Hydrogen Fuel-Cell Powered Electric Aviation Powertrain | Hacker News Reader

Hydrogen Fuel-Cell Powered Electric Aviation Powertrain

zeroavia.com

42 pointshootbootscoot38 comments

Hydrogen fuel cells make sense for electric flight scenarios primarily because they have 1/200 the specific weight of lithium ion batteries and 10x the specific energy, which means a lot less weight to pick up of the ground. The challenge of course is safely carrying that volume of compressed hydrogen, and producing it at scale without fossil fuels.

For making the hydrogen, if fossil fuels are being used, the process has to be more efficient than the propulsive efficiency of current aircraft engines:

https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#/medi...

Electrolysis itself is 80% efficient, and a combined cycle gas plant is 60% efficient, so that production efficiency is only 48%, which doesn't beat the 80% peak propulsive efficiency of a fuel powered turboprop. Steam reforming of natural gas to make hydrogen is only 75% efficient.

Therefore renewable electricity based hydrogen production is essential for this to work.

Re safety, when I talked to the founder, he mentioned that they are building really strong tanks for compressed hydrogen with walls way thicker than normally needed for that kind of pressure, so that these tanks could survive high impact. Basically, they are bullet proof. And they weigh more than the fuel itself, iirc

Love the idea. Great guys.

As a happy user of an eMotorWorks EV charger (it seems to be a lot of folks from that firm), I'm also confident that they are doing real stuff.

However, I would think that they would want to engineer the tanks to minimize slow creeping failures. I would imagine a more likely dangerous situation than impact would be a sudden H2 containment failure that occurs without any impact at all, but due to stress cracks, etc, in the H2 vessel.

Correction: I meant 10x the specific volume, not the specific energy.

Re safety: I was pointed out that the dangers of hydrogen are often exaggerated. Hydrogen is flammable, not explosive. It is an oxygen-hydrogen mix that is explosive. It is probably slightly safer than fuel due to the fact that while fuel would tend to leak and accumulate on the ground, hydrogen flies into the atmosphere.

The great thing about electrolysis is that it combines really well with intermittent sources like solar panels or wind turbines. When too much energy than necessary is being produce, store it in hydrogen. That's free fuel for you (free as in "marginal cost of zero").

If we had efficient electrolysis capacities and a market for hydrogen, that would make the case for intermittent renewables much, much stronger.

What industries are competing for platinum group metals? Mike Strizki is my reference for platinum electrode electrolysis. Also CodysLab YouTube channel had an episode harvesting very small amounts of platinum from dust along an interstate (catalytic converter decay over time)

Catalytic converters are the main users I know - back in the 00s landyacht tailpipes were regularly sawn off by thieves since the approach to pass emissions involved stacking a ton of catalytic converters apparently.

Cash-for-clunkers occurred just as the Roadster was being sold in small batch production. Now that Tesla is setting up shop in multiple hemispheres with production continuing to increase output twelve years later - I wonder if the imminent federal administration reconfiguration would intervene similarly and grant EV vouchers instead of cash. Demand is still much higher than supply - slashing the price in this way may boost wait times.

Sure, these trade-ins could be resold, but that's a lot of platinum ( 1-3g per car, 12-15g for trucks, assuming semi?). If converter removed, then not emission compliant. Bodies could be re-purposed for EV? I wouldn't mind driving around a retrofitted ICE body using the diminished capacity and power of batteries removed from a high mileage Tesla. I don't need to go 0-60mph in 3 seconds - I just want it to be emissionless, electric (<90% energy converted to locomotion instead of heat), and quiet.

Mechanics in subsidized retrofit shops would standardize the process of removing the old engine block from the well-understood drive-train. Known fuel tank dimensions, and space taken up by the traditional combustion engine block would provide exact specifications for 3D printed battery casings. But by now Tesla has their battery housings standardized for the low center of gravity modular undercarriage block. This may be far to complex to perform, especially at scale even with tax-funded resources. I'm thinking an auto-body shell with its existing seats, windows, axles, tires, could be a usable resource for the renewables transition period. But the average engine compartment post-ICE may not be spacious enough to accommodate the amount of batteries at the current energy density/volume ratio. Maybe if battery packs got smaller and more modular with a similarly modular coolant plumbing interfacing method, we could snake tubes and install more packs in vacant undercarriage space? Jehu Garcia seems to have pulled it off on his VW.

Distribute all that platinum for use in renewable energy components like fuel cells and electrolysis electrodes?

* >90%

Why not make a dual plane concept? Basically a vtol-tug, for lifting off and landing- and a propelled glider for travelling.

80% is propulsive efficiency from the shaft to useful thrust, there's a lot more energy lost between the fuel input and shaft output (thermodynamic efficiency). The thermodynamic efficiency is where most energy is wasted. For small turboprop engines, this is only 25-30%.

There are a lot of advantages to a fuel cell commuter plane: -lower exterior noise: important for accessing smaller, less congested airports -lower interior noise: noise is a big reason airlines use regional jets instead of more efficient turboprops -potentially lower operating costs: a small turboprop might cost $300/hour in fuel and $150/hour in engine maintenance. A fuel cell could potentially be lower cost overall. -redundancy: can still generate thrust on battery or fuel cell power

> 80% is propulsive efficiency from the shaft to useful thrust, there's a lot more energy lost between the fuel input and shaft output (thermodynamic efficiency). The thermodynamic efficiency is where most energy is wasted. For small turboprop engines, this is only 25-30%.

Ah, I see, so "propellant" in propulsive energy refers to the ignited fuel/air mixture, not accounting for thermal losses caused by fuel ignition. Given that, the efficiency case for H2 fuel-cell flight is even better than I expected (and it was already pretty good). I'm guessing they also don't lose efficiency to noise and vibration.

