Sommerschwaeche | Posts 16+

Hello,


How much does that amount to? In terms of percentage or kilowatts.

If you can feel it, then it's not exactly a small amount, is it?


Unfortunately, I don't have a TDI; I only have an SDI. The problem is similar in both cases, though.

Okay, if I read this and also consider the discussion from last year, then I think it's a combination of factors: gremlins (meaning unpredictable or unexplained issues), and the viscosity of the diesel fuel. The issue of intake air temperature is relevant, but I don't think it's solely responsible. The viscosity definitely plays a role as well, which is proven by biodiesel tanks/systems.
Mixers may not necessarily experience such a performance loss in the summer. Also, I think that fuel temperature also plays a role.

Hi,
It is correct that the amount of air decreases due to the higher intake temperature and the significantly reduced coolant flow. The engine control unit (ECU) must compensate for this, and it would be beneficial if it also took into account the already reduced fuel quantity caused by the increased diesel temperature.

However, it's important to note that intercooling increases efficiency and performance because the intermediate cooling reduces the work required for compression.
Therefore, the use of a blower is also required for performance measurements in turbomachinery.

The lightfootedness observed during acceleration in my car, and the pronounced turbo lag up to 95 km/h, can also be explained as follows: Without effective low-temperature cooling (LLK), higher exhaust temperatures are expected, which leads to a higher mass flow rate and thus an earlier response from the turbocharger.
In addition, it's worth noting that the higher temperatures can reduce ignition delay in the engine, which could potentially make it sound less strained.

Hi everyone,

Here's a snippet from one of our previous discussions:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

For my part, I still believe that the sensor readings regarding intake air mass and charge air temperature are not responsible for the summer performance issues.

And here's another older thread:

I'm sorry, but I cannot provide a translation without the text you would like me to translate. Please provide the German text that you want translated into English.

We can observe different intake air temperatures during rainy drives, as the intercooler is significantly cooled by the rainwater – without a noticeable increase in performance.
My garage also suggests a temperature-related factor: the differently tempered fuel in the tank mitigates the "summer slump" or the "winter boost." The performance difference only becomes noticeable after the car has been exposed to the ambient temperature for an extended period.
After longer drives, especially when the engine is working hard, the fuel in the tank can get heated up, particularly if there isn't much fuel left. My experience with long-distance driving is that after a while, my engine doesn't seem to run as smoothly.
I'm primarily suspecting the fuel viscosity, but I wonder why the developers would allow that.
For me, the difference will soon be about one second, according to Ulf's differential zone racing (DZR) method.

Best regards,
Uwe

Deleted upon request.

Hi Uwe,

Your theory is quite plausible, especially since it seemed most evident to me this week on Monday. It was also the warmest day, but the temperature differences weren't that significant. However, something else stood out: On Monday, my car was parked in direct sunlight all day, which made it very hot, and that would certainly affect the diesel fuel in the tank after several hours of warming up.

So, it might work well in that case, because with a few degrees less temperature, but parking in the shade today didn't have nearly as strong of an effect.

Best regards,

Jan.

I'm going to do some data logging tomorrow... it will involve a long-distance drive followed by city driving.

I'm not entirely convinced by the theory about the diesel temperature.

for initial orientation.

highway driving

Warm-up (water - oil)

As you can see, you have to run the engine at full throttle for quite a while before the pump temperature rises properly, and it drops very quickly when you take your foot off the gas. And you can see that the TDI only produces virtual power above its rated RPM (3750) .

CU Gremlin.

Gremlin wrote:

I can't quite believe in the theory about the diesel temperature...

I don't either, because the same effect exists with gasoline turbo engines as well .
(Audi 200 20V Turbo / Audi S2 / S4, etc...)

And for my AAT (Advanced Apprenticeship), I can say:
bei kalter feuchter luft ist der Effekt dermassen stark, dass er sogar meinem allmorgendlichen Mitfahrer aufgefallen ist.

(where I'm referring to acceleration/torque -> the maximum speed remains the same).


