DPF Regeneration .... could someone explain please .... :)

[OmegaV6]

OK .. an extremely old petrol-head here, and this is my first diseasel motor, so obviously my first contact with a DPF and I'm getting highly confused !!!

I fully understand (I think) what a "regeneration" actually does .... when the DPF temperature gets high enough it burns off all the soot particles that the DPF has collected, through running a low temperatures/stop-start/around town etc etc.... so reducing the soot on the "filter" but leaving a small amount of ash in the DPF, thus restoring its efficiency. If running correctly the ash should not block the DPF until over 100,000 miles.

Hopefully that is about right ???

The question is therefore.... when does a "regeneration" happen ??? .. and this is the bit that confuses me .... I read about a "forced" regeneration, and a "normal" regeneration ( fans run/fuel consumption increase/posible smells) .. but in 2 years have never experienced any of these .. so I asked the indie who services the car if I should be concerned .... his answer causes me even more confusion ....

He basically said that my car does what he called "continuous regeneration", in that on a decent run (over 20 miles non-stop driving at "normal" speeds) the exhaust (DPF) will get hot enough through normal use to burn off any soot, and given the way I use the car that will happen 99% of the time and I should not worry about it.

If I were to start using the car for multiple short journeys then the DPF would start to block up, at which point the "system" would instigate a regeneration by injecting fuel into the exhaust (?) to burn in the DPF and burn off the soot, this being the increased fuel consumption/smells some refer to, but he could not explain why the fans would run on switch off. The "system" can be "told" to start this procedure using the diagnostic software on his plugin device. He guesses that folks are refering to the first as a "normal" regeneration, and when ordered by the software as a "forced" one.

The information in the handbook is scarce, and "google" is NOT my friend on this as there are many conflicting versions out there .....

So, does my Audi actualy have 3 regneration modes ? "Continuous", Normal", "Forced" ?? or is he speaking bovine excrement ?? If the latter, could someone give a SIMPLE explanation as to how the system works, and why I've never experienced the fans/smell/increased fuel consumption symptoms ???

As a pointer, I do not use this car for journeys of less than 20 miles - the wifes shopping trolley (Renault Clio) does them - most trips are in excess of 30 miles non-stop, and about 75% of them are with the tin-tent on the back, so the revs tend to be higher as she sits in D6 when below 55 and 60 is only legally attainable on motorways/dual carrigeways.

Perhaps I'm just being thick (not unusual).. but I would like to understand, properly, how this thing works ... it is a dream to drive and probably the best tow car I've ever had, but still getting used to putting the devils brew into a motor !!

Many thanks for any education you can provide !!

[beemerboy9]

So your indie's "continuous regeneration" is not really a regen at all. Due to your use mode, the car never senses that a "Normal Regen" (inject extra fuel etc.) is necessary

I am trying to use my 2014 car in a similar manner to you.

[Whippy53]

This
Diesel particulate filters - everything you need to know (https://www.whatcar.com/advice/owning/diesel-particulate-filters-everything-you-need-to-know/n1181)

Covers the basics. A forced regeneration is usually done when the 'active' regeneration fails to clear the filter and is usually done by the workshop by initiating it via software, not pretty.

[OmegaV6]

Many thanks for the answers... so .. the "continuous" regen the indie described is what you guys call "passive regeneration", and the "active" regen only occurs if a) multiple short journeys cause the DPF to start to block when the ECU says .. "get clean" or b) when told to by someone programming the software with a plug in module so "forcing" a regen ..... is that about right ????

Still can't get my head around 3 aspects I've read about ... if extra fuel is forced into the exhaust stream to burn off the soot, how does it "ignite" ?? ... why do the cooling fans run when they are a long way from the DPF ?? .... and why is there so much talk about the fuel getting into the oil system and overfilling/diluting the oil ??

I guess I'm being even more dense than usual, and it probably doesn't matter how it does it, but I would just like to understand the process properly... it might turn me from a "petrol-head" to a "diseasel-head" !!

Thanks in advance for any education provided !!

[johnsimcox]

Many thanks for the answers... so .. the "continuous" regen the indie described is what you guys call "passive regeneration", and the "active" regen only occurs if a) multiple short journeys cause the DPF to start to block when the ECU says .. "get clean" or b) when told to by someone programming the software with a plug in module so "forcing" a regen ..... is that about right ????

Still can't get my head around 3 aspects I've read about ... if extra fuel is forced into the exhaust stream to burn off the soot, how does it "ignite" ?? ... why do the cooling fans run when they are a long way from the DPF ?? .... and why is there so much talk about the fuel getting into the oil system and overfilling/diluting the oil ??

