TDIs Sommerschlappheit - immer noch rätselhaft | Posts 16+

In principle, there are even alcohol/water mixtures or pure water injection systems for diesel engines to further cool the intake air. After compression and a temperature exceeding 700°C, the humidity is likely to play a very minor role.

When driving on wet roads or in rainy conditions, I'm more likely thinking about the performance gain achieved by using a water-cooled liquid cooling system, similar to the sprinkler systems used for liquid cooling.

Perhaps what's more interesting is the oil temperature. Typically, the engine's optimal performance is achieved at around 80°C; below and above this temperature, the power output decreases. In the summer, the temperature is likely to be in the higher range, while in the winter, the colder outside air lowers the water temperature, and the oil temperature is also reduced by the heat exchanger. I think this could potentially lead to a performance deficit in the summer.

I believe the Volkswagen Golf 3 TDI was not originally equipped with an oil cooler from the factory, right?

Okay, I just dug out my old documents.

It takes 1 calorie to raise the temperature of 1 gram of water by 1 Kelvin.
1 calorie (cal) = 4.1868 Joules.
So: What is the combustion temperature of diesel? 700 degrees? 800? Unfortunately, that's not my area of expertise. In any case, you would need to expend approximately 700 * 4.1868 Joules to raise 1 gram of water present in the air to its 'operating temperature.'
The calorific value of diesel is approximately 42,000 kJ/kg. Those who are interested can continue the calculations here.

The absolute humidity is RhoD = m/V [g/m^3].
Relative humidity is represented as RhoD/RhoS, which means 'the actual amount of moisture in the air at a specific temperature, divided by the maximum amount of moisture the air can hold at that same temperature.'
RhoS = Saturation amount.

Okay, gib mir den Text, den du übersetzt haben möchtest.

0 degrees Celsius: Relative saturation density (RhoS) = 4.8 g/m^3.
10 degrees Celsius: RhoS = 9.4 g/m^3.
20 degrees: 17.3
30 degrees: 30.3

If the relative humidity is 50% at a temperature of 0 degrees Celsius in winter, then the amount of water in the air is 0.5 * 4.8 = 2.4 grams per cubic meter of air.
In the summer, at a temperature of 30 degrees Celsius with 50% humidity, one cubic meter of air already contains 0.5 * 30.3 = 15 grams of water.

It makes a difference of about 13 grams of water per cubic meter of air between summer and winter. And these 13 grams reduce the calorific value of the diesel... I'm not going to deal with that anymore. I'll leave it to you.

best regards

Adrian.

@ SunMan

There is indeed a difference in relative humidity in the summer when it's 30 degrees Celsius (between rainy weather and sunny weather). This difference also exists in the winter.

best regards

Adrian.

@adrian: It's already clear that in the summer, with the same humidity level, there's more moisture in the air...
As you've already calculated, the absolute humidity in the summer is approximately 6 times higher. This is comparable to a relative humidity of 10% on a dry day and 60% to 80% on a rainy day. However, I've never been able to perceive a noticeable difference.

Here's another note regarding your calculation: Water transitions to a gaseous state starting at 100°C... and the heating behavior of steam is completely different from that of 'liquid' water... I remember this from the power plant engineering lectures .

I don't think it's going to be that easy.

thank you anyway...

sunman

Hi SunMan,

You're right, it certainly requires significantly less energy to heat the steam.
The specific heat capacity of water vapor is 1.9, while that of water is 4.19 J/(g*K). Thank you for the information.
However, it doesn't change the fact that energy is lost due to the water vapor.

'Unfortunately,' I come from the field of 'civil engineering.' So, my knowledge ends here. If I could continue, I would calculate how much air the TDI needs per ignition and how much energy is lost through water vapor. If that is roughly proportional to the power loss, that, in my opinion, would be the solution to the puzzle.
But, as I said, I'm a novice in this field.

best regards

Adrian.

Okay, I found a new table:

Specific heat capacities in J/(g*K) for gases:

Water vapor: 1.9.
Air: 1.0
Hydrogen: 14.9
Oxygen: 0.9
Carbon dioxide: 0.8

best regards

Adrian, on the verge of wisdom .

... so, I would also like to add that, in the winter, even with higher humidity, the function of the intercooler is more effective than it is at already high ambient temperatures of 35 degrees Celsius.

werwolf07 wrote:

... so, I would also like to add that in the winter, even with higher humidity, the function of the intercooler is more effective than when the outside temperature is already 35 degrees Celsius...

Hi.

That is, of course, correct. But what changes compared to summer? The amount of air being drawn in increases, and the charge air temperature decreases.
We tried to simulate both (increasing boost pressure --> more airflow, and artificially lowering the temperature signal) without any gain in performance .

Also, @Rainer:
Recently, someone posted here that they had simulated intake air temperatures between 0 and 100°C using a potentiometer, but without any noticeable effect on performance.

"It's probably not getting any worse" (compared to the EDC).

I consulted with a professor who previously worked in diesel development at BMW. He mentioned that a naturally aspirated diesel engine can experience a drop in performance during the summer due to the lower air density.
However, there is no logical explanation for this with a TDI engine. The fuel overheating mentioned should only occur in extreme situations.
He said that if it's truly possible to observe something like that, there's probably some kind of 'error' in the control/regulation system, or an effect that has nothing to do with the actual diesel process.

