[kasem]

Для химиков

From: Robert Harris <bob@bobthecomputerguy.com> 
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.