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Hydrogen as a Fuel for Automobiles

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Posted by The proud Infadel on October 10, 2003, 11:57 am
 
Hydrogen as a Fuel for Automobiles
On first glance, hydrogen seems to be the ideal fuel for automobiles and
other vehicles. It doesn't seem like one could get any cleaner burning,
since hydrogen burns (oxidizes) to form simply water vapor. No pollution!
What a seeming advancement over our current internal combustion engines that
put thousands of tons of pollutants into the Earth's atmosphere, as well as
giving off massive amounts of heat that contribute to global warming, and
many other environmental problems.
Hydrogen (H2) plus Oxygen (O) makes H2O, water, or actually, water vapor, at
higher temperatures. And Hydrogen is actually capable of nearly meeting
those high expectations.


Environmental Impact
There are a couple minor environmental issues. Our Earth's atmosphere is not
pure Oxygen, but it is a mixture of gases, with around 4/5 of it being
Nitrogen and around 1/5 being Oxygen, and a lot of other gases in small
amounts. When Hydrogen (or any other fuel) burns in our atmosphere, a lot of
heat is generated (which is sort of the whole point!) When the Nitrogen in
the air, it also can oxidize. It can combine with the nearby Oxygen atoms in
a variety of ways, such as NO2, NO3, N2O5, and many others. These new
compounds are collectively referred to as NOx, and they generally are
considered to cause an assortment of health problems in people and other
living things.
In addition to NOx production, if the device in which the burning occurs has
any lubricants, like oil, there are also oxidation products of the Carbon in
them, which can contain CO, carbon monoxide. When Hydrogen is burned in a
decently designed device, these environmental problems are fairly minor and
they are rarely considered to be any great danger.


Logistics
Hydrogen does have some more significant drawbacks. One of the most
difficult to deal with is that it is such a light gas! A pound of Hydrogen
contains around 61,000 Btus of latent energy in it, which seems like a lot!
For comparison, a pound of regular gasoline only contains around 20,500 Btus
in it! Sounds good!
However, a pound of Hydrogen is HUGE! At standard atmospheric pressure and
temperature, it takes up around 190 cubic feet of space. In contrast, that
pound of gasoline only takes up about 1/50 of a cubic foot.

We can say this same thing in terms of "gallons". A gallon of gasoline
contains around 6 pounds, or 125,000 Btus of energy in it. A gallon of
hydrogen (gas) only contains around 40 Btus in it. Quite a difference!
Instead of a two cubic foot gasoline tank (15 gallons) in your car, you
would need a tank more than 3,000 times bigger, over 6,000 cubic feet, for
the equivalent Hydrogen! That's a little more than TWO standard semi
trailers (8'wide x 8'high x 45' long or 2900 cubic feet each). Pretty big
gas tank!

Well, that is obviously not going to happen! So, the many ongoing
explorations into using Hydrogen as a fuel always involve carrying
COMPRESSED Hydrogen in very thick, heavy tanks. If you have ever seen the
kinds of tanks used for the Oxygen for a worker's oxyacetylene cutting
torch, that's the kind. Such tanks can hold Hydrogen at around 100 times
atmospheric pressure, or 1500 PSI, an extremely high pressure.

Well, at 100 times atmospheric pressure, the Ideal Gas Law tells us that the
Hydrogen would now only take up 2900/100 or 29 cubic feet. That works out to
around 60 of those high pressure storage tanks (to match the effective
capacity of the 15 gallon gasoline tank.). Each tank is very massive to
withstand the very high pressure, and each weighs nearly 100 pounds empty.
(And around 1/4 pound more when filled with Hydrogen!) So the normal
American car which presently weighs around 2800 pounds would have around an
extra 6,000 pounds added, so the vehicle would now weigh more than three
times as much as current cars! (This tremendously affects acceleration and
other performance, and it would be like that car pulling a huge 6,000 pound
trailer behind it.


