How is the amount of ash determined? Is it simply calculated theoretically based on the amount of fuel burned? Or does each DPF regeneration add a specific amount of ash?
That it is somehow calculated is logical. A scale is certainly not something a DPF would have.
The question is whether the calculation follows a simple model that only considers the operating points of the engine and the specified fuel type, or whether the actual number of DPF regenerations is taken into account.
"For my 2.0 TDI BMM engine, it should be calculated like this:"
Ash content (g) = Distance traveled (km) * Average fuel consumption (liters) / 100 * Ash coefficient (0.0046 g / liter)
"And that seems to fit quite well; I don't think the number of regenerations is explicitly taken into account there."
It probably shouldn't, but the average consumption increases the more often it is regenerated.
However, I believe that such a simple calculation overlooks several important factors.
Frequent transitions between partial load and full load likely result in a soot cloud in the exhaust manifold. I can't explain the relatively spontaneous response of a CR-TDI with a DPF in any other way, especially when compared to a EURO3-TDI, which was so sluggish in transient operation to avoid producing soot.
It is possible that the effect described above plays a quantitatively insignificant role, so it may be possible to ignore it in some cases.
'Regarding soot emissions, there are definitely differences in diesel fuel. This was clearly evident in my old EURO3 TDI with the soot limiter deactivated. With certain gas stations, the car consistently produced significantly more soot.'
Apparently, this effect, which causes varying amounts of soot to be produced, is also being ignored.