LLK-Wirkung teilweise enträtselt? | Posts 16+

Dan.jel wrote:

What would actually be the benefit of additionally spraying the LLK with water droplets?

Reducing the intake air temperature -> yes.
Performance improvement usually -> no

If that part gets hotter than 100°C, you've essentially created a vapor cooler that can dissipate significantly larger amounts of heat. Of course, it works even better the hotter the liquid coolant is.

Hey guys!

We once rode along with a VW Motorsport racing car at the Nürburgring, and that vehicle had a pressure switch installed under the accelerator pedal that, under full throttle, would empty the windshield washer reservoir towards the engine's cooling system. According to VW Motorsport, this significantly reduces the engine temperature.

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Logically, the intake air will become cooler.

However, the standard software and the standard motor are adapted to the high temperature.
Therefore, the amount of fuel injected is not increased when the temperature decreases.

The increase in air mass is not implemented in the TDI system.

It's already the case with gasoline engines, but the performance gain is likely to be quite small.

Water injection only makes sense for specific driving profiles, such as high boost pressure but low vehicle speeds (rallying), drafting, or when there is limited space for the intercooler.
In a standard production vehicle, it's only likely to be useful for the next traffic light race .

CU Gremlin.

What would it actually achieve to additionally spray the LLK with water droplets?
Has anyone ever tested this before?

I would like to repurpose some of the unconnected SRA (Surface Roughness Analyzer) units and then, for a while, pour distilled water into the washing water reservoir!

I had planned to do that at the beginning of the semester break.
The fact is that the freezing point of water is much lower than the air temperature.
This means that, for example, at a dew point temperature of 50°C, the water surface will have a temperature of approximately 20°C. This can be determined from an h,x diagram. This is due to the evaporation of the water.

It might actually help in my case, because my car produces a lot of black smoke above 3000 RPM due to the chip. So, I'm going to install a windshield washer system from a scrapped car into it! I'll post the results.

Hello.

I just remembered something else:
Improving the efficiency of the lubricant allows for more air to enter the cylinders, meaning that the mass airflow increases while the boost pressure remains the same.

However, this in turn means that the compressor must deliver more power (compressor power = volumetric flow rate on the suction side * pressure increase).

And how is the increased charging power achieved?
Regarding the boost pressure control loop, a more aggressive control of the variable turbine geometry (VTG) or the wastegate increases the pump losses of the engine.

Conclusion: The further the intake air is cooled down, the...
-> The higher the pressure, the greater the stress on the charger (at the same charging pressure!).
-> The engine has to deliver more power to the turbocharger, which in turn means that this power is not available as useful output -> engine power loss!! (although it may be minimal).

The latter consequence only applies to normally tuned and intact TDIs, where the soot limit is above the torque limit.

Is that correct, or am I making a mistake somewhere?

Hello,

I just remembered something else:
Improving the efficiency of the lubricant allows for more air to enter the cylinders, meaning that the mass airflow increases while the boost pressure remains the same.

However, this in turn means that the compressor must deliver more power (compressor power = volumetric flow rate on the suction side * pressure increase).

And how is the increased charging power achieved?
Regarding the boost pressure control loop, a more aggressive control of the variable turbine geometry (VTG) or the wastegate increases the pump losses of the engine.

Conclusion: The further the intake air is cooled down, the...
-> The higher the pressure, the greater the stress on the charger (at the same charging pressure!).
-> The engine has to deliver more power to the turbocharger, which in turn means that this power is not available as useful output -> engine power loss!! (although it may be minimal).

The latter consequence only applies to normally tuned and intact TDIs, where the soot limit is above the torque limit.

Is that correct, or am I making a mistake somewhere?

Cooling the intake air in the intercooler would reduce the pressure if the turbocharger doesn't supply enough fresh air. This results in lower back pressure, allowing the turbocharger to pump more air. (The reduced pressure is not measurable because it's compensated for by the turbocharger. Consequently, the variable geometry turbine (VGT) / wastegate will adjust to maintain the target pressure!)

Conclusion: the further the intake air is cooled down, the...
-> The higher the altitude, the greater the stress on the turbocharger (at the same boost pressure!).
-> The engine has to deliver more power to the turbocharger, which in turn means that power is lost as it's not being used for propulsion -> engine power loss!! (although it may be minimal).


Generally, your reasoning is correct, because a charger (also known as a VTG) is only optimized for a specific ratio of pressure and flow rate.

With extremely increased low-temperature cooling, the ratio of required flow rate to required pressure increase shifts, causing the turbocharger to leave its optimal operating range. Above a certain flow rate, the boost pressure gradually decreases, and the target pressure can no longer be reached. The turbocharger's efficiency decreases (whether this can be achieved solely through extreme low-temperature cooling is debatable).

