Hydrogen is a candidate fuel for non-polluting automobiles of the
future. Its combustion product is water. Aside from hydrogen powered
fuel cells, which are a remote possibility as an automotive power
source, if hydrogen were used as fuel for an internal combustion
engine, as a replacement for gasoline, the fuel explosion in the
cylinders would also produce nitrogen oxides, would it not? Although
CO2 is eliminated, other pollutants are formed. Thus, the question is:
Is it possible to design a non-polluting internal combustion engine?

knowitall22-ga,

Yes, NOx emissions are present in hydrogen powered internal combustion
engines (ICE), but they are substantially reduced compared to gasoline
powered engines.  I'll refer you to this article:

Ford P2000 Hydrogen ICE Car Debuts:
http://www.autointell.com/News-2001/August-2001/August-2001-4/August-22-01-p8.htm

As far as a nonpolluting ICE is concerned, let me offer this... Human
beings can be considered a source of pollution depending on where you
set the standard for a nonpolluting "engine".  In the process of
living we take in oxygen and produce substantial amounts of CO2 over
the course of our lives (our product cycle if you will).

Based on that comparison, lets consider a "nonpolluting" ICE.  The
engine has to emit something in order for it to produce energy from
chemical reactions (which is how an ICE works).  Lets assume that we
can use pure hydrogen and pure oxygen for our fuel and oxydizer. With
proper stoichiometric conditions we will emit steam (H20).

Of course, in the real world, "reality" gets in the way.
Stoichiometric conditions can be hoped for, but never perfectly
attained... Meaning that we will probably end up with some "polluting"
chemicals in the emissions.  At the very least, the engine will need
some kind of lubricant to keep it from seizing up. Lubricants, whether
synthetic or natural, are made of hydrocarbons and other chemicals.
The burning of the tiniest amount of lubricant and we will end up with
polluting emissions: hydrocarbons, CO, CO2, NOx, and others.

The real question is "what is an acceptable amount of polluting
emissions". You must also consider the manufacturing process for the
engine itself as well (since this can be considered part of the
product life cycle). Casting an engine block, producing rubber seals,
and making the various other parts of an ICE will produce polluting
chemicals.

Hope this answers your question.

krobert-ga

Thanks, Krobert-ga. As I suspected, there is indeed some NOx emission
from a hydrogen powered ICE. It is a lesser amount than a conventional
ICE (assuming the Ford engineers aren't fudging). The pollutants
resulting from construction are not relevant to operation. A
stoichiometric feed would require N-free oxygen supply...we can forget
about that. Apparently fuel cells are the few truly non-polluting
power sources known...if you don't mind waiting two hours for them to
warm up.
  I feel obliged to comment on your comment about we humans producing
CO2 and thus contributing pollution. Actually we, and all air
breathing animals exhaling CO2 have derived our carbon intake from
matter which has captured CO2
from the atmosphere somewhere in the food chain. Thus it is a
steady-state process which is in balance. It used to bother me that
our breathing increases the quantity of CO2 until I learned the above.
Similarly,trees and vegetation in general are touted as CO2 sinks but
actually are not. When a tree dies and decomposes, all its carbon is
released back to the biosphere. Just another example of conservation
of matter and energy.
Thanks,
knowitall22-ga

Dear Knowitall22,

You suggest that "Hydrogen is a candidate fuel for non-polluting
automobiles of the future".

It is easy to make the mistake of believing that hydrogen-powered
vehicles give rise to no pollution, but this is not the case.  There
is no natural source of hydrogen in the world, so it must be prepared
by a process that itself will create pollution.

One way is to split water into its constituent hydrogen and oxygen,
but this requires the input of as much energy  - in a practical
system, somewhat more - than that realised in the road vehicle.  This
energy can come from fossil fuels, in which case the same pollution is
created at the power station as would be if the vehicle used it
directly.  But it is possible, of course, to use nuclear energy or
renewables such as hydro, solar, wind, wave, and tide to create the
hydrogen, each less polluting that fossil fuels and impractical in a
road vehicle.

Another way of creating hydrogen is from hydrocarbon fuels, but this
is effectivley burning part of the fuel to create the hydrogen, and
again creates its own pollution.

In considering all this, it is worth separating the local and global
effects of pollution.  If we are concerned about, say, oxides of
nitrogen and of sulphur as injurious to health, then moving the use of
fossil fuels from the vehicle to the power station is an advantage,
both because the power station (unlike the vehicle) can be sited away
from dense population and because it is economic to provide
lower-polluting technology at the power station than is possible in
the vehicle.  Flue gas desulphurisation is surely cheaper in a power
station chimney than in a vehicel exhaust.  But global pollution, for
example oxides of sulphur contributing to acid rain and carbon dioxide
adding to the greenhouse effect, are not reduced by the use of
hydrogen: merely moving the emissions does not in this case reduce the
total effect on the global atmosphere, which is what matters.

There is a letter from an academic written to the Northeastern
Pennsylvania Times Leader explaining this at:

http://www.timesleader.com/mld/timesleader/4100273.htm

I trust this helps.

Carnegie

carnegie-ga: Many thanks for your comment. The phrase *non-polluting
automobile*
is of course not precise...it would have been better to use *minimum
polluting automobile* or the like. I am well aware of the problems of
shifting the energy source. As I mentioned above, the law of
conservation of mass and energy is another way of saying *no free
lunch*. CA legislators get a warm fuzzy feeling by passing a law that
requires a % of zero emission autos. The emissions are merely
transferred to the power plant, which may be more efficient in
controlling them, but they are not zero.
  You state that substituting H for other fuels would not reduce total
global pollution. But theoretically it could, if produced by nuclear
energy splitting water into H and O; there are no gaseous pollutants
emitted, even if one considers nuclear power as unacceptable. In the
quoted article, Anson argues that there is insufficient generating
capacity to produce significant quantities of H...true, but it is not
impossible to conceive the scenario. Anson lumps nuclear with other
power sources as polluting. Nuclear, solar, hydroelectric, and wind
power could theoretically split water without emissions.
Now, I am a retired chemist and I fully appreciate the conflict
between theory and reality, having battled it for 45 years. I am not
saying it will happen, only that it is possible.
Thanks,
knowitall22