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For a diesel, in my very ignorant opinion, having water in liquid form in the combustion chamber just cancels out the heat energy of the fuel. I had calculated exactly how many ml of fuel a liter of water will cancel in another thread.
Water in gas form displaces air (and its oxygen) so under high fueling it is reducing the capacity to burn fuel. It is beneficial if you are getting really high egts. But from an ecomodding perspective it is not much use in a diesel.
So when can it be beneficial for an ecomodder? If you cool the intake charge on a diesel efficiency goes up. So again in my very ignorant opinion, as ecomodders we do not run very high afr's. So the benefit comes from cooling i.e. the evaporative cooling of the water.
So if you filled your intercooler up to half with water the air passing through would cool down by extracting the vapor from the water. But this may not be preferred as you would be unnecessarily heating up the water. But if you measure air humidity, air pressure and mass then you can calculate the amount of water needed to bring it to %100 humidity. And that is the amount that will provide cooling. Any more and you have liquid water floating about.
The injection is beneficial (vs just having water stand around in the intercooler) as small droplets have a lot more surface area and are easier to evaporate.
PS: filling the intercooler is a stupid idea, it was just an example.
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