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#1
16-07-2006, 07:48 AM
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Compressor surge in pre-compressor injection
Has anybody else experienced this?
During pre-comp injection, as the compressor map is shifted to the right and upwards we move the choke line further away so we can extend the useful range of our turbo. Which is nice.  However we also move the surge line, which is not so nice. I cannot tell if the surge line moves rightwards proportionately to the choke line - may it moves quicker, thereby narrowing our useable range in the compressor map. I'm thinking that it might also have to do with the effective narrowing of clearances at the compressor tips - something that would increase efficiency but potentially aggravate surge. This might be one of the 'gotchas' of this technique (hey, what did we expect - a free lunch? :wink: ) 
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#3
17-07-2006, 06:02 AM
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I have, that's why I'm asking if anyone else has experienced it
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#4
06-12-2006, 04:04 AM
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It sure is great to have this forum back, I love reading the information on here!
Anyway, on to my question: Assuming that pre-impeller injection either moves the entire compressor map to the right, which is what I gather the correct conclusion must be if it pushes the choke line to the right AND moves the surge line to the right, then would the following be a correct statement?: Pre-impeller injection is a good technique to employ if your turbo is a bit small for your application, but NOT if your turbo is large enough that surge is a concern. In that case, some location post compressor is the better option for the nozzle to be located. ? ? ? Thanks!
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#5
06-12-2006, 12:22 PM
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Quote:
So we get the best of both worlds: quick spool of a small turbo, and extended top end of a bigger one. If the turbo is big to begin with, I wouldn't bother.
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#6
07-12-2006, 01:24 AM
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Thanks John, this is some really good information to have some idea of how to manipulate the compressor map like this (both directions).
I doubt there is any really good way to describe it, but would you be willing to try to describe how much the map can be shifted? In other words, how much can a too-small turbo be stretched over with pre-turbo injection?
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#7
08-12-2006, 04:35 PM
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I've seen up to 15% of airflow myself, but I keep it conservative (whatever that means with pre-compressor injection :wink: )
It can probably go much higher if someone is brave enough to saturate the hell out of it. It has worked in documented experiments. Most probably there will be diminishing returns from a point onwards, but I haven't got a clue how far that point is.
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#8
11-12-2006, 06:04 AM
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The NACA reports have some tests on jet engine compressors that show (as I recall) maximum effect on the compressors performance was at about 3% of air flow. Beyond that you may still gain some performance as the water will get carried through the system as if you injected it later, but will lower the thermal effeciency of the intercooler if you have one.
Its very hard to isolate one effect from the other --- bottom line is you keep tuning until performance does not improve, and who cares which one of the effects made the difference  Personally I only ran 2% - 4% of intake air flow on my car and was quite happy with the results, but the turbo was so small I really could not run killer boost levels, so could not investigate (actually had no need to investigate) higher flow rates. Larry
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#10
14-12-2006, 08:54 PM
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Quote:
That's more than twice of what I've used. We've got some way to go, eh? :smile:
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