If you want to look at alternative liguid fuels for the existing fleet
consider Butanol (Butyl alcohol). It has about the same energy content as
gasolene, burns at the same air-fuel mixture and has an octane rating of 94.
It can be made from biomass at better net energy yeld than ethanol. Since
you can mix it with gasolene at any ratio with no changes needed in the
engines, it looks better to me than ethanol.

Bill Daniels


"Martin Gregorie" wrote in message
...
Capt. Geoffrey Thorpe wrote:
If we don't have the energy to extract the hydrogen, then what makes it
"the future"? I've never understood that angle - "we will need hydrogen
for when we run out of oil" - but we need oil to extract the hygrogen,
eh?

Seems to me like we need "something" as an energy source for when we run
out of oil, and what kind of fuel one would generate for transportation
would depend a lot on what that "something" is. Might be H2, very
possibly won't.

Hydrogen isn't an energy source, just a way of storing energy in a
transportable form, same as battery or biofuel.

It has a few disadvantages too - when you combine electrolysis to get H2
with fuel cell efficiency the overall efficiency is around 66%. Thats good
compared with an IC engine's typical 25-35%, but other storage methods,
e.g. Li-poly batteries, which have a charge/discharge efficiency of around
85%. The proof of this is that direct drive (no storage) solar electric
UAVs and those using Li-poly storage have already flown successfully but
no solar fuel cell system has, AFAIK, yet flown.

Now consider that liquid H2, which is what cars will probably run on. This
needs cryogenic storage (if you don't cool it to liquid you either need
heavy HP gas cylinders or you adsorb it in a carrier and that material
isn't all that light either). In practice cryogenic tanks boil off
hydrogen to cool the remainder, which reduces the overall efficiency by
15% if you immediately drive until the tank is empty and by up to 100% if
you just park the car.

I think some other liquid fuel, such as ethanol, would be a lot less
hassle, but, like hydrogen, it needs to be manufactured industrially using
solar or nuclear power if enough is to be produced to entirely replace
fossil vehicle fuels.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |