Katatrappe beim AFN | Posts 48+

To add another argument to the interesting and lively discussion so far:

When the back pressure (from the KAT, silencers, etc.) is eliminated in a system with a VTG (Variable Turbine Geometry) turbocharger, the turbocharger initially has to do more work. As a result, the VTG vanes must adjust to reduce the boost pressure to the desired level. The adjusted VTG vanes mean less flow resistance for the turbine, as less work is extracted from the exhaust flow. This, in turn, means a lower back pressure of the exhaust gases at the same boost pressure, resulting in a higher overall system efficiency (the engine produces more torque due to less negative moment at the exhaust stroke).

ulf wrote:

...but by what factor is the exhaust volume flow greater than the fresh air volume flow? As long as you don't know that, you can't calculate the pressure requirements of the turbine

.

You should have access to this data. Years ago, there was already a TDI specification document for the AFD (~1Z) industrial engine. It contains two diagrams: "Intake air mass flow" and "Exhaust gas mass flow."
A value from the table at 2100 RPM: Intake: 200 kg/h; Exhaust: 210 kg/h.

SeatArosa1.7SDI wrote:

... This, in turn, means a lower back pressure of the exhaust gases at the same boost pressure, which results in a higher overall efficiency of the system...

If you assume that the engine control unit does not compensate for the normal efficiency loss by varying the injection parameters not, then you are correct.
Unfortunately, the defined exhaust gas tract (and its back pressure) is also included in the engine control unit (and therefore its parameters). Therefore, such a statement is pure speculation. It is quite possible that you could even worsen the overall efficiency.

Hello,

'With electronically controlled engines, very little to nothing changes when driving without a catalytic converter. You might experience slightly faster acceleration, potentially a minimally lower fuel consumption, and reduced thermal stress – those are my thoughts.'

However, due to the reduced resistance, the engine has the potential to rev higher. This is particularly noticeable in T4 TDIs, where the absence of a catalytic converter can increase the top speed by as much as 10-15 km/h.

On my Ducato 2.5 TDI with mechanically controlled injection, the catalytic converter was immediately replaced with a pipe upon purchase...

Best regards, Rodion.

Bertil wrote:

ulf wrote: ...but by what factor is the exhaust volume flow greater than the fresh air volume flow? As long as you don't know that, you can't calculate the pressure requirements of the turbine . You should have access to this data. Years ago, there was already the TDI specification from AFD (~1Z) for the industrial engine. There are two diagrams available: one for "Intake air mass flow" and another for "Exhaust gas mass flow". A value from the table at 2100 U/min: Intake: 200 kg/h; Exhaust: 210 kg/h

Well, but the (formula I know) for compressor performance doesn't require mass flow rates, but rather the volumetric flow rate.
It seems quite logical that you can't keep a turbocharger running with approximately 5% more mass (the combustion products of the diesel fuel) in the exhaust compared to the fresh air side, especially considering that the overall efficiency (across the turbine and compressor) is likely around 50%.

Therefore, the power absorbed by the turbine should also be calculated based on the volumetric flow rate, and this makes the entire process temperature-dependent -> question as above.

Quote:

However, due to the lower resistance, the engine has the ability to rev higher. This is particularly noticeable in T4 TDIs, where the absence of a catalytic converter can increase the top speed by up to 10-15 km/h.

Wow, let's just assume 160 km/h instead of 150 km/h. That would be an increase of 6.7%, and to overcome the higher air resistance, 21% more power would be required alone... something that many "power box" providers dream of, for example .

ulf wrote:

Therefore, the power absorbed by the turbine should be calculated based on the volumetric flow rate, and this makes the entire process temperature-dependent -> question as above.

Okay... all values at 2100 RPM:
Exhaust temperature: 465°C
Intake Temperature before IC: 118°C
Intake Temperature after IC: 55°C
Exhaust back pressure: 75 mbar.

Quote:

Quote: However, due to the lower resistance, the engine has the ability to rev higher. This is particularly noticeable in T4 TDIs, where the absence of a catalytic converter can result in an increase of up to 10-15 km/h in top speed. Wow, let's just assume 160 km/h instead of 150 km/h. That would be an increase of 6.7%, and to overcome the higher air resistance, 21% more power would be required alone... many powerbox providers dream of that, for example

.