Conclusion: In my opinion, extreme LL cooling only makes sense if a more powerful charger (with a higher volumetric flow rate) is used, along with adjusted engine characteristics. Unless the original charger still has some performance reserves.

Conclusion: the further the intake air is cooled down, the...
-> The higher the altitude, the greater the stress on the turbocharger (at the same boost pressure!).
-> The engine has to deliver more power to the turbocharger, which in turn means that power is lost as it's not being used for propulsion -> engine power loss!! (although it may be minimal).


Generally, your reasoning is correct, because a charger (also known as a VTG) is only optimized for a specific ratio of pressure and flow rate.

With extremely increased intercooler cooling, the ratio of required flow rate to required pressure increase shifts, causing the turbocharger to leave its optimal operating range. Above a certain flow rate, the boost pressure gradually decreases, and the target pressure can no longer be reached. The turbocharger's efficiency decreases (whether this can be achieved solely through extreme intercooler cooling is debatable).

Conclusion: In my opinion, extreme LL cooling only makes sense if a more powerful charger (with a higher volumetric flow rate) is used. Of course, with adjusted engine characteristics. Unless the original charger still has performance reserves.

Okay, that makes sense! If the charger has uneven pins, it can't build up any pressure, which is understandable.
The cylinder filling at the same pressure is a function of the density! Assuming the turbocharger provides a higher volumetric flow, the mass difference can be calculated based on the temperature: density = initial density * (initial temperature / current temperature) * (current pressure / initial pressure).
where the temperatures are to be entered in Kelvin!
Let's calculate the change from a pressure of p_barometr.1 bar (1265 kg/m³) and a temperature of t=20°C to a pressure of 1 bar above atmospheric pressure and a temperature of 50°C.
We obtain a density of 2295 kg/m³.
At 40 °C and 1 bar, we obtain 2368 g/m³.

'So, relatively speaking, it's producing 3% more air in the cylinder .'

SeatArosa1.7SDI wrote:

Quote: Conclusion: the further the intake air is cooled down, the... -> The higher the altitude, the greater the stress on the turbocharger (at the same boost pressure!). -> The engine has to deliver more power to the turbocharger, which in turn means that power is lost as it's not being used for propulsion -> engine power loss!! (although it may be minimal). Generally, your reasoning is correct, because a charger (also VTG) is only optimized for a specific ratio of pressure and flow rate . . .

OK, thank you for the confirmation.

"Funny" it might be, especially with engines that are only chip-tuned, where the increase in boost pressure pushes the turbocharger right to the point of incipient overload.
If it needs to deliver even more throughput (thanks to a larger LLK), it will go even further into the red zone -> premature failure of the charger due to LLK tuning .

A case for a specialized article on LLK tuning; I will add to it.

Hello,

Here's another thought:
For example, according to the description of an industrial turbocharger with variable geometry (VP), the intake air temperature is also used for fine-tuning the boost pressure.

With , it would be possible to prevent overloading of the charger due to a "Gigant" - LLK (-> excessive mass flow) if the charging pressure is reduced so that the mass flow ideally remains constant.
Then, according to the characteristic curve, the turbocharger might even be relieved: a lower boost pressure at the same mass flow requires a lower turbocharger speed.

Will this actually be implemented, or has anyone ever seen a corresponding boost pressure correction map before?

Okay, I've taken some measurements of the LL temperature.

The results are somehow strange.

At an ambient temperature of approximately 17°C, and with full-throttle acceleration from about 1500 to 4500 rpm in 3rd gear (approximately 120 km/h), the low-level temperature rises to about 78°C, with the maximum value being reported approximately 3 seconds after releasing the accelerator.

In 4th gear, and at a speed of 170 km/h, the temperature is practically the same.

For comparison, I also conducted the tests in 3rd gear with the LLK (low-temperature coolant) outlet taped off, but in that case, only a relatively insignificant 92°C was achieved.
My rough estimate put the temperature at around 115°C (calculated as 1.3 bar behind the LLK * 75 K / bar, plus the ambient temperature).

How can the discrepancy of over 20°C between theory and practice be explained?
The airflow from the spoiler inlet to the low-temperature coolant system is virtually free of any openings through which cooling air could potentially flow, even if the front grille is taped over.

While the air passes through an approximately 40 cm long aluminum tube located within the engine casing, which is surrounded by the heat from the engine compartment, this component likely won't be able to provide 20°C of cooling.

And a heat transfer coefficient (HTC) of approximately 15,000 (as the difference between an unconstrained and a constrained cooling air inlet) with a temperature difference of approximately 70,000 between the cooling air stream is also not particularly high .
My CPU cooler looks clean externally, with no bent fins, and the airflow passages are clear...

Are there any intercooler logs available from other 96kW Performance Drive systems that I can use for comparison?

The story continues with a different theme:
Okay, I'm ready. Please provide the German text you want me to translate.