TDI Performance Measurement: Calculating the Nominal Performance?

Hello,

According to Bosch' calculation guidelines for standard performance, the following corrections must be taken into account when measuring deviations from the standard conditions (+20°C and 1013 mbar) (approximate rules converted to metric units):

-> per 6K warmerer Luft plus 1% Leistung
-> for every 10mbar lower pressure plus 1% performance.

What happens, however, if a TDI is measured in (moderately) warm or high ambient conditions?

Because the fuel restriction is usually a few mg/stroke above the torque limit, higher temperatures (-> slightly decreasing LMM values) do not directly result in a noticeable reduction in the injection amount.

When the pressure is too low, only the load is slightly increased to maintain the target absolute load pressure value -> the LMM value remains the same.
The higher drive energy for the charger essentially comes "at no extra cost" from the exhaust gases, so that even the slightly increased back pressure does not result in a significant loss of engine power.

So, zum Beispiel, wenn ein TDI beispielsweise bei +32°C und 953 mbar gemessen wird, wobei die Papierleistung (nehmen wir den ATD / AXR) genau den Papierstandards entspricht, erhält er eine Bestätigung seiner Normleistung:
-> Measured Result = 100 HP
-> 2% surcharge for the heat
-> 6% surcharge for environmental pressure.
(60 mbar "too low" pressure corresponds to a storm or an altitude of 750 meters above sea level).

Makes 108 hp on paper, which is an 8% variance upwards, even though it's under normal conditions according to the aforementioned. Considering that it could potentially produce only 100 PS.

I can easily imagine that the often measured TDI performance variations, which tend to increase, are largely due to exactly such, unnecessary correction calculations.

What do you think?

Hello Ulf,

I agree with you that the engine control unit should, in principle, maintain the power output, at least within the moderate temperature/pressure range that you have defined.

Nevertheless, we know from experience that TDI works better in cold temperatures than in hot temperatures. Even though in both cases, the torque limitation only effectively works, that is, the Russ limit is still always above the torque limit.

So, Bosch has at least phenomenologically the right to introduce a correction factor here.
(and maybe someone at Bosch also knows the cause - it still hasn't become clear to me why TDI's have more power when the and MSG control is active in the cold, compared to the summer heat)

Best regards, Georg

Georg_G wrote:

So, Bosch hat zumindest phänomenologisch Recht, hier einen Korrekturfaktor einzuführen.

That's a universal correction, regardless of the engine. Therefore, primarily for gasoline-powered engines, because they are most sensitive to air density.
Sorry, I should have written that earlier.

Quote:

and maybe someone at Bosch also knows the cause - it hasn't yet become clear to me why TDI's have more power with the same MSG control in the cold than in the summer heat

Hm, my AFN actually had better DZR values in winter than in summer.

However, it seems that the ASZ engine doesn't really care about the season, so I mainly see the mysterious TDI summer slump (-> Search ) on VP37 engines...

Georg_G wrote:

...Nevertheless, we know from experience that TDI works better in cold temperatures than in hot temperatures, ...

Subjectively ( ), I have the impression that my (ASZ) feels better in dry weather than in wet weather. However, I cannot prove this with measurements. Maybe humidity affects the LMM???

Also, mein mechanischer TD hat bei trockener Luft (0°C) am besten funktioniert, und zwar ohne jegliche elektronische Sensoren. Ich habe einfach festgestellt, dass die kalte Luft einen höheren Sauerstoffgehalt hat, und mein TD war sowieso schon recht fett eingestellt (rußgrenze - was ist das? ).

joegolf wrote:

Emotionally, I have the impression that my (ASZ) feels better in dry weather, than in wet weather. However, I cannot prove this with measurements. Maybe the humidity is affecting the LMM???

As soon as the road is wet or damp, the rolling resistance increases (test: in Getriebe-LL, try rolling down a longer hill and observe the speed increase or "Vmax"), which could be perceived as a slight limp by sensitive drivers when accelerating in higher gears.

The DZR (German Racing School) times also extend on wet tracks...

Assuming that an engine is tuned on a dynamometer under normal conditions, certain limits must be met. These include, among other things, exhaust gas temperature, throttle position, cylinder pressure, and cylinder pressure rise rate, etc. By adhering to these conditions, I will achieve a power output of x! If the ambient air temperature and/or pressure changes, the engine can no longer achieve performance level x, as this would violate the specified limits.

