Where to place nozzles?

[SpyderVenom]

I'm going to be boosting in the 20 to 25 psi range on a 2l engine and on the outside could make 350 to 400hp. The car is being set-up specifically to autocross and road race and I can make any changes that I want.

Due to the nature of autocrossing, I need a quick spool turbo which also will spool high. Which means that I need to make concessions about where on the efficiency islands of the turbo I can run. Basically, I'm going to be running in the 65% efficiency range at the high end. That means heat.

I have heard that you should not place the water injector(s) before the IC, why is that? My thoughts were that it would take some of the heat out of the charge before it hits the IC. Although it would remove some of the efficiency out of the IC, it wouldn't heat soak as fast. Plus, I'm going to be running multiple injectors so one before and one after the IC would be in the works.

In addition, wouldn't injecting water between the turbo and IC increase the efficiency of the turbo? Assume the first restriction after the turbo is the IC. If we cool the air charge between the turbo and IC, we would reduce the volume of air by reducing the temperature. That volume decrease would also result in a defacto pressure drop. With a pressure drop, the turbo could pump more air into that area easier. Resulting in a more dense charge with the same pressure. Or am I thinking about that wrong? Or is the resulting "steam" from the injector going to increase the volume and pressure?

[Brad]

Trial and error has proven to inject water after the intercooler. Let the intercooler do what it can and finish it with water. You could spray wate on the intecooler.
If you are going to spray before the intercooler the air will become over saturated with water.
For autocross you might consider bypassing the intercooler and run only water with a little less boost. The spoolup time will be much quicker and the engine will react more like a natually asperated car. This will allow you to throttle steer the car more effectivly.

[Forum Admin]

Defining efficiency of the intercooler as the drop in charge temperature that it provides against its drop in pressure - yes injecting water before the IC will decrease the efficiency with which it does its work.

However, we are not just looking for IC efficiency but total charge intercooling efficiency.

To the extent that injecting before the intercooler results in lower entry and still lower IC exit temperatures and increased densities this is a good thing even if the entrance to exit drop in temperature is decreased, the exit temperature is what is important.

As you said injecting before the IC also helps with heat soak both during staging or on road tracks where intercoolers can become interheaters.

Lastly injecting before the IC lengthens the induction path of the water spray - giving it more time to absorb heat and also more time to mix smoothly before the plenum.

[Warren_from_PINZ]

Hi, I'm new in here but I thought I'd post my 2 cents worth... (I have a degree in Physics).
There's been quite a bit of debate about where to inject it and I'd go with those that have actually tried all the possibilities and measured the results. I would expect that you'd get a better result from going after the IC because the IC won't have as much work to do if the incoming air is already "cold". In other words the amount of heat the IC will take out depends on the difference between the cold air coming in the front of the car and the hot air going through the IC. So that suggests not to put a nozzle before the IC so the iC can do its thing first.

On the other hand, if you're drag racing, for example, it might be handy to have a nozzle before the IC just to cool the IC down before you get the green light.

As for putting it before the turbo compressor, I can tell you that if the water is introduced in a stream instead of a pulverized vapour you can get notches on the compressor wheel. I know... I did it. I'll try to get some photos of it. But whether a fine mist would do the same I don't know for sure. I'd be surprised if it did but I haven't tested it.

After much discussion, there seems to be a general concensus that injecting before the compressor should move the efficiency islands towards the higher flow rate of the compressor map, ie. you would get maximum efficiency at a higher flow rate. Has onyone tried this?

Cheers

[robbilau]

I'd like to see those pics, as I'm considering injecting before the turbo myself.

[SpyderVenom]

I can't imagine that having water injected before the turbo would be good for the hot compressor blades...

I was asking about this because I'm planning on a "X" nozzle set-up in two stages (where "X" is yet to be determined). When a high boost condition exists where I'm boosting beyond the efficiency island of the turbo, I was wondering about cooling the intake charge before the IC so that the IC would not heat soak. I'm looking at total efficiency of the system vs. local efficiency of one component.

I have a lot of freedom to place nozzles both in and out of the intake. So, currently, the set-up looks like this: At 15psi boost, a 3 GPH nozzle right before the throttle plate and two 1GPH nozzles come on to spray on the IC. At 20psi, a 5GPH nozzle before the throttle plate and a 5GPH nozzle comes on between the turbo and IC.

[hotrod]

If done properly, injection prior to the turbo compressor will work and not destroy the compressor impellers.

There is some debate about the desirability of the various injection points. the common wisdom is if you have an intercooler the injection point should be between the intercooler and the throttle body. If there is no intercooler the injection should be infront of the compressor.

I suspect it is not quite that simple, and if you want to be sure you should run some comparative tests.

By way of example the WWII fighter planes and bombers using the R2800 Pratt and Whitney aircraft engines injected both fuel and ADI (water injection) into the "eye" of the compressor of their superchargers. The trick is the spray into the compressor needs to be set up so no large droplets impact the blades. If it is a very fine mist is appears to vaporize as it enters the inducer due to all shear forces and rapid changes in direction and pressure.

Quite a few of the tractor puller folks use pre-compressor injection on at least one stage of sequential turbos.

There is one user that I know of that places a nozzle so it sprays directly on the tip of the turbo compressor shaft. The water is instantly microatomized on contact with the rapidly spinning shaft before it ever reaches the compressor. Water introduced into the compressor as a solid stream or in the form of a coarse water dropplet spray will quickly "sand blast" the compressor blades.

The ideal may be a combination of both. Spray as much water as you practically can between the IC and the throttle body. If you find you still need more water, I would add an additional injection stage infront of the compressor so it sprays only during the highboost, high heat load part of the boost cycle.

Larry