Thank youThe trouble with evaporative cooling, is that if you pressurise the whole system it stops it from evaporating in the first place, its extremely difficult to allow it to boil-off at some point after the engine, and still maintain a high pressure inside the engine. There are a few things you can do with flow restrictions and so on to get the benefit without letting the metal temperature in the engine get too high, but its on a knife-edge the whole time, and if the engine power demand suddenly increases, you can get significant boiling happening inside the cylinder head etc, then you`re done for. There is a lot of interest in evaporative cooling today in automotive engines because of the very high cooling possible by allowing boiling (i.e phase change) you can get away with a much lower flow rate of coolant which means smaller pumps etc, but it requires a lot of very clever controls to make it work, which has so far not seen it being adopted in production. Even when it is set up perfectly the metal temps in the head in some typical studies are 10 degrees higher. Which might not sound much, but if you have a high performance engine, it might be enough to cause problems - and thats if it works perfectly. I`ve never used such a system, so I only know what I`ve read on it.
Some modern studies in evaporative cooling for engines are:
http://sro.sussex.ac.uk/id/eprint/63582/1/A REVIEW OF EVAPORATIVE COOLING SYSTEM CONCEPTS.pdf