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D.I.Y Injector flow bench 
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Joined: Thu May 05, 2011 2:27 pm
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Built my self a injector test bench.
I'am using this setup to test different injector drivers.

http://peterdahlman.wordpress.com/

Any kind of suggestions and input regarding this mini project are welcome.


Sun Jan 08, 2012 9:42 pm
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Lovely welding on the tank! :-)

You should test the injectors with the same driver system that you plan to use on the vehicle if you plan to use the rig to get dead time data as well as flow data.

Is your C# app simple enough to use with mono? If you could keep the really new API use to a min, it'll run on Linux too, then.

Nice project! :-)

Fred.

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Sun Jan 08, 2012 11:49 pm
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Thank's!

Well about the welding....i'am rarely using the TIG theese days....but at least it's sealing :)
There was a little too big gap between the plates so i had to use pretty much electrode to make it feel ok.

The Windows application is written in C#, but it's really small..pretty much just send commands to the controller board, so it should
be quite easy to get it running with mono.


Mon Jan 09, 2012 8:51 am
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Image
Credit where credit is due: Nouri, J.M., Hamid, M.A., Yan, Y., Arcoumanis, C., Spray Characterization of a Piezo Pintle-Type Injector for Gasoline Direct Injection Engines, Proceedings of Third International Conference on Optical and Laser Diagnostics (ICOLAD 2007), City University, London, 22-25 May 2007, 2007.

Your project reminded me of this, sorry it took me so long to figure out where I'd seen it. I don't know how serious you are about testing all kinds of injectors, but it would be pretty cool if you could also test direct injectors under higher outlet pressures. I don't know how you would program it, but say you started injecting at 1.2Bar and ended between 3 to 7 Bar depending on the engine load. You could get a more accurate amount of fuel sprayed since I'm sure less fuel gets sprayed at higher cylinder pressures.

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Wed Jan 11, 2012 3:14 am
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Peter, that's cool! :-) However the regulator maintains a constant pressure across the tip of the injector for some good reasons. One is that without that, you need to complicate your algorithm to get accurate fueling. Another is that I bet you that they upped the voltage to the injector for those 12bar tests, most injectors will lock from the pressure and fail to open well below 12bar. Thus you tend to run them at a point when the pressure is high enough for good atomisation and low enough for a fairly quick opening time. OEMs tend to call that 3 bar differential :-) That shows up as closer to 2 bar absolute pressure at idle due to the high vacuum present which and compensated for.

Fred.

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Wed Jan 11, 2012 9:22 am
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Fred wrote:
However the regulator maintains a constant pressure across the tip of the injector

I think we had a miscommunication here. I don't know, but I'm pretty sure the fuel pressure is the same in all three examples. The 1, 4, and 12 Bar is the air pressure that the fuel is being sprayed into.

I was thinking along the lines of the Bernoulli equation. I think the flow rate over the time of the injection is going to decrease, because the cylinder pressure is increasing. It would mostly depend on whether the injection was close to BDC or closer to TDC.

Image
Ando. H., Takemura, J., Koujina, E., A Knock Anticipating Strategy Basing on the Real-Time Combustion Mode Analysis, SAE Paper.890882, 1989.

This is my impression of of how direct injection is done. The first injection being under vacuum to atmospheric pressure, and the second injection with the piston two thirds of the way up the cylinder. I don't know how different the flow rates would be, but I would assume a little.

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Wed Jan 11, 2012 4:05 pm
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Oh, I apologise! I naturally assume port injection. Yes, I guess there is some difference depending upon the exact profile of the rod ratio/stroke combo and even the bore and injector location. I imagine that the OEMs do indeed take care of this in their code, not doing that would be negligence, wouldn't it? Thanks for the pictures, again! :-)

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Wed Jan 11, 2012 7:12 pm
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Thank's for the feedback.

Actually i have future plans to look in to GDI injectors. (The injector drivers seems to be a little bit more sophisticated than classic Peak and Hold)
From what i've heard, the spray patterns of modern GDI injectors can be validated at a pretty low pressure comparing to their actual working pressure. (200 bar?)
I've looked into those ASNU machines that seems to support testing of GDI injectors, from what i understand their pump system only working with lower pressures (<=10 Bar). http://www.asnu.com/gdi.htm
I have my doubts...but maybe someone here has tested this?

Regarding the "chamber pressure" effects on the spray pattern (on "old" <=10 Bar fuel systems)...
This maybe could be simulated with a plexiglas pressure chamber connected to an air compressor with regulation.


Wed Jan 11, 2012 9:17 pm
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Btw...seems like interesting SAE documents...is there any form of compilation available of such material?


Wed Jan 11, 2012 9:31 pm
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I don't know much of anything about direct injectors. If you search google for S.A.E. you can find their site, and they have a library with a demo membership. I don't have any interest in paying them.

http://www.springerlink.com/content/978-3-540-68901-0#section=101546&page=1
This is the book I got those two pictures out of, and I think its free to read online.

EDIT: It's only free for me to read if I'm logged in though my University account. You can only read parts of it as a guest.

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Thu Jan 12, 2012 9:14 pm
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