I guess I'm being even more dense than usual, and it probably doesn't matter how it does it, but I would just like to understand the process properly... it might turn me from a "petrol-head" to a "diseasel-head" !!

Thanks in advance for any education provided !!
A regen essentially is a fire being lit in the DPF to super heat what has been collected and turn it in to ash. I think there is some sort of electrical device in the DPF that ignites the file. This is why you can sometimes smell an acrid burning odour when you get out of the car and it is doing a regen. The temperature is very high and therefore the fans get turned on to cool the engine, I think this is merely a side effect of the regen process and not something that is part of the process itself. If too much diesel gets pushed into the DPF during a regen then it has no where to go and gets pushed back up the exhaust into the engine and then into the sump. None of the diesel (5) A6s or (2) golfs I had from 2009 onwards experienced any DPF problems or diesel getting back into the oil although of course as they get older the chance of the DPF clogging increases

[Roverfan]

Many thanks for the answers... so .. the "continuous" regen the indie described is what you guys call "passive regeneration", and the "active" regen only occurs if a) multiple short journeys cause the DPF to start to block when the ECU says .. "get clean" or b) when told to by someone programming the software with a plug in module so "forcing" a regen ..... is that about right ????
Passive regeneration is possible but unlikely as normally the exhaust does not operate at those temperatures. An additive can be used to lower the temperature of regeneration. Even then it is difficult to achieve a passive regeneration without a plan.

Short journeys do not cause the dpf to start to become blocked, all size of journeys do that, short journeys inhibit the ecu's ability to complete a regeneration.
Forced regeneration is done purely for comfort of not having to drive the car through a regen cycle. There is a level of soot loading where after the ecu will not conduct or allow a regeneration. This is because the temperatures may possibly cause a fire risk. So the ability to command a standing regeneration is quiet useful as it prevents a situation where even more soot is added to the system especially in cases some other fault is preventing regeneration.



Still can't get my head around 3 aspects I've read about ... if extra fuel is forced into the exhaust stream to burn off the soot, how does it "ignite" ?? ... why do the cooling fans run when they are a long way from the DPF ?? .... and why is there so much talk about the fuel getting into the oil system and overfilling/diluting the oil ??
Diesel self ignites with temperature not needing a spark or igniter. The fans run so the engine temperature remains stable as the process leads to increased temperatures throughout the system till the dpf reaches 600c.
Since there is an injection of fuel into the cyclinder "post injection" to increase exhaust temperaure, some of this diesel can go past the cylinder rings into the oil pan. If excessive regenerations are happening this may become noticeable. In the open the diesel ignites, this increases temperatures some more so other diesel particles ignite but does not create an explosion as it does at the end of compression stroke as its not compressed in the exhaust.

[BradenWalker]

As someone who has also recently entered the world of diesel engines, I can definitely understand your confusion regarding DPF regeneration. I can definitely relate to the frustration of finding conflicting information online, but it sounds like you've got a good mechanic who's familiar with your specific car and can provide you with accurate information. As for the ford dpf cleaning (https://www.30minutedpfclean.com/product/ford-dpf-cleaning-services/) services you mentioned, I'm not sure if that's relevant to your specific car. But it's always good to have options in case you do run into any issues with your DPF in the future.

[swalker]

I Am also new to DPFs and i just learned yesterday that the glow plugs play a part and do an intermediate heat - while the engine is running, to get extra heat up to allow a Regen, and this to me ties in with the fans running.

[Crasher]

The fans run because during regeneration the DPF can hit 700 degrees C so the engine bay gets very hot.

[folkwagen]

As my DPF approaches 240k km/150k miles, I've been researching what can be done if it requires intervention. A current scan shows;

Model Year: 2015
Model: A6 3L Quattro
Trans: 7 stronic dsg
KM: 228k Km, (142k miles)
Dpf differential pressure on idle: 14hPa
Oil Ash Volume: 240ml
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 180k km "check/replace dpf" and if it passes the check, whatever that is, recheck at 30k km intervals. No mention of replacement, 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, whenever that becomes necessary (frequent regens, high dpf differential pressure, or if the ecu lights up to say its time). This 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 adblue injection, (the LNT stage, Lean Nox Trap, is further down the exhaust line), which makes it a pricey beast to buy. There are commercial cleaning services to which you send your removed DPF/catalyst/ Nox adblue unit and they will professionally restore it for about €200.
Heres my obdeleven scan. The replace particle filter label in German I'll take with a pinch of salt, as these labels are user submitted, I suspect that's the calculated suggested service or cleaning interval to check the dpf, nominally 150k km and every 30k km after.

39049

Further reading here. Ash Accumulation in Diesel Particulate Filters (https://dieselnet.com/tech/dpf_ash.php)