Injecting prior to turbo comp' impellers

[Greenv8s]

Originally Posted by PuntoRex

It's hard to predict the changes to sensor reading & it's reliability.

I'm fairly confident the changes would be adverse. Hotwire sensors are very vulnerable to surface contamination, so water droplets reaching the element would cause an instantaneous overread and also affect the accuracy subsequently.

[PuntoRex]

Oh well, I think I must quit this pre-compressor injection camp, too. :sad: .....

I've been using the pre-compressor injection since early Nov. last year, so it's more than 5 months.

The jet was 0.5mm initially & swapped to 0.4 later, placed near an elbow in front of the compressor, only about 20cm away. It injects when high flow/high boost, controlled by a comparator circuit & a solenoid, metered by system 2D, and shares the pressure source with another pre-throttle jet.

The turbo in my car is installed deeply between fire wall and engine block, hardly accessable. Today I finally have some time to dig these all out & take a look. Actually I can not see it directly, through a camera instead.

Here's the pic:
[img] I have contacted PuntoRex to retore this picture[/img]

As can be seen, the outer edges of the blades are damaged obviously.

I think the pressure is still not high enough, thus the droplets are too big for this application.

Anyway, in these days, the turbo was working fine & giving me 22psi of boost. And, on the driver's seat, I always feel the turbo & engine love this pre-compressor injection.

However, seeing this damage, I can not persuade myself to keep using it. I disassembled the jet, plugged the hole, took out the hoses & solenoid...

[Greenv8s]

That looks rather nasty. I've no experience with turbos, but I assume that much erosion is abnormal and is definitely caused by the water?

Obviously the blade speed would be highest at the outer edges which would explain why the damage occured there. If somebody clever could think of a way to focus the water droplets towards the center of the turbine, would that reduce the problem? Perhaps it would be possible by mounting the jet axially quite close to the turbine, or something like that? Always easy to speculate when it's somebody else who has to do the work and foot the bill.

[PuntoRex]

Strangely enough, with this damage, I never felt the turbo was working badly. I didn't see boost drop or slow spool up.

So I'll keep using this turbo until it's bearing & seal go bad.

[Richard L]

The picture posted has exceptional details, goog steady hands.

It is most annoying that this has happened because we have had great results from it. I would if I can develope special 5-50um nozzle for you to continue this test rather let it continuing eroding the blades.

I need some time but I have a few ideas how to design this nozzle.

[hotrod]

Its my suspicion that that sort of damage ( which I also had) is due to small water dropplets collecting on the walls of the intake tract and running down the surface toward the turbo compressor like rain drops being blown up a windscreen.

Note that only the lead blades are eroded the second set of blades look nearly perfect. My theory is that the front most blade blasts these dropplets apart and they never make it back as far as the second set of blades.

If that theory is correct, than I think there is a solution but I need to build a test rig to verify it. If you installed a small step (about 1mm high) in the wall of the intake tract facing upstream toward the air filter, when the water dropplet hits that step is should be ripped apart by the fast moving air as it tries to climb the step. There are other possible configurations, like golf ball dimples on the interior of the intake tube ahead of the compressor to try, but I really need to build a flow bench with a few vacuum cleaner motors and some plexi tube so I can see what the water spray does.


It will cost me several hundred dollars to put together a home brew flow bench but I think it would be really useful to get live action shots of the water spraying into a fast moving air stream to see what nozzle locations and designs do in the real world, not in free quiet air.

Larry

[masterp2]

Punto Rex, How many miles on the turbo? How many miles using preturbo misting? It must be said. Unless you shot a pic of the turbo before you started misting it, you can't make a conclusive statement on the cause of the damage.

Larry,

Superb observations. You beat me. I am sure you are 100% correct. And the biggest problem with the hardware is that the nozzle shoots right into the opposite wall. Right on target! The water just collects into large drops or a stream more likely (water surface tension is a very strong force..)

Richard, you may be able to reduce the drop size a bit, but I don't think that will solve the problem unless you can get an 80% distribution under 30 micron (true fog). I hate to say it, and be a doubting Thomas. I haven't seen anyone do that under 500 psi. I don't really feel that particle size is the biggest problem.

(Thinking out loud) Even fog shot to the opposite wall with any velocity may still get to the wall. And while a larger particle does erode more effectively, this picture (nice pic) is classic leading edge erosion from FOD, caused by large drops or wall stream. It looks just like my lawnmower blade. Some degree of the wear must be considered normal wear and tear. While some impingement damage is visible across the entire leading edge, the majority of the damage is on the outer 10% of the blade, no doubt from something traveling up the wall.

Good ideas Larry, not knocking your step idea larry, I hadn't thought of that. In my mind, the real solution is aligning the nozzle(s) into the airstream, from the CENTER of the conduit, and using a narrow cone pattern (to minimize wall pooling), and then only at the highest practical MAF threshholds. If we can brainstorm to create a dual nozzle setup that will help even more. a smaller capacity nozzle (better atomization) then can be used at the highest practical pressure. Maybe put the nozzles back-to-back.

Larry a leaf blower can be used to show how 2 different nozzle orientations (within a conduit) will have dramatically different pooling characteristics. I will have to do this myself. Just collect the pooled water at the end of the conduit over time and compare.

Michael

[hotrod]

I agree, a co-axial spray setup is one of the things I have been thinking about.

Imagine a carburator venturi type nozzle suspending centrally in the air intake. The high air speeds in the venturi should keep the spray as a relatively compact plume that should travel down the center of the duct, with the mist impacting the compressor impellers near the center where their radial speed is relatively small.

In my next version I will be only using the pre-compressor injection at high engine rpms and boost ( pressure switch and rpm switch in series ). I could do the same with some sort of a maf voltage, trigger as well.

Larry

[PuntoRex]

Originally Posted by masterp2

Punto Rex, How many miles on the turbo? How many miles using preturbo misting? It must be said. Unless you shot a pic of the turbo before you started misting it, you can't make a conclusive statement on the cause of the damage.

Well, fair enough, I totally agree.

Here is my records:

2/28/2002 83125km The first turbo service
12/28/2002 99094km The second turbo service + engine rebuild
11/06/2004 131593km Pre-compressor injection installed
4/2/2005 139671km Damage blades were found

I have a photo of the turbo before the 2nd turbo service (12/28/02). Which is, it's 10-month-old & had serviced for 15969km.

Unfortunately that picture is not so detailed as this one. (it's a hard copy & I don't have a scanner to share it here) However, on that picture, the outer edges of the blades were obviously in a much better shape than this. The tips are mostly in a pretty sharp right angle, instead of rounded out like this current one.

Pre-compressor injection has been deployed for 5 months & approx. 8000km on it. TBH, it's only a short service time.

It's a pitty that I missed the chance to take a picture when the first service to the original stock turbo with 4 and half years and 80 thousands km of service. And I don't have many experiences with old/abused turbos... Maybe someone around here with more experiences could share more info.


Richard, thanks for the compliment. This photo is chosen from a collection of about 10 shots.

[PuntoRex]

This is(was) my pre-compressor jet seat:



The compressor inlet is on the left bottem of the picture. In the engine bay, the whole thing actually turns 90 degree...

As can be seen, the jet is facing a half-open space. Even when no air is flowing, near half of the spray cone should hit the compressor directly, well, sort of. The spary cone is so wide that unavoidably hitting the wall.

Without significantly higher pressure, samller droplets, much narrower spray pattern & precisely injection angle, I think we can hardly get away with the damages. :sad:

As to close co-axial installed jet, in my car, it's almost impossible to deploy. :cry: