com/

Teknoman117 4y ago
What's the justification to expect that 25-50% of human climate impact will be from aviation by 2050? Growing population? Lower cost of access to flight? Other industries decarbonizing and causing aviation impact to just be a larger fraction of overall impact?
- jabl 4y ago
  IIRC it's a combination of air travel continuing to expand at the roughly 2.5% yearly rate it has been doing for the past decades, and other sectors of the economy successfully decarbonizing.
kwhitefoot 4y ago
Isn't a contrail a condensation trail? In a hydrogen fuel cell the waste product is H2O so surely there is a contrail.
- cesaref 4y ago
  I believe contrail formation requires nucleation sites, which is normally provided by soot particles from the burning fuel.
  - kwhitefoot 4y ago
    Good point, thanks.
  - labster 4y ago
    It doesn’t in a really moist layer. Ice condensation nuclei are relatively rare (thus the silver nitride seeding idea), so a lot of times ice clouds form when a parcel of air gets supersaturated. This is pretty common.

DrewADesign 4y ago

I'm not a subject matter expert, but think much of the value stems from lignin being so abundant because it's a byproduct of paper making rather than some advancement in chemistry, itself.

deleted 4y ago

[deleted]

abazeeeeeee 4y ago

once_inc 4y ago
Wh-Whut? Is that supposed to be six contrails?

danhor 4y ago

There are indications that SAF burn cleaner and thus produce less than half the contrails: https://www.nasa.gov/press-release/nasa-dlr-study-finds-sustainable-aviation-fuel-can-reduce-contrails https://www.nasa.gov/press-release/nasa-dlr-study-finds-sust... and lowers the effeet on global warming.

labster 4y ago
This should be the top reply to me. Cool research. I wouldn’t have thought about it (though I did worse in my atmospheric chemistry class than anything else I studied in atmospheric science, so not surprising).

ZeroGravitas 4y ago

Batteries make sense for shorter flight today and will slowly increase their range, future plane designs will likely use hydrogen fuel cells, but yes, for existing planes and the next couple of decades the industry is looking at a range of Sustainable ways to make e-kerosene to burn in existing engines, several of which are at pilot (no pun intended) stages.