Beobachtung zur Sommerschwäche - ALH | Posts 16+

However, it would be important to understand how the adjustments are made for intake air temperature, ambient temperature, diesel temperature, and intake/ambient pressure. This is so that one can infer potential causes for the summer performance issues from the logged data, and whether they are intentional or simply could not be compensated for.

Also das Rußkennfeld besteht nur aus Drehzahl, Luftmasse/Hub und Kraftstoffmasse, ohne Einfuß der LL-Temp.

For me, the soot map is not solely determined by the air mass measurement. While air mass measurement can be a useful optimization tool, it's not strictly necessary, and the engine could still produce a soot map even without it.

I didn't say that the adjustment of temperatures and pressures should be included in the air mass injection limiting system, but rather in the torque map, so that I can utilize additional air mass in winter. This is because it's expected that the air mass will be higher.




I'm still focusing on the diesel temperature issue.
The lower density of the hotter fuel is compensated for by extending the injection duration 'backwards,' which shifts the overall process more towards a state of equal pressure and thus reduces efficiency.
Ob das allerdings schon die gesamte Sommerschlappheit erklären kann, weiß ich nicht . . .

Do those few percentage points of extra diesel really have such a significant impact on the efficiency? In a real diesel engine, the combustion peak should be around 15-20° BTDC (Before Top Dead Center). And in a script diagram, there's hardly any noticeable decrease in efficiency (around 1%) within a range of approximately +/- 5° BTDC.

Best regards, Ernst.

Also z.b. könnte man das Mehr an Luftmasse bei niedrigen Temperaturen auf jeden Fall für eine höhere Leistung ausnutzen.

Last summer, I tried the DZR (Direct Injection Resonance) experiment with increased boost pressure, which means more air mass. However, the stopwatch showed no improvement whatsoever.
Also kann die Luftmasse IMO nicht die eigentlich begrenzende Größe gewesen sein.

Exactly because I don't believe that the air mass measurement is influenced by temperature, but rather that the torque limitation could be adjusted. So, you would have to make your control unit believe that all temperatures are at a winter value. Then, in summer, more fuel would be injected (which would heavily load the engine and significantly increase the NOx emissions), or the air mass sensor itself would become the limiting factor even under steady-state full load conditions (which it shouldn't actually be).


Glaube ich nicht: Das Drehmoment'kennfeld' des AFN ist eigentlich nur eine simple Tabelle mit rpm und mg/Hub. Also auch ohne jeglichen Temperatur-Einfluß.

It's possible that the value logged by VAGCom doesn't actually contain any adjustments. However, an adjustment is definitely being made (I just don't know how extensive it is). All the values displayed in VAGCom, such as diesel temperature, intake air temperature, etc., also influence the fuel injection amount, and there are other factors like load adaptation as well.


Probably, the torque limit is set slightly lower 'from the factory' to allow for some leeway initially (with a new mass airflow sensor), so that performance isn't immediately lost during such operations.

Yes, I am quite certain of that. And in the winter, there would be a slightly larger margin for adjustment. This extra margin could then be used for torque limitation. The air-fuel ratio would remain the same, so I wouldn't expect any higher peak temperatures. I would only have a few more Nm (Newton meters) of torque in the winter. This happens automatically in many (but not all) naturally aspirated gasoline engines because there is more available airflow, and then, due to the lambda control, more fuel is injected.
The legal regulations for performance measurement include standard conditions and conversion formulas to account for temperature influences. Therefore, it is permissible to have a higher power output in the winter.

Why shouldn't a TDI engine take advantage of this increase in air mass during the winter? It would be strange for a TDI driver to outperform a gasoline engine in the summer, but then fail to do so in the winter because the gasoline engine can utilize the increased air mass while the TDI cannot.
That's why he does it... I think .

Okay, to maintain a constant top speed, I also need an increase in power that exactly matches the increase in air resistance. And air resistance increases directly with the density of the air!

Best regards, Ernst.

Last summer, I tried the DZR experiment with increased boost pressure, which means more air mass. However, the stopwatch showed no improvement whatsoever.
Therefore, in my opinion, the air mass was not the actual limiting factor.


Just a moment...

If I remember correctly, you simulated a lower boost pressure for your EDC system using resistance. So, it will adjust the boost until it reaches its target of 0.9 bar again.

0.9 bar

The EDC doesn't really care about the actual boost pressure you have. It assumes a value of 0.9 bar and adjusts the injection amount accordingly .



