Turbocharger Issues: Impact of Exhaust Volume | Posts 32+

Hi,

*blows dust off*

Regarding the practice of blocking the EGR valve with a metal plate or similar material, there is sufficient information and discussion on this topic in this thread and other related articles.
As can be seen in other threads, the "metal method" is no longer easily possible on EU4 Diesels. (I only found one thread on this topic by "bee").
The solution in this case is to increase the target air mass value.

But what exactly happens during this adaptation? Is the entire air mass target map shifted upwards?

Okay, I have the following questions about motor control:

1.) Low load condition: Minimal exhaust emissions, so the turbocharger generates very little pressure. The EGR valve is now controlled in a way that achieves the desired airflow rate (as determined by the mass airflow sensor).
a) Due to the high adaptation of the target value, the intake air is now enriched with cold, oxygen-rich air. Since the density of cold air is greater than the density of warm exhaust air, shouldn't the pressure in the cylinder increase? Does this cause a measurably higher rate of wear?
b) Could someone with a background in chemistry tell me if the exhaust volume leaving the engine compartment through the exhaust manifold (and driving the turbocharger) increases? Based on the subjective descriptions here in the forum ("engine responds better to the throttle," "turbocharger spools for longer"), it seems that should be the case, right? This would mean that the turbocharger spins faster with a reduced EGR rate. What about the turbocharger's durability? After all, the turbocharger's speed, at least at low load and low RPM, should be significantly higher with the increased exhaust volume compared to when using recirculated exhaust gases, or not?

2) What is the technical rationale behind the mass airflow sensor (MAF)? Certainly, it measures the mass of air, but why? Is it simply to allow the engine control unit (ECU) to know how much fuel can be injected without producing excessive soot? Couldn't the air mass be calculated more simply based on engine speed and displacement? This would eliminate one sensor, which costs money and can fail. And it wouldn't require complex MAF sensors that can differentiate between pulsating and non-pulsating air masses.

3.) Full Load Operation: The AGR (Abgasrückführung - Exhaust Gas Recirculation) is active regardless, but the target air mass map is shifted upwards. The turbocharger builds up the boost pressure necessary for this load condition, and together with the engine speed, the amount of air that can be forced into the combustion chambers can be calculated (excluding losses). If the target air mass value is highly adapted, the engine may not be able to reach this higher value at full load. Should the engine control unit not detect this manipulation and store a fault code? (Or is there perhaps no defined target air mass value for full load? In any case, there is no such value listed in the technical data for the AXR engine here in this forum.)


Regards,
Sure, here is the translation of the text from German to English:

"Micha"

Hi,

*blows dust off*



2) What is the technical rationale behind the mass airflow sensor (MAF)? Certainly, it measures the mass of air, but why? Is it simply to allow the engine control unit (ECU) to know how much fuel can be injected without producing excessive soot? Couldn't the air mass be calculated more simply based on engine speed and displacement? This would eliminate one sensor, which costs money and can fail. And it wouldn't require complex MAF sensors that can differentiate between pulsating and non-pulsating air masses.


Regards,
Micha

Hello,
2.) How is the engine supposed to know what the boost pressure is, and therefore how much air mass is available for the combustion of the fuel?
Best regards,
Günther.

Hi Günther,

There's a measurement block for the boost pressure. I assume there's a corresponding pressure sensor for it. If I remember correctly from a thread here in the forum, it's located on the intercooler.
Please correct me if I'm saying something wrong.

Regards,
Sure, here is the translation of the text from German to English:

"Micha"

Mephisto wrote:

But what exactly happens during this adaptation? Is the entire air mass target map shifted upwards?

Basically, yes.

Quote:

Due to the high adaptation of the target value, the intake air is now enriched with cold, oxygen-rich air. Since the density of cold air is greater than the density of warm exhaust air, shouldn't the pressure in the cylinder be increased, or? Does this cause a measurably higher wear?

At a lower cylinder filling temperature (due to a lower proportion of hot exhaust gases), the density will also be higher, even at the same pressure .

Quote:

b) Could someone with a background in chemistry tell us whether the exhaust volume that leaves the engine compartment through the exhaust manifold (and drives the turbocharger) increases? Based on the subjective descriptions here in the forum ("engine responds better to the throttle," "turbocharger spools for longer"), it seems that this should be the case, right?

Not necessarily.
The EGR valve is less open and can close completely more quickly when the accelerator is suddenly pressed. This causes the mass airflow sensor (MAF) value to increase more rapidly and to a higher level -> the fuel injection quantity can be increased more quickly (without producing soot), which in turn causes the turbocharger to spool up faster.

Quote:

This means that the turbocharger spins faster with a reduced EGR rate. What about the turbocharger's durability then? After all, the turbocharger speed, especially at low load and in the lower load range, should be significantly higher due to the larger volume of exhaust gases, compared to when using recirculated exhaust gases, right?

Even if the engine speed is slightly higher in the low load and lower load ranges compared to full EGR operation, these speeds are negligible compared to high load conditions. Therefore, these engine speeds will likely not significantly reduce the lifespan of the turbocharger.

Quote:

2.) What is the regulatory background for the LMM (Lambda Measuring Module)? Certainly, it measures the air mass, but why? Is it solely to ensure that the engine control unit knows how much fuel can be injected without causing excessive soot?

And (mainly) as a control variable for EGR -> read the relevant articles!

Quote:

Can the air mass not be calculated more easily based on engine speed and displacement?

