Theory behind water injection?
 

Just curious as to what exactly water injection does?

I may sound like a noob, but i've heard of people adding water injection systems to their engines and i just sorta wondered how exactly it increased performance..

It's to prevent the fuel from igniting early due to the rotor faces being too hot.

92% chance I'm wrong, but I'm bored.

Cools intake temperatures and raises octane, IIRC.

"The main function of these systems is to suppress detonation caused by high temperature and pressure developed within the combustion chamber when the effective compression ratio has been taken beyond the auto-ignition point by either a turbo or a supercharger."

"A turbocharger essentially compresses the air going into the engine in order to force more air than it would be possible using the atmospheric pressure. More air into the engine means, automatically, that more fuel has to be injected in order to maintain the appropriate stoichiometric value of the air/fuel ratio (around 14:1). More air and fuel into the engine leads to more power. However by compressing the inlet air the turbocharger also heats it. Higher air temperatures lead to thinner air and therefore an altered stoichiometric ratio which results to richer mixtures. Over-heated air intake temperatures can cause detonation.
Detonation, an effect also known as engine knock or pinging, occurs when the air/fuel mixture ignites prematurely or burns incorrectly. In normal engine operation the flame front travels from the spark plug across the cylinder in a predefined pattern. Peak chamber pressure occurs at around 12 degrees after TDC and the piston is pushed down the bore."

Yay for Google.com....

The water is dispersed through the intake charge and then vaporizes in the combustion chamber reducing the overall temp of the air making it denser. The exact same principal as an intercooler but using water rather than air-air heat transfer.

The system is usually run with water and or alcohol.

It also adds to the octane of the fuel being burned and allows people to run much higher boost on street gas. For example rather than needing c16 to run 22lbs, one may be able to run 22lbs on 93 octane + methanol injection.

In the end it just protection against detonation. Cooler/denser air.

also, in theory, water vaporizing into steam would increase pressure in the combusion area, causing a power increase and a cleaner burn

thanks guys, that makes alot of sense

Actually it will cause you to loose power due to the water taking up volume in the combustion chamber of where the O2 would have normally been before using water injection, it will make the tune run richer, so you have to tune and lean out the mixture to keep the same power levels. It does NOT cool the intake charge, it cools COMBUSTION temperatures.. now using straight Methanol will do both.

yup

dry air is DENSER than water vapour.

Cold and dry is best. hot and humid is worst

Yes, yay for google... incorrect information.

"Detonation, an effect also known as engine knock or pinging, occurs when the air/fuel mixture ignites prematurely or burns incorrectly." This is wrong. Premature ignition is a condition known as "preignition," and is completely seperate from "detonation." Detonation is purely a case of multiple flame fronts occuring at different times in the cylinder once the spark has occured. Usually the cause of detonation is a non-homogenous air/fuel mixture in different parts of the combustion chamber (I guess you could call it "stratification?"). This is why quench pads work so well: they squeeze the air/fuel mix from the hard to reach outside areas of the cylinder towards the center where it can ignite consistently.

Water injection not only cools down the cylinders, but the expansion to steam provides additional force on the crank, and the water actually facillitates combustion. If you want to know more than this, do some research yourself at www.waterinjection.info.