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A comment on Aviation Is on a Low-Carbon Flight Path. Parent comment

Re:Aviation Is on a Low-Carbon Flight Path by darksaints on Thursday November 07, 2019 @02:35PM (#21476514)
Solid Oxide Fuel Cells are reaching 2.5kw/kg power densities, Electric motors are reaching 15kw/kg power densities. Combined, that is already better than current jet engines. With cogeneration, SOFCs are reaching 80-85% efficiencies, double that of jet engines. Liquid hydrogen has an energy density of 39kwh/kg, compared to JP8 at 13kwh/kg, but SOFCs could run on pretty much any hydrocarbon. They don't even need cryogenic storage, because fuel consumption rates would be higher than evaporation rates.

All the pieces exist for fuel cell powered jets. They've already got the performance levels needed. All they need is to put them together into a cohesive package, and put a shit ton of effort into reliability engineering.

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Re:Aviation Is on a Low-Carbon Flight Path by 08-15 on Thursday November 07, 2019 @03:49PM (#21477108)
> Combined, that is already better than current jet engines.

Wikipedia lists the GE90-115B at 10kW/kg, four times better than your SOFC. Did you just combine motor and fuel cell to get 17.5kW/kg? That would be hilarious.

> With cogeneration, SOFCs are reaching 80-85% efficiencies

That's creative accounting. You're counting waste heat as if it was useful.

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Re:Aviation Is on a Low-Carbon Flight Path by londons_explore on Thursday November 07, 2019 @02:52PM (#21476682)
Cogeneration isn't much use on a plane...

Granted a little heat for the cabin is handy, but the rest is largely useless.

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Re:Aviation Is on a Low-Carbon Flight Path by darksaints on Thursday November 07, 2019 @03:01PM (#21476765)
I meant in the context of energy conversion. Solid oxide fuel cells produce high grade heat (~800C) that is perfect for conversion via organic rankine cycles (which will convert ~30% of that heat to electricity) or supercritical co2 brayton cycles (~50% heat to electricity with extremely high power densities[0]).

Even without heat capture, SOFCs run at 60-65% efficiency, which is probably good enough.

[0] https://www.ge.com/reports/call-ecomagination-ge-building-co...

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Re:Aviation Is on a Low-Carbon Flight Path by kortilla on Thursday November 07, 2019 @04:37PM (#21477575)
Energy density of jet fuel is 45MJ/kg. Fuel is a significant portion of the weight on the plane. Requiring a 10x+ increase in fuel weight is a non-starter no matter how light the engines.
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Re:Aviation Is on a Low-Carbon Flight Path by darksaints on Thursday November 07, 2019 @05:03PM (#21477798)
If you're measuring in MJ/kg, hydrogen is 141MJ/kg. Hydrogen, in terms of weight, is absolutely better than jet fuel, not worse. It's not very dense (kwh/l) though, and that could be a problem.
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