Turel
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Water's Role in Combustion Support
Water, though nonflammable, is not inert in the combustion process in an enclosed environment, most specifically in an internal combustion engine.
This is an article I read at another unrelated forum, that I found incredibly interesting, and wanted to share:
"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 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."
-T
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Marvin
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One of my books has an experiment to demonstrate that CO is non flammable in very dry air. Not something that would be printed now I think. It also
says that phosphorous can be distilled in very dry oxygen without noticable oxidation. Weird stuff. Fortunatly most fuels contain hydrogen so they
make their own water as they burn.
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Quantum
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Whats a 'haywood'?
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Turel
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Texts
http://www.amazon.com/exec/obidos/ASIN/007028637X/qid=107830...
http://www.amazon.com/exec/obidos/tg/detail/-/0122858522/qid...
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axehandle
Free Radical
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This could also be the explanation for the fact that black powder with a humidity of 5% burns much faster than BP with 0% water. I always wondered
why, it's counter-intuitive.
My PGP key, Fingerprint 5D96 E09E 365D 1867 2DF5 C2FE 4269 9C19 E079 CD35
\"Verbing nouns weirds the language!\"
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Turel
Hazard to Others
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H2O2, The N2O Killer
Makes me wonder intensely about the potential of H2O2 injection, instead of H2O injection. Liquid 20% w/v H2O2/H2O for example has far far far greater
available excess oxygen density than N2O gas.
A very small quantity of H2O2 could introduce the same mass of extra oxygen as a strong N2O induction, and would be much safer (not to mention cheaper
and easier to implement) as well. Not only would this provide a higher concentration of oxygen, but it provides it in the exact form responsible for
oxidation of hydrocarbons, according to the article.
If hydroxyl radical is indeed the prime oxidizer and catalyst, and it is indeed largely produced by splitting of HOOH molecules, then providing oxygen
in the form of H2O2 would be superior to providing it as diatomic oxygen gas.
Very interesting indeed.
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