Newsgroups: sci.energy
Subject: Re: Internal Combustion Engines
From: srgxbhh@grace.dsir.govt.nz
Date: 11 Apr 92 14:18:05 +1200
Organization: DSIR, Gracefield, New Zealand

In article <1466300055@igc.org>, Environmental Studies School <ssu@igc.org> writes:
> 
> 	To answer some of your questions: First, a gaseous fuel is delivered with a closed, sealed pressurized carburetor. The main concern is getting all 
> fuel to the combustion chamber. As for low NOx, some fuels (i.e. Hydrogen) don't
> really have this problem. However, there are 2 methods that should help even
> without a catalytic converter. H2O injection should help, but may not be a
> total solution, depending on the fuel(this is best with propane, CNG and H2).
> A more certain method is to pre-cool intake air by drawing air through the
> radiator and then into the air filter.If you really want to maximize 
> performance and cut all pollution with an internal combustion engine, use H2.
> 
> 		- Matt Karber, SSU

I'm sure somebody with some knowledge of combustion will provide a more
comprehensive response, but some of the above appears to ignore the
documented problems of Hydrogen as a fuel for internal combustion engines.
Hydrogen does have a problem with NOx combustion products - as neither
gasoline or hydrogen have nitrogen in the fuel the NOx apparently are
produced from the nitrogen in the air. I believe some of the significant
factors are the combustion temperature ( the higher the temperature then 
the more NOx formed ) and the availability of oxygen ( lean operation ).

The NOx problem of Hydrogen fuels was discussed in New Scientist last
year, but I don't have a copy handy. I do have some information on the
flame temperature of premixed gases at atmospheric pressure and at
stoichiometric mixture that would suggest hydrogen would produce more
NOx than propane ( a typical gaseous hydrocarbon )

  Fuel         Oxidant         Temperature        Burning Velocity
                                degrees C            cm sec -1
 Hydrogen      Air                2045               324 - 440
 Hydrogen      Nitrous Oxide      2690                  390
 Hydrogen      Oxygen             2660               900 - 3680
 Propane       Air                1925                   43
 Acetylene     Air                2400               160 - 266
 Acetylene     Oxygen             3140               800 - 2480   

I'm not suggesting these are completely relevant to this discussion,
but I don't have data for combustion in engines optimised to perform
on the selected fuels. I also have vague recollections of other toxic
compounds ( peroxides? ) forming during hydrogen/air combustion, so it 
should not be assumed that the output is only pure drinkable water, although 
it will be a major component. The water content of exhaust gases from
common fuels  ( if my calculations are correct ! ) in % volume is
approximately :-

    Gasoline                         13.5
    Methane ( 70% of CNG )           19
    Methanol                         23.2
    Hydrogen                         34.6

Obviously Hydrogen combustion can not produce carbon dioxide, but the
flame conditions can cause dissociation? ( may be some other mechanism )
of other air components, thus providing additional exhaust compounds not
in the fuel or air.

Bruce Hamilton            SRGXBHH@grv.dsir.govt.nz