Ill post some pics up tommorrow.. I have a new Avo silcon intake on my rex and where it comes from underneath the manifold and does the bend to goto the AFM they have a 3/4in breather port thats bunged off which is id say now at a guess 9in away from the turbo,so what i did was machine a fitting to place the jet low enough so it flush mounted the face of the jet with surrounding side wall of the pipe so the water would inject into the airstream correctly.(i'll get a pic of that 2) I was injecting at 13psi boost which on my car is 3300rpm approx depending on gear and that was with a 0.7 jet.It has only been for 3 weeks i think if it wasnt for the other turbo going on i would have never known. :shock: ..

Compressor Blades After WI

Jet placement

location of jet from the turbo

Vf24 compressor wheel before water inj

your WI
 

Your injection rate appears to be pretty close to my 4 gallon/hr nozzle that I ended up down sizing to a 3 gph ( may go to a 2 gph in the future depending on temp readings when I get my intake air temp stuff in).

Your injection location is just about identical to mine. I am wondering if in both our cases part of the problem is water dropplets forming on the intake tract wall and then skinning down the surface of the intake tube ( like water dropplets run up a wind screen at speed ).

If that is the case -- aside from reducing the injection rate one possibility would be to put a small step in the intake tract just before it reaches the turbo. This would force the large surface dropplet to break off and re-suspend in the air stream.

I would love to do some experiments with a plexiglass tube to see if that is what is happening, and what step shape would pickup the dropplet and re-introduce it into the air stream.


Just a thought.

Larry

Larry, i totally agree with you in saying that water droplets are forming on the side walls of the intake tract and that's whats causing the comp blade damage, but as too where the droplets are forming or how far away from the injection point its happening would be good to know?

Im wondering weather on gear changes and wide open throttle the water injection has a bit of run on effect and injects the mist on to the opposite side walls of the inlet tract thus causing formation of droplets for fraction of time your off the throttle between the changes?

It would be good to figure out how to stop the compressor wheel damage as i believe that injecting pre-compressor has good benifits..
Andy..

What if the water jet is placed at the center of the compressor wheel? the radial speed is at it lowest and also give the the water droplets to fan outwards rather than hitting the tips randomly.

Finding a way to inject pre-comp without blade damage will be hard but it will raise the compressors efficiency to a degree!!!

injection point
 

That has been used successfully. I've mentioned in the past a guy that injects directly onto the impeller hub. When the liquid hits the rapidly spinning impeller shaft it is instantly atomized.

NACA also did some experiments along these lines developing a drilled compressor hub that channeled the ADI fluid directly into the impeller it self.

(see NACA Memorandum Report E6C25 May 1946 --- "Hydraulic Characteristics of the NACA Injection Impeller" & NACA Memorandum Report E4L23a "Effect of the NACA Injection Impeller on the Mixture Distribution of the Wright R-3350 Engine" Available as NACA TN 1069 1946, also Report 821 "Effect of NACA Injection Impeller on Mixture Distribution of Double-Row Radial Aircraft Engine)

Unfortunately these sort of investigations ground to a halt when the transition to turbojet engines began in the late 40's early 1950's

Larry

"Drilled compressor hub", what a good idea.

If the compressor wheel is anodised or nickel plated, it will resist any corrosion.

I would like to reply to the pre-comp dilemna. You are experiencing exactly what everyone before you experienced. Impingement kills blades. A 50 micron droplet appears to be able to cause impingement. The mass of the drop hitting the blade is too large=erosion. Controlling the particle size is the answer, and I have some ideas on that. Our biggest problem is the practical limit to available pressure.

Maximize:
1. Pressure,

2. number of 'smaller" nozzles, with smaller spray patterns,
temp of fluid,

3. travel distance to the turbo, (debatable)

Minimize:

1. Viscosity, (a 50/50 mix is more viscous than water or meth alone)

2. Base nozzle choice on the SMA (sauder mean average particle diameter) of the nozzle. Get the smallest rated SMA possible. Generally, smaller nozzles have lower SMA

3. mounting nozzles on a conduit wall-big mistake, mount so as to flow out concentric to the conduit.


One way to keep any pooled water from getting to the turbo is to run the mist "uphill". Pooled water will be heavy, and will run down, just give it a place to collect.

Do not use a method of metering fluid that places a reduced duty cycle on the pump, use only the max pump pressure, higher pressure=lower SMA. One shurflo pump can deliver over 150 psi easily into smaller nozzles (flow)

Just some thoughts on how it "should" be done, to stir discussion. Pre comp injection should not be based on the same techniques used for post IC injection, different fruits. i believe it is a good idea, where extreme moderation techniques should be employed.

When you say this you mean to place the jet in the middle of the pipe correct? Going back to post comp injection, if i was to replace my intercooler with a correctly sized pipe from the turbo to the intake manifold and i placed a jet or jets which way would you face it or them? into the oncoming air stream or having face going away with it???..