Originally Posted by VetteOwner
that and i dunno, sure it might work in theory, but water and metal usually doesnt =good. especially the fine machined smooth walls of a cylinder....
You get plenty of water in there just by burning hydrocarbons
water expands 1600 times when it changed to steam which adds to the pressure in the cylinder giving you more power.
At the cost of heat -- a phase change like that requires a helluva lot of heat... More heat going into phase change will mean lower temperatures = less thermal efficiency. (ideally, you'll have lower temperatures and more entropy to yield equivalent efficiency). That is unless you're dealing with an engine that has problems with knock and compensates by adding more fuel. That assumes the engine management is monitoring knock
The theory that makes the most sense to me (when you're not doing this to prevent pre-ignition) is that water displaces available O2 effectively reducing the fuel required to maintain ~14:1 a/f.
Keep in mind that the reason water injection was used on WW2 planes is directly a result of engine knock. The choice was to go with a less powerful engine, or increase power with water injection. So yes, it was done then - but for different reason
I remember coming across an SAE paper (or a book from the library
) on WI from the 80's or something like that.... Going off of memory, I think their testing found an increase in unburnt fuel emissions, a reduction in NOx and no appreciable change in CO2 emissions. I'll have to see if I can find the specifics and a citation