Re: Interesting engine?

On Tue, 6 Dec 2005 12:31:29 +0000, Chris Wells
<Chris.Wells.1zmm00@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

>
>Someone said >
>
>By coincidence, the energy in a gallon of liquid H2 is in the same
>ball park as a gallon of gasoline, so figure a 50 gallon tank. But a
>gallon of liquid H2 is just over 1/2 pound -1/12th the density of
>gasoline. That - and the need to keep it at minus 423 degrees F-
>makes for some interesting design tradeoffs. ;^)
>
>
>Can someone post a cite? Everything I can find suggests a gallon of
>liquid hydrogen has much less energy than a gallon of even automotive
>gasoline. I'm not quibbling, I'm really just interested in knowing the
>specifics. Thanks.

You hit a topic that I've just been researching and I have never seen
so many *different* results from comparisons or such bias in studies.
The only thing with more conflicting results and promises was Alcohol.

But I can give you a few specifics which should be undisputed.
First, to directly answer your question: A gallon of gasoline has
about 120,000 BTUs, A gallon of liquid hydrogen has about 30,000 BTU,
so it takes 4 gallons of liquid hydrogen to equal the energy in a
gallon of gas. So the weight savings although substantial is not
nearly as much as it appears.

*OTOH* I believe (I'm trying to relocate the source of that one) an
engine running on straight H2 can be about twice as efficient as one
burning gas. (this is not quite as straight forward as it sounds),
but that means we only need half as much fuel to go the same distance.

"In general" the industry thinks of Hydrogen like a battery, rather
than a fuel. It is an intermediary where you put in energy to make H2
and then you get the energy back out.

Like charging a battery it takes more energy to make Hydrogen than you
can get back out of it. It is difficult to make and costly depending
on the method used.

Proponents like to cite esoteric ways of making hydrogen that cost
little, such as wind and solar energy, but those are only dependable
in a few geographic areas. They forget that the installation of a
suitable solar array is quite expensive and depending on location the
maintenance can also be expensive. Wind generators are not cheap
either.

So in reality it's expensive and it's difficult to store in quantity,
but there is some promise in using metal hydrides as metal sponges.
Unfortunately you just lost the weight advantage when using metal
sponges for storage.

Like electricity, the energy to create the Hydrogen has to come from
some where and there just aren't that many places where solar and wind
are dependable and/or predictable.


Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
.

Relevant Pages

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