Mailinglist Archive: opensuse (5130 mails)

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Re: [SLE] Warning to Americans!(now going OT)
  • From: David McMillan <skyefire@xxxxxxxxxxxx>
  • Date: Wed, 03 May 2006 15:39:24 -0400
  • Message-id: <445906EC.6070109@xxxxxxxxxxxx>
Kevanf1 wrote:
On 02/05/06, James Knott <james.knott@xxxxxxxxxx> wrote:

Kevanf1 wrote:

> There are alternatives but one is branded a conspiracy theorist if you
> so much as hint at the oil companies perhaps keeping them quiet. There
> is no reason why we shouldn't have safe engines running on
> water. There is no need to have a tank of highly flammable hydrogen
> gas (from the split H20) as it can be split in small quantities and
> fed into the engine that way.


Splitting water into hydrogen and oxygen takes energy. Where does that
energy come from? Remember, you can never exceed 100% efficiency and
are unlikely to even reach it.

Solar power. Admittedly, solar panels take energy to make them but I
don't think they break down fast. So, this would mean that the energy
put into making them can be regained from the use of the sun over its
lifetime. The solar energy is then used to split the water. It
doesn't take much in the way of electrical power to produce the two
gases after all.

..have you ever done the energy calculations for this? I doubt there's a solar array on Earth small enough to fit onto a car that can crack water into H2/O2 fast enough to keep up with the demands of an internal combustion engine. Solar is good for a slow, steady *trickle* of electrical power.
Not to mention, H2 as a gas is compressible -- water is *not.* And H2, even if you liquify it, is a huge headache for storage, handling, and has literally the worst mass/volume ratio going -- ask any rocket scientist. The *only* reason that it's used in rocket engines is that it gives just about the best ISP possible for current technology in an engine that has enough thrust to get from sea level to orbit (ion engines and their kin have much higher ISPs, but have thrust levels measured in ounces). There's a vigorous minority among rocket scientists who believe that LOX/Kerosene comes close enough to matching LOX/H2, once you consider the mass savings in the huge cryogenic tankage that H2 requires, that if you're going for overall efficiency rather than max performance, LOX/Kerosene probably makes a better choice.
To match the total energy of a tank of petrol, you have to have a *much larger* volume of H2 -- the fuel/air ratio is backwards. An ICE burning petrol uses a small amount of fuel combined with a large amount of air. An ICE burning H2 would have to use *twice* as much H2 as air, even if the air was pure oxygen -- with open air being largely N2, it's even worse (note to chemists: I'm leaving aside molar numbers vs volume for the sake of simplicity). You can beat this to a certain extent by using compression, but H2 doesn't compress well, being the lightest element (hence the headaches for rocket scientists). And sufficient compressions produce explosion (from pressure, not falmmability) and/or cryogenic hazards.
This is all why most of the leading work in H2-powered automobiles has been concentrating on using H2 "sponges" or fuel-cell equivalents, rather than gaseous H2. If carrying a tank of water and electrolyzing it on-the-fly were *that* easy, we'd be doing it already. And if the automotice companies weren't, then the DIYers who build their own electric cars would be.

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