Perhaps another idea... maybe it has little to do with the engine itself, but rather with the engine control system, which could be causing a potential loss of power... Which control parameters in the engine computer are temperature-dependent? I'm rather a novice in this area, but perhaps we can get closer to the problem through these parameters...

Hello, Sunman.

Johannes wrote:

According to my calculations, the filling in the cylinder should increase by approximately 10% when the temperature is reduced. However, this only considers the ambient air temperature. How does the intake air temperature behave? Does it change proportionally to the ambient temperature? It should also be considered that if you burn a smaller amount of fuel, you will also have less power available to drive the turbocharger. Have you ever recorded the boost pressure?

Could it be that you are reaching the maximum boost pressure, but just more slowly?

Hi Johannes and everyone,

Sorry that I haven't been participating much in "my" thread; I'm currently dealing with some time-consuming problems }.

I didn't measure the intake air temperature, but based on the following reasoning, it should largely follow the outside temperature.

Coolers, with a constant mass flow rate, provide the same cooling capacity (in °C) "internally" and "externally," and with the same temperature difference between the internal and external sides, regardless of the absolute temperature.

The same principle should apply to the heating of the air by the turbocharger.

If the air temperature at the charger inlet is 30°C warmer in the summer (due to the outside temperature), the same applies to the air entering the liquid cooling system (LLK).
At the same time, the flowing cooling air is 30°C warmer (also the outside temperature), so the temperature at the outlet of the liquid cooling system is also 30°C warmer.

Regarding the burned mass: The amount of diesel should be the same. With the same boost pressure, but a higher intake air temperature, there will be less oxygen in the cylinder, but still "too much" = the diesel principle of excess air.
Could this "leaner" winter fuel mixture (--> higher combustion temperature !?) be responsible for the seasonal differences in fuel performance?

Regarding the boost pressure: When accelerating at full throttle, starting around 1300 rpm, the boost pressure reaches its target value of approximately 1 bar (summer and winter) at 2000 rpm, which is when the measurement begins.

Could this 'leaner' winter fuel mixture (--> higher combustion temperature !?) be responsible for the seasonal differences in fuel performance?


Hi Ulf!

As the air-fuel mixture becomes leaner, the combustion temperature decreases. (A Lambda value of 1 corresponds to the highest temperature; as the mixture becomes leaner, the temperature decreases again. In a TDI engine, the richest value at full load is approximately Lambda=1.6.)

The amount of diesel injected isn't the same... The mass airflow sensor (MAF) indicates the air mass, and the engine control unit (ECU) then adjusts the fuel injection up to a certain lambda value (soot limit). So, in winter, there's more air mass, which means more diesel is injected, and therefore more acceleration.
Wäre eigentlich logisch, nur mein Prof. sagt, daß es bei einem Turbomotor nicht sein darf. Und weil der schon in der Dieselentwicklung tätig war, glaub ich ihm das. Vorerst.

Best regards, Ernst.

Ernst S. wrote:

The amount of diesel is not the same... The MAF sensor indicates the air mass, and the control unit then adjusts up to this full-load lambda value (soot limit). Therefore, in winter, there is more air mass, and consequently, more diesel, which results in more acceleration.

Hi Ernst,

Based on what we believe to know, that is not entirely correct.

The air mass (soot level) is only one of three important limiting criteria for the fuel injection amount. The other two are the throttle position and the torque map, which protects the powertrain from mechanical overload.

In practice, the "most restrictive" limit is usually the torque curve, especially when the engine is running at full load and is in good condition.
As a result, when there's "more headroom" (referring to the boost pressure), no more fuel is injected --> compare this to my attempt with only increasing the boost pressure, which also results in more air being drawn in. Nevertheless, I didn't get even a tiny bit more power.

Hi Ulf!

Here's an older post of mine.


It seems that below a certain temperature (around 16°C), the performance remains consistent (with sufficient air mass to achieve the rated torque), but above approximately 16°C, the power decreases with the air density.


-> Regarding the extra power of the TDI engines, it's impossible to say right now whether they don't normally run at 30°C, and whether the 'extra' power only comes below that temperature.
It doesn't matter whether there's more at the bottom or less at the top; I already wrote that there shouldn't be this temperature-air mass effect (and therefore more or less fuel injection) in a turbocharger .


Now, let's go back to what it might actually be:
Perhaps there's an exhaust issue that VW is addressing by reducing power at high temperatures. The reduced intercooling and, consequently, the lower maximum power output (or increased fuel consumption in the summer, excluding air conditioning) could indicate a problem with nitrogen oxides. However, this is just a speculation.


P.S. to Ulf: You wanted to know what the professor says about the DZR: you can find it under 'Further attempts to explain the DZR'.

Hello everyone!

I've been following this forum with great interest for quite some time now. The current discussion is very interesting.

Question:

Could it be that an activated air conditioning system is responsible for the power loss?

Sure, that's really interesting. But it can't be a problem with the AC unit, because they even turn it off when trying to simulate realistic environmental conditions.