Safety Considerations
There are obvious safety considerations in trying to drive a 9,000 pound
vehicle down the road. Handling and stopping would be very seriously
affected. But there is a bigger concern.
Those 60 very high pressure tanks present another complication. If
industrial workers ignore proper safety rules when working with a high
pressure Oxygen tank, it could fall over. As the hundred pound tank falls
over, it quickly develops a lot of momentum. If there should happen to be
something in the way on the floor, where the neck and valve of the tank hit
it, the neck and/or valve tends to just snap off. Suddenly, 1500 PSI of
compressed gas has an easy way out, and it all goes out almost immediately.
Isaac Newton told us about the Law of Action and equal Reaction. The hundred
pound body of the tank then zooms off at extremely high speed in the other
direction. There have been many industrial accidents where such Oxygen tanks
flew many hundreds of feet through the air and passed completely through
many concrete walls.

Most suppliers of industrial Oxygen display photographs of vehicles where
ONE such Oxygen tank had not been strapped down properly and the neck wound
up snapping off. Usually, the vehicles shown in those pictures are hard to
tell as being vehicles, except for maybe a tire somewhere in the picture.

Get the point? Imagine having 60 such tanks in a car. Either one vibrates
loose from its clamps, or the guy who last replaced them didn't strap them
all down properly, or an accident occurs where you hit another vehicle or a
tree. If even one of those tanks ruptures, bad things would result. And have
you ever even seen what happens to any car when a semi hits it?

Notice that this issue is not actually related to any hazard of Hydrogen
itself, but rather the fact that it would have to be stored at extremely
high pressures due to its very low density. Whether it was a high-pressure
Oxygen tank or a high-pressure Hydrogen tank, this danger is virtually the
same, and is entirely due to the pressure that the gas is compressed to.

Because of this extraordinary safety hazard, which is only due to the very
high pressures involved and really has nothing to do with the Hydrogen
itself, there is no imaginable way that the US Government would ever allow
such vehicles to be licensed. It would conceivably be safer to drive a
dynamite truck!


Cost Considerations
It would be wonderful if massive amounts of compressed Hydrogen were easily
available. In that case, except for the safety and size considerations just
discussed, Hydrogen would be a nearly ideal fuel for vehicles. However, no
compressed gas of any kind exists naturally and so mechanical compression is
required. An air compressor that can commonly be bought for $00 can
compress air to around 100 PSI, around seven times natural atmospheric
pressure. However, compressors that are capable of 1500 psi or 100 times
atmospheric pressure are very large, very complex, and VERY expensive. In
addition, every pipe and every fitting used must also be able to safely
withstand such pressures. (Normal pipes would just burst.) In addition,
whoever operated such a compressor would have to be very extensively
trained, to keep all of its parts from bursting from the pressure and
killing someone. The point: People are not ever likely to have their own
Hydrogen compressors, and so they would certainly always have to buy the
Hydrogen from some large corporation. Logically, it figures that that
corporation will be the very same ones that now own all the oil and gasoline
companies!
However, even if there was some way to do all that compression, it takes a
good amount of electricity for the compressor motor to drive the compressor.
A significant cost would be involved for that compression, even if you
somehow had your own compressor.

In addition, free Hydrogen does not exist. All of the Hydrogen that might be
collected is now in various compounds. The simplest to deal with is water.
If you had Chemistry in High School, then you hooked up some electricity to
an apparatus that contained water, and you saw little bubbles of Hydrogen
form in one upside down test tube and Oxygen form in the other. That is
called Electrolysis, or the Dissociation of water. It is obviously pretty
easy to do.

But those are just little bubbles of Hydrogen that you collect. Remember
that you are going to need an amount of Hydrogen that would more than fill
two semi trailers, to just equal one tank of gasoline! It is possible to
calculate the amount of electricity needed for that, but you must get the
idea that it is a LOT of electricity! So, you get to pay your electric
company for that, too.

So, you would wind up paying for the electricity to Dissociate the water in
the first place, plus the cost of the electricity needed for the extreme
compression. Of course, all of this would be after you bought the necessary
equipment!

