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

On Tue, 09 Sep 2014 07:59:41 GMT, 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

Hello Brian,

Thanks for your interest in this topic.




================================================== ===================
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From: Larry Dighera
Newsgroups: rec.aviation.piloting
Subject: Electric Motorglider Flies
Message-ID:
References:




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On Tue, 15 Apr 2008 01:05:04 GMT, wrote in
:


Despite the fact that electric motors must use iron/steel in their
construction, they are significantly lighter (50%) than their
internal combustion counterparts. But when the wiring, controls,
batteries and perhaps fuel-cells are considered, I would guess the
weight of an electrically powered aircraft would be roughly comparable
to one powered by an internal combustion engine. So, with
significantly less power/energy density than gasoline, batteries will
not provide the same range/duration until they are improved further.
But it is encouraging to see progress being made at last.

Not going to happen.


I hesitate to attempt to infer your meaning in that phrase, but if you
mean Li-ion batteries, perhaps. If you're referring to electrically
powered aircraft, they have already happened, and development is
progressing.

Energy densities

fuel MJ/kg MJ/L

JET-A 43 33
ethenol 30 24
Li-ion battery (projected) 1 2
NiMH battery .2 .4
ultracapacitor .02 .05

Regenerative fuel cell come in a bit under 2 MJ/kg.

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


Thank you for the factual data. It's interesting that gasoline is
omitted:

http://hypertextbook.com/facts/2003/ArthurGolnik.shtml
Liquid Fuel MJ/litre litre/Tonne GJ/Tonne MJ/kg
Gasoline, aviation 33.0 1412 49.6 36.4


Here's a little more data on Li-ion cells:

http://en.wikipedia.org/wiki/Lithium_ion_battery
Specific energy density: 150 to 200 Wh/kg (540 to 720 kJ/kg)
Volumetric energy density: 250 to 530 Wh/l (900 to 1900 J/cm³)
Specific power density: 300 to 1500 W/kg (@ 20 seconds and 285
Wh/l)



There's a great comparison chart of energy densities he

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


Here are a few of the entries:

Storage Type Energy Density By Mass (MJ/kg)
================================================== ================
lead acid battery 0.090.09?0.11[36]sm=n
lithium ion battery-present capability 0.230.23?0.28
lithium ion battery-predicted future capability 0.540.54?0.9sm=n
Regenerative Fuel Cell (fuel cell with internal Hydrogen reservoir
used much as a battery) 1.62
Lithium ion battery with nanowires 2.54-2.72
TNT 4.184
dry cowdung and cameldung 15.5
calcium (burned in air) 15.9
PET pop bottle plastic 23.5?23.5
ethanol 30
aluminum (burned in air) 31.0
Jet A aviation fuel 42.8
gasoline 46.9
compressed natural gas at 200 bar (2,900.8 psi) 53.6
compressed hydrogen gas at 700 bar (10,423.5054 psi) 143
Enriched uranium (3.5% U235) in light water reactor 3,456,000
nuclear fission (of U-235) (Used in nuclear power plants)
88,250,000


From the data in the chart it would appear that a best-case Lithium
ion battery with nanowires (2.54-2.72 MJ/kg) that would provide the
equivalent energy of a given amount of gasoline (46.9 MJ/kg) would
weigh 17.24 times as much as the gasoline it replaces. That doesn't
look too terribly feasible for aviation use. Oh well....

However, hydrogen gas compressed to a pressure of ~10,500 psi (143
MJ/kg) would only weigh ~1/3 as much as the equivalent gasoline energy
it replaces. If that hydrogen were used along with atmospheric oxygen
to produce electricity by a fuel-cell with a typical efficiency of
~36% http://en.wikipedia.org/wiki/Fuel_cell#Efficiency, and the
efficiency of the electrical motor, wiring, and controller were 90%,
and the weights of the total systems were roughly equivalent, it would
appear that there would be a close approximation of performance of
today's aircraft including waste heat, but not noxious emissions nor
noise. I'm not sure exactly how the overall efficiency would be
affected by the use of pressurized oxygen, or if both the hydrogen and
oxygen were produced by the electrolysis of water by photovoltaics.
(Now, if the compressed hydrogen were carried in a tubular wing spar,
imagine it's rigidity... /dream mode)

Of course these rough theoretical calculations are predicated on
existing technologies, and don't consider the inevitable future
technical advancements.

Thank you for providing the catalyst that led to this insight into the
issue.


Electricity is great stuff, but damn awkward to carry around.

So it appears.

================================================== ===================

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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http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?