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Old 02-11-2004, 05:04 PM
boostm3 boostm3 is offline
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Default Location of Water Injection Nozzle relative to Intercooler

This is about a discussion weve been having on a bmw forum in the Forced Induction section. One of the most popular setups on our E36 M3s is a Vortech supercharger cooled by an rms Aftercooler which is a water to air unit placed inline between the blower and the throttle body, and an Aquamist 1s system with the nozzle placed right after the aftercooler core, just before the throttlebody.

I have instrumented results in the above setup, before the aftercooler was installed, with the water injection alone, with the nozzle placed between the SC discharge and the throttle body. I found that Intake Air Temps (IATs), prior to the boost kicking in, ie, cruising IATs ran Ambient PLUS 100 degrees F. Then, when the WI was triggered, the IAT at redline showed a 50 degree reduction. On an 80 degree day, part throttle cruising, no boost, showed IATs of 180 degrees. When the boost was invoked with a WOT run to redline, this went up.. And, the WI was triggered, at about 4 psi, or about 4500 rpms. IATs at redline had dropped to about 130 degrees, which is over a 50 degree reduction.

Now, when the aftercooler was installed, the nozzle was placed on the outlet side of the aftercooler, just after the core, and just ahead of the throttle body, in a similar location as to where it had been mounted without the aftercooler having been installed.. Cruising around part throttle IATs, no boost, with the aftercooler, now read ambient plus about 35 degrees, or, about 115 degrees, showing about a 65 degree IAT reduction (80 (ambient) + 100 - 65 (aftercooler) == 115 degrees) .. Going WOT and taking an IAT reading at redline, we see a new IAT of about 100 degrees (115 from above - 15 degrees from WI), showing that the water injection caused a further reduction of about 15 degrees over the temps I saw when cruising.. Had the WI been as effective as before when it was sprayed into the non aftercooled 180 degree air instead of the 115 degree air, now cooled by the aftercooler, wed see a new IAT of about 65 ( 115 minus 50 degrees). Why did the WI produce a minus 50 degree result without the aftercooler being installed and 'just' a minus 15 degree result With the aftercooler being installed? I believe its because the water evaporates much more efficiently in hotter air than in cooler air.

Given this observation, it kind of begs the question, why not mount the water injection nozzle BEFORE the aftercooler core, ie, between the supercharger discharge and the aftercooler, instead of the common way to mount it, after the aftercooler core? That is, why not take advantage of the fact that water evaporates more efficiently in the hotter air which
we have before the aftercooler core?

I would think that moving it to before the aftercooler core would be a no brainer. Except for one possible question, the answer to which I havent worked out yet. The real question, it seems to me, is does the aftercooler behave like the water injection, ie, does it remove more heat from air that is hotter, and less from air that is colder? Thats certainly how the water injection works... But since evaporation isnt a factor with the aftercooler, I didnt think so.. But... Now im not so sure.. While its clear that with the aftercooler evaporation isnt the factor at work, I nevertheless have noticed that as the ambient air temps are now near 50, I dont continue to see the same ambient plus 35 to 40 degree iats. Moreover, Im pretty damn sure that when ambient is 40 degrees, I wont see iats of 75 (without wi). In other words, the colder the ambient air, it seems that the less percent cooling we see from the aftercooler. When ambient is 25, will we see IATs, without wi, of 60 degrees? I think we reach a point of diminishing returns. So, perhaps it does act similarly to the way the water injection behaves in the face of falling temps in the immediate environment. I would think this might be the decisive factor in making the decision to move the nozzle location or not.

Id love to hear your comments, experiences, etc, with this issue. Richard, if you have any theoretical info to help clarify this problem Id love to hear.. Thanks...
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'99 White M3; < 69K miles; Dinan SC kit with 6" RMS crank pulley and water/air Aftercooler: 11 psi-367 SAE rwhp/304 ftlbs; Custom Tuning by Nick G; AA Aquamist Water/Methanol Injection and AA exhaust; Fikse FM-10s;
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  #2  
Old 03-11-2004, 12:20 AM
Richard L Richard L is offline
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I am not sure, please test the theory by experiment.

IMO, pre-CC will lessen the efficiency of the CC, but I could be totally wrong.

Take a look at this post from Gelf:
http://www.aquamist.co.uk/phpBB2/viewtopic.php?t=514

He managed to cooler the inlet below ambient.
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Old 03-11-2004, 07:52 PM
JohnA JohnA is offline
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Default Re: Location of Water Injection Nozzle relative to Intercool

Quote:
Originally Posted by boostm3
...does the aftercooler behave like the water injection, ie, does it remove more heat from air that is hotter, and less from air that is colder? ....
As Richard suspects, the answer is YES!
The CC is a heat exchanger, and its efficiency is maximised when the temp differences are maximum.

