Sommerschwaeche | Posts 16+

Hello,


How much does that amount to? In other words, what is the percentage or the kilowatt value?

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


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

Okay, so when I read this and also consider the discussion from last year, I think it's a combination of factors: the gremlin contribution and the viscosity of the diesel. 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 the biodiesel tanks.
Mixers may not necessarily experience such a performance loss in the summer. Also, I think the 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 amount of fuel already being reduced due to 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 of turbomotors.

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, higher exhaust temperatures are to be expected, which in turn leads to a higher mass flow and, consequently, earlier turbocharger response.
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 the amount of air being drawn in and the temperature of the intake air are not responsible for the summer performance issues.

And here's another older thread:

/viewtopic.php?t=1034&highlight=

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 a longer period.
After longer drives, especially when the engine is working hard, the fuel in the tank can get heated up, particularly when there isn't much fuel left. My experience with long-distance drives is also that the engine doesn't seem to run as smoothly after a while.
I'm primarily suspecting the fuel viscosity, but I'm wondering why the developers would allow something like that.
For me, the difference will soon be about one second, according to the ULF DZR method.

Best regards,
Uwe

Deleted upon request.

Hi Uwe,

Your theory is quite plausible, especially since I noticed the most significant difference this week on Monday. While it was also the warmest day, the temperature differences weren't that large. However, something else was different: On Monday, my car was parked in direct sunlight all day, which made it very hot, and that, of course, also affects the diesel in the tank, especially with so many hours of warming time.

So, it could actually work well, because with just a few degrees less temperature, and parking in the shade today, I didn't experience that effect nearly as strongly.

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 a considerable amount of time 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, I can say:
In cold, humid air, the effect is so strong that it has even been noticed by my daily passenger.

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


Please provide the text you would like me to translate from German to English.

Hello!

Regardless of the diesel temperature, what's the actual difference in degrees? When I think about it and do a small test, I get the following results. I measured the temperatures around my car; it's important to note that my T4 is black. Yesterday, the outside temperature was 31.3°C (according to a home thermometer), inside the car it was 52°C, and the car's outside temperature display showed 33°C. Under the car, it was just under 29°C. The hood of the car, in this case, was facing away from the sun, so it wasn't directly exposed.

It's clear that the tank will at least reach the ambient temperature, which in this case is approximately 30°C. However, 30°C is actually a temperature that is rather insignificant from a technical perspective. Nevertheless, it does lead to a slight decrease in performance.

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

I'm now interested in how diesel behaves in relation to 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'm not sure how it is in the T4) is located between the rear wheels, where it's not directly exposed to the sun or the heat of the interior. Perhaps it would be worth checking the diesel temperature immediately after starting the engine on a hot day, but it probably won't reveal much.

So, it remains a mystery... although it's also possible that multiple effects are overlapping in their impact.

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 behavior of 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 has a negligible effect, whereas the change in viscosity at (technically) low temperatures is very significant.

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 in the pump will also increase (assuming laminar flow). The throttling at the nozzle orifices is very likely to be turbulent, so the conditions here remain independent of viscosity.

Therefore, the "diesel theory" as a cause for 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 3.5 hours after being turned off while still warm.
- Outside temperature: 19-22°C
- 70% fuel level
- ECON climate

The first third of the journey is the green hell of 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 being an overtaking maneuver.

Unfortunately, the trip didn't go exactly as I had hoped; especially in the city, I encountered almost exclusively green waves.

However, a trend is emerging. Driving at 70 km/h in the truck convoy had no effect on the diesel temperature. Only when it continued with two lanes at 130 km/h does the diesel temperature increase. 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 mostly idle while rolling. Before the traffic light, the intake air temperature continues to rise... This is an indication of 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, but rather at a brisk pace.
and when the traffic light turns green, you experience the usual slow acceleration.

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

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