AGR Impact on Engine Efficiency

Hello TDI community,

In the latest special issues of ATZ and MTZ, I came across an article on exhaust gas recirculation that I found very interesting.
The article describes technical measures for complying with future emission limits for diesel engines, particularly concerning NOx emissions. The focus is on cooled exhaust gas recirculation, which allows for a further reduction in NOx emissions. For this purpose, an exhaust gas coolant heat exchanger is used, which cools the recirculated exhaust gas flow.

"Quote from the article:"

Quote:

The NOx reducing effect of EGR is based on lowering the oxygen concentration of the air-fuel mixture by adding exhaust gas to the fresh air. However, in order to ensure the combustion of each fuel unit, the flame must capture and heat a larger mass of charge. This reduces the temperature and speed of combustion. Due to the exponential dependence of the NOx formation rate on temperature, this results in a significant reduction in NOx emissions. The additional cooling of the recirculated exhaust gas further enhances this effect. In addition, it improves cylinder filling and increases the EGR compatibility.

When the EGR system is faulty, the efficiency increases primarily because the combustion speed rises. This brings the process closer to an isobaric (constant pressure) process, which manifests as a slightly increased mechanical load on the engine (higher peak combustion pressure compared to a functioning EGR). However, this should not be critical, as the peak combustion pressures at partial load are always lower than the peak combustion pressure at full load, which is identical with and without EGR.
According to that, one should theoretically be able to observe an increase in torque at partial load if the EGR system is defective, right?

Later in the article, cooled exhaust gas recirculation was compared with other systems for reducing emissions.

Quote:

Compared to NOx reduction in the SCR process, the system costs of cooled EGR are significantly lower. Especially if it is possible to achieve the PM limit without using a particulate filter. However, the lower system costs are offset by a higher fuel consumption

. Therefore, for each application case, it must be re-evaluated which system "makes sense".}

Here, the disadvantage of reduced efficiency is once again clearly highlighted, as it results in higher consumption.
Beim neuen V6-TDI werden bereits AGR-Kühler verbaut. Ich bin schon gespannt, wann die ersten Probleme mit diesen Motoren auftreten. Wenn bei kaltem Motor der Abgasstrom durch die AGR-Kühler strömt, dann wird zwangsläufig der Taupunkt der Abgase unterschritten. Dadurch gibt es einerseits einen Säureangriff auf AGR-Kühler und Ansaugbrücke. Andererseits gelangt so auch Kondensat in die Ansaugbrücke. Ob das how good is it?
In addition to soot and oil vapor, exhaust condensate is now also being produced in larger quantities. How will this affect the engine in the long run?

Regards,
Alex.

All Euro4 PD-TDIs already have this EGR heat exchanger installed!

Regards,

Manuel.

It would be interesting to see if the EGR cooler could be repurposed as an additional intercooler in case of a shutdown. However, it's doubtful whether the EGR systems on the newer TDIs are as easily disabled as those on the older models.

Okay, disconnecting the EGR valve on a dynamometer can increase torque by approximately 10-15 Nm, depending on the engine, but only within the operating range of the EGR system.

for statistical purposes only:

My ALH automatic also has a cooled EGR system, and the heat input into the engine is significant. With a faulty EGR valve, the car takes noticeably longer to warm up in the winter...

The principle is the same as with the fresh air intake: lower temperature, higher density, which allows for more exhaust gases to be introduced... all for the sake of the environment.

CU Gremlin.