[hotrod]

The 10 micron drop size would be ideal, but appears to not really be necessary in a practical real world system.

Most common spray mist nozzles can achieve sprays with drop sizes down near 50 microns, plus you have evaporation that takes place as the mist moves down the induction path, which reduces the maximum drop size.

I just finished a turbocharger swap, and I took a good look at the compressor impeller on my old turbo which I had pre-compressor injection on for several months at about the 3% rate. (4 GPH nozzle max rated air flow for the compressor at sea level is about 25 lbs/min. Here at altitude of 5800 ft it is probably about 20 lbs/min.)

If the nozzle was spraying at its rated 4 GPH that would be about 252 cc/min or about .55 lb/min which works out to 2.7% of air mass at max flow. My turn on point is 8 psi so at the turn-on air flow, the mass fraction would be higher, probably near 5%.

On casual examination you could see no evidence of compressor blade errosion, just the normal discoloration you see after the turbo has been in use for some 37 thousand miles. On very careful examination under high magnification (about 10x), you can just see a small bit of roughness on the outermost 1 - 2 mm of the compressor impeller blades at the very leading edge.

I will need to do a similar examination of another turbo of the same design that was never exposed to water injection to determine if this is normal wear. This engine (like most Subaru WRX engines) has a crankcase breather inlet in the inlet tract a few inches ahead of the turbo inlet. Under high boost, these engines can blow noticiable amounts of oil mist into the intake. This over time results in a build up of a very thin layer of oil and dust "crud" on the inside of the inlet pipe and I'm sure that from time to time bits of this crud, and small oil dropplets gets suspended into the intake air stream under high air flow conditions.

I also on 2 occasions ran this engine with no air filter for a couple of drag strip passes to determine how much influence air filter resistance had on performance, so there was most likely a small amount of dust ingestion from those experiments.

Lastly when I first fabricated the system I assembled the prototype with a 35 psi pump which would not have given best misting behavior by the nozzles. The last couple months was with the system running at 100 psi max pump pressure which should have given a much finer mist.

Larry