that self study is a great read.
Greg - under "fuel quality" (right at the end) I would read that as good new for you. i.e - if you have a dpf delete, and no regen cycle happenning, then bio should be sweet.
Its great that it actually explains why rather than not. I always thought it was strange the way vw stopped saying bio was ok for their diesels right around the time the DPF's came in - before that it was just about encouraged!
anyway - as the self study mentions - the main DPF structure is made of silcon carbide coated with alumina (aluminium oxide) which is good for the platinum to bond to. the silicon carbide is a ceramic material very commonly used in these kind of applications.
You mentioned that there was a lack of black soot but a lot of ash - i would put forward a theory that the incorrect engine oil was being used - or - the oil was overfilled. This would lead to large amounts of oil vapour/ash being burned in the exhaust and subsequently clogging the DPF.
I have read one horror story from the states witha guy who bought a brand new jetta with a dpf. after just 10,000km the engine stopping at inconvenient times, because the DPF had become completely blocked. The reason - the dealer had used the wrong oil spec (he had a very early dpf car), AND had overfilled the oil at the first service. when i say the engine was failing - shutting down/refusing to restart due to fault codes.
there is an ongoing legal battle....
