DPF Questions: Skoda Superb 3U (BSS)

Hello everyone,

After my beloved Volvo, with its (almost) maintenance-free AEL engine, finally gave up the ghost, I bought a newer diesel car and am now completely at the mercy of all the problems related to the DPF. The new car is used, and I'm wondering when I'll need to replace the DPF.

Skoda Superb 3U, engine code BSS.
Year: 12/2007, Mileage: 137,000 km.
The service was performed at 120,000 km and included a timing belt replacement and topping up of the DPF additive.

MWB 68.2 indicates an ash content of 168 g.
According to my understanding, with this additive system, a maximum ash loading of 150 g has been reached, which means the DPF needs to be replaced.

However, the vehicle has full power and consumes very little fuel (approximately 5.5 liters with my gentle driving style). There are no error messages indicating a full DPF. I don't want to replace the DPF unnecessarily and would now like to access the data from the differential pressure sensor to determine whether the DPF is actually clogged and creating excessive back pressure.
As far as I know, the differential pressure is displayed in MWB 67.

Now, my question:
What is the maximum allowable pressure difference? I assume this measurement needs to be taken dynamically, meaning with full acceleration in 3rd gear, from 1500 to 4500 revolutions per minute.

Sure, here's the translation:

"One more question:"
What is the login code to reset the ash mass in channel 12 using VCDS?
I'm planning to remove and verschandeln my DPF.

Thank you in advance for the answers!
Best regards, Georg.

..can you determine if the rinsing process has already been completed and if the ash mass was simply forgotten to be adjusted?

Hello,

Is channel 12 blocked for you? Try using "12233" as the login.

Caution: Simply resetting and continuing without cleaning the filter can trigger the emergency program and, in the worst case, cause a defect!

Best regards, Rainer.

Hello.

I haven't tried changing the value in adaptation channel 12 yet. I just assumed that any adjustment would require a login. So, I'll try it without logging in first.

Subject: Regarding the potentially flushed DPF:
The engine was completely replaced under warranty at 60,000 km. The damage was a hole in the piston. I strongly suspect that the DPF (Diesel Particulate Filter) was also replaced at that time, because it must have been completely clogged due to oil entering the crankcase and then the cylinders. Unfortunately, I don't have the original workshop invoices, so I can only speculate. This damage occurred when the previous owner had the car.

"However, my suspicion is that the DPF is not as full as the 137,000 km mileage might suggest. The displayed value of 168 g corresponds quite accurately to the manual calculation method (to be used when data is unavailable, e.g., after an ECU replacement) according to VCDS: Ash load = (Mileage / 1000 km) * 1.21 g."
This would give me a crucible loading of 166 grams.

Does anyone know what the maximum allowable differential pressure is?
Surely this size is the most important factor for the well-being of the engine, or am I mistaken?

Best regards, Georg.

If the DPF (Diesel Particulate Filter) becomes full, you'll notice that it's constantly regenerating (every 50 to 150 kilometers).

Whether the part was replaced and what exactly was done should be traceable in the repair history by any authorized workshop, as this information is normally stored centrally.

Unfortunately, you won't see much by just looking at the differential pressure; it changes so dynamically that a deep understanding is required. I haven't been able to find that information anywhere yet.

If anyone has information, please share it.

I just cleaned it out for the second time. The amount of ash is important for calculating the correct soot load; if it's not right, it either regenerates too infrequently or too frequently.

The channel does not require a login.

Hello Benni,

Thank you for the response.

The regeneration process is quite strange: Mine hasn't regenerated at all in the last 400 km. Therefore, the filter can't be completely full, which is surprising considering the 168 grams of ash mass it's supposed to contain.

Well, I need to observe the whole thing for a bit longer. I've only had the car since last weekend, and I've basically only driven it once – those 400 km in one go. I drive TDI cars just for the enjoyment of it, and not because it's somehow economical .

Do you know how complicated it is to remove the DPF on a Passat? I don't have a lift, just some axle stands. I'm thinking about having a local garage remove the DPF, then having it cleaned, and then having it reinstalled.

Best regards, Georg.

OT: I personally find axle stands to be too wobbly. Try getting some stable (and sufficiently wide) ramps! With two, you can raise one axle or one side of the vehicle by about 20 cm. With four, you can raise the entire vehicle.

With the parking brake engaged and the gear in place, your vehicle will definitely be secure. An old mattress makes a good surface to lie on for this purpose, especially if you don't mind working on it while lying down.

Just a little tip: When I inquired at my local hardware store, they rewarded my interest in buying four ramps with a 25% discount. So, four ramps for the price of three. However, they were very dusty and seemed to have been sitting on the shelf for a long time.

Hello hat enthusiasts,

"The tip about using axle stands is a good one. I'll try it tomorrow, but for now, I'm going to use the self-lifting workshop, as I just want to quickly get the car onto the lift and then back down."