This is clearly illustrated here:

http://www.aquamist.co.uk/phpBB2/vie...er=asc&start=0

look how the pre and after-intercooler temp differences are eliminated as the WI nozzle gets larger. (it is before the compressor)
With the largest nozzle, the pre-after temps are the same as NO W.I. AT ALL!
Intercooler giveth, WI taketh away... :wink:
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Old 02-05-2007, 06:40 AM
ForcedInduction ForcedInduction is offline
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So where is the best location for the nozzle after the intercooler?

At the outlet of the intercooler endtank so it has time to evaporate in the tubes leading to the intake, at the intake mouth or pointing against the airflow into the intake?


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Old 20-06-2008, 12:28 PM
stevebez stevebez is offline
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If the I/C water path is linked to the motors coolant circuit (as some cars are), you avoid adding heat to this system by placing the injector ahead of the I/C core. This is for a water/air units obviously.

Placing the injector after the I/C unit will mean the cars system absorbs more of the heat, reducing overall efficiency even though the I/C is more effcient at removing heat from the higher temps.

One could also argue that if the I/C is insufficient to start with - that again overall efficiency would be improved by taking as much heat out of the system before you hit the I/C, allowing the under spec I/C to cope better.

If there is an issue with corrosion on the I/C core I would not know but I expect being mostly ali and the like they should be pretty robust, unless some funky fluid blends are used.
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Old 20-06-2008, 03:52 PM
masterp2 masterp2 is offline
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Part of the answer to this question rests in another question: How much evaporation can I expect from small droplets in the .1 seconds that they exist in the induction tract???

The answer: it depends...it hinges on humidity, charge temp, and one very important aspect...disturbance potential. liquid water must interface with a lot of air to fully evaporate, and entrainment in a moving airstream does nothing to help this process. So most people injecting post CAC, at most, see 10% evaporation...my educated opinion.

Want to evaporate liquid water? It must be injected pre-compressor. Assuming adequately low humidity, you will get close to 100% evap rate because of the air interface and high temps.

Lets face another reality, getting more air in is about getting it moving slower (condensing) through your plumbing. That lowers the "negative boost" that needs to be overcome to transport air. The air pump (turbo) does less work when charge is condensed early in its travels. This allows the compressor to operate more efficiently at overboost rpms, with less off-map consequences of heatup.

Anyway, post-CAC injection is not good for anything, except improving combustion quality (on a dry day), and lowering EGT. On a 50 F day in the NE U.S., there is already lots of water in the air, so the only real gains will be pre-turbo, and then only with overboost use, or real inneficient induction plumbing.
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  #7  
Old 14-08-2010, 06:26 AM
fr8tdog fr8tdog is offline
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Default Re: Location of Water Injection Nozzle relative to Intercooler

with regard to pre IC I would be concerned about water pooling in the IC and causing corrosion. I think a dual system would be perfect....water/meth pre blower and water/meth post blower. Dont know about corrosive problems with the blower though
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Old 19-09-2010, 01:03 AM
RICE RACING RICE RACING is offline
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Default Re: Location of Water Injection Nozzle relative to Intercooler

Quote:
Originally Posted by fr8tdog View Post
with regard to pre IC I would be concerned about water pooling in the IC and causing corrosion. I think a dual system would be perfect....water/meth pre blower and water/meth post blower. Dont know about corrosive problems with the blower though
I have used pre turbo WI for a long time now, the "pooling" myth is just that.

Some basics of physics are required to explain this.

Pooling is only going to happen when the water droplet sizes is substantial only then will it want to accelerate out of the air stream when going around a radius (easy to work out), this function is directly proportional to the size of the droplet and thus its mass. You also need to realize the air speed is quite slow in the induction plumbing and in the cooler itself, the radius's involved usually are quite large as well, and all of this means that small mass water droplets won't get thrown out of the air stream and onto the walls nearly as badly as people may think.

When you have a finely atomized water droplet you greatly reduce its mass, also to remember these fine atomized droplets have gone through a phase change into steam (in mostly all cases) all the way up to and most of the way into the charge cooler. What you see after the charge cooler is amazingly fine water droplets that are so small they stay in suspension in the air stream (well after the car has been run). You can see this if you have a pressurized water tank. I have never ever found pools of water in a charge cooler nor none of the pipes leading to the engine, have seen plenty pools of oil though far bigger problem than any pre turbo WI system I'd suggest.

Hope this helps?
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  #9  
Old 06-11-2010, 10:45 AM
thefalls thefalls is offline
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Default Re: Location of Water Injection Nozzle relative to Intercooler

Does the pre turbo injection of water/methanol have any ill effects on the turbo itself?
Any corrosion?
thanks.
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  #10  
Old 07-11-2010, 11:53 PM
RICE RACING RICE RACING is offline
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Default Re: Location of Water Injection Nozzle relative to Intercooler

Quote:
Originally Posted by thefalls View Post
Does the pre turbo injection of water/methanol have any ill effects on the turbo itself?
Any corrosion?
thanks.
Non at all, there is never any corrosion anywhere in the system when doing pre turbo.
The only effects are massive increase in power on normal fuel and a cooler running less sensitive engine.
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