Water and its effect on combustion.

[Bruce Plecan]

Thank you Mr Harris,
I was hoping one of the smart guys would jump in with the Plasma mention.  I
got as far as spark, and ran out of vocabulary.   Was sharping pencils while
thinking about Plasma.

Anyone have a good current definition of inert, my teachings were the only
inert things are Argon Zeon Neon, and a couple other gases.
Thanks
Grumpy




> Let us take a quick look at ignition.  Those who have a Heywood can look
it up
> - mines on loan so going by memory.  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 methanal, 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 st
ep
> 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 develope 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.
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