6 ms·

> In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft

> In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft. I was excited about the use of hydrogen in aircraft for a while but the more I looked into it the less likely it seems. I think the advantages of liquid fuels are too great and that even if there were no oil production it would still make more sense to synthesize jet fuel or some other liquid fuel for use in aviation. This has nothing to do with feasibility (the Soviet Union had an airliner that ran on hydrogen, so hydrogen aircraft are absolutely feasible), just with lock-in effects and ease of use.

TylerE 6y ago
It's not just liquid vs gas. Hydrogen has a couple of "unique" properties that make it especially disadvantageous. Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle. I think hydrogen is basically a dead-end as energy storage, except in a few niche applications where it's produced as a byproduct and can be consumed immediately.
- _ph_ 6y ago
  Steel production, where the hydrogen is a chemical reagent, might be one of the few exceptions where hydrogen is really the best choice.
- cultus 6y ago
  Not to mention liquid H2 has quite a bit lower energy density than liquid fossil fuels. Many rockets have used kerosene in their first stages for this reason. Not the end of the world for aircraft, but certainly another major disadvantage.
  - funcDropShadow 6y ago
    But the energy density per mass is still better than Li-ion batteries.
    - nickik 6y ago
      Li-ion batteries are improving at a faster rate, and you can use your gravitational energy to recharge the battery.
      - dmurray 6y ago
        How does that work? You run your propellor in reverse like a wind turbine? This doesn't sound completely ridiculous but is there even any proof of concept for that? The gravitational potential energy doesn't seem all that high - most airplane fuel is burnt maintaining height, not gaining it - to justify the complexity of recovering some small fraction of it. Still, I once thought the same about regenerative braking in electric cars.
      - 8note 6y ago
        Hydrogen is a storage mechanism; there'd be a way to reclaim your energy either way
- tempestn 6y ago
  It's also prone to explode, and is a potent (indirect) greenhouse gas if it leaks into the atmosphere. Agreed that it will have some niche applications though. As well as the byproduct situation, there are likely situations where batteries wouldn't be feasible due to insufficient capacity or too great of weight. Aerospace maybe?
  - tgflynn 6y ago
    How is hydrogen a greenhouse gas (and what do you mean by "indirect") ?
    - ben509 6y ago
      I think it'd be an "indirect" GG because it's electricity intensive to obtain it, and that likely comes from a carbon emitting source. The same argument is often made about electric vehicles.
      - IanCal 6y ago
        In this case it's about how it interacts with OH radicals in the atmosphere, meaning other GHG stay in the atmosphere longer. So it's not a greenhouse gas, but it makes others hang around longer. > The reaction of hydrogen with OH radicals has a further side-effect of reducing the availability of OH radicals with potential impacts on the build-up of greenhouse gases. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/760538/Hydrogen_atmospheric_impact_report.pdf https://assets.publishing.service.gov.uk/government/uploads/...
      - godelski 6y ago
        Well you don't typically get hydrogen from H2O, you get it from CH4. So your byproduct isn't oxygen, it is carbon. Unlike electric vehicles, it doesn't get greener as the grid changes to wind/solar/nuclear/hydro. There's just more hydrogens per hydrocarbon than water. Not to mention dealing with oxidation.
  - CyberDildonics 6y ago
- Hypx 6y ago
  > Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle. Both claims are wildly wrong. Neither actually happens except at high temperatures and only with certain metals.
  - theamk 6y ago
    Could you elaborate about “wildly wrong”? I am not an expert on this, but random internet searches such as [0] indicate that common materials, like high strength steel, are susceptible to both diffusion and embrittlement at room temperature [0] https://www.energy.gov/sites/prod/files/2014/03/f10/pipeline_group_feng_ms.pdf https://www.energy.gov/sites/prod/files/2014/03/f10/pipeline...
