WATER INJECTION CHEMISTRY
 
 
The first thing that happens is a plasma
cloud is formed by the arc consisting of super heated electron stripped atoms.
When this cloud "explodes" a ball of high energy particles is shot outward. 
 
The highest energy particles are the hydrogen atoms - and they penetrate the
charge about 5 times as far as the rest of the particles. As they lose energy
and return to normal temps - about 5000 k - they begin to react chemically
with any surrounding fuel and oxygen particles. The effectiveness of spark
ignition is directly related to the availability of free hydrogen. Molecules
containing tightly bound hydrogen such as methanol, nitromethane, and methane
are far more difficult to ignite than those with less bonds.
 
During combustion - water - H2O ( present and formed ) is extremely active in
the oxidation of the hydrocarbon. The predominate reaction is the following:
 
 OH + H ==> H2O
 H2O + O ==> H2O2
 H2O2 ==> OH + OH 
 Loop to top and repeat.
 
The OH radical is the most effective at stripping hydrogen from the HC
molecule in most ranges of combustion temperature. 
 
Another predominate process is the HOO radical. It is more active at lower
temperatures and is competitive with the H2O2 at higher temps.
 
 OO + H ==> HOO
 HOO + H ==> H2O2
 H2O2 ==> OH + OH
 
This mechanism is very active at both stripping hydrogen from the HC and for
getting O2 into usable combustion reactions.
 
Next consider the combustion of CO. Virtually no C ==> CO2. Its a two step
process. C+O ==> CO. CO virtually drops out of early mid combustion as the O
H reactions are significantly faster and effectively compete for the available
oxygen.
 
Then consider that pure CO and pure O2 burns very slowly if at all.  Virtually
the only mechanism to complete the oxidization ( Glassman - Combustion Third
Edition ) of CO ==> CO2 is the "water method".
 
 CO + OH ==> CO2 + H
 H + OH ==> H20
 H2O + O ==> H2O2
 H2O2 ==> OH + OH
 goto to top and repeat.
 
This simple reaction accounts for 99% + of the conversion of CO to CO2. It is
important in that fully two thirds of the energy of carbon combustion is
released in the CO ==> CO2 process and that this process occurs slow and late
in the combustion of the fuel. Excess water can and does speed this
conversion - by actively entering into the conversion process thru the above
mechanism.
 
The peak flame temperature is determined by three factors alone - the energy
present and released, the total atomic mass, and the atomic ratio - commonly
called CHON for Carbon, Hydrogen, Oxygen, and Nitrogen. The chemical
reactions in combustion leading to peak temperature are supremely indifferent
to pressure. The temperatures and rates of normal IC combustion are
sufficient to cause most of the fuel and water present to be dissociated and
enter into the flame.
 
As can be seen above, water is most definitily not only not inert but is a
very active and important player in the combustion of hydrocarbon fuel.
Ricardo and others have documented that under certain conditions ( normally
supercharged ) water can replace fuel up to about 50% and develop the same
power output, or that the power output can be increased by up to 50% addition
of water. This conditions were investigated by NACA and others for piston
aircraft engines. It is important to note that these improvements came at the
upper end of the power range where sufficient fuel and air was available to
have an excess of energy that could not be converted to usable pressure in a
timely manner.
 
As a side note - Volvo recently released some SAE papers documenting the use
of cooled EGR to both reduce detonation and return to a stoic mixture under
boost in the 15 psi range - while maintaining approximately the same power
output. Notice - they reduced fuel and still get the same power output.
 
When you consider that EGR consists primarily of nitrogen, CO2, and water ( to
the tune of about two gallons formed from each gallon of water burned ), you
might draw the conclusion that it also was not "inert". They peaked their
tests at about 18% cooled EGR - which would work out to about 36% water
injection and got about the same results under similar conditions that the
early NACA research got.

The carbon cleaning effects of WI are well documented. I've never pulled the heads on a WI car but have seen first hand the effects of water on carbon build up.

Many years ago 1950-1970's it was a common tune up "trick" used by many hotrodders to remove carbon buildup on the high power V8's in use at the time. Carburators were jetted quite rich to control high load detonation.

Carbon build up became a problem, especially in the 1970's when the oil crisis hit and folks were trying to run cheaper grades of fuel or high octane fuel simply disappeared from the market.

We would take an engine that was well warmed up, set it at a fast idle and trickle a thin stream of plain old water down the throat of the carburator, gradually opening the throttle until you got to about 3000 rpm or so, then increase the water flow until the engine seemed to have trouble with the excess water (sounded like the engine was strangling). It is truely astounding how much water you can pour down the bores of a large V8's carburator at a high throttle setting.

On an engine that had heavy carbon build up on the spark plugs prior to the "treatment" they would be nearly as clean as new if you pulled them afterward. If the engine was pinging due to carbon build up, it would magically go away after just a few minutes of this process.

Red hot carbon and steam react in a process called the "water gas reaction" --- look it up. It converts the carbon to gaseous CO and hydrogen both of which burn off inside the engine. This was used to by industry for many years to produce combustable "water gas" ( substitute for natural gas ) from coal.

You may need to back off your excess fuel a bit if you add water injection, to avoid a slight power loss caused by the combination of too much fuel and WI, but that would be the only down side I can see.