'And sorry, Ulf, if I'm experiencing moderate weather with a charging air temperature of 20°C and high summer temperatures of 60°C, no one can blame the engine performance on diesel temperature...'

I will start logging the fuel injection amount in the future.

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

'Cu Gremlin'

Gremlin wrote:

ulf wrote: Last summer, I tried the DZR experiment with increased boost pressure, which means more air mass. However, the stopwatch showed no improvement whatsoever. Therefore, in my opinion, the air mass could not have been the actual limiting factor. Just a moment... If I remember correctly, you simulated a lower boost pressure for your EDC system using resistance. So, it will adjust the boost until it reaches its target of 0.9 bar again. 0.9 bar The EDC doesn't really care about the actual boost pressure you have. It assumes a value of 0.9 bar and adjusts the injection amount accordingly

.
Hi Ralf,

You described my attempt correctly (whether it's 0.9 or 1 bar doesn't really matter here).

But for injection quantity limitation based on the soot map, the boost pressure is irrelevant; only the air mass = MAF sensor value matters.
And it increases with higher boost pressure, while all other conditions remain the same.
However, according to the DZR test results (multiple runs), the approximately 7% additional fresh air introduced into the cylinders by increasing pressure was not used to increase the fuel injection amount.
Similarly, manipulating the values of the LL temperature (-20°) and the engine temperature (-10°) did not result in any performance gains.

Quote:

und sorry ulf, wenn ich bei mässigem wetter 20° ladelufttemp. habe und bei hochsommer 60°; da kann mir keiner mit dieseltemp. zur leistungsschwäche kommen...

Of course, you can stick with the explanation regarding the LL temperature setting – but for me, it remains questionable.
Do you know anything about a possible decrease in efficiency with increasing low-temperature operating temperatures without a simultaneous reduction in injection volume?

Quote:

In the future, I will log the fuel injection amount.

I'm looking forward to the results!

Okay...

I just finished reading through a 500-page document.

The following values apply for smoke control:

- air mass per cylinder
- engine temperature
- speed (referring to revolutions per minute)

The air mass per cylinder is calculated based on:

- measured air mass (HFM5)
- turbo pressure
- intake air temperature
- cylinder fill level (constant, or variable depending on engine speed and design).

In this process, the engine temperature and speed are used as correction factors. Specifically, a cold engine operating at full load receives a higher fuel injection amount than what is normally allowed for smoke-free operation. This is because, without this adjustment, the power output would be severely limited due to smoke restrictions (nobody wants their car to stall at an intersection).

The actual boost pressure ratio is determined (we have an external pressure sensor). For the intake air temperature, a correction factor can be set depending on the application to account for the location of the sensor (e.g., because the temperature may increase further along its path).

I kept pushing the mill up the hill a few more times, and sure enough: the driver's request was significantly ABOVE the air mass limit.
'The 10-cent cigarette still smells very strongly when it's 30°C outside, but not when it's only 13°C, like this morning.'

Logging continues, more updates to follow...

CU Gremlin.

Just a reminder: The mass airflow sensor (MAF) measures the volumetric flow rate based on air velocity and a constant intake cross-section. To calculate the actual mass flow (mass airflow), you also need the state variables of temperature and pressure. Based on the engine speed, the amount of air per cycle is then calculated. The cylinder filling level isn't actually relevant for this calculation when balancing the intake, unless the exhaust gas recirculation (EGR) system interferes.
Why should the temperature increase further along the path after the sensor? Wouldn't the pressure loss and heat transfer to the surrounding air counteract this? Unless the ambient temperature in the engine compartment is higher than the intake temperature due to the heating up of the engine.
Stay cheerful.
OlBe
P.S.: The injection amounts will tell the story... (I don't think you can subjectively notice the efficiency losses that are being discussed here).

@olbetec:

Quote:

Just a reminder: The mass flow sensor (LMM) measures the volumetric flow rate based on air velocity and a constant intake cross-section. To calculate the mass flow (LM) from this, you also need the state variables temperature and pressure.

I believe you haven't fully understood how an LMM (Mass Air Flow sensor) works. The LMM measures the mass airflow, not the volumetric flow. The air density and temperature are automatically taken into account in this measurement principle because the airflow passing over the hot-film element has a different "cooling effect" on the element depending on the density and temperature of the air.

