Summer weakness

Hello everyone,

Was it also that hot where you are today?

"Left Bielefeld at midnight the day before yesterday... It was 6 degrees Celsius, and the TDI engine had plenty of power. And today, on the way home from work... it's 33 degrees Celsius, and the air conditioning is running full blast... THAT is a really stark difference and a good demonstration of the TDI's summer weakness."

Did you notice that as clearly today?

Best regards,

Jan.

Jan6K wrote:

Did you notice that as clearly today?

Hi,

Yes, I noticed ! Today, I had to replace my TDI with a 1.4-liter 75 horsepower gasoline "monster." Every time I went uphill, I felt like I wouldn't make it!

My AXR is lost again... where is it?

So, my 130 horsepower in the AWX didn't seem significantly more tired than usual. And yesterday, on the way home with the camper, I also didn't notice any significant differences.

However, with my 1Z, I also experienced this 'summer slump' to a very extreme degree.

Hello!

Yes, yes, this summer slump. I've noticed the typical weaknesses at higher temperatures in both my AHU (Air Handling Unit) and now also in my ACV (Variable Air Volume system). Furthermore, when driving in the city, the coolant gets so hot that you have to drive a considerable distance before it cools down enough to provide any actual cooling again.

I had some ideas already, like a cooling fan controlled by a thermostat, or a water spray system that's activated by the kickdown switch on the accelerator pedal. On the T4 (ACV), the radiator isn't really exposed to much airflow. What else can be done there without immediately converting to the larger radiator from the 111kW 2.5 TDI? (Plans for that conversion are known.)

Thoughts and plans. I was also told that a low air-to-fuel ratio can lead to higher thermal stress on the engine because there is more oxygen available for combustion.

Please correct me if I'm wrong.

Greetings, Peter.

My AAT (presumably referring to a vehicle) handles in the opposite way. It feels particularly nimble when it's warm.
However, it's not necessarily producing less smoke than when the engine is cold. I know that theoretically, the intercooler should make it produce less smoke, but there must be other factors at play.

joergs wrote:

also meine 130 pferdchen im awx kamen mir nicht wesentlich müder vor als sonst. . . . allerdings bei meinem 1z hatte ich dieses sommerloch auch extrem.

Hello everyone.

This confirms my long-held suspicion that the temperature compensation of the railway switch (RWG) is not 100% accurate.
PDs don't have a rear wheel drive (RWD).

I wanted to log the group's data with the quantity limits (throttle, torque, and soot) during a dynamic stability test while it was cold, and then repeat the same process when it was hot.

If the soot limit doesn't shift significantly, it would, in my opinion, mean that the EDC believes it is injecting the same amount of fuel all the time, which is probably not the case.

Unfortunately, I missed the cold weather period. Does anyone else have a CSV file for a reproducible full-load test that was conducted in very cold weather? Perhaps someone could run a comparison test when it's "nicely" hot (ugh, sweat!).

Hi,

My AAT results are quite ambiguous.
I notice a less responsive feel in the city, or generally when accelerating quickly from a standstill and at low engine speeds, especially in hot weather (as I also experienced with the 1Z).
The maximum speed, on the other hand, remains quite impressive.
I finally got to drive at full speed on the highway today and reached almost 220 km/h according to the speedometer. That's roughly my winter top speed, maybe even a bit higher.

Hello!

I can fully confirm the behavior that Markus H. observed in his Golf III (AFN), although his number 220 needs to be replaced with 205.

Greetings, Klaus.

Hello.

There's a conversion formula for power.

P = PNorm * pLuft / 1013 * sqrt(293 / (273 + tLuft))
PNorm ... Standard performance.
pLuft ... Pressure in millibars (mbar).
Air... Temperature in degrees Celsius.

So, a vehicle with an 81kW engine actually has around 76-84 kW depending on the season and weather conditions. This should affect naturally aspirated engines much more severely than turbocharged engines, which would need to compensate for it. I have no idea why VW doesn't do that.

The constant top speed makes sense because the air resistance decreases by the same factor as the power.


Best regards, Ernst.

Deleted upon request.

We already discussed this topic during the last hot summer. We have two TDIs in our household: an older AHF with a VE injection system and an AJM with a PD injection system. Both of them exhibit this "summer weakness."
The last theory, which has not been disproven, was that the change in fuel viscosity causes this effect, and that the engine control unit does not compensate for it.
Due to the higher viscosity of colder diesel fuel, there are fewer leakage losses in the injection pump, resulting in more fuel being injected. My own observations confirm this. My vehicles are parked in a temperature-controlled garage and their performance is affected by the temperature inside the garage. This "summer weakness" effect only occurs after they have been exposed to higher ambient temperatures for an extended period, which suggests that it's not due to overheating of the cooling system, but rather to components or the fuel itself gradually adapting to the outside temperature.My theory is also supported by the use of biodiesel: with a low mixing ratio, the driving performance improves significantly and fuel consumption increases, even though the biodiesel has a lower calorific value. However, when running solely on biodiesel, the driving performance drops dramatically. Biodiesel has a higher viscosity than conventional diesel, and adding it makes the contents of the tank more viscous.I think it sounds quite obvious, doesn't it?

Best regards,
Uwe

Deleted upon request.

With my 5 questions, I don't want to 'put you on the spot' right now, but I was simply interested in what basis you used for your statement. Perhaps I phrased my question incorrectly, so please excuse me if that's the case, and I understand if you choose not to respond.

