SDI Engine: What is the purpose of this throttle valve?

Hi!

Thank you to the forum for the valuable information about AGR and its deactivation for motorsport purposes !

I have a 1.7 SDI engine. I disabled the AGR (Exhaust Gas Recirculation) system by sealing the control hose with two-component adhesive in two places.

Today, I observed the behavior of a valve that I initially thought was the shut-off valve. It is located on the suction side, in front of a large plastic box that is directly flanged to the intake manifold. Presumably, the box is an intake noise silencer, possibly with Helmholtz resonance tuning. The 4 intake ports (from the 4 intake valves) protrude into it, like bass reflex ports.

Actually, a bypass valve is supposed to close briefly when the system is turned off and then open again after a few seconds, right?

Observed behavior:

Engine off: Always open.
Engine starts: open, then runs for 3 seconds.
Partial load (I heavily loaded the Lima for simulation purposes, approximately 2000 RPM): to be determined.
During acceleration and at medium load: open.
When the engine is turned off: it immediately snaps back.

Conclusion: If it always immediately clicks when the engine is turned off, it's probably not a shut-off valve, right?

What is it then good for?

Sure, here's the translation:

'Thank you in advance.'

My ex-girlfriend owned a Polo 6N2 1.7 SDI, so the engine code (MKB) is AKU.

I only noticed the AGR valve and the shut-off valve on the intake manifold.

Try to disable this unidentified valve.

How does the engine behave then?

m;

Can you take pictures of the unknown person?

Hello,
To my knowledge, the valve is used to increase the vacuum in the intake manifold, which is normally very low or non-existent in a naturally aspirated diesel engine (and certainly not present in a turbocharged engine). This allows for a higher EGR (Exhaust Gas Recirculation) rate.
Deactivating it won't hurt, especially if the EGR system is already deactivated.

Best regards,
Albrecht.

Thanks for the answers, I'll take some photos. Talk to you later...

I have now taken 2 photos (they are already on my hard drive), but I don't have a server where I can upload them.

Let me think about what I can do here. In some forums, you can upload photos directly to the forum, and I think that's better.

That's exactly what the "Img" button is for!

Cool thing, right?

m;

[img]c:/my documents/misc/flap1.jpg[/img]

The valve is designed to give the intake air the necessary swirl as it flows into the cylinder, so that it can mix optimally with the diesel fuel.
You're missing the turbocharger to achieve the swirl effect.

Do not deactivate the valve; the engine's efficiency in partial load conditions will decrease significantly. This will result in heavy soot formation and carbon deposits.
As far as I know, the SDI doesn't have a shut-off valve, but I'm not entirely sure.

No, unfortunately, it doesn't work without a server where I can upload the image.

But I have uploaded the image here.

http://www.elektronik-kompendium.de/forum/messages/22808.htm

@Julian: Drall? But at low loads, the flap is closed except for a small gap. And besides, it doesn't have an aerodynamic shape that could create turbulence. It's just like a normal throttle valve. And from medium loads onwards, it opens completely and abruptly, so there's no turbulence anymore. Also, the flap leads into a large box with a volume of about 10 liters (resonance chamber? See photo). Turbulence at the box inlet wouldn't achieve much. It's more likely to occur at the 4 intake ports that protrude into the box from the inside (about 12cm deep).

Manually actuating the valve while idling resulted in no changes whatsoever in terms of engine noise, smoothness, vibrations, or black smoke (although my car doesn't produce any black smoke anyway).

I think the theory involving the creation of additional vacuum to ensure proper AGR function is the closest to the truth.

Okay, if you say so. However, closing it accelerates the air, which then enters the intake manifold at a higher speed and therefore creates more swirl. A positive side effect of this is that the EGR system also works better. But for a soot-free combustion, the swirl is extremely important.
I believe that my theory probably comes closer to reality...

by the way
It's quite something when you ask a question, get a reasonable answer, and then think you know better. That's not the way to make friends, sorry, see also your other posts.

It's annoying when you ask a question, get a reasonable answer, and then act like you know better. That's not how you make friends, sorry, see also your other posts.

Incorrect, I usually get several answers. And which of these different answers I choose to believe is something you'll have to leave up to me, sorry.

In this thread, I find Albrechts answer to be the most insightful. If I have offended you in any way, I am sorry. That was not my intention. Nevertheless, thank you for your response. However, I have presented my concerns about your assumption in a factual manner. (In the subsequent airbox with a volume of >10 liters, the turbulence caused by the flap would become almost ineffective.)

It enters the intake manifold at a higher speed and therefore creates more swirl.

That would be true if it went directly into the intake manifold then. But take a look at the photo. The flap (on the left side of the box, with the intake hose removed) opens into a huge, hollow box and flows very slowly across it. I unscrewed the box. There is really a lot of space inside. The intake ports for the valves protrude into the rear of the box. The turbulence from the flap probably has very little influence there. If you stand in a room with a draft from the window, you won't feel the turbulence from the opposite, half-open door anymore.

Hello Julian,

The valves you're referring to are located directly in the intake channels (e.g., FSI) or in diesel Mercedes vehicles (CDI), which is known as an exhaust gas recirculation system (EGAS). However, there are certainly other types as well.
However, a large opening in front of the air intake (as in this case) primarily has no influence on the turbulence inside the cylinder. It only serves to increase the vacuum, as I described earlier!

Best regards,
Albrecht

Thank you again for all the answers.

I temporarily disabled the valve (for motorsport purposes) and will conduct a fuel consumption test in very urban traffic conditions (with a lot of low-load operation).

Best regards,

The valve controls the EGR (Exhaust Gas Recirculation) rate. The naturally aspirated diesel engine doesn't have as early exhaust valve opening timings as a turbocharged engine, so a vacuum is created by the throttle valve in the intake manifold to draw in more or less exhaust gas...
As Albrecht said...
Stay cheerful.
OlBe

PS: The swirl is created by the fuel injector. The injector nozzles are arranged in such a way that the individual fuel jets are swirled. This is clearly visible in the slow-motion recordings of direct injectors... A more sophisticated, but unfortunately patent-protected, version of this was implemented in the Elsbet engine.