Calculated v actual soot mass

[Pikpilot]

Can someone please explain the difference between these two readings. Thanks, Mike

[admin]

I still did'n find a good answer. I'm sure that the calculated value is used by the ECU to manage the regeneration process, nut the measured value is stil mysterious for me: for example it can go down to negative values that are meaningless for me. Some users told me that in case of failure of some sensor, the measured value is the only one useful to understand the condition of the DPF system. In my experience I didn't tested that kind of situation, but trusting those users, I added the measured soot mass value to the app.

[wacholek]

First of all it has to be stated that all soot level is calculated. There is only one direct metod to actually measure how much soot is in DPF is to remove it, measure the weight of the filter, regenerat it with a similar method but outside the car and measure the weight of the DPF again. The difference would be the weight of the soot.
For obvious reasons direct measure cannot be done during normal use of a car. However there is at least one indirect method that can calculate the weight of the soot in DPF and it is quite accurate. Pressure difference.
There is no simple math like 2+2 to calculate the soot level. It is more like a set of maps for different RPM, engine load, differential pressure and so on to precise calculate soot level.
Before WLTP there was only one parameter called in VAG DPF a calculated soot level. Among other parameters it used differential pressure as well.
Value from about 6 after to 24g before regeneration. Mileage between regeneration could be as high as 800km or even more. During fast highway driving the soot level was decreasing.
And than WLTP and AdBlue happened.
Now we have two soot level values. One which is called "calculated" one which is called "measured"(Than you !!! so much admin that you decided to place it in VAG DPF).
WLTP Calculated soot level does not count in DPF's differential pressure. It calculate the value based on engine load, EGT, speed of the car, RPM. Probably many more but those are the main parameters easy to notice during test driving. It has the same level of soot ( 6g-24g) as before but now it is actually meaningless in terms of real soot level. It can be very close to real value sometimes but in most of the time is far off. VAG DPF's "Soot level measured" is the same, real soot level as it was pre-WLPT calculated value.
This is the only real parameter of the soot level and, which is even more important, condition of your DPF.
From unknown reason "Measured soot level" is now between -9.99g to 24g. It is simply badly calculated. It converges logarithmically to 24g value so at 24g it is a real 24g of soot in DPF. A measured soot level is more less related to real soot level from about 9g.

Both soot level values will trigger regeneration at 24g ( whichever reach it first).
Both will trigger DPF dash error light at 32g (whichever reach it first).
And also after driving 738-742km without regeneration ECU will induce regeneration process no matter what the soot level will be.
I am preparing a proper calculation function for "soot level measured" parameter so that it will again be within ~6g-24g range. Maybe admin will use it in future versions.
Admin or any one else wonted to know more about how I managed to drive over 700km between regeneration and in the same time have completely empty DPF please PM.
Best regards,
Chris

[admin]

Good explanation thanks.

I always thought it was a calculation error, but it's very strange that in more than 10 years of car end ecu development, this error hasn't been corrected by vag engineers. It seems that it has some useful meaning, also with those negative values.

[wacholek]

I calculated the early stage of polynomial equation to calculate real measured soot mass. Based od my accumulated data worst error is 0,5g but in 95% range 5-35g is in less than 0.2g. I still has to work on that. Please send PM for further notice.

[wacholek]

Preliminary formula was send to your PM but still waits to be received.

[admin]

I have been stuck for many days due to flu, I should give a deep check to your message in next weekend.

[JanuszSk]

This is to Chris Wacholek:

Yes, I'd like to see your "hack" how to drive over 700km between regeneration please - but I can't send PM yet.

Thanks!

[nfranq]

This is to Chris Wacholek:

Yes, I'd like to see your "hack" how to drive over 700km between regeneration please - but I can't send PM yet.

Thanks!