Correlation between AGR rate and noise

Hello everyone!
Yesterday, I experimented a little with VAG-COM on a Golf 4 with an ALH engine.
When I adjusted the EGR rate, I noticed a significant change in the sound of the combustion. As the EGR rate decreases, the engine knocking sound at idle becomes noticeably louder.
In the ALH (presumably a specific engine or system), the factory setting for adaptation channel 3 is 32768, which corresponds to an air mass flow rate of approximately 255-260 mg/hour. The adaptation limit allows for a maximum value of 33768, which results in a mass flow rate of 360-365 mg/H.
Purely subjectively, the turbocharger seems to respond a bit better to the accelerator pedal with this modification.
Maximizing the use of... The adaptation value is located approximately in the middle between the factory setting and the complete deactivation of the AGR (Aktivkohlefilter/Activated Carbon Filter).
Therefore, the amount of oil entering the intake manifold should also be significantly reduced with this modification.
I also noticed a slight change in the exhaust smell, with a tendency moving away from direct injection (DI) towards indirect injection (IDI).

Regards,
Alex.

Hi,

donalexo wrote:

....When changing the EGR rate, I could perceive a noticeable change in the combustion noise.

It should be the same after the actuator diagnosis is performed, according to the description.

My 1Z sounded different in the actuator diagnosis as well.

But I would say that it sounded more rumbling with the valve open.

Meanwhile, the connector on the pressure transducer has come loose, and I only have 10% fuel in the tank, so the thing is running very "quietly" – quiet for a 1Z, that is.

m;

Hello colleagues,

Unfortunately, I wasn't entirely sure whether I should revive this old post (from 2004) or start a new one. Anyway, this shows that I used the search function .

Unfortunately, the answer to that question is still unclear for me, and there is no explanation available here. Therefore, to reiterate the question, but phrased according to my concern:
Why is a TDI engine noisier (knocking) after the EGR system has been deactivated?

I couldn't find it through searching, so maybe someone can explain it to me in a simple way?

"In my opinion, there should be enough oxygen in both cases. Could it be related to the lower combustion temperature?" Or perhaps a later/slower combustion (mine runs quieter with a later injection start, basic setting MWB4).

I was already able to read about the effect on exhaust emissions, but I couldn't quite connect it to the noise...

Regards,
Tom.

I'm familiar with this effect. With a (high) EGR (exhaust gas recirculation) rate, the gas temperature before combustion starts is higher, similar to warm weather, which means better ignition with less delay. However, once combustion is running, the burning speed is lower. I'm not sure what causes this. A refrigerated AGR (Activated Granular Adsorbent Resin) system in a vehicle might be helpful if people aren't already aware of it.

Hello,

The exhaust gases displace some of the fresh air. Consequently, less oxygen is available for combustion, which results in a cooler and slower, thus softer, burn. The pressure increase is also lower. Lower combustion temperatures result in fewer NOx emissions.

A cooled EGR system, in conjunction with the most commonly used throttle valve, further increases the volume of exhaust gas that is recirculated because it increases the density of the exhaust gas. The cooling system further reduces the combustion chamber temperature.

That makes sense. Thank you all again!