DPF regeneration..according to Audi

[Greg Roles]

Found this today on the AU Audi site. Last part mentions active regen as often as each 1000k! I've noticed the higher idle around 1000rpm several times now, and I assume this is indeed the active regeneration cycle. Need to get me EGR hooked up to be sure.

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A diesel particulate filter is a system for removing diesel particulates from diesel exhaust. Audi uses a system that exploits the most advanced state of the art: the "catalysed soot filter" (CSF for short) has a filter coating containing precious metals which acts in two ways. The passive regeneration process involves the slow, environment-protecting conversion of the particulates deposited in the catalytic converter into CO2. This process takes place within a temperature range of 350 - 500 degrees and occurs continuously without any special measures being required, predominantly when the car is being driven at motorway speeds.

Only if the car is used for any length of time at low loads, for instance in urban traffic, is the temperature of the exhaust gas actively raised to around 600 degrees every 1,000 to 1,200 kilometres, to prompt additional regeneration of the filter. The particulates captured in the filter burn off at this temperature.

[gldgti]

hypothesis:

so from what i can gather, the dpf works like a slow combustion stove.... trapping the soot (carbon) and allowing it to burn inside the dpf to form C02. since diesels pump plenty of excess oxygen under normal consitions, theres plenty in the exhaust to support this combustion process.

as you block up the system, i would guess that exhaust pressure sensors on either side of the dpf indicate that "regeneration" or more accurately 'burn off' is required. i would guess that then the ecu adjusts the fuel maps to run excessive boost, thereby supplying extra 02 to pass through the exhaust system and aid to burn the built up carbon.

remembering that with a diesel, power output is a function of how much fuel you are able to burn in a stroke, NOT dependant on boost pressure, per-say. the burn off phase would equate to a "lean" running condition, not really applicable to diesels, buth the analogy stands.

[Logzy]

I've noticed the higher idle around 1000rpm several times now, and I assume this is indeed the active regeneration cycle.

+1 .

[Russ59]

Anyone happen to know what would happen if the car decides to do this whilst still not at operating temperature ?? I had an incident with mine today where I had driven around 70 km's turned the car off and returned a couple of hours later. I started the car as normal but it appeared to be running a bit a rough and I was having to rev it more than usual to take off. I had to stop and start at a few sets of traffic lights on a couple of hills and it didn't like it very much and appeared to a bit jerky on take off, I then had to stop at another set of lights and it was at that stage idling at 1000 rpm (200 rpm higher than usual) it was still not quite at operating temperature and when I went to take off it wouldn't rev and stalled. I had my foot on the clutch and when I tried to start the car it was dead ( lights were on but nothing happened when I turned the key) nearly ended up with a Rav 4 up my ar$3. I turned the key off and then back on again, it started and I drove off again having to use more accelerator than usual as it wasn't running right. I stopped a few k's along when I could get off the road and it was still idling at 1000 rpm and was jerky on take off and still needing a bit more throttle than usual. By the time I got another couple of K's along the idle had dropped to normal again but the car was still feeling jerky especially when backing off the throttle and slowing down through the gears.

Russ

[gerhard]

Anyone happen to know what would happen if the car decides to do this whilst still not at operating temperature ?? I had an incident with mine today where I had driven around 70 km's turned the car off and returned a couple of hours later. I started the car as normal but it appeared to be running a bit a rough and I was having to rev it more than usual to take off. I had to stop and start at a few sets of traffic lights on a couple of hills and it didn't like it very much and appeared to a bit jerky on take off, I then had to stop at another set of lights and it was at that stage idling at 1000 rpm (200 rpm higher than usual) it was still not quite at operating temperature and when I went to take off it wouldn't rev and stalled. I had my foot on the clutch and when I tried to start the car it was dead ( lights were on but nothing happened when I turned the key) nearly ended up with a Rav 4 up my ar$3. I turned the key off and then back on again, it started and I drove off again having to use more accelerator than usual as it wasn't running right. I stopped a few k's along when I could get off the road and it was still idling at 1000 rpm and was jerky on take off and still needing a bit more throttle than usual. By the time I got another couple of K's along the idle had dropped to normal again but the car was still feeling jerky especially when backing off the throttle and slowing down through the gears.

