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[Differential pressure-air flow volume] ratio analysis

Posted: Tue Aug 20, 2019 4:20 pm
by admin
Today I logged some values from my TDI and placed in a graph ;)

I included also the DPF gas volume that isn't present in released app, just to understand the relationship between the ratio [differential pressure/air volume] and the [soot mass calculate].
As reported in technical documents, in fact, the ECU uses that ratio to calculate the soot mass deposit.

All values are related to the left vertical axis but the ratio value (and its trend line) that's related to the right axis.

As you can see, the ratio value (in brown) oscillates but its trend line (in red) is constant. This was a short trip so the soot mass value (in purple) didn't increase enough remaining more or less constant too.
The next step will be to log a long trip to verify if the ratio trend line will increase proportionally with the soot mass calculated value.
In a tech document I've found a graph that let me calculate the limit values for the ratio between a filter full of soot mass and a filter empty, but I'm not sure these values can be used for all kind of DPFs. So I'm going to verify them in my DETA engine.

What I've found:
  • ratio (differential pressure [mbar]) / (dpf air mass [m3/h])
  • 0,48 = filter full (I think full for a field regeneration)
  • 0,075 = filter empty
  • < 0,04 = filter defective

Re: [Differential pressure-air flow volume] ratio analysis

Posted: Thu Sep 05, 2019 10:29 pm
by dedkus
Hi, I am interested if you can validate this idea, do you have any news in this topic? I would be interresting if thevlues from ECU is computed so "easy", even I think there will be some more you plan to add info about air mas to application?

Re: [Differential pressure-air flow volume] ratio analysis

Posted: Fri Sep 06, 2019 10:30 am
by admin
I'm studying the relationship between differential pressure and air mass just to understand if the ratio is constant. Looking the average values it seems yes, but I think the big problem is the reading speed of the app. Unfortunately I can't have realtime values so for these kind of parameters that change very quickly, to calculate a reliable ratio is difficult.
My idea is to use the average value of previous readings for example, but in this case is important the sampling frequency. Reading a value every about 1 second isn't accurate I think.

I'm verifying these considerations and I'm waiting to log next regeneration in my car to have more data available.
I don't know if this ratio would have sense, because probably this calculation is already made by the ECU to give us the soot mass calculate. But I like to go deeply, also just for my knowledge ;)