Regards,
Alex.

Gremlin wrote:

ich hab mich eben mal durch 500 seiten doku gelesen...

Hi Ralf,

I envy you for your "sources" .

Quote:

The following values apply for smoke control: - air mass per cylinder - engine temperature - speed (referring to revolutions per minute) The engine temperature and speed are used as correction values in such a way that a cold engine under full load receives MORE fuel injection than is permitted for smoke-free operation, because otherwise, due to the smoke limitation, only a small amount of power would be available. (Who wants to starve at the intersection?)

Okay, I was only familiar with the map that shows air mass, engine speed, and diesel injection quantity.

Quote:

The amount of air per cylinder is calculated based on: - measured air mass (HFM5) - turbo pressure - intake air temperature - cylinder filling level (constant, etc., depending on engine speed and engine type)

Funny, why is it so complicated?
My thoughts on this are:
All the air that the mass airflow sensor (MAF) measures, for example, per minute, must also pass through the engine during practically the same time period (but with a delay corresponding to the total length of the intake manifold).
Also teilt man den gemessenen Massenstrom pro Minute durch die Anzahl der Saughübe pro Minute (beim 4Zyl. die doppelte Drehzahl) und schwuppps hat man die (mittlere) Luftmasse pro Zylinderfüllung. {

Quote:

For the charge air temperature, a correction factor can be set depending on the application, which takes into account the location of the sensor (e.g., because the temperature may increase further along its path)

.

"In my opinion, this is also unnecessary: Since there should be no air loss or gain between the mass airflow sensor (MAF) and the engine, the actual intake manifold temperature is actually irrelevant."
Because: The less hot air mass that flows "through" the engine, the less air is simultaneously drawn in "from the front" by the Mass Air Flow sensor (MAF).

So, what's the point of all this calculation? The only explanation I can think of is a dynamic fine-tuning, for example, to calculate the actual air mass as precisely as possible during rapid load changes.
Dazu würde mich interessieren, Ob dieser denkbare Präzisionsgewinn nicht von vorneherein durch die Toleranzen und Altersdrifts der LMM ad absurdum geführt wird . . .

Quote:

ich hab die mühle noch ein paar mal den berg raufgehetzt, und siehe da: drivers request lag deutlich ÜBER dem air-mass limit.

Okay, then, in my opinion, a simultaneous increase in boost pressure could have allowed the airflow to exceed the driver's requested level.
I'll try that out on my tractor sometime soon.

Quote:

weiterhin raucht das 10cent sehr deutlich wenns draussen 30° hat, aber nicht wenns (wie heut morgen) nur 13° hat.

So it seems that the excess air is higher at 13° than it is at 30°.
What can be concluded from this?
For example, that at 30°, the charger doesn't suck in as much "unnecessary" air, and the overall energy balance of the engine is at least more favorable at this point at 30° than at 13° .

Quote:

logging geht weiter, more to come...

Yes, please keep us updated. Maybe we'll actually solve the mystery someday...

@donalexo
You are right: it measures the mass of air being drawn in (kg/h). I was confused myself, so I read it again. Therefore:

Quote:

"Quote:" The air mass per cylinder is calculated based on: - measured air mass (HFM5) - charging pressure - intake air temperature - cylinder fill level (constant, or variable depending on engine speed and design). Funny, why so complicated? My thoughts on this are: All the air that the mass airflow sensor (MAF) measures, for example, per minute, must also pass through the engine during practically the same time period (but with a delay corresponding to the total length of the intake manifold). So, you divide the measured mass flow rate per minute by the number of intake strokes per minute (which is twice the engine speed for a 4-cylinder engine), and voila, you have the (average) amount of air per cylinder filling.

Es wird aus den zusätzlichen Zustandsgrößen die tatsächliche Zylinderfüllung berechnet. Die AGR, die Kurbelgehäuseentlüftung, Kennfelder für die Ventilüberschneidung (f(n)), Höhenkorrektur und ein Saugrohrmodell, das die Speicherwirkung berücksichtigt, fließen in die Korrektur des vom LMM gemessenen Wertes ein. Im eingeschwungenen Zustand sind sie bis auf die Kennfeldwerte der AGR und der Kurbelgehäuseentlüftung gleich dem Wert des LMM. DaheIt's so complicated...
Stay cheerful.
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

olbetec wrote:

Es wird aus den zusätzlichen Zustandsgrößen die tatsächliche Zylinderfüllung berechnet. Die AGR, die Kurbelgehäuseentlüftung, Kennfelder für die Ventilüberschneidung (f(n)), Höhenkorrektur und ein Saugrohrmodell, das die Speicherwirkung berücksichtigt, fließen in die Korrektur des vom LMM gemessenen Wertes ein. Im eingeschwungenen Zustand sind sie bis auf die Kennfeldwerte der AGR und der Kurbelgehäuseentlüftung gleich dem Wert des LMM. DaheIt's so complicated...