Russ

I think you have a different problem.

[gerhard]

so from what i can gather, the dpf works like a slow combustion stove.... trapping the soot (carbon) and allowing it to burn inside the dpf to form C02. since diesels pump plenty of excess oxygen under normal consitions, theres plenty in the exhaust to support this combustion process.

as you block up the system, i would guess that exhaust pressure sensors on either side of the dpf indicate that "regeneration" or more accurately 'burn off' is required. i would guess that then the ecu adjusts the fuel maps to run excessive boost, thereby supplying extra 02 to pass through the exhaust system and aid to burn the built up carbon.

remembering that with a diesel, power output is a function of how much fuel you are able to burn in a stroke, NOT dependant on boost pressure, per-say. the burn off phase would equate to a "lean" running condition, not really applicable to diesels, buth the analogy stands.

Mostly correct, but I believe the extra heat is created in the exhaust by supplying MORE fuel, not less.

Diesels are highly sensitive to overfuelling, to the extent that pistons will burn if overfuelling is consistent, such as you might get in a poorly tuned Cruiser diesel with aftermarket turbo.

[Greg Roles]

I've a whole tech bulletin on it, and I do seem to recall something about late injected fuel timing so it ignites in the DPF, thus heating it up to burn off the extra soot. Can't be @rsed looking right now sorry!

VW also mention that the DPF will progressively get blocked from the rear forwards, so it's a throw away item at some stage. I doubt it will be a cheap part!

Russ, that sounds exactly like the regen cycle, everything but the jerkyness / lack of power. I've turned the car off mid DPF regen before, and found it wants to do the typical 10 mins regen cycle all over again on hot restart, but I've yet to do a cold start, where I do assume it would do the same thing.

I've found that apart from the increased idle, the car still drives as per normal, and still goes like the clappers if you up it. When it's hot anyhow!

I would guess that a regen / late injection cycle on a cold start could make the car run poorly, so let us know if it's back to normal tomorrow.

You always have to turn the key all the way off to restart it too mate, quite embarassing to stall it in peakhour, but I think all us manual oilers have been there...several times

[Russ59]

Hey Greg,

I sent an email through tonight to the salesman and have asked him to forward on the details of the symptoms to the service dept. for me and ask them if they have any idea on the cause. I am guessing from what I have read about the DPF regeneration cycle that it may be responsible for what I experienced cause I'm pretty sure it wasn't my driving as I am used to the clutch now and having to give it a few revs to take off. I'll keep you all posted !!

Cheers
Russ

[gregozedobe]

..... and when I went to take off it wouldn't rev and stalled. I had my foot on the clutch and when I tried to start the car it was dead ( lights were on but nothing happened when I turned the key) nearly ended up with a Rav 4 up my ar$3. I turned the key off and then back on again, it started

Russ,

I can't help you with your rough running problems, as I haven't experienced anything like it. My Transporter has a DPF, but as it does nearly 100% highway driving, it has probably never needed to "regenerate".

I can say that what happened when you stalled your engine is 100% as intended by VW. You must switch it off completely before you can operate the starter motor again. Just to hazard a guess it is to stop people trying to run the starter motor when the engine is already running (as if anyone could NOT notice that their TDI was already running ). IIRC it is detailed somewhere in the owner's manual.

[Greg Roles]

I'd have to second that, as I'm finding blasting around in the city my diesel is regenerating every few weeks.

Russ, good luck mate, and if your car continues to run rough you could always consider unhooking the battery for a good hour and seeing if this defaults the car back to zero....then again i guess the DPF will still be sending pressure differences and wanting to start a recycle if it is indeed blocked, and it'll happen all over again!

Anyone near you have a vag com to check for error codes?

Anyone??

[Greg Roles]

OK, here's the info in the service bulletin about Active regeneration:

Lasts about 10 mins.
designed to heat the rear of the DPF up to 600-650 degrees.
The DPF has more platinum in the front over the back. The front runs hotter and this is where the passive, all day soot burn off occurs. When the colder rearward part blocks up, