Water Injection Thoughts

[Barry E. King]

> -----Original Message-----
> 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????

I wondered about something along these lines.  Fine idea.

> 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.

Even finer idea.  I am no stranger to castor based oils.  I ran 20:1 in my
Pro 250GP bikes for years.  Leftever pre-mix was tossed into the tow
vehicle's fuel tank since once mixed I either burned the fuel or dumped it.

> 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.

My tow vehcile seemed to like it.  I swear it kept the top-end cleaner not
unlike a bit of diesel fuel would now and then.

> 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.

Something worth checking.  I don't have a temperature sensor in the inlet
tract but plan to do that sometime.  I'd bet that once the I/C's are
heat-soaked the temperatures get up that high.

> 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 the droplets are small enough however, won't this effectively be the same
deal?  Clearly we don't want puddling, and we need "vapor" (small airborn
droplets) that can take heat from the air charge to allow more fuel to be
dumped in (but not so much that the water displaces required fuel).

> 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.

Hrm.  That is whacky.  Need to think on that.

> 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.

Absolutely.  Dynamic compression is what matters.

> 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.

Precisely, which is why my system is planned to engage at a settable MAP
level known to be the point where detonation is imminent with the given
fuel.  I don't plan to squirt below that level even though there would be
benefits.  I am looking for benefit during that "all out mode", not during
"normal" operation.

> 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.

I think this is called "reality", something best avoided (based on my
observation of other people).



Regards,

Barry