water injection and then some (long!)

[Greg Hermann]

>Chris,
>
>are there any other side effects to water injection? Like corrosion, oil
>contamination in case of less-than-perfect blowby? Would you use a set
>of spare injectors to the manifold (say below at 180°) to inject water?
>
>Also, this would be an absolutely great solution to the problem of
>detonation, but wouldn't you have to re-calculate the efforts in the
>connecting rods and wrist pins to account for the increased momentary
>pressure? I am not sure that all stock rods (especially Honda's, heh)
>could take that?.. I will go back to the open-system analysis and try to
>figure a few orders of magnitude. I do not find it so obvious to figure
>it with forced induction.
>
>Thanks for the great input,
>
Most engines will take higher pressures OK It is higher temps which get 'em
for the most part. Also sharp spikes in pressure (such as with detonation).
For the most part, H2O injection lowers the temps, and raises the pressures
slightly more than enough to make up the difference. But the added
smoothness and lower peak temps is IMHO, more than enough to make up for
the added pressures in terms of mechanical strength of parts.

I realize that Cummins' and Hondas are different kinds of animals--but look
at the tractor pull 855's that are running 150 psig boost (and more) on a
block that was originally built to run NA!! This gives a pretty vivid
illustration of how far pressures can be raised without catastrophic
effects on the mechanicals.

Quick fix for something on the ragged edge might be to lower the red line
for a motor by 500 or 800 rpm, and raise the boost enough to more than make
up the difference. Bottom end stress has a whole lot more to do with
turning it fast than with cylinder pressures.

This illustrates the farce in the claim that Indy engines should have
gotten less expensive on account of boost limitations--all the boost
limitations did was force them to turn faster to get their power, and thus
drive the costs up, not down!!

As to the oil contamination, H2O is already a product of combustion, all
you are doing is adding a bit more. The lower piston crown temps with water
injection probably help the oil (less oxidation) more than the extra water
hurts it. Plus, the lower peak temps MAY (a little help here, Chris??)
reduce the formation of some chemical precursors to acids which really chew
oil (and other things ) up pretty badly.

What does deserve (and rarely gets) careful consideration in terms of  oil
contamination is that both sulphuric and nitric acids have much higher dew
points than water. In the real world, this means that the first thing to
condense on a too cool engine surface will be rather strongly concentrated
, highly corrosive acids. A seriously water injected engine might burn
enough cooler to justify running a significantly hotter thermostat in order
to help avoid acid condensation! I SUSPECT that this phenomenon may be the
real root of corrosion troubles in alky motors, too. OVER cooling is NOT a
good thing. Boiling point of sulfuric acid at 1 bar is about 350 degrees F.

Regards, Greg