Water Injection for power?

Robert J. Harris bob at bobthecomputerguy.com
Tue Sep 10 09:42:21 GMT 1996


Remember the Reichstag

----------
> From: Thor Johnson <johnsont at falcon.mercer.peachnet.edu>
> To: DIY EFI Maillist <diy_efi at coulomb.eng.ohio-state.edu>
> Subject: Water Injection for power?
> Date: Sunday, September 08, 1996 4:31 PM
> 
> 
> I just looked at the current issue of "Midnight Engineering," and saw an 
> article that may be of interest.  The author suggested that, instead of 
> the usual fan/radiator/et al, the cylinders be cooled by injecting water 
> (diesel style) during the latter part of the power stroke.  The H2O would

> flash into steam, thereby changing the heat (normally exhasted) into 
> mechanical power.
> 
Why bother?  The British in their pre-war experiments with water injection
directly injected the water in a fine mist into the inlet of the mechanical
supercharger of the Rolls Royce engine powering the spitfire.  At any 
reasonable injection rate  engine thermal loss's went down as the per cent
rate of water to fuel went up.  If memory serves me correctly at about 30
percent the engines water cooling was no longer a factor.  Methyl Alcohol
was added in a small percentage as an antifreeze - tis no such thing as a
warm day at 30,000+ feet altitude.

I Remember two relevant curves - holding fuel constant, power went up 
linearly with water on a percent by percent basis.  100% fuel 10% water, 
+ 10% power etc. until a practical limit of about 50% was reached.

Holding power constant, each percent of water displaced a percent of
fuel until about a 50 50 ratio was reached.

WTF does it work?  70% plus of chemical energy released by combustion
leaves the engine as excess heat.  Absorb any of that EXCESS heat and
turn water to steam and you gain either power or fuel economy or both.

PS   Ever wonder what is really going on during combustion.  Check the
pressure temp curves of the three major gasses present after combustion.
CO2, N2 and H2O.  Check out how much partial pressure each contributes
to the mix.  Then remember, that as a rough approximate, one gallon of
gasoline makes 2 gallons of water in the exhaust. 

PS  During the 70's phony gas crisis's a dozen different people came out
with aftermarket water injectors.  About eighty bucks for a windshield
washer
pump, bottle and some very crude controls worth maybe 10 bucks. All of 
them varied the pump with the RPM and used various gimmicks such as 
"air temp" sensing to separate you from your dollars.  You can do much
better just by sensing airflow, computed fuel flow and metering H2O to the
FUEL flow and simply varied the percentage until you are happy.



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