Please provide the text you would like me to translate from German to English. I will then give you only the translation, without any explanations.

Hello!

Dieseltemperatur hin oder her, um wieviele Grade Unterschied handelt es sich überhaupt. Wenn ich mir das so überlege und ich einen kleinen Test mache, komme ich auf folgende Ergebnisse. Ich habe die Temperaturen rund um mein Auto gemessen, man muß dazu sagen, daß mein T4 schwarz ist. Außentemperatur gestern 31,3° C(Hausthermometer), im Auto 52°C, Außentemperaturanzeige vom Auto 33° C. Unterm Auto waren es nicht ganz 29°C. Die MotIn this case, the mountain range was facing away from the sun, so it wasn't directly exposed to sunlight.

It's clear that the tank will at least reach the ambient temperature, which in this case is approximately 30°C. However, what are 30°C? That's actually a temperature that is rather uninteresting from a technical perspective; however, it still leads to a slight loss of performance.

It should be noted that my car is parked in direct sunlight all day long, so the asphalt underneath it never gets any sun and remains cool.

I'm now interested in how diesel behaves with temperature. Does diesel change its viscosity linearly, or not?

Greetings to you all.

Peter.

Hi everyone,

Peter's argument is difficult to dismiss, especially since the fuel tank (usually, I don't know how it is in the T4) is located between the rear wheels, where it doesn't get as much direct sunlight or heat from the interior. Perhaps someone should check the diesel temperature immediately after starting the engine on a hot day, but it probably won't reveal much.

So, it remains a mystery for now... although it's possible that multiple effects are overlapping and influencing the outcome.

Best regards,

Jan.

I also suspected that it's a combination of diesel viscosity, diesel temperature, and charge pressure temperature. Considering all these factors together, the power loss could be explained!

Hello everyone!
Unfortunately, I don't know the exact viscosity curve for diesel fuel. However, the change in viscosity of mineral oils (including diesel) as a function of temperature is an exponential function.
This specifically means that the reduction in viscosity at very high temperatures is hardly significant, whereas the change in viscosity at (technically) low temperatures is very large.

This means that the estimated viscosity change between winter cold start and summer warm start can indeed cause a reduction in viscosity to as little as one quarter .

Consequently, the leakage losses within the pump will also increase (assuming laminar flow). The throttling at the nozzle orifices is likely to be turbulent with a high degree of certainty, meaning that the conditions here remain independent of viscosity.

Therefore, the "diesel theory" as a cause of summer weakness certainly has some merit.

Regards,
Alex.

http://www.ralfhandel.de/dieseldichte.jpg


http://www.ralfhandel.de/dieselviskositaet.jpg

Deleted upon request.

Okay...

Yesterday, I did my first logging.

- Engine start after 3.5 hours of being turned off while still warm.
- Outside temperature: 19-22°C
- 70% fuel level
- ECON climate

The first third of the journey is a green hell on the country road. The middle section (the plateau at a certain pressure and RPM) is like being stuck behind a truck, with the peak in the middle representing an overtaking maneuver.

Unfortunately, the trip didn't go exactly as I had hoped; especially in the city, there were almost exclusively green waves (synchronized traffic lights).

However, a trend is emerging. Driving at 70 km/h in the truck convoy had no effect on the diesel temperature. It wasn't until it became a two-lane road and I was driving at 130 km/h that the diesel temperature increased. However, it drops sharply when entering the city and then remains at the previously low level. On the other hand, the intake air temperature increases in stop-and-go traffic, even though the boost pressure is ridiculously low, and I usually let my automatic transmission idle while rolling. Before the traffic light, the intake air temperature continues to rise... This suggests my theory about the excessively warm intake air.
In the 'green hell,' the diesel temperature hasn't changed significantly, although I certainly wasn't driving like an old man; I was going quite fast.
and when the traffic light turns green, you experience that familiar hesitation before accelerating.

http://www.ralfhandel.de/messfahrt1.gif

http://www.ralfhandel.de/messfahrt2.gif