Especially with a wardrobe system (T4).

Hi!

By reading through the thread, I came up with an idea that doesn't really have much to do with the original topic.
The turbocharger boost control can be achieved in common TDI engines either through a wastegate (which vents excess pressure) or through a variable geometry turbo (VTG). Wastegates are less efficient, while VTG mechanisms are more prone to failure.

How about adding a third component to the turbocharger shaft that utilizes excess energy (within the boost pressure control range) in a beneficial way, but can also temporarily inject additional energy into the turbocharger when needed?
This unit would be a small electric machine (motor/generator)!

When there is excess boost pressure, it feeds energy back into the vehicle's electrical system and reduces the load on the conventional alternator.

Beim kurzzeitigen Volllast-Beschleunigen erfolgt ein Lastabwurf von beiden Lichtmaschinen, und der Lader wird kurzzeitig zusätzlich elektrisch unterstützt, mit ~0,5kW Antriebsleistung. D'as' has 2 consequences:
1) Faster, more spontaneous acceleration.
1a) Reduction of acceleration soot emissions.
1b) A more spontaneous concern regarding engine performance.
2) For a short period, a few percent higher continuous power output (with an adjusted, increased injection quantity). The duration of this period is calculated by the engine management system, depending on the battery's state of charge and the load on the vehicle's electrical system.
3) Slightly higher operational reliability, as in certain operating cycles and with specific onboard power demands, the charging alternator can completely take over the power supply if the main alternator fails. A special emergency operating mode may be available in case of main alternator failure.
4) Pressure surge oscillations can be completely suppressed electronically, through extremely rapid braking and acceleration impulses of the turbocharger, and this can be achieved without any mechanically moving parts.

SeatArosa1.7SDI wrote:

... Wastegate is lossy. ...

I'm sorry, but VTG has significantly higher losses.
The VTG (Variable Turbine Geometry) only provides a wider range of usable boost pressure characteristics. The higher losses are secondary in this case. These losses are largely compensated for by intelligent control systems on the engine side.

Your idea has been implemented for a long time. It exists in many different variations.
The most brutal systems are found in WRC (World Rally Championship) vehicles. In these cars, a portion of the compressed air is diverted directly to the turbocharger's turbine, even when the throttle is closed. A small amount of fuel is then added, and the ALS (Anti-Lag System) works exceptionally well. However, the noise generated is immense. With this system, the turbocharger builds up tremendous boost at engine speeds of 2,000-3,000 RPM. As a result, the engine delivers full power instantly from a standstill.
Similar systems exist in road traffic, but they operate in a more sophisticated manner.
However, the system requires a turbocharger with a wastegate and a bypass valve.

With the throttle valves closed, a portion of the compressed air is diverted directly in front of the turbine. Then, a small amount of fuel is added, and your ALS (Anti-Lag System) works absolutely great.
It's essentially just a small gas turbine (to be precise, an ATL is nothing more than that). As far as I know, this principle was mainly used in tank engines.

Okay, so the ALS system essentially operates the turbocharger as a gas turbine for a short period (through post-injection) to achieve full boost pressure from a standstill. Not bad... especially for tractor pulling and similar applications.

Well, my idea was more in the direction of a sensible car, without various additional injection systems .

I actually meant hyperbaric oxygen therapy. ALS (Amyotrophic Lateral Sclerosis) works differently.

I'm sorry, but VTG has significantly higher losses.


'Please explain this to me; I always thought that VTG (Variable Turbine Geometry) turbochargers were essentially 'too big' and that this was compensated for by variable control. However, the efficiency of a wastegate turbocharger is only optimal within a narrow operating range. Beyond that, the necessary exhaust backpressure increases disproportionately, and the efficiency drops significantly. In the lower RPM range, it takes longer to build up boost. How exactly does it work? So, in theory, VTG should provide better turbocharger efficiency...'

Nebelwerfer_TDI wrote:

... I always thought that VTG loaders were actually "too large," and that this was compensated for by variable control.

You've already provided the explanation yourself.
You need a larger turbocharger, but you "castrate" it by using a VTG (Variable Turbine Geometry) to reduce its performance to that of a much smaller wastegate turbocharger.

Quote:

The efficiency of the wastegate turbocharger is only optimal within a narrow operating range.