. . . plus turbocharger pressure and LLT!
However, this only applies to a "fixed flow resistance" throughout the entire motor.
As soon as, for example, the catalytic converter or the intake manifold becomes clogged with AGR sludge, or the exhaust system is modified in a way that affects airflow, the entire calculation becomes useless...

Quote:

3.) If the target mass airflow (MAF) value is highly adapted, the engine may not be able to reach that higher MAF value under full load. Shouldn't the engine control unit then detect this manipulation and store a fault code? (Or is there perhaps no full-load MAF target value? In any case, there is no such value listed in the technical data for the AXR engine here in this forum.)

Hm, that's a good question. As far as I know, errors are not saved.

I suspect there's a "maximum limit" for the desired air mass, which applies even when parts of the highly adaptive EGR characteristic map have higher values.

Hi Ulf,

Quote:

Quote: 2.) What is the control engineering background for the Mass Air Flow (MAF) sensor? Certainly, it measures the mass of air, but why? Is it simply to allow the engine control unit (ECU) to know how much fuel can be injected without causing excessive soot? And (mainly) as a control variable for EGR -> read the relevant articles!

I have already read the relevant article (and not just once, until I understood everything ), and I think your idea about using AGR sludge, etc., is quite close to the solution: It essentially expands the tolerance range in which the engine operates properly. Without a mass airflow sensor (MAF) and with a clogged intake manifold, the clogging would accelerate: Less and less air (the engine doesn't notice it) with the same amount of fuel injected --> more and more soot --> increasingly higher flow resistance... I don't even want to think about the consequences.

Regards,
Sure, here is the translation of the text from German to English:

"Micha"

This only applies to a 'fixed flow resistance' throughout the entire motor.
As soon as, for example, the catalytic converter or the intake manifold becomes clogged with AGR sludge, or the exhaust system is modified in a way that affects airflow, the entire calculation becomes useless...

This could be circumvented by measuring the boost pressure directly in front of the intake valves, and additionally measuring the exhaust pressure at the exhaust manifold. This would require 4 measured values to calculate the air mass: engine speed, lambda (air-fuel ratio), boost pressure, and exhaust pressure. (The engine control unit should be able to reconstruct the exhaust density based on the injection quantity).

What can still cause problems are tolerances in valve timing, valve lifters, and leaky valve seats.

I believe that true value would be a car with, for example, a 10-year warranty against sensor, actuator, and MSG failures. VAG has created a terrible workaround with the mass airflow sensors. I don't know if diesel cars from other manufacturers are also this susceptible.

Fortunately, an SDI with VEP doesn't have an LMM, and it also has a handful fewer sensors.

Regards,
Holger.

I believe that true value would be a car with, for example, a 10-year warranty against sensor, actuator, and MSG failures. VAG has created a terrible workaround with the mass airflow sensors. I don't know if diesel passenger cars from other manufacturers are also this susceptible.

Fortunately, an SDI with VEP doesn't have an LMM, and it also has a handful fewer sensors.

Regards,
Holger

Hello,
Consent; what doesn't exist can't 'cause trouble' or 'interfere.'
Best regards,
Günther.

Hi,

Seit letzter Woche ist mir bei meinem Fabia (ATD) ein selstames Ruckeln im Teillastberiech aufgefallen. Habe dann mal hier im Forum ein bisschen gestöbert und als evtl. Lösung das Abklemmen der AGR gefunden. Jetzt ist mir heute aufgefallen, dass bei mir dieser dünne Luftschlauch (Messung Druck im Luftfilter?) vom Luftfilter zu irgendwas ab war. Könnte das Ruckeln auch daher kommen? Also, Schlauch drauf und trotzdem mal AGR abgeklemmt. Dann hab ich mal ne Runde gedreht und das Ruckeln ist mir bis jetzt nicht mehr aufgefallen. Beim Abstellen ist mir kein großartiges Nachlaufen aufgefallen, nur, dass er jetzt recht ruppig ausgeht. So ähnlich wie beim Absaufen. IIs that normal?

Greetings, jbst.

Yes, that's normal if you disconnect the wrong hose. You've triggered the shut-off valve; I would reverse that.

Yes, it's normal if you remove the wrong hose. You've triggered the shut-off valve; I would reverse that.

Hi,

I only disconnected the hose connected to the actuator that controls the EGR valve. Or are there more than one?

jbst

Hello,
This button likely controls the parking brake lever.
Best regards,
Günther.

Hm,

The valve is exactly the one shown in the technical article. Are there two of them?

jbst

Hello jbst,
Take a look at which actuator (valve) your can is connected to. If it's located in the intake section, then it's the shut-off valve.
Unfortunately, I'm not familiar with your engine at all.
Best regards,
Günther.

Hi,

The ATD is the 74 kW PD diesel engine in the Škoda Fabia. The solenoid actuator controls a valve that is located in a connection between the exhaust manifold and the intake manifold. This must be the EGR valve. However, this engine is quite common. Does anyone else know anything about it?

jbst

Hello,
Okay, then it's the EGR valve.
Best regards,
Günther.

Hi,

Ich hab meinen Fehler gefunden. Auf dem Bild im Fachartikel, die schwarze Dose ist zur Steuerung der Abstellklappe und die silberne die für das AGR Ventil, woll? Hatte tatsächlich den Schlauch der schwarzen Dose abgeklemmt. Ups. Hab das jetzt korrigiert und mal den Schlauch der silbernen Dose abgeklemmt. MI see.

jbst