Water Injection Thoughts

[Robert Harris]

For those considering the use of normal fuel injectors for water injection,
consider adding some lubricant to avoid the corrosion problems.  For straight
water, nothing beats dirt cheap machinist's cutting oil - completely water
soluble.  About 3 tablespoons per gallon (memory serving me right) and it
makes the milky white lubricant that you see around all machine shops. Enough
to lubricate but not enough to effect combustion.  PS this two buck a can
stuff makes about 500 gallons or more of "water pump lubricant" - who says
there is no profit in hucksterism????

If you are running some alcohol or other joy juice, consider adding synthetic
castor oil ( two cycle oil ) in a small percentage.  Its a truly excellent
lubricant and its good enough to be the sole lubricant for a 20,000 rpm plus
two cycle engine after being diluted by straight nitromethane and methanol -
stuff that turns auto oils into yellowish snot.  Remember that model airplane
fuel is a blend of nitro, methanol, and oil.  And these fuel components are
less than kind to metal - yet they last a long time and only professionals
bother to flush and spray lubricate yada yada yada.

A side note - some karters running four cycle engines add synthetic castor oil
to the fuel.  They report the engine runs smoother and about a 1000 rpm
faster.  Makes sense.  A small amount of high quality lubricant with extreme
film strength would keep the cylinder above the rings lubricated and might
have a significant effect on friction.  Remember again - this in not Dino Oil
- tis a very high temperature lubricant designed to lubricate in a highly
corrosive mixture all the rotating and sliding parts of a two cycle engine and
have a minimal effect on combustion.

A last thought on evaporation.  The evaporation rate of water is very low
below its boiling point 100c stp.  Unless your intake charge temperature
exceeds 100 c or hot spots in between, you will be carrying droplets into the
cylinder.  The primary effect of adding methanol to water for injection is
that it greatly increases the evaporative cooling effect, even though alcohol
will absorb less than 1/4 the total heat that water will.  Due to lower
boiling point and far faster evaporation rate.  Simply atomizing water will
not cause it to change from a liquid to a vapor - it takes 100c STP to
accomplish that.  

If you were "whacky", you might consider adding steam after the throttle at
*** PART THROTTLE ***.   This would greatly reduce the pumping work and
recover some waste heat.  At less than wot, this would not cause a loss of
power.

David Vizard has written repeatedly about water injection and high compression
NA - considers it an excellent compromise.  Small factoid to consider.  Ignore
geometric compression ratio - geekishly useless trivia.  Consider effective
compression ratio.   Static effective compression ratio is the cylinder volume
at intake valve closing divided by the chamber volume at piston TDC - a number
that is considerably less then geometric and reflects the effect of cam and
rod geometry as well.  Dynamic effect compression ratio is simply static
effective compression ratio multiplied by volumetric efficiency ( VE )  100 %
= 14.7~ PSIA in the cylinder.  Boost increases it accordingly.  Throttle
reduces it.  

Water injection for detonation control is needed only when the dynamic
effective compression ratio exceeds the octane rating of the fuel - usually a
very small percentage of time.  Vizard and others recommend using just enough
to control detonation.  More than that takes you into diminishing returns -
but hey, I like being out there anyway.  Too much, too much, too much is never
enough anyway.

For perspectives sake - think about PC magazine - where the goodness of the
review is factored by the bigness of the advertising spread.  Ever see an
advertiser with 5 pages of ads get slammed in a review?.  Corky Bell sells
intercoolers at a grand a pop - electronic wazoo whoop de do's at bazillions
etc.  It would not be in his own enlightened self interest to slam a simple
effective way that does not transfer massive bucks to his wallet.  But I guess
I am cynical to think that simple water injection - good enough for WWII
fighter pilots to bet there life on, proven and effective for almost a century
is now junk and must be replaced by Crock of Sheeeets latest high priced
catalog wonder item.  Silly me.






The Luddites were RIGHT!!

Habaneros - not just for breakfast anymore