Curb weight of the 2021 Mirai is about 4200lbs.

That's for a car with 400 miles range, 180hp and 5 passenger seating.

It seems like Toyota is solving these problems.

That's the equivalent of maybe 12 gallons of gas and probably uses 500 lbs of tanks to store it.

Tank pressure is 87.5 MPa, 12,700 PSI (!!!). Total hydrogen on board is 5.6 Kg, 12.3 lbs. Takes a LOT of tanks to store a LITTLE hydrogen.

5.6 Kg is 670 MJ total energy. That 5.3 gallons of gasoline for the same energy.

Mike C.

Folks are looking at the idea.

https://www.cummins.com/news/2021/04/15/cummins-hydrogen-power-takes-flight

A reasonable substitute for Hydrogen is methane. that is why Spacex is using it for their superfuel it liquifies at a reasonable temperature for storage and has a pretty high energy content.

or

there are also some hydrides being developed that will store H2

https://www.ifam.fraunhofer.de/en/Profi ... orage.html

For small aircraft, I'm not convinced that methane has advantages over heavier hydrocarbons that can be stored as liquid. The higher mass energy density of methane may not make up for higher weight / complexity for cryogenic tanks. For large aircraft it may make sense.

I don't know how efficiently methane can be produced in a net zero carbon way.

OTOH, I don't think aircraft are a good place to try to reduce carbon emissions - its such a highly constrained application that it may not be worth the effort. Once industry and non air transport is carbon free, we are probably fine.

That's the equivalent of maybe 12 gallons of gas and probably uses 500 lbs of tanks to store it.

Tank pressure is 87.5 MPa, 12,700 PSI (!!!). Total hydrogen on board is 5.6 Kg, 12.3 lbs. Takes a LOT of tanks to store a LITTLE hydrogen.

5.6 Kg is 670 MJ total energy. That 5.3 gallons of gasoline for the same energy.

Mike C.

Unfortunately, storing it is a problem.

As a low pressure gas, it take ENROMOUS space, think Hindenburg.

As a high pressure gas, it takes very heavy cylinders to handle the high pressure.

As a liquid, it requires cryogenic handling and it boils off sitting around, so you only fuel just before use (like rockets). Any fuel left over evaporates before next flight. Also, the process of turning it into a liquid uses a LOT of energy.

95% of hydrogen produced today comes from fossil fuel, with a lot of CO2 released, so not exactly changing the basic problem.

Saying hydrogen is high energy density but ignoring the storing problems is like saying electric motors are high power density and ignoring the batteries. The whole system has to be considered.

Mike C.

You have to count the total cycle energy.

You have to make the hydrogen. Currently 95% of that is from fossil fuel, mostly methane.

You have to pressurize it, that takes energy particularly at pressures like 12,700 PSI.

If you use liquid hydrogen, you have to use energy to cool it that low.


Well, so far, you can actually buy a number of electric airplanes, but no hydrogen fuel cell ones.

Mike C.

- https://fuelcellsworks.com/news/new-dlr ... t-airport/


[youtube]https://youtu.be/ZtQvDUN2ukE[/youtube]

Once gasoline and Diesel go, Methane is next on the hit list. It's a far more effective greenhouse gas than just about any other. The powers that be aren't going to allow Methane to stay in widespread use for too long.

Really? You're now a proponent of rechargeable battery flight?

There's a really good shot for hydrogen fuel cell airplanes to have substantial range and endurance to the point of being useful.

I was pointing out that electric airplanes do exist commercially, which is WAY ahead of any hydrogen fuel cell project.


Doesn't really compute when the weight of hydrogen storage is accounted for.

About the best viable battery is 350 WH/Kg. When you add up the hydrogen tanks and the fuel cell to make it into electricity, what sort of energy density do you get? Numbers I see are around 500-600 WH/Kg, so a little bit better but not a real change in magnitude. Battery development might reach those levels at some point.

Hydrogen may win on refuel/recharge time, but it doesn't feel like it is changing the basic energy density issue.

For comparison, jet fuel is 11,900 WH/Kg. Even considering a hugely less efficient engine versus electric motor, that's still WAY more energy dense than any battery or hydrogen system.

Mike C.

Not clear to me which is the safer option in an accident:

3 big hydrogen tanks at 12,000 PSI.

750 lbs of LiIon batteries.

15 gallons of gasoline.

They all have issues. If a hydrogen tank goes, it will be a BIG bomb just from the pressure. Any flame source and the H2 fire will add to the calamity.

Mike C.