Model Year: 2015
Model: A6 3L Quattro
Trans: 7 stronic dsg
KM: 231k Km, (144k miles)
Oil Ash Volume: 240ml
Oil Type: Total Quartz Ineo
Avg. MPG: 42
DPF ash load limit: 327.63 gm
Dpf replacement: 226630km.
The Ash volume appears to be a calculated amount at the rate of 1ml/1000km. The Ash limit is in grams, and its difficult to relate to volume unless the density is assumed at 1gm/ml. I recall reading that weight is used to check a removed dpf for an accurate measure of Ash content.
An additional reading from my ecu live data is 'milage to change the particle filter', which at 226,630km or 140k miles seems to be in the region of the EPA Ash cleaning interval. The Audi 3l tdi service schedule states at this km/milage "replace dpf", but I don't think that's happening, as I'm certain it can be cleared of ash by removal and back pressure. There's been a lot of Dpf cleaning advances since the car was built end of 2014.
Ash is not soluble, and can't be forced through the ceramic filter substrate, so needs to be blown back, or flushed out in reverse. There are many services that use liquid flush in situ, but there are technical papers that warn that wetting the dry Ash that is lying in the filter tubules will only push it to the tubule ends where it will set like cement, (the filter tubules at the inlet side are closed at the outlet end and vice versa, and gasses pass through the ceramic substrate to the tubules that are open at the exit end only, the in and out tubes are interlaced in parallel, but not open to each other).
I'm hoping to get mine removed and reverse cleaned, which should push out the Ash, dissolve any oil soot hanging around from the last regen, and also remove urea/adblue crystals from the final stage catalyst that breaks down NoX. The dpf on the 3L vag clean diesel Tdi is a multi filter device, with DPF filter followed by the SCR catalyst, and even possibly an LNT stage (Lean Nox Trap), which makes it a pricey beast to buy.
Further reading here.
https://dieselnet.com/tech/dpf_ash.php
Edit: on further research, and examination, the emissions system in my 3l diesel. Engine code CRTE, consists of a combined catalyst and dpf, in a U shape bolted very close to the top of the engin. The SCR, selective catalyst reduction filter is straight after the turbo, it's outlet pipe then turns in a sharp U and enters the DPF. On this U bend is mounted the adblue injector, which I removed to examine and discovered that the approx 25mm inlet opening was almost completely closed with urea crystal from the edge to the center, maybe 4mm hole left. This was easily removed with a pick tool. The final filter in the exhaust, the LNT, is a seperate unit further down the line near the rear of the car before the spilt to the twin silencer boxes. While I had the adblue injector off, I attached a domestic vacuum to the opening, and blew some air with a leaf blower back through one of the exhaust pipes, blocking the other. Mad, I know, but I think I got rid of some ash, measured DPF differential pressure on idle was the lowest I've seen since I started monitoring, and with the addition of a new air filter (really dirty old one overdue by 40k km, oops,), car is definitely running better, more power, mpg is up, regen is a little less frequent, so I'll watch and wait. The entire DPF/SCR unit is removable from the top once you lift out plenum panel, so it should be a diy job to remove, bring to the specialist ionised steam flush cleaner place, about €200, and refit like new for the next quarter million km.
