Geoff Knight here. I have been building turbo and SC systems since the mid 70's and we used W/I and W/Alcohol/Inj for many years. There are some things that do happen--depending on the purpose of the injection. Yes, for W/I was use as an anti-detonant for the turbo & supercharged WW2 fighters, as well as NOX. The water-alcohol was used with great success. Alcohol was included to eliminate freezing of the water. We used it in the 70's to raise boost capabilities as 89 octane was as good as it got, and 5 psi would cause detonation w/o injection on a wedge-head V8. With water-alcohol we could run 7-9 psi. Alcohol is 100 octane+, so that helped a bit, and the water lowered the EGT by several hundred degrees. There was somethjing else that we discovered. The elimination of carbon buildup on the combustion chamber, as well as elimination of additional fuel enrichment was a benefit fof W/A injection. In a book I have somewhere there is a graph that shows the addition of water to a supercharged engine during testing in the 30's in France. The results were that the mixture needed only to be slightly richer, and the water seemed to cool the combustion process to the point of eliminating fuel enrichment completely. Cool stuff.
In ' 78 I worked with a retired Colonel who invented something awesome. A ceramic ventury was glued into a tube. The tube had a hole in it allowing distilled water to be added to the area between the ventury and the tube causing air which passed through the tube to pick up 100% humidity. Ceramic is porous, so the ceramic 'cone' would only allow water in particles to escape through it. It was called the 'Power Pack', and was featured on a 100mpg car on the TV show 'Thats Incredible'. There was a tremendous amount of world-wide testing which proved some crazy things--and this went on for years. A huge increase in negative ions was one thing that had everyone puzzled. Like driving in a constant thunderstorm, the fuel economy would go through the roof. We tested hundreds of cars, as well as Semi trucks. The Semi's gained .5 to 1 MPG, and when a trucker goes from 4MOPG to 5 MPG he is quite impressed. UPS tested some as well. The colonel and I even took two cars to the EPA testing facility in Wash, DC. A Mazda GLC 1.5 liter getting 70MPG, and a huge behemoth 460 Grand Marquis getting over 20MPG. A week later both cars were stolen--no bull, and all the 'stuff' dissappeared as well. While at the EPA for testing, we received the initial report by accident from an engineer who did the first city cycle simulation dyno run. CO, HC, etc were all down, and only CO2 & NOx remained static. In some areas the NOx went up 1-2% because it is a function of combustion chamber temps. But HC and CO were down a TON. MPG was WAY up (20%+) For comparison testing all they did was remove the water from the ventury and allow the unit to fully dry--no other mods were done. However, when the 'official' report was received several weeks later, all the results were WAY different. Everything was the same as stock or worse. I saw these with my own eyes--it is scary sometimes to think what is done by certain segments of the gvmt.
There are a lot of unexplained functions when using water during combustion. Water has two molecules of hydrogen and one of oxygen. Obviously the temps are not enough to seperate the molecules, but I am sure they are somewhat destabilized. That in itself could be some of the answer. Combustion temps run 600-800 degrees during cruising, and the water could lower that by a considerable amount, as well as eliminating the carbon buildup inside the combustion chamber. For anyone who has ever dismantled an engine after w/i is added, you will think the engine was just built. Not a trace of carbon will be left in the combustion chamber. This holds true for a 100K engine--if run with w/i for several months it will look new inside.