An alternative, of course, would be to buy (rent actually) tanks of
industrial Hydrogen that is already compressed. Current prices for
Industrial Hydrogen (the lowest purity available) are around $2 for a
large, very high pressure tank which contains 197 standard cubic feet of
Hydrogen, plus a monthly rental fee for the tank. The 2900 cubic feet that
we had earlier determined were equal to one 15 gallon tank of gasoline,
would therefore be around 15 of these tanks, which would cost around $30
for the compressed Hydrogen plus the monthly rental of around $50 for the
tanks themselves.

We complain today at paying $ per gallon for gasoline, which would be $0
for our 15 gallon tank. How many people would be willing to pay $30 and
more for the same trip?


Flame Speed
Even if all the other hurdles are overcome regarding using Hydrogen as a
fuel, it seems to have yet another disadvantage, one that it shares with
most other gaseous fuels: the speed at which a flame front travels is rather
slow for the purposes of conventional engines. With an ideal Hydrogen-air
mixture, a flame front can travel at around 8 feet/second. For comparison, a
gasoline-air mixture creates a flame front speed that ranges from around 70
feet/second up to around 170 feet/second in normal engines.
Consider the inside of an engine cylinder in a normal car engine traveling
down the highway. The engine may be rotating at 2,000 rpm, or 33 revolutions
per second. The piston must therefore move upward and downward 33 times
every second, and its speed in the middle of its stroke is around 45
feet/second. If a fuel burning in the cylinder is to actually push down on
the piston, in order to do actual work in propelling the vehicle, the
fuel-air mixture needs to burn at a speed faster than the piston is moving!
Otherwise, the slow-burning mixture would actually act to SLOW DOWN the
piston! It would not only not do productive work, but it would require work
FROM the piston.

The fact that a Hydrogen-air mixture has a flame-front speed of around 1/10
that of a gasoline-air mixture seems to indicate that only a very slowly
moving mechanism could be used. That might be possible, but it suggests that
yet another hurdle might lie in front of Hydrogen ever becoming a common
motor fuel.


Conclusion
Yes, fuel cells, which are effective mechanisms for converting Hydrogen and
Oxygen into water vapor and releasing a lot of energy, certainly seem to be
fascinating potential sources of energy for vehicles. However, it certainly
seems that sufficient Hydrogen cannot be stored in a car for any length of
trip without compressing it to extremely high pressures. THAT fact causes
both cost and safety considerations which seem to make practical use of
Hydrogen remain a fascinating dream which will probably never become
reality.
Yes, Hydrogen can be demonstrated in experimental vehicles, and they can
have impressive acceleration and speed. But that's with a rather small
Hydrogen tank aboard. If you ever see an impressive demonstration like that
of a Hydrogen powered vehicle, make sure to ask how long that vehicle could
continue to perform like that. The answer is certain to be no more than a
few minutes at most. So, as a demonstration, Hydrogen can seem quite
impressive, because it is! But in actual practical applications, the details
probably make it never to be usable in our vehicles.



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Posted by Dave Hinz on October 10, 2003, 12:34 pm
 
On Fri, 10 Oct 2003 11:57:26 GMT, The proud Infadel

No pollution at point of use, perhaps, but how do you propose to get
the hydrogen?


Of course.  What fuels are you burning or reforming to get the hydrogen?
Logistical issues aside (your volume & pressure info), all this would
do is displace pollution from point of use, to elsewhere.  The folks at
"elsewhere" shouldn't have to breathe the pollution that the people at
the point of use are making.


Posted by Max on October 11, 2003, 3:43 am
 


I'm not sure if you realize this, but there are no fuels one can burn
to get hydrogen.

Posted by Dave Hinz on October 11, 2003, 1:31 pm
 
Really?  I assume you're getting it through breaking down water; what
energy source are you using to do so?  What fuel powers *that* energy
source?


Posted by Max on October 11, 2003, 4:41 pm
 

You probably don't realize this but electrolyzing water is not a
burning process.  
Please tell us, what fuel can one burn which will directly produce
hydrogen like you claimed.

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