Sinnloser Ladedruck im Schubbetrieb? | Posts 16+

Ulf, the answer to this question becomes clear once you look into the emissions regulations and the strategies that engine manufacturers use to comply with them.

Keywords: Black smoke emission during sudden acceleration, sluggish behavior of Euro-4 diesel engines.



Looking at your signature, I would first rule out any issues with the engine tuning and make sure the exhaust gas recirculation system is functioning correctly before drawing any premature conclusions.

CU.

@ulf

I would doubt that the intake airflow is equal to the exhaust airflow. In my case, with a wastegate turbocharger, I've observed that the boost pressure, during acceleration, is higher at the same engine speed when the engine is warm compared to when it's cold.
In the compression chamber, heat energy is transferred to the air through the cylinder walls, which then results in a higher volumetric flow rate during the exhaust stroke. As the speed increases, the increase in volumetric flow rate per unit of time also increases, leading to the build-up of boost pressure.

I would tend to believe that the optimal operating characteristics for your VTG (Variable Turbine Geometry) systems are still achieved by simply trying to build up the maximum possible boost pressure. In practice, this is essentially a pressure-regulating blow-off valve for VTG diesel engines.

Happy Easter.

donalexo wrote:

2. Reduction of oil consumption (the gap seal on the compressor side is supported by the pressure gradient)

Hi Alex,

If a warm engine has an estimated oil pressure of 4 bar at 2000 rpm, which presumably also applies to the turbocharger shaft bearing, how can a boost pressure of only 0.2 bar significantly prevent oil from being pushed back?

Quote:

Regarding the characteristic behavior of your VTGs, I tend to believe that the best approach is to continue trying to build up the maximum boost pressure. In practice, it's essentially a regulating pop-off valve for VTG diesel engines.

If the set pressure in the "1 bar absolute" range is being displayed, and the actual pressure is 0.2 bar higher, then that probably isn't correct...

Incidentally, the engine behaved the same way before the tuning.

Hello everyone,

In the truck sector, VTG (Variable Turbine Geometry) is used to significantly increase engine braking power. The more air the engine "wastefully" pumps, the more energy is lost.

For passenger cars, the dynamic behavior is certainly the main reason.

Best regards,
Albrecht.

Hello,
However, with trucks, the VTG adjustment is not 'only' used during engine braking.
Best regards,
Günther.

ulf wrote:

The corresponding logs show an actual value of approximately 1200 mbar, while the target value is approximately 1000 mbar. Looking at the throttle response of the engine (32% at 2000 rpm in boost), it becomes clear that this is an intentional design choice by the developer.

After reading the sentences you quoted, I wonder if we are approaching the root cause analysis correctly.

According to the logs, the developer does not want any boost pressure (set value = 1000). He only wants to prevent the duty cycle from dropping below 32%. If the developer had actually wanted to maintain a certain amount of boost pressure, he could have simply programmed a boost pressure of 1200 in the turbocharger map at the specified speed for the thrust mode (i.e., fuel injection amount = 0). However, he did not do that. Therefore, I wonder if we are looking for the correct reason.

Another idea is that he wants to prevent the magnetic valve from "sticking." In that case, it would also make sense to set the target LD to 1000, but not to allow the minimum duty cycle to drop below 32%.

While I don't know for sure if that's really the case, based on Ulf's data, I would tend to think in that direction.

Regards,
Guste.

guste100 wrote:

According to the logs, the developer does not want any boost pressure (target=1000). He only wants to prevent the duty cycle from dropping below 32%. If the developer actually wanted to maintain a certain amount of boost pressure, he could have simply programmed a boost pressure of 1200 in the turbocharger characteristic map at the specified speed for the thrust mode (i.e., fuel injection amount=0). However, he did not do that. Therefore, I am wondering if we are looking for the right reason.

It seems that's all there is... I don't know what else to say right now.

I'll revisit the thread if there are any new findings.

Thanks everyone, see you later.