Water injection in a NA engine.

[tommurphy73]

This is a quote from another forum. I wish I had paid more attention in chemistry class but it sounds really interesting. What do you guy think. Would water injection in a NA engine increase power and/or increase fuel efficiency? Water would be a little less expensive than oil at more than $80 a barrel today.


From: Robert Harris
To: DIY_EFI@lists.diy-efi.org
Subject: Water and its effect on combustion.
Date: Mon, 10 Jul 2000 10:24:08 -0700
Message-ID: <9ptjms0uu4oe292mpk6a6vhm2hn8bu9h1j@4ax.com>

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.

quote" The effectiveness of spark
ignition is directly related to the availability of free hydrogen". Actually it's directly related to atomization.




The following SAE paper seems to be in total disagreement with the above Water Addition to Gasoline--Effect on Combustion, Emissions, Performance, and Knock



Best Regards

[Cammer]

Several spark ignition theories exist.

Yes, I said theories!

While many profess to know what goes on in a running engine we are just beginning to understand some of this puzzle.

A running engine does not do the same thing twice!

____________________

[tommurphy73]

Some further info supporting the addition of water can give rise to increased fuel efficiency and power. However it appears that the improvements are available only in jet engines where the combustion temperatures are much higher. Maybe with very high compression ratios and suitable air/fuel ratios the combustion temperatures might be suitably high to reap some of the benefits.


Gasoline-water emulsion - Patent 4158551

[Stan Weiss]

Try searching the internet. Water injection use goes back to piston driven aircraft in W.W.II

[rskrause]

I have done a little experimenting with it on a chassis dyno. Not enough to prove anything. Don't have the time to really pursue it but here's what I suspect: on applications where timing has to be retarded to supress detonation it may offer an advantage. That is to say it will allow optimal timing by raising the resistance to detonation. The experimentation was on an LT1 with the knock sensor enabled. It appeared that the knock sensor was retarding the timing less with water using 89 octane unleaded swill. There was less retard and more hp with the water.

The LT1, in case not everyone is familar, is a "gen 2" SBC . Just like gen 1 but with an optical distributor and relatively high compression with reverse cooled aluminum heads. It is prone to detonate even on premium unleaded and therefore has a pretty aggressive knock sensing circuit.

BTW: the injection fluid used was a 50:50 water:methanol mixture.

Richard