Larry thanks that really helps!

I guess I just figured higher pressure would atomize the water better. I know if you start getting paranoid about injecting water pre compressor you shouldn't do it. The problem is I have a brand new $1000 turbo about to go on the engine and I really want great atomization to avoid problems.

Had another thought. If you are using a MAF in draw through and injecting pre compressor with an atomizer nozzle, won't the air you inject be unmetered and make you go lean?

Pre-Compressor Injection Advice
 

I completed my pre-compressor injection set up a couple of weeks ago on my 2003 Lancer Evolution VIII. I am still running the stock 16G turbo and am using a .3mm pre-compressor nozzle mounted on a custom axial mount. The .3mm nozzle that I?m using is an unreleased nozzle that Richard supplied me to experiment with. It has an internal progressive spring loaded valve so it opens about 2-3 psi later than my primary post intercooler .7mm nozzle. The .7mm is set to come on at 13 psi, so I figure that the pre-comp nozzle is spraying at about 15-16 psi. The maximum peak psi I see is 22-23 psi and it tapers down to 18 psi by redline. Here?s a link to pictures of my installation if anybody would like to check it out: http://www.aquamist.co.uk/phpBB2/viewtopic.php?t=654

I was able to go to my local Dragstrip yesterday to see what sort of results I would find. Unfortunately, my car fell off in power. I usually run 12.80?s @ 104-105 mph. My first pass was a 13.27 @ 100 mph. I then richened up my air/fuel mixture a little thinking that I may have leaned out with the pre-comp injection. I ran even worse, a 13.48 @ 99 mph. I decided to disconnect the pre-comp nozzle and run again on my regular .7mm post intercooler nozzle along with my previous fuel map. The car responded to a 12.90 @ 104 mph. The car was acting like the engine was receiving too much water mixture. My thoughts were that by using a small .3mm pre-comp injection nozzle, the water mixture would have evaporated by the time it exited the turbo. I was going to reduce the nozzle size post intercooler to see if the car would respond, but unfortunately the track was closed shortly after due to high winds. I?m hoping that maybe some of you that have had more experience with pre-compressor injection could offer some advice.

This is a very good practical example of the pre-T injection.

Such a small amount of spray has such big effect, a mystery yet to be fully exploited! Pity you cannot complete more test before track is shut.

You might find it would be better to cut back the size of you post intercooler jet to about a.5mm.
I found that in my setup I was over spraying quite a bit and have kept reducing the size of my pre-compressor jet.
I started with 4 gal/hr (240-250 ml/min) and ended up using a 2 gal/hr (120 ml/min) and I still think I was using a bit too much. I am re-engineering my setup and will be trying a couple other options.
I want to set the pre-compressor injection up so it only comes on at high boost pressure so I am planning on put a boost switch and another solenoid on the pre-compressor jet so it only comes on at boost pressures that I know will be maxing out the turbo's air flow (around 20 psi + ).

Larry

Larry, thanks for the response. I'll try a .5mm nozzle since I have one on hand. I also have a .4mm and .6mm also to play with. The only thing that concerns me is that since I was tuned for a .7mm post intercooler nozzle and a .5mm nozzle may run slightly lean for a moment until the pre-comp nozzle kicks in. The engine just had the symptoms of too much water mixture being ingested and reducing the post intercooler nozzle definitely makes sense. The first chance I get, I'll hit the dragstrip again. Luckily the track was kind enough to give the racers a free race pass for having to close down the track early so I can return and tune for free :smile:

Joe

How did the car react when you were spraying too much pre-compressor through the turbo? Similar to an overly rich condition, where the car stumbles and chugs a bit? Did it hamper spool or boost response at all?

I ask because I've got a 3 gal/min nozzle planned for my pre-compressor setup and don't want to be spraying too much right out of the gate.

Re: Pre-Compressor Injection Advice
 

joe, i have a question about your setup...

you say that the pre comp nozzle has an internal spring valve that causes it to open 2-3psi "later" than the other nozzles in the car. i can't see how this spring valve inside the nozzle would be opening with 2-3psi more BOOST--it doesn't "see" the boost at all... it sees the pre compressor inlet pressure on one side, and the water injection pump's output rail on the other.

i CAN see the valve opening up once the RAIL pressure is 2-3psi higher than when the other nozzle(s) open up.

perhaps richard can chime in here and offer some insight as to the construction/use of the prototype nozzle?

the other advantage i can see to an internal 2-3psi check valve would be a decreased tendency to drip after flow is ceased... a "good thing" particularly pre compressor.

in any event, thanks for posting up your experience,
ken

Re: Pre-Compressor Injection Advice
 

Ken, I'll have to have Richard explain more about the nozzle design.

Re: Pre-Compressor Injection Advice
 

I believe joe was trying to say the 0.3mm (pre-turbo), spraying at 65cc/min comes on at 15psi due to an inline 15psi checkvalve being installed. If his car is boosting 12psi, the 0.3mm will come on at 15 psi. The 0.3mm nozzle is a standard aquamist nozzle with a 25um filiter inside.

Having only just managed 14 pages of posts in my first read, maybe I should apologise for posting a reply/comment prematurely... but won't, as this is such a necessary and compelling thread! And I think I might be able to fill out some aerodynamic theory, as a lot of my thermodynamics has gone the way of the wind and tide :smile:

The step at the compressor inlet is almost certainly there to trip the boundary layer - if it's still laminar (likely), to fully turbulent. Many misconceptions around (not suggesting here, particularly) about laminar/turbulent boundary layers and separated/non-separated flow regimes - they're inter-related but very different things...

I've seen Mach No. (M), mentioned, it's important, but unless I missed it or comes after Page 14, not Reynolds No (Re), this being another non-dimensional parameter that determines the ratio of kinetic to viscous energy in the flow, and has a profound effect on boundary layer and flow separation. And of course the operation of turbo-machinery, as well as heat-exchange...

The effective Reynolds No. (Re) is low - and in turbo-machinery terms, perhaps very low, as the characteristic size of vehicle turbos is small (inlet hose diameter, impeller diameter) until things are changed dramatically as the flow really picks up speed (and is then immediately diffused).

We're talking 'dimpled' golf-ball behaviour here, where the payoff in delayed separation at the rear of a bluff body easily outweighs any extra frictional drag from a thick non-laminar boundary layer.

Suffice to say, that I'm not contributing directly to the debate on pre/post compressor WI, but suggesting that it might be worth establishing what's going on aerodynamically before the really complex bit - entry into the world of high-speed, but very small-scale turbo-machinery.

One possibility, is that a boundary-layer trip a bit further back up the inlet hose, might well help evaporation if injection is taking place well before the impellere eye - a wire, glued circumferentially around the inside of the hose, might do the trick... pulling flow energy down onto the surface (turbulent bl's have a much higher exchange of energy between the surface and their outermost extent).

One other point is a few mentions back there of sharp turns in the hose just before the turbo-compresor inlet... and a few raised eyebrows perhaps? Whilst a reasonably tight 90 degree bend probably isn't too much of a flow impediment, a common solution when a really tight bend is necessary is a banjo style design. An enlarged radius just prior to compressor entry being fed from the inlet hose at right angles to it - if that is a good enough picture in words. Acts a bit like a settling chamber before the flow changes direction

I have such a banjo elbow on my candidate vehicle (due an engine mounting within 4 or 5 inches of the compresor inlet), and thinking about it, might present an ideal area to inject straight into the impeller's eye from just a few inches away...

Enuff for now, must read-on...