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Re: Water Injection - Intercooler Pipe or Manifold?


Rausch Galant VR4.org Moderator
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Galant VR-4 org Post #: 359591 posted 07/16/06 08:52 AM     Remind Me!  Send Private Message   Edit Post      
Quote:

Will the mist erode the compressor wheel over time if your not careful?


was kinda wondering that myself. i would think that you may see a little wear over a substantial amount of time, but without any overwhelming pressure or volume, i would assume it would come down to placement and flow. just a guess though. i'm sure someone knows better than i do, though.



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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 359613 posted 07/16/06 11:01 AM     Remind Me!  Send Private Message   Edit Post      
To prevent erosion of the compressor wheel you need to keep water droplets below 50 microns and ideally at about 10 microns. The nozzle pisces showed does that. If you inject up close and personal as he intends to right on top of the impeller, it should be fine. Pre turbo injection is actually nothing new.

Curtis suggested the possibilty of injecting water WITH my propane kit using a NOS fogger nozzle set injecting water/alky mix instead of fuel and propane instead of nitrous. At -40 degrees and roughly 400 psi it would cool down the compressor wheel somewhat. Maybe too much? Also I'm not sure what size water droplets these "fogger" nozzles would create.



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jogalant
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Galant VR-4 org Post #: 359635 posted 07/16/06 01:14 PM     Remind Me!  Send Private Message   Edit Post      
I wonder if there is any data out there that shows an added benefit of introducing water injection pre-turbo. Absent that I say let the intercooler do its job then have the water injection after the intercooler. Seems this would offer a cooler charge prior to combustion, no?



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cheekychimp Galant VR4.org Moderator
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Galant VR-4 org Post #: 359642 posted 07/16/06 02:13 PM     Remind Me!  Send Private Message   Edit Post      
Quote:

I wonder if there is any data out there that shows an added benefit of introducing water injection pre-turbo. Absent that I say let the intercooler do its job then have the water injection after the intercooler. Seems this would offer a cooler charge prior to combustion, no?




YES, there is data. The point is that if you look at pre compressor injection from the stand point of cooling charge air ONLY, you have completely missed the point.

Substantially reducing the temperature of the charge air pre intercooler creates problems. Inject enough water and the intercooler becomers an interheater because all intercooler efficiency is lost and charged air temps at the intercooler outlet are HIGHER than those at the inlet.

This is pointless unless you intend to completely remove the intercooler and rely 100% on injection to cool the charge air, which incidentally quite a few people have done.

The object of pre compressor injection is to push compressor efficiency away from adiabatic to isothermic allowing the compressor to flow more at lower boost due to increased air density.

With a properly tuned pre turbo injection setup you can actually shift the entire compressor map. It is an ideal setup for high altitude and this was ONE of the reasons it was introduced in forced induction internal combustion aircraft in WWII to counteract the effects of altitude (thinner air).

I have said this before but no-one listens.

If you just want to cool the charge air, you are entirely correct, just do it after the intercooler, prior to the throttle body or at the intake manifold (i.e. direct port).



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jogalant
jobidet
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Galant VR-4 org Post #: 359652 posted 07/16/06 03:39 PM     Remind Me!  Send Private Message   Edit Post      
I see your point now about improving the turbo's efficiency. Frankly, I'd like to even eliminate the need for an intercooler. This might be the way to go... pre and post turbo.



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pisces
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Galant VR-4 org Post #: 359681 posted 07/16/06 05:36 PM     Remind Me!  Send Private Message   Edit Post   
If you're serious about water injection, and would like to read an excellent thread on pre-compressor injection, sign up on Aquamist's forum. http://www.aquamist.co.uk/phpBB2/index.php There's SO much good info there, it's almost impossible to sum it all up here in this thread. Go there, you'll see.

Also, as Paul said, there are a few caveats to injecting pre-compressor. I mentioned them earlier, but it was kind of muddled in the middle of a paragraph and not 110% clear. Here's a breakdown:

1) Inject directly into the compressor wheel if you can, not at a 90* angle to it.
Injecting directly into the compressor, at the correct distance from it, will keep water off of the walls of the intake pipe and mouth of the compressor cover where it can converge into larger droplets and wreak havoc on the blades of the compressor wheel. It's not cheap or easy to mount the nozzle pointed directly at the compressor wheel nut, but it's the best way to do it.

2) Inject with as fine a mist/fog as possible.
Again as Paul already mentioned, droplets in the 10-50 micron range are preferred. If they get larger than that they can start to really chew up the compressor wheel. The Bete PJ nozzles I mentioned earlier in this thread are perfect for this application.

3) A high pressure pump (100 psi+) is very preferable.
The higher pressure will contribute to greater atomization and smaller droplets. You might be able to get away with a 60 psi pump, but I wouldn't recommend it. And don't even think of running a 45 psi Shurflo pump!

Hope this helps...


Edited by pisces (07/16/06 05:38 PM)

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