    - Hypx 6y ago
      Those tests seem to be at >200˚C if I’m not mistaken. Hardly room temperature. Regardless, the main trick is to avoid using certain types of high-strength steel, line exposed surfaces with polymers, or using composites where ever possible. The problem is for the most part solved.
      - TylerE 6y ago
        So you're admitting the problem exists, which is my entire point. It's hardly a theoretical-only problem, either: https://en.wikipedia.org/wiki/Eastern_span_replacement_of_the_San_Francisco%E2%80%93Oakland_Bay_Bridge#Bolt_failure https://en.wikipedia.org/wiki/Eastern_span_replacement_of_th...
        Hypx 6y ago
        In the same sense all chemicals have handling issues. In practice, it is basically solved. That's probably due to them using a vulnerable alloy, and was likely exposed to hydrogen while at a high temperatures. This is nothing like a gas tank filled will hydrogen.
  - 6y ago
- stewbrew 6y ago
  That's why some bet on ammoniac.
PaulHoule 6y ago
It astonishes me how far behind aviation is behind surface transport when it comes to sustainable fuels. They still use leaded gas! It seems you would try methane before you try hydrogen: https://energynews.us/2013/08/26/midwest/could-natural-gas-fuel-commercial-flights-of-the-future/ https://energynews.us/2013/08/26/midwest/could-natural-gas-f... Petroleum-based liquid fuels contain mixed entity hydrocarbons that match a specification; if you have the perfect feedstock and markets for the fractions you don't use this is cheap. Worst-case you have to synthesize them with Fischer-Tropsch chemistry https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_proces... which is such a PITA (normally a chem E would be delighted that you can use iron as a catalyst, but it works so poorly that a desperate search of the other 91 elements found just 2 that sorta-kinda work) The issue there is you are sticking C's onto the end of a chain and you have to deal with a network of reactions that produce products you couldn't care less for, such as petroleum jelly that gums up your catalyst, sticks up your downrisers, etc. Sustainable motor fuels tend to be single entities such as 1-butanol, dimethyl ether, etc. You might need to blend something in for low temperature starting, but it's possible for a single entity fuel to be synthesized with decent yield. General av is seen as a backwater that is barely hanging on and couldn't possibly get the lead out. The USAF has done biofuels trials, but commercial av is spooked to try anything that could leave passengers up in the air.
- dnhz 6y ago
  General aviation fuel is leaded but jet fuel does not contain lead.
- ohazi 6y ago
  > General av is seen as a backwater that is barely hanging on and couldn't possibly get the lead out. The issue is infrastructure. Modern engines run fine on unleaded fuel, but the little airstrips in the middle of nowhere all have 100LL and/or jet fuel, so that's what pilots use. I know a few pilots who are prefer to use unleaded in their Rotax engines to prevent spark plug fouling, and they have to jump through some pretty ridiculous hoops to get gas, while their buddies just fill up with whatever is on the field.
- 6y ago
shawndrost 6y ago
Why not both? ;) Airbus is experimenting with liquid hydrogen: https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html https://www.airbus.com/innovation/zero-emission/hydrogen/zer...
benhurmarcel 6y ago
A lot of the concepts for hydrogen aircraft use liquid hydrogen though.
- jeffreyrogers 6y ago
  It's hard to store, transport, and handle though, so I don't think it has much of an advantage.
Hypx 6y ago
Synthetic jet fuel will need hydrogen as an input chemical. This is not an "either-or" question.
- jeffreyrogers 6y ago
  I didn't say we don't need hydrogen though. I just said it makes more sense to use liquid fuels rather than hydrogen in aircraft.
  - Hypx 6y ago
    That falls under the “maybe” category. Synfuel are not easy to make, and will add a substantial layer of extra complexity to an already complex process. If it can’t be done cheaply then it might not happen or make sense. Hydrogen is not an alien substance BTW. It’s possible that we figure out hydrogen before synfuels get cheap.