Hi OlBe,

Regarding KGE and AGR, I don't understand what you mean.

Because both times, the engine is drawing in gases other than fresh air, or volumes of gas that do not pass through the mass airflow sensor (MAF).
(In the case of EGR, the mass airflow sensor (MAF) signal is even used as a feedback variable to control the system. Therefore, the EGR function cannot simultaneously serve as a "calculating" correction of the MAF signal, because that would create a circular dependency.)

As corrections, I now have:
- the intake manifold model in terms of its storage effect -> dynamic behavior.
- the loss due to valve overlap (air passes through the mass airflow sensor but is immediately lost towards the exhaust), which depends on the pressure difference between the intake side (boost pressure) and the exhaust side (atmospheric pressure).
Understood.

But maybe someday I'll understand it completely.

ulf..

You are too focused on the term 'air mass.' The air mass measured by the MAF sensor only provides meaningful information as an absolute measurement in a naturally aspirated engine.

As you know, air density depends on pressure and temperature. And here's where the problem begins in a turbojet engine. As the air is compressed and heated, its density changes. Especially at high pressures, the temperature increases significantly.

The LMM measures the mass of air per unit of time. That's fine. However, the cylinder is a closed volume, and the amount of air inside it depends heavily on the pressure and temperature of that air. The EDC (Electronic Diesel Control) essentially does nothing more than calculate the air density.

If we use the ideal gas law formula, for example, the following result might be obtained:

The standard value is 1.2922 kg/m³ at 273.15 Kelvin and 1013.25 mbar.

At a pressure of 980 millibars and a temperature of 20°C, the result is approximately 1.165 kg/m³.
1980 millibars and 20°C result in approximately 2.354 kg/m³.
1980 millibars and 60 degrees Celsius result in approximately 2.071 kg/m³.

And pay attention, we always have the same volume here (also known as a cylinder).

Therefore, you can't simply use the value of the mass airflow sensor (MAF) to determine the exact amount of air entering the cylinder.
because both pressure and temperature are factors to consider.
'I have a temperature of 30°C and a pressure of 1600 millibars. To achieve the same air density per volume, I would need approximately 1750 millibars at a temperature of 60°C.'
If you want to know the exact values, you can't avoid calculating based on boost pressure and temperature. Otherwise, you're wasting potential, or the engine might smoke terribly. Also, don't forget about the scavenging losses, which in a turbocharged engine are mainly dependent on the boost pressure.
That's probably why 'summer sag' isn't as noticeable in older TD models, because they aren't being pushed to their limits.


two more things:

Of course, the air can be heated again from the intake manifold to the cylinder (correction factor for the lambda sensor). Take a look at different engines and see what kind of strange structures are sometimes installed... In gasoline engines, the air is even intentionally warmed up to prevent icing.


and OF COURSE, the laser module will be monitored for drift. Yes, live and in color...
BUT: the evaluation and display are only required for OBD-II systems. The mass airflow sensor (MAF) is monitored using the exhaust gas recirculation (EGR) system because, according to the calibration data, the air mass should correspond to specific values based on the EGR control settings. Changes that are too drastic (either sudden or gradual) will trigger an error. However, this only applies in the USA; otherwise, we would all be driving around with malfunctioning EGR systems.
'However, the mass airflow sensor (MAF) is checked for zero-point drift during the post-run procedure. Unfortunately, this check doesn't happen if the MAF sensor is simply coated with dirt.'

CU Gremlin.

The fact that the EGR system is controlled using the mass airflow sensor (MAF) signal has nothing to do with the calculation of cylinder filling. Okay, the EGR system uses the MAF signal as an input and a target value (lookup table) for control. However, since what is actually injected into the cylinders is dynamically tracked (calculated), the EGR or EGV only serves as an input parameter, not as a controlled variable.stay calm.
OlBe

@gremlin
The air mass (more accurately, the air mass flow rate in kg/h) is a calculated value. Once the engine is running properly, it's only affected by factors like exhaust gas recirculation (EGR), knock control (KGE), and valve overlap; nothing else changes it. Therefore, you don't need to look at cylinder pressure or temperature to determine what's happening inside the cylinder.

