Ruckeln-Vibrieren-Hoppeln, PD TDI bei 1.600 bis 2.000 rpm | Posts 16+

It says right there: this works with engines that have a controlled intake manifold flap.

Rainer K. wrote:

It says right there: this works for engines that have a controlled intake manifold flap.

In a way, yes.

Sepp wrote:

I chose the method for deactivating the EGR system that uses the fresh air bypass channel, where all actuators and valves remain active and do not produce any error messages. Also, the "soft" shutdown behavior is preserved.

It would be interesting to see AGR (Air Gap Ratio) logs sometime, specifically to understand to what extent and under what operating conditions the target and actual air mass can be regulated to achieve consistency or "acceptable" deviations.

Hi K. Rainer,
The controlled intake valve doesn't necessarily explain it to me.

How do I force fresh air into the intake manifold of an engine when there is already positive pressure there?

The controlled intake manifold flap allows for Exhaust Gas Recirculation (EGR) even in situations where the exhaust pressure before the turbine is not much higher than the boost pressure in the intake manifold. However, it cannot be used to introduce fresh air directly into the boost pressure.

If the valve is closed, no air should be coming from the charger.

perwollf wrote:

Hi K. Rainer, The controlled intake valve doesn't necessarily explain it to me. Or how do I pump fresh air into the intake manifold of an engine

when there is already overpressure there?
IMO, it's not necessary.

A hole between the mass airflow sensor (MAF) and the intake manifold can be patched with a simple solution: wrap it with a nylon stocking (as a filter).

The AGR is mechanically locked.

When the throttle valve begins to close, a vacuum is created behind it, which draws in "false air" behind the mass airflow sensor (MAF), causing the MAF value to decrease.

I probably can't express myself properly...

I'm going to try one last time:

The goal of using AGR (Abgas Rückführung, or Exhaust Gas Recirculation) is to reduce NOx emissions. In the future, similar limits are likely to be imposed as those already in place for gasoline engines.
To achieve this, you need a DeNOx catalyst (see Toyota) or a very high level of EGR (which would be an internal engine measure), even under heavy engine load where the turbocharger is operating.

If I understand correctly, your solution only works if there is a vacuum in the intake manifold compared to the ambient pressure.

However, that's not enough. NOx should also be eliminated under load. Therefore, the EGR system should function even when the turbocharger is already operating, meaning when there is overpressure in the intake manifold.

It works well as long as the pressure before the turbine is much higher than the pressure after the compressor. To expand this operating range and reduce dependence on the turbine-compressor characteristics, a throttle valve is installed.

Well, if that's still not understandable, then the problem is probably on my end...

Again: It is IMPOSSIBLE for positive pressure to build up in the intake manifold if both the EGR valve and the "throttle valve" (also known as the "additional EGR valve") are closed.

Please explain where the corresponding air is supposed to come from, considering that the engine is constantly drawing air in.

Rainer K. wrote:

Again: it IS NOT possible for overpressure to develop in the intake manifold if the EGR and the 'throttle valve' aka 'additional EGR valve' are closed. Please explain where the corresponding air is supposed to come from, considering that the engine is constantly drawing some in.

Hm... I think "perwollf" is using the great VAG term "Saugrohr" to refer to the entire area between the air filter and the intake valves.
So, also also for the section from the compressor outlet to the engine .

Yes, I may have used the term 'Saugrohr' incorrectly. I was referring to the intake manifold, or whatever that part is called where the throttle valve and EGR valve are located. It's the part that's located behind the turbocharger and intercooler.

And of course, there's also overpressure!

Rainer. K, perhaps you mean that the exhaust gases are fed back into the intake manifold *before* the compressor, mixing with the fresh air? If that's the case, I would understand your contributions better. I am not familiar with such a design.

In the MTZ 1/2005 issue, there is an interesting article titled 'Two-stage controlled supercharging.' It states, for example, that in commercial vehicle engines, exhaust gases must even be recirculated under full load (!!!) due to new emission regulations.
And that's why it might even be necessary to inject exhaust gases into the compressed fresh air, even against the maximum boost pressure.

If the pressure difference is not sufficient: you can slightly close the throttle valve. This will reduce the fresh air pressure in the intake manifold and increase the exhaust pressure before the turbine (because the turbine also has to compensate for the increased throttling).

And in this way, the necessary pressure difference can always be generated, regardless of the turbine-compressor characteristics.

If the pressure difference is not sufficient: you can slightly close the throttle valve. This will reduce the fresh air pressure in the intake manifold and increase the exhaust pressure before the turbine (because the turbine also has to compensate for the increased throttling).

And in this way, the necessary pressure difference can always be generated, regardless of the turbine-compressor characteristics.

Hmm, I think this is a very questionable method. Why not simply handle the whole thing via VTG? Is there any information about this available online?

Yes, it's probably not the most elegant solution, but it's a nice way to decouple it from other control processes, such as boost pressure regulation via a wastegate or variable geometry turbocharger.

Just the thought of installing a throttle body designed for a diesel engine is a disaster... (now I'm not talking about the 'digital' throttle that closes when the engine is turned off).

There is no online version of the 'motortechnische zeitschrift' (a magazine about engine technology). You can order it at www.all4engineers.com. It's extremely expensive, but it's worth it!

Back to the topic: In the same issue, DC developers wrote about the small three-cylinder diesel engine for the Smart, produced by Mitsubishi.

'The necessary high levels of exhaust gas recirculation (up to 40%) require a corresponding flushing volume between the exhaust gas recirculation cycle and the compressed fresh air intake system.'

'Through numerous attempts to optimize the flow conditions, the pressure losses in the entire return line were kept so low that an additional control valve to create a pressure difference was no longer necessary.'

Okay, I should start with this quote right away. At least it was formulated in your 'mother tongue,' not in my hybrid German .