Okay. The VTG loader consistently has a lower efficiency, but over a wider range.

Quote:

As a result, the back pressure in the exhaust system increases disproportionately, and the efficiency drops significantly.

However, this is the same for both the VTG and the wastegate. In fact, the larger VTG turbocharger is even more disadvantaged in this regard.
When the chargers are of the same size, the charger concept does not play a role in this aspect.
The larger the turbocharger, the less exhaust gas can pass through it.

Quote:

In the lower RPM range, it takes longer for the pressure to build up. How exactly does that work? - In theory, a VTG (Variable Turbine Geometry) should provide better turbocharger efficiency...

If you restrict the exhaust flow to control the turbocharger, you always reduce efficiency (through the variable geometry turbine vanes). It's the same as putting a restrictor plate in the exhaust to reduce the exhaust pipe diameter. This is done to increase the speed at low exhaust flow rates, allowing the variable geometry turbocharger to spool up earlier.

Genau. Der VTG Lader hat konstant einen schlechteren Wirkungsgrad, aber über einen breiteren Bereich.


Deswegen werden für Stationär- und Industriemotoren noch immer Wastegatelader verwendet.......

Da ist der größere VTG Lader sogar noch mehr im Nachteil.
Bei gleichgroßen Ladern spielt das Laderkonzept in diesem Aspekt keine Rolle.


Je größer aber die Laderturbine ist umso weniger Abgas kann hindurch.


Müßte sich aber im oberen Drehzahlbereich positiv auswirken. Eine größere Turbine verursacht bei gleicher an den Läufer abgegebener Leistung einen geringeren Gegendruck, weil sie auch niedriger drehen muss (-> weniger Drehzahl, mehr Drehmoment). Eine kleine Turbine hingegen, die schon bei geringeren Abgasmassenströmen auf Drehzahl kommt, muss aber umsohöher drehen, um auf die gleiche Leistung der großen Turbine zu kommen. Die Geschwindigkeit des treibenden Mediums ist (zumindest bei Wasserturbinen) im Normalfall immer auf den Doppelten Wert der Schaufelgeschwindigkeit der Turbine ausgelegt. Also muss bei einer höherdrehenden Turbine die Druckdifferenz (=Abgasgegendruck) auch dementsprechend höher sein, um die notwendige Strömungsgeschwindigkeit zu erreichen.

Irgendwie seh ich da einen Widerspruch.......

[Translating...]

Nebelwerfer_TDI wrote:

Deswegen werden für Stationär- und Industriemotoren noch immer Wastegatelader verwendet.......

Genau.

Quote:

Eine größere Turbine erursacht bei gleicher an den Läufer abgegebener Leistung einen geringeren Gegendruck, weil sie auch niedriger drehen muss (-> weniger Drehzahl, mehr Drehmoment).

Und der Verdichter?
Der hängt auch noch am Turbo dran . Der Verdrängt mehr Luft und umso größer ist sein "Luftwiderstand" welcher die Abgasseite mehr abbremst.

Bitte das komplette System betrachten, nicht immer nur eine Seite. Wir sind noch nicht in der Lage ein Perpetuum Mobile zu bauen

[Translating...]

Bertil wrote:

SeatArosa1.7SDI wrote: ... Wastegate ist verlustbehafteter ... Tut mir leid, aber die VTG hat deutlich höhere Verluste. Die VTG erzeugt nur ein breiteres nutzbares Ladedruckverhalten. Da sind die höheren Verluste zweitrangig. Die werden über intelligente Regelsysteme Motorseitig weitestgehend egalisiert.

Das möchte ich schwer bezweifeln.
Ich erinere mich da zum einen an den G3, die parallel mit dem 90PS 1Z
und dem damals ersten VTG, dem AFN verkauft wurden.
Der AFN verbrauchte trotz Mehrleistung im Schnitt immer um 0,3L weniger.
Zum anderen wird beim Wastegate vor dem Verdichterrad ein hoher Staudruck erzeugt, der dann über das Wastegate-Ventil abgeblasen werden muss.
Das ist im Grunde pure Energievernichtung.
Hingegen werden beim VTG alle Auspuffgase durch die ("sanfter geformten") Turbinenschaufeln
geblasen. D.H. alle Gase tragen zur effektiven Energieumwandlung bei.