TylerE 6y ago

It's not just liquid vs gas. Hydrogen has a couple of "unique" properties that make it especially disadvantageous. Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle. I think hydrogen is basically a dead-end as energy storage, except in a few niche applications where it's produced as a byproduct and can be consumed immediately.

_ph_ 6y ago
Steel production, where the hydrogen is a chemical reagent, might be one of the few exceptions where hydrogen is really the best choice.
cultus 6y ago
Not to mention liquid H2 has quite a bit lower energy density than liquid fossil fuels. Many rockets have used kerosene in their first stages for this reason. Not the end of the world for aircraft, but certainly another major disadvantage.
- funcDropShadow 6y ago
  But the energy density per mass is still better than Li-ion batteries.
  - nickik 6y ago
    Li-ion batteries are improving at a faster rate, and you can use your gravitational energy to recharge the battery.
    - dmurray 6y ago
      How does that work? You run your propellor in reverse like a wind turbine? This doesn't sound completely ridiculous but is there even any proof of concept for that? The gravitational potential energy doesn't seem all that high - most airplane fuel is burnt maintaining height, not gaining it - to justify the complexity of recovering some small fraction of it. Still, I once thought the same about regenerative braking in electric cars.
    - 8note 6y ago
      Hydrogen is a storage mechanism; there'd be a way to reclaim your energy either way
tempestn 6y ago
It's also prone to explode, and is a potent (indirect) greenhouse gas if it leaks into the atmosphere. Agreed that it will have some niche applications though. As well as the byproduct situation, there are likely situations where batteries wouldn't be feasible due to insufficient capacity or too great of weight. Aerospace maybe?
- tgflynn 6y ago
  How is hydrogen a greenhouse gas (and what do you mean by "indirect") ?
  - ben509 6y ago
    I think it'd be an "indirect" GG because it's electricity intensive to obtain it, and that likely comes from a carbon emitting source. The same argument is often made about electric vehicles.
    - IanCal 6y ago
      In this case it's about how it interacts with OH radicals in the atmosphere, meaning other GHG stay in the atmosphere longer. So it's not a greenhouse gas, but it makes others hang around longer. > The reaction of hydrogen with OH radicals has a further side-effect of reducing the availability of OH radicals with potential impacts on the build-up of greenhouse gases. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/760538/Hydrogen_atmospheric_impact_report.pdf https://assets.publishing.service.gov.uk/government/uploads/...
    - godelski 6y ago
      Well you don't typically get hydrogen from H2O, you get it from CH4. So your byproduct isn't oxygen, it is carbon. Unlike electric vehicles, it doesn't get greener as the grid changes to wind/solar/nuclear/hydro. There's just more hydrogens per hydrocarbon than water. Not to mention dealing with oxidation.
- CyberDildonics 6y ago
Hypx 6y ago
> Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle. Both claims are wildly wrong. Neither actually happens except at high temperatures and only with certain metals.
- theamk 6y ago
  Could you elaborate about “wildly wrong”? I am not an expert on this, but random internet searches such as [0] indicate that common materials, like high strength steel, are susceptible to both diffusion and embrittlement at room temperature [0] https://www.energy.gov/sites/prod/files/2014/03/f10/pipeline_group_feng_ms.pdf https://www.energy.gov/sites/prod/files/2014/03/f10/pipeline...
  - Hypx 6y ago
    Those tests seem to be at >200˚C if I’m not mistaken. Hardly room temperature. Regardless, the main trick is to avoid using certain types of high-strength steel, line exposed surfaces with polymers, or using composites where ever possible. The problem is for the most part solved.
    - TylerE 6y ago
      So you're admitting the problem exists, which is my entire point. It's hardly a theoretical-only problem, either: https://en.wikipedia.org/wiki/Eastern_span_replacement_of_the_San_Francisco%E2%80%93Oakland_Bay_Bridge#Bolt_failure https://en.wikipedia.org/wiki/Eastern_span_replacement_of_th...
      - Hypx 6y ago
        In the same sense all chemicals have handling issues. In practice, it is basically solved. That's probably due to them using a vulnerable alloy, and was likely exposed to hydrogen while at a high temperatures. This is nothing like a gas tank filled will hydrogen.
- 6y ago
stewbrew 6y ago
That's why some bet on ammoniac.

PaulHoule 6y ago

It astonishes me how far behind aviation is behind surface transport when it comes to sustainable fuels. They still use leaded gas! It seems you would try methane before you try hydrogen: https://energynews.us/2013/08/26/midwest/could-natural-gas-fuel-commercial-flights-of-the-future/ https://energynews.us/2013/08/26/midwest/could-natural-gas-f... Petroleum-based liquid fuels contain mixed entity hydrocarbons that match a specification; if you have the perfect feedstock and markets for the fractions you don't use this is cheap. Worst-case you have to synthesize them with Fischer-Tropsch chemistry https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_proces... which is such a PITA (normally a chem E would be delighted that you can use iron as a catalyst, but it works so poorly that a desperate search of the other 91 elements found just 2 that sorta-kinda work) The issue there is you are sticking C's onto the end of a chain and you have to deal with a network of reactions that produce products you couldn't care less for, such as petroleum jelly that gums up your catalyst, sticks up your downrisers, etc. Sustainable motor fuels tend to be single entities such as 1-butanol, dimethyl ether, etc. You might need to blend something in for low temperature starting, but it's possible for a single entity fuel to be synthesized with decent yield. General av is seen as a backwater that is barely hanging on and couldn't possibly get the lead out. The USAF has done biofuels trials, but commercial av is spooked to try anything that could leave passengers up in the air.

dnhz 6y ago
General aviation fuel is leaded but jet fuel does not contain lead.
ohazi 6y ago
> General av is seen as a backwater that is barely hanging on and couldn't possibly get the lead out. The issue is infrastructure. Modern engines run fine on unleaded fuel, but the little airstrips in the middle of nowhere all have 100LL and/or jet fuel, so that's what pilots use. I know a few pilots who are prefer to use unleaded in their Rotax engines to prevent spark plug fouling, and they have to jump through some pretty ridiculous hoops to get gas, while their buddies just fill up with whatever is on the field.
6y ago

shawndrost 6y ago

Why not both? ;) Airbus is experimenting with liquid hydrogen: https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html https://www.airbus.com/innovation/zero-emission/hydrogen/zer...

benhurmarcel 6y ago

A lot of the concepts for hydrogen aircraft use liquid hydrogen though.

jeffreyrogers 6y ago
It's hard to store, transport, and handle though, so I don't think it has much of an advantage.

Hypx 6y ago

Synthetic jet fuel will need hydrogen as an input chemical. This is not an "either-or" question.

jeffreyrogers 6y ago
I didn't say we don't need hydrogen though. I just said it makes more sense to use liquid fuels rather than hydrogen in aircraft.
- Hypx 6y ago
  That falls under the “maybe” category. Synfuel are not easy to make, and will add a substantial layer of extra complexity to an already complex process. If it can’t be done cheaply then it might not happen or make sense. Hydrogen is not an alien substance BTW. It’s possible that we figure out hydrogen before synfuels get cheap.