Yes, I think you're overthinking it... that's simply the standard formula to account for the variable density of air (and not a special TDI formula that I developed after extensive testing).
I copied it from the textbook 'Design of High-Speed Internal Combustion Engines' (by the way, the author is from AVL). However, you can probably figure this out even without the textbook, because I think everyone learns about the factors that influence air density in physics class.

And then it's also logical to think that with a turbocharger already present, one could compensate for all of this. Perhaps you can tell me why VW doesn't do that, or what other factors cause the summer weakness (or winter strength).

Best regards, Ernst.

Comment from a non-expert!

Hello!

I hope you won't take this the wrong way, but my thought process was as follows.

Die Dichte des Diesels nimmt durch höhere Temperaturen ab, also er dehnt sich ziemlich aus, was heißen will, daß ich mehr Kraftstoff und mehr Luft benötige um die gleichen Fahrleistungen zu erreichen. Also kann ich mir diese gewollte Sommerschwäche nur dadurch erklären, daß die VW Leute sonst mit ihren Verbrauchsangaben nie und nimmer zu ihren angegebenen Normverbrauchswerten hin kommen. Es There's a new regulation stating that manufacturers must adhere to their stated fuel consumption figures, with a permissible deviation of only a few percent.

Hello Uwe!

Ganz hab ich das mit dem Bio"p"iesel nicht verstanden. Biodiesel hat einen geringeren Brennwert. O.K. Wenn ich eine "geringe" Menge zumische, erhöht sich zwar die Leistung aber der Verbrauch steigt? Soll das heißen, daß ich zwar die Viskosität des Diesels so weit verbessere, daß ich mehr Leistung habe, aber die EDC so regelt, daß ich einen höheren Verbrauch habe? Durch die verbesserte Viskosität erreiche ich ja eigentlich genau das gleiche, wie bei kühlerem Kraftstoff, es gelangt eigentlich die richtige Menge an Kraftstoff in den Verbrennungsraum, wie in kühleren Jareszeiten. Und bei der geringen Beimengung von Biodiesel, fällt ein Mehrverbrauch wirklich auf? WiHow much biodiesel did you mix in?

If the EDC system were to effectively compensate for the high air temperatures, why is there such a significant increase in soot content that all TDI engines start producing excessive smoke?

Greetings, Peter.

Um...

I'm also familiar with the summer weakness, especially when starting from a traffic light... There are no problems driving on highways.

But I don't think it's related to the diesel engine...

The composition of the combustion chamber is essentially determined by the charge pressure and the temperature of the intake air.
While the former cannot exceed a maximum value, the latter depends on the temperature of the intake air and the coolant. If the car only receives hot air just above street level in the city, or even no air at all (due to traffic lights or stop-and-go conditions), how can it cool the charge air when suddenly subjected to full load?

The EDC (Engine Control Unit) only registers something like 'oops, 70° charge air temperature, reduce injection slightly or it will smoke,' and even then, the TDI engine starves for fuel if it's running lean.

It also perfectly matches my observations on country roads...

On occasion, I used to lie about something, but today it's supposed to be about bicycles.

CU Gremlin.

Mc_Givertechnik wrote:

Ganz hab ich das mit dem Bio"p"iesel nicht verstanden. Biodiesel hat einen geringeren Brennwert. O.K. Wenn ich eine "geringe" Menge zumische, erhöht sich zwar die Leistung aber der Verbrauch steigt? Soll das heißen, daß ich zwar die Viskosität des Diesels so weit verbessere, daß ich mehr Leistung habe, aber die EDC so regelt, daß ich einen höheren Verbrauch habe? Durch die verbesserte Viskosität erreiche ich ja eigentlich genau das gleiche, wie bei kühlerem Kraftstoff, es gelangt eigentlich die richtige Menge an Kraftstoff in den Verbrennungsraum, wie in kühleren Jareszeiten. Und bei der geringen Beimengung von Biodiesel, fällt ein Mehrverbrauch wirklich auf? WiHow much biodiesel did you mix in?

Hi Peter,

I added about 10 to 20% biodiesel to the fuel tank. However, I want to point out the uncertain compatibility of the biofuel; my car has run for 100,000 km on it and is still running, but I'm not using it anymore.
With my mixture, the viscosity doesn't improve; it actually increases. This means the juice becomes thicker.
Die Pumpe baut Druck auf. In dem sich verkleinerndem Volumen sind logischerweise Ritze, durch die sich ein Teil des Sprits zurück in den Kreislauf durchdrückt. Dieser Teil gelangt dann beim Einspritzvorgang nicht mehr in den Brennraum. Ist die Viskosität höher, ist der Leckverlust kleiner und die tatsächlich in den Zylinder gelangende Spritmenge größer. Damit steigt die Leistung bei zunächst gleichem Wirkungsgrad, durch den gesunkenen Brennwert und den erhöhten gefahrenen Fahrleistungen jedoch steigt der Verbrauch an. Bei In a purely biogas-based system, I observed differences of up to one liter, while in a mixed system, it was around 0.3 liters.
Ich gehe bei dieser Theorie allerdings davon aus, dass die Steuerung zumindest die Temperaturänderung nicht kompensiert. In der ESP sitzt ein Kraftstofftemperaturgeber, das Steuergerät weiß also bescheid. Es wäre ein leichtes für das Steuergerät, die Einspritzmenge bei Kälte zu reduzieren. Scheinbar tut sie das nicht. Die Änderung der Viskosität (evtl. auch die Oberflächenspannung?) allein kann das Steuergerät nicht erkennen. Also ein 0-cent tuning??

Best regards,
Uwe