"By the way, does anyone know what the valve overlap is on a TDI engine?"

Hi.

'Once the LMM has measured the mass, that's the mass, and it won't be changed later by pressure or temperature... That's what I always thought too.'

But how does the mass flow meter measure the mass flow? Is it through the cooling effect caused by the heated film?

If we have the same mass flow rate twice, for example, once with cold air at low pressure and once with hot air at high pressure, such that the density is the same... wouldn't the LMM (likely referring to a Laminar Flow Meter) be cooled down more by the cold air and report a higher mass flow rate?

So, the mass flow meter must know the temperature of the ambient air in order to be able to determine the heat loss based on the mass flow rate.

@ Ulf: Regarding your attempts to simulate an external temperature, this would mean that the mass airflow sensor (MAF) would interpret the low simulated temperature as a small air mass flow rate because it wouldn't be cooled down as much as it would expect at -10°C. And then, once again, the 'Nm Limit Airmass' feature ruined your attempt to compensate for the summer weakness.

That was not an argument , but rather a question about the exact function of an LMM.

Best regards, Ernst.

Hello,

Unfortunately, I couldn't find anything about the Bosch parts, but it wouldn't surprise me if they were quite similar.
The Pierburg HFM is definitely temperature-compensated.

http://www.kolbenschmidt.de/pdfdoc/lms_e.pdf

Best regards, Rainer.

HFM5:
Auf der Sensorfläche sitzt ein zentral angeordneter Heizwiderstand und hält sie auf einer konstanten Temperatur. Außerhalb dieser geregelten Heizzone fällt die Temperatur zu beiden Seiten ab. Auf diesen Stromaufwärts und -abwärts liegenden Zonen wird die Temperatur mit NTC's gemessen. Durch die vorbeiströmende Luft verschiebt sich das Temperaturfeld. Die an die Luft abgegebene Wärmemenge und damit der Temperaturverlauf auf der Sensorfläche hängt von dem vorbeiströmenden Luftmassenstrom ab. Die Temperaturdifferenz ist dabei unabhängig der absoluten Temperatur der vorbeiströmenden Luft und zudem richtungsabhängig. Durch Due to the low mass of the sensors, the response time is very fast (settling time < 15 ms).
The additional temperature sensor is an optional accessory and is not required for this measurement principle.
Stay cheerful.
Olbe.

P.S.: Since the heat flow released by the air passing by depends on the heat transfer coefficient, an increasing level of contamination (which degrades the heat transfer coefficient) will result in a steadily lower heat flow/temperature difference, and consequently, a lower airflow rate being measured...

... The temperature difference is independent of the absolute temperature of the flowing air...
'... The additional temperature sensor is an optional accessory and is not required for this measurement principle.'



... mit zunehmender Verschmutzung (Verschlechterung des Wärmeübergangskoeffizienten) ein stetig geringerer Wärmestrom / Temperaturdifferenz und damit Luftmassenstrom gemessen...

With that first statement, you are contradicting my explanations from the LMM meeting.

With the second statement, you are contradicting yourself!

If a heat flow is dependent on a heat transfer coefficient, then it is also dependent on a temperature gradient. Heat always flows from hot to cold, and the greater the temperature difference, the larger the heat flow.

Wenn der Luftmassenstrom durch den Wärmestrom(der bei Alterung kleiner wird) gemessen wird dann hat die Temperatur der Luft auch eine Auswirkung. Wenn das Meßprinzip nur durch relative Unterschiede am Heißfilm funktioniert, so wie du es zuerst beschrieben hast, dann nicht(Und die Alterung kann auch nicht durch einen kleiner werdenden Wärmestrom beschrieben werden). Entscheide dich bitte. USorry if I misinterpreted something and read a contradiction into what you said that wasn't actually your intention.



The Pierburg HFM is definitely temperature-compensated.


Does this mean that the difference is compensated in the output signal through a measurement of the air temperature? Or is the temperature difference already compensated for within the measurement process itself, making the air temperature irrelevant and eliminating the need for any measurement? Unfortunately, I didn't understand anything from the link.

Best regards, Ernst.