Craig,
I'd always thought the photos of the hindenburg looked odd for hydrogen, the flame was
too bright, more consistant with the colors metals make when you stick them in the
flame of a bunsen. Also the light hydrogen should have rushed upward when released so
any fire ball should also rush upward. The hydrogen filled balloons we set alight back
in high school had no visable flame, and the heat haze signature rose very rapidly.
Hydrogen storage is important for the development of hydrogen as a fuel for cars. It's
a matter of what comes first the chicken or the egg. Fuel won't be at the bowser until
there are cars that can take it. Current storage practices include compressed gas,
liquified (as found in space shuttle boosters), or metal hydrides (where hydrogen
molecules are stored through absorbtion in metal powders. Personally I wouldn't want
liquified hydrogen or compressed gas bottles letting go in an accident . Metal
Hydrides give the highest kJ/Litre storage, about 50% more than the liquified storage
medium but are very heavy, still they have further room for development both in
kJ/Litre and kJ/kg whereas liquified doesn't. I'm quite sure internal combustion
engines can be relatively easily be produced for hydrogen. The major stubling block in
the past has been the storage aspect, and a cheap source of electricity to produce it.
As for the use of fossil fuels to produce hydrogen, it takes less energy to produce it
from fossil fuels than water, and fossil fuels provided a denser storage medium for
the hydrogen. It varies between fossil fuels but one fossil fuel molecule can store
enough hydrogen for many H2 molecules. However hydrogen isn't renewable until we are
producing it from water. If we are to go down the Fuel Cell/Electric motor path then
the hydrogen storage issue becomes a competition with batteries. kJ/kg, kJ/Litre and
efficiency ( best practice water to hydrogen is about 60-70% efficient at the moment,
combined with the 70% or so efficiency of fuel cells) become the issue as the hydrogen
is simply acting as a stable storage medium for the electricity energy that was used
to seperate the water.
Should be very interesting over the next twenty odd years!
Craig Overend wrote:
> Luke,
>
> I really can't see the point of storing Hydrogen on board a car at the
> moment. At one time there was a BUS in the US that was trialling running
> on a Hydrogen IC Engine, the problem is where does it fill up. NASA has
> used Hydrogen for years lifting the space shuttle into orbit and for the
> electrics on board using fuel cell technology, they use it because of
> its high energy content. I have read that GM were cooling the Hydrogen
> to something like -218deg celcius in order to store it for use with
> their fuel cell technology.
> I'm just waiting for onboard Hydrogen reformers to become available for
> use on Internal Combustion engines.
> GM and ExxonMobil have supposedly recently developed an on-board fuel
> processor/reformer that can extract 80% of the Hydrogen from petrol for
> use with their fuel cell. Funny their doing research on petrol to
> Hydrogen and not H2O huh? Problem is most current car electric motors
> will only do ~50kW, and storing and suppling the power for that
> continually is the problem. The new 42V system, is an improvment but
> only for accessories still nowhere near enough for a drivetrain.
>
> Check out the following information I found regarding different fuels.
>
> -------------
> Typical values for commercial fuels in megajoules/kilogram are [37]:-
> Gross Nett
> Hydrogen 141.9 120.0
> Carbon to Carbon monoxide 10.2 -
> Carbon to Carbon dioxide 32.8 -
> Sulfur to sulfur dioxide 9.16 -
> Natural Gas 53.1 48.0
> Liquified petroleum gas 49.8 46.1
> Aviation gasoline 46.0 44.0
> Automotive gasoline 45.8 43.8
> Kerosine 46.3 43.3
> Diesel 45.3 42.5
>
> Obviously, for automobiles, the nett calorific value is appropriate, as
> the water is emitted as vapour. The engine can not utilise the
> additional energy available when the steam is condensed back to water.
> The calorific value is the maximum energy that can be obtained from the
> fuel by combustion, but thereality of modern SI engines is that thermal
> efficiencies of only 20-40% may be obtained, this limit being due to
> engineering and material constraints that prevent optimum thermal
> conditions being used. CI engines can achieve higher thermal
> efficiencies, usually over a wider operating range as well. Note that
> combustion efficiencies are high, it is the thermal efficiency of the
> engine is low due to losses. For a water-cooled SI engine with 25%
> useful work at the crankshaft, the losses may consist of 35% (coolant),
> 33% (exhaust), and 12% (surroundings).
> ------------
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