Injecting prior to turbo comp' impellers

[hotrod]

Interesting concept!

You would also have the issue of ice crystals forming during the evaporation process, the alcohol will evaporate more rapidly than the water so you get a distillation process as the mist moves down stream. An ice crystals that form would have a more agressive errosive effect on the compressor than the liquid water, so that is one issue to avoid.

With Propane injection you also have a balancing act going on between charge density due to cooling and oxygen dilution by the propane. This increases the volume of gas that must be compressed. As a result of that I would think you are looking for a happy medium where you get the benefits of some charge cooling, some increase in fuel octane, and better vaporization in the combustion chamber without over diluting the intake charge the turbo needs to compress.

Like you mention the cooling effect occurs at the point the liquid changes to gas, so by moving the solenoid to the injection point the cooling would move to the nozzle.
years ago I used to work in a gas station and one of my dutied every night was to blow off the compressed air in a pressure washer tank. In that case the point of expansion was at the outlet valve and that is where the frost formed. It might be ideal in your application to run the liquid propane through a heat exchanger as it expands to capture that cooling power and use a finned heat sink to cool the air charge.

Larry