water into efi system before injectors.

[Greg Hermann]

>>Precisely. What is going on is the compression stroke begins to act a lot
>>more like an isothermal process than an adiabatic one. Consequently, much
>>less power goes into the compression stroke. Temperature at TDC (ignition
>>event) is MUCH lower--on the order of 235 to 250 degrees F, instead of 900
>>degrees or so.
>
>That seems like a *very* large difference - can you approximate the minimum
>level of water injection for the largest drop in TDC temperature ?

It's pretty much proportional. The 75 to 80% numbers that I gave are the
approximate upper limit, beyond which any more water is NOT beneficial. The
trick is to get it to where the partial pressure of water vapor in the
chamber just reaches "saturation" conditions --a bit more water, and the
chamber would be too cool, and some of the water would not be evaporated
due to no energy being available to provide the needed latent heat, a bit
less water, and the chamber would get a bit hotter, and the saturation
point with respect to water vapor pressure would not be reached.
>
 most people
>dismiss it as a waste of time and point to risk of corrosion to engine
>and exhaust from Nitric acids - reality is less Nox produced due to lower
>charge temp...There's also the inconvenience factor of adding water
>all the time.

This talk is mostly poppycock! As long as the temperature of the exhaust
leaving the chamber does not drop below the dew point of the acid involved,
not much danger of such corrosion exists, at least internally to the
engine. The CHANGE in water content in the exhaust is only on the order of
25 or 30% anyway, besides! Remember, water is already a product of
hydrocarbon combustion!
>
>Does it really have to be distilled water - can regular tap water be
>used given the turbulence in the chamber would likely flush out most
>deposits.

I would guess that any tap water up to perhaps 300 or perhaps 500 ppm TDS
(Total Dissolved Solids) would be just fine. Just use stainless fuel system
parts, and injectors rated for alchohol. Some solutes found in tap
water--particularly gypsum (calcium sulfate)--experience reduced solubility
as the water temperature rises, so one needs to be careful of this
phenomenon in the water plumbing near the engine (where it gets warm).
But--since the system is essentially a through flowing system, the
dissolved solids will not tend to build up in the system, as they would,
say, in a boiler, where the solids keep getting added, but only the water
leaves.
>
>One local did say that using WI for long periods results in far less
>carbon buildups in the chamber.

Absolutely.
>
>>Lots of folks don't realize that engines running straight methanol fuel
>>have _NOT_ evaporated all of the fuel at TDC!! Not enough work available to
>>provide the needed latent heat! The first part of the burn provides heat to
>>finish evaporating the fuel.
>
>mmm - Tah - never knew that either

It is why, despite the fact that methanol provides MORE heat of combustion
per pound of air pumped through an engine, the engine will have poor fuel
efficiency. It is also why methanal fueled engines have such a propensity
for fouling their plugs before they are completely warmed up.
>

>>Never seen any, Riccardo published as much as I have seen.
>
>Don't know of that - any pointers ?

"The Internal Combustion Engine"--by Sir Harry Riccardo.

You might also want to try "Internal Combustion Engines and Air Pollution"
by Edward F. Obert..

Try Amazon.com, that's where I got the latter.

Greg


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