the_zerox said:
Can anyone tell me why water injectors (into the intake or TB) do not damage an engine ie, common sense would tell me that you would have problems with oil and water mixing or rust right?
Z
In properly executed water injection systems, no damage occurs for several reasons:
First, the water is atomized by either a nozzle/pressure arrangement (similar to how a spray bottle works) or ultrasonically (like those heatless humidifiers you might have seen) and enters the intake tract as a fine mist. Even if it made it all the way to the combustion chamber in this form, it would still be compressible as opposed to a volume of liquid water.
One of the key things about water injection is that the general idea is to not have the water enter the combustion chamber in even an atomized form but as a vapor. When you boil a pot of water, the "steam" you see doesn't actually appear until a little bit above the surface of the water and is simply vapor that has condensed back to an atomized liquid form. You can't actually see the vapor because its, for all intents, a gas. The bubbles you see in boiling water...they're water vapor bubbles, not air.
In order for the atomized water to vaporize, it needs to absorb heat from its surroundings - the air in the inlet tract - and this is what water is quite good at doing, with a fairly high latent heat of vaporization. Because of this, the intake air can be cooled quite a bit (of course, how much depends on the heat of the incoming air: compressed air (i.e. turbocharged) is far hotter than ambient air and thus more heat transfer can occur if more water is added.)
As far as rust, the combustion chamber of an operating engine is an environment where that doesn't much support the formation of oxides of iron. Indeed, one of the byproducts of normal combustion is water. The heat of combustion, oil washing, wiping action of the rings and even the mixture swirl all ensure that the water isn't resident on the cylinder walls long enough to start oxidizing the iron.
The oil will be fine too. If enough water is injected to wash as a liquid into the sump, the engine probably would have grenaded due to hydro-static lock so water-dulited oil is the least of the engine's concerns. The amount of water injected is (should be!) really small.
Of course, in the old days (back in the 70s

, it wasn't uncommon to take a garden hose set to a trickle (and I mean a trickle!) and feed that directly into the air horn of the carb while revving the engine. The general idea was that the water would flash-vaporize in the combustion chamber and would literally steam-clean the piston crowns and heads etc. I'd never do that now, but lots of engines survived the process