To estimate the effect of filter flushing, I measured the back pressure using G450/VCDS, measuring block 67.3, while the filter was still full and un-flushed.

The SSP 330 document, "The diesel particulate filter system with additive," contains some information regarding the pressure drop of the DPF.
On page 17, there is a diagram that shows the differential pressure (pressure drop caused by the DPF) as a function of the exhaust flow rate. According to this diagram, a full DPF results in a pressure drop of approximately 250 mbar at an exhaust flow rate of 500 m³/h. For a new (empty) DPF, the pressure drop at this exhaust flow rate is approximately 40 mbar.

Unfortunately, I can't measure the exhaust flow on my TDI. I've simply assumed that I produce a flow rate of 400 m^3/h at full throttle and 4000 rpm. Based on this conversion, the following graph was created, which shows that my DPF is not yet at its limit. However, be aware that the validity of the characteristic curves from the SSP depends on and is limited by the conversion between engine speed at full load and exhaust flow.

Here are a few more questions about this:

Does anyone know the physical unit of MWB 67.3? I assume it's millibars.

Does anyone happen to know the exhaust flow rate at full load for the TDI engines?
Otherwise, I'll just sit down and calculate it based on the boost pressure, the amount of CO2 produced given the fuel consumption, and the exhaust temperature in the DPF.



Best regards, Georg.

Hello everyone,

Here's a rough estimate of the exhaust gas volume flow produced by our TDIs.

Assumptions:
The ideal gas equation is valid. It's an approximation, but it's quite accurate at high temperatures.
* The pressure is determined exclusively by the air particles, which only become hotter due to the diesel combustion. The additional mass introduced by the diesel injection process is neglected. This causes only a small error: The average chemical formula of diesel is C12H23 (source: Wikipedia), which results in a particle number balance of...
C12H23 + 21.5 * O2 --> 12 * CO2 + 11.5 * H2O.
On the left side, there are 22.5 particles, while on the right side, there are 23.5, which is only 4.44% more.

Approach:
A specific volume V1 of air is forced into the combustion chamber per crankshaft revolution by the turbocharger, at a pressure p1 and temperature T1. Inside the combustion chamber, the air is heated by the diesel combustion process, and it exits the exhaust with a temperature T2 and pressure p2.

The ideal gas equation is used to calculate the ratio between the initial and final volumes as follows:
V2/V1 = (T2 * p1) / (T1 * p2)

VCDS/Vag-Com zeigt bei mir eine typische Abgastemperatur im DPF von von ca. 300 Grad Celsius bei typischer Vollast an, also ca. 600 K an. Den Druck im DPF schätze ich auf 1.2 atm. Der Turbolader schaufelt Luft mit 2.5 atm bei einer geschätzten Temperatur von 400 K in die Brennräume. Es therefore, it results in...
V2/V1 = (600 K * 2.5 atm) / (400 K * 1.2 atm) = 3.125

A 2.0-liter 4-stroke TDI engine, operating at 1000 revolutions per minute with the specified turbocharger pressure and temperature, draws in a volume of...
0. 5 * (1000 /min) * 0.002 m^3 * 60 min/h = 60 m^3/h
The factor of 0.5 arises from the four-stroke operating principle.
Due to the volume expansion, the current flow rate of 60 m³/h must now be multiplied by the factor of 3.125 calculated above.
We have an estimated exhaust flow rate of 3,125 * 60 m^3/h = 187.5 m^3/h at 1000 revolutions per minute.
At 4000 revolutions per minute, the corresponding volumetric flow rate is 750 m³/h.


With the above conversion, the diagram will then look like this: (attached)

Best regards, Georg.

Georg_G wrote:

Based on this diagram, a full DPF results in a pressure drop of approximately 250 mbar with an exhaust flow of 500 m^3/h. For a new (empty) DPF, the pressure drop at this exhaust flow is approximately 40 mbar.

*entstaub*

Does anyone happen to know any benchmark values for typical TDI catalytic converters at their respective engine maximum power output?
For example, one could perhaps provide concrete figures to support the statements often found on champagne corks.

I don't think the absolute pressure drop caused by the DPF or catalytic converter will be significantly different (pure speculation).
However, the DPF will become clogged more frequently (resulting in a more frequent increase in back pressure compared to the oxygen sensor = on average, more back pressure), and crucially, there's an extra amount of diesel fuel that isn't used for propulsion but is instead used to regularly regenerate the DPF.
haithamina

While the following may not directly relate to Ulf's question, it is still interesting for those of us who have already delved deeper into the topic of the DPF.

By entering specific keywords into Google...

Code:

phd stratakis experimental investigation of catalytic soot particulate filter

Sometimes, when you search online, a link to a doctoral dissertation appears as the second or third result.
It contains pretty much everything anyone has ever wanted to know about DPFs .

I specifically noticed that the author also uses a simple water flush of the DPF in the reverse flow direction between test runs. According to his measurement records, this seems to be sufficient to restore it to a like-new condition.

Best regards,
Georg