How does water injection work?

[TylerEss]

Why are we all talking about latent heat of vaporization in intake charge temps? The boiling point of water is 100C/212F and Ethanol is 78C/170F.

Unless we're running charge temps much higher than those numbers, we're not going to get any vaporization going on in the intake tract. Furthermore, if we ARE getting vaporization happening, we're not going to be able to drop our charge temps any lower than that boiling point.

All we're doing is adding more thermal mass to the intake charge (in the form of water or ethanol), "spreading the heat around thinner" and that's what's dropping our charge temps.

The preignition fighting action of water injection can't possibly come all from this small drop in intake charge temp, can it?

[Frank]

Great question... this is my understanding... please correct me if I am wrong.

Charge temperatures go pretty high, especially once you enter the heat soaked plenum and port. In addition, the mixture is even more homogenized in the combustion chamber during combustion and swirl. After intercooler temperatures can be seen in the order of 130 to 180 degrees on variously sized intercoolers and boost levels. In addition, I believe vaporization and boil point is not the same??? I know the later happens at at 45C when it is a gas. So is it a liquid or gas when it is atomized by a mister or injector in the airstream? Adding water or methanol slows the burn rate, which allows for more timing. Detonation can still occur, however the effects of it begin later in the piston travel where normal pressures are experienced. This is the primary reason for doing it. The removal of BTU's in the charge air is just a nice side effect which promotes better flow and mixing.


Frank

[turbovanman]

Your doing 2 things, cooling the air charge down which has more oxgyen and cooling the combustion chamber down which fights preignition, detonation and lets you run cheaper gas or more timing or both!

Have you sprayed yourself with a fine water mist on a hot day, you instantly feel cold, thats basically what happens when you spray water into the intake. I don't know the exact theory but that works for me,

[Aries_Turbo]

evaporation is different than boiling point... if it werent, rain would never evaporate and we'd be swimming all the time. the combination of the cooling of the air due to evaporation and the slowing of the combustion process is the reason for the increase in knock resistance. Frank, my charge temps are ~110-115 in the summer with my cooler when at normal speeds. lower than 130.

Brian

[Frank]

Playing safe with cooling temps, etc. I know some coolers are pretty warm even when they are advertised that they shouldnt be.


Frank

[Aries_Turbo]

gotcha

yeah mine runs pretty cold which is fine by me

Brian