Hydrogen can be generated by dissociation powered directly by sunlight, with no side trip through electricity, yielding much higher efficiency.

Nobody has found a use for the oxygen that would be released at the same time, although it might be usable for purification, if it could be delivered as h2o2. Then again, concentrated h2o2 is usable directly as rocket fuel.

I wonder how similar the technology is to that used by Toyota Mirai. Having enough power density (fuel cell) and energy density (compressed H2), the aircraft application seem logical... but there surely are lots of details.

The Mirai seems to have had a huge cost problem that the fuel cell cost a lot more than Toyota thought it would be by the time the car shipped. So they used a small one with poor peak performance, and it's a much less exciting car than an electric car, but still costs extra and has annoying refueling.

Planes need a lot of peak power for takeoff.

There is a new Mirai planned for 2021. Also, Bosch and BMW seem to be recently looking into fuel cell technology.

I smell a scam. If they've got something that works, surely they would have at least applied for a patent by now, yet my searches so far have turned up nothing. (Please correct me if I'm mistaken.)

ICE burns hydrogen and emits water, is that zero emissions ?

Using fuel cells, the resulting water can be brought back, without releasing water in any form at the altitude.

They aren't going to bring back any water. It's too heavy.

Agree :) that would be logical.

LinkedIn profile smells differently. https://www.linkedin.com/in/vmiftakhov

Patents

    MODULAR, CUSTOMIZABLE AND SCALABLE MECHANICAL DESIGN FOR THE ELECTRIC CAR ASSEMBLY BASED ON THE EXISTING VEHICLE CHASSIS
    Issued November 1, 2014United States

This patent has nothing to do with a hydrogen-powered engine.

There was at least a test flight: https://www.youtube.com/watch?v=du1TBWuyKi4

Range and scaling up to be seen though.

They never showed the engine in this video, though. It could be an ordinary gas-powered one.

Don't know why they can't just drop an empty battery w/ a parachute once the plane gets to a high enough altitude.

Does jettisoning that weight have a tremendous impact on cruising efficiency?

My impression is that the main advantage of dumping a take-off battery is reduced landing weight, which is certainly an issue with existing commercial jet airframes. They can't land with a full fuel load without damaging the plane.

But I'm not clear on what affect it has on range/efficiency.

At this point they could as well use an electric cable that detaches once the plane has reached a certain altitude/distance from the airport.

Batteries don't handle impacts well. People living near airports don't appreciate battery packs crashing through their roofs when the parachute fails to open. It's expensive to have someone drive around with a truck and pick up the dead batteries. When weather conditions get a little rough, real airplanes can still fly but parachutes get blown all over the place.

This would work for cars.

All fuel cell cars are also electric cars in that they use batteries and electric drivetrains in addition to the hydrogen fuel cell itself. The result is more complexity and hence cost, which is one big reason fuel cell cars haven't taken off.

The other reason is the lack of sufficient hydrogen distribution infrastructure. Cars need a dense network of refueling points for convenience. For EVs, this already exists in the form of the existing electric grid and local distribution network (yes, I know it's harder for apartment dwellers right now). A similarly dense hydrogen distribution network doesn't exist, and would have to built from scratch.

Airplanes, on the other hand, have far fewer refueling points (they're all at airports), so it's a lot easier to build those.

In the future, as the cost and size of fuel cell tech drops, one can maybe see them being use for range extending applications for rapid refueling in long distance drives, but then again, rapid charging and high range EVs are making even that advantage somewhat moot.

IMO fuel cells could also be better for freighters, which can’t use batteries for weight reasons as well.

> A similarly dense hydrogen distribution network doesn't exist, and would have to built from scratch.

Or we can add hydrogen to the existing fuels on traditional petrol stations.

Sure, but those stations would still need a invasive and expensive retrofit, adding new underground tanks. You'd also need a new fleet of hydrogen delivery tankers to parallel existing fleet of fuel delivery tankers.

And remember that compressed hydrogen's energy density is 5x lower than gasoline [1], so to store the same amount of energy as gasoline, you need 5x the amount of storage volume on site to store the same amount of energy. Fuel cell drivetrains are about double the efficiency of typical gas engines, so that might bring the storage needs down to 2.5x the storage needs for gasoline, but then you also need special equipment to keep the hydrogen contained (it's harder to contain than liquid fuel). You also need 2.5x the number of hydrogen tankers to move that fuel to the stations, or 2.5x the frequency of tanker trips.

Compare that to the relatively minimal cost of attaching an EV charging station to an existing building's power supply, and there's not much comparison. At most, you need to upgrade transformers and the local power substations to handle potentially higher demand at peak charging hours, but even that can be done incrementally based on demand profile changes, and mitigated substantially with smart coordinated charging during off-peak hours.

1. https://en.wikipedia.org/wiki/Energy_density#/media/File:Ene...

Oh absolutely, the technology will require plenty of updating. But in a typical distribution system the logistics is usually a much more complex and difficult issue. And hydrogen has enough similarities with the existing fuel (unlike electricity) to require barely any changes in the logistics.

> And hydrogen has enough similarities with the existing fuel (unlike electricity)

Electricity already has a regional and local distribution network. It is an "existing fuel" by definition.

The electrolysis and fuel cell process is significantly less efficient than charging/discharging batteries. It's also significantly less safe and more complex, while offering little benefit - cars are not that sensitive to the weight of batteries.

For aircraft, the equasion is different because there weight is directly proportional to fuel use.

Toyota has a new version of Mirai coming out in 2021. Bosch and BMW are also looking into fuel cells.

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