Electroflight Team Aims To Fly 300 MPH On Batteries

Skywise wrote:
Larry Dighera wrote in
:

She also said the hydrogen would be compressed to ten bar,
which would raise its energy density comparable to that of
gasoline.

I'm not so sure about that.

An article I found many many years ago, published in 2002,
discusses such things. If the information in the article is
correct, it is extremely difficult to beat gasoline for
energy density.

It lists gasoline as having an energy density of 9000Wh/l
(watt-hours per liter).

150 bar H2 is only 405 Wh/l.

Liquid H2 is 2600 Wh/l.

Lithium batteries are listed as 250 Wh/l, but mind you
this was published 12 years ago. Battery technology has
made large leaps since then. Even if they've only
doubled in energy density since then, that would still
beat 150 bar H2.

http://www.tinaja.com/glib/energfun.pdf

Brian

For aviation use, the energy density by weight and volume are both important.

Try he

http://en.wikipedia.org/wiki/Energy_density

Note none of these account for any required container, which in some
cases can be very significant.



--
Jim Pennino

wrote in :

For aviation use, the energy density by weight and volume are both
important.

Quite right.


Try he

http://en.wikipedia.org/wiki/Energy_density

Using information from above...

source MJ/kg MJ/l MJ/kgl
H2 liquid 141.86 8.491 1204.53
H2 690 bar 141.86 4.5 638.37
gasoline 46.4 34.2 1586.88
100LL 44.0 31.59 1389.96
Jet A 42.8 33 1412.4
Li-ion .875 2.63 2.30 (best values for range)

I calculated the MJ/kgl by multiplying the two other values.
This gives an efficiency factor by which to compare fuels.
As can be seen, liquid hydrocarbons outperform even liquid
hydrogen.

The energy is in the hydrogen atoms. The reason hydrocarbons
outperform pure hydrogen is that gasoline simply has more
hydrogen atoms in it that even pure liquified hydrogen due
to the hydrocarbon molecular structure. That's why there is
more energy per unit volume, which more than makes up for
it's much lower energy per unit mass.

And this doesn't even take into account the storage container.
I'm sure a wing tank in a Cessna 172 weighs a lot less than
a compressed H2 bottle for an equivalent amount of total
energy. I doubt LH2 would ever fly (pun intended) as it
requires cryogenic storage design which adds yet more weight.

Another factor not considered is energy conversion. The total
mass of the engine (ICE or fuelcell/electric motor) and it's
conversion efficiency. Is a hydrogen fuel cell motor system
light enough to offset the extra weight of the storage
container? Is the system more efficient at converting the
theoretical energy values listed above into usable work?

Li-ion sucks. Though I love 'em for RC airplanes. No mess.

Brian
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