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And I remember Larry had a similar picture here somewhere. The damage was not so severe, though.
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My compressor erosion pictures are on page three of this thread. My damage is less severe and I
KNOW that some of my damage was due to dirt ingestion during a couple unfiltered drag strip runs.
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Your diagrams still seem to show the water spraying onto the whole face of the turbine. I assume that the water erosion could be avoided by ensuring that the water didn't impinge on the tips of the blades, could this be achieved by having a narrow jet on the center line very close to the turbine? I mean within an inch or two. I'm envisaging something like a pitot tube inserted into the air intake close to the turbine.
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Yes it is likely it can, you just discribed the setup used by one guy that has been running pre-turbo spray for years. He injects directly on the compressor shaft nut with a narrow jet. The rapidly spinning shaft nut simply blasts the water stream into a fine cloud. I suspect the effect is not dissimilar to a 1000 psi impingment fog nozzle. The advantage of that system is as you say little or no chance to wet the intake tract walls, and the water is ejected tangientially outward inline with the compressor blades so little relative speed difference should exist. This is also very similar to the configuration used in WWII combat aircraft where they injected both fuel and WI "into the eye of the compressor".
The problem with that setup is it is not easily setup on many systems as the available space near the compressor inlet is quite limited in many cars, and service (ie to change jet size) would be quite difficult.
One of the things that may have limited my compressor damage is that I set the system up with a constantly pressurized system and the flow was controlled with a solenoid only about 4 inchs from the jet, so after drip would have been essentially eliminated, and rise time to full spray pressure at the jet should have been very short. Mine was also a continuous spray rather than a modulated spray as you would get with the HSV turning the spray on and off for folks using that style of system.
I also had a manual test spray button that at times I would briefly test the spray at low rpm to confirm my system was working. Based on this discussion, I now consider that to be a bad practice and will avoid it in the future, unless the engine is at a fairly high air demand, so that intake velocity would be likely to keep the plume from heavily wetting the intake walls.
Larry