Hello everyone, I thought I would contribute my knowledge on this matter. I currently work for a diesel engine company that uses DPF in their trucks. From what I have learned you can burn off soot (which is unburned diesel)>this creates ash which is carbon.
Most vehicals do passive regen when you are driving but this is not hot enough to burn the soot completly so eventually you have to do a "parked regen."
Here is Regeneration as laid out by our company.
Regeneration
Periodically, the soot and ash particulates in the DPF must be burned off. This process is called regeneration and it can occur passively, actively, or by a driver-initiated procedure.
Passive regeneration of the DPF simply means that, at normal highway operating temperatures, the exhaust system gets hot enough to ignite these particulates in the DPF. This automatically cleans, or regenerates, the filtration material in the DPF, extending its usable life.
Active regeneration is initiated automatically by the aftertreatment system when passive regeneration is not effective enough by itself. This can be necessary in cold climates or during light duty cycles in which normal operating temperatures are not always reached. During the Active Regeneration process, fuel is injected into the exhaust stream and ignited at the DOC, raising the temperature of the DPF enough to burn the particulates.
The third is Driver Initiated or Parked Regeneration. This is where the truck is parked and the throttle valve is closed to and the rpm's are increased. This goes on for about 20 minutes to allow the DPF to get hot enough to burn off all of the soot.
Eventually the DPF gets to full of ash from regens and operation. Our DPF's are rated for 150,000 miles before they need to be cleaned out. But this can depend on what kind of driving is being done.
So I'm assuming that the VW's work similer to the trucks. Whether they have a doser or not I don't know but I'm sure their DPF's are rated for similar milage before they need to be cleaned out. BUT.....knowning stealerships they will probably just replace the whole DPF with a new one instead of just cleaning out the DPF.
The drive of our truck is signaled when to do a regen by the ECU which uses a delta pressure sensor that connects to both the front and rear of the DPF. This measures the amount of back pressure caused by containment build up.