If the ambient temperature increases, for example, to 30°C, the intake temperature will also increase, and consequently, with a constant injection volume, the exhaust gas temperature will also increase and exceed the limit value. Therefore, there is a [INTAKE AIR TEMPERATURE] correction after the torque map, which corrects the desired injection amount by a specific factor downwards... resulting in a decrease in power.

The same applies to a reduction in ambient pressure. Since the ATL is controlled by absolute pressure, it should theoretically compensate for the missing pressure. This would be achieved through stronger control. However, this would cause the ATL to over-rotate, making the required loading pressure under normal conditions unachievable. Consequently, the target loading pressure must be reduced. Loading pressure is decreasing...Air mass is decreasing...Therefore, the injection quantity must also decrease, otherwise the exhaust gas temperature will be too high.

The reduction in cylinder pressure is achieved using a special 3D-KF (Knock-Free), where the cylinder pressure (DRZ) is plotted on the x-axis, the ambient pressure on the y-axis, and the cylinder pressure on the z-axis. The injection amount is reduced in the torque-KF. Here, the torque is plotted based on the speed and ambient pressure. The highest torque curve is plotted at normal pressure. Therefore, there is no performance increase if the ambient pressure is above the normal pressure.

If there is also a corresponding increase in ambient temperature, the injection quantity will be further reduced according to the above description, using an additional correction curve. Also, the fuel injection amount is not increased if the ambient temperature is below the normal temperature.

The reason that the injection amount or boost pressure is not increased when the conditions are 'more favorable' than the normal conditions is the cylinder head pressure limit!

Best regards, Ben

Ben1972 wrote:

Example: If the ambient temperature increases, for example, to 30°C, then . . . Increase exhaust temperature and exceed the limit . . . performance decreases. The same applies to a reduction in ambient pressure. . . Air mass decreases...Therefore, the injection quantity must also decrease, otherwise the exhaust gas temperature will be too high. . . .Therefore, there is no increase in performance if the ambient pressure is above the normal pressure. The reason that the injection amount or boost pressure is not increased when the conditions are "more favorable" than the normal conditions is the cylinder head pressure limit!

Hi Ben,

It's been a long time since I've heard from you!

The reduction in boost pressure with decreasing ambient pressure is known to me as "Altitude Boost Protection".

In the initial posting, I wrote: ". . .when a TDI is measured in (moderately) warm or high ambient conditions . . ."
...before the engine's RPM or overheating protection system kicks in.

Do you know the (approximate) limit values for ambient temperature and pressure, at which the safety functions are activated?

Hello Ulf,

Sorry, that I haven't been in touch for so long, but I've been very busy.

Specifying exact limits is difficult. This primarily depends on how much distance you have from the mechanical limits. The quality of the air-intake cooling is also very important. I know engines where adjustments are already made at 25 degrees Celsius outside temperature, because the air intake already reaches over 70 degrees Celsius due to the air-intake cooling. If you have a better LLK (Low-Level Kicker) that allows only 40 degrees to be reached in the suction tube, then the limit at which you need to correct is, of course, higher.
'When it comes to turbochargers, the standard tuning typically utilizes the maximum possible continuous ATL (Air-to-Liquid) boost speed at the rated power output, so that the ATL doesn't need to be made larger than necessary (turbo lag, poor throttle response).' A disadvantage is, of course, that you then have to reduce the boost pressure by approximately the same amount, even at 100 mbar, because the air pressure is already lower.

Best regards, Ben

Hello Ben,

Regarding limitations, such as boundary detection fields, etc.

I have expanded and sealed the air duct from the engine compartment to the LLK (presumably referring to a specific component, possibly a climate control unit) on my Polo.
As a result, I was able to reduce LLT by ~ 20K compared to the original state, meaning that the loader now needs to handle correspondingly higher flow rates, which causes it to rotate at a higher speed.

On the other hand, the LLT essentially shifts in parallel with the ambient temperature, meaning that the charger is now only charging at "only" the amount that it would have been at 10°C without the modification, at 30°C.

Extreme case: The loader is now working so hard at -20°C that it's doing the same amount of work as it would have done at -40°C without the modification.

Does the EDC actually allow for over-revving the fuel pump in this way, or is there somewhere a "fuel pressure limit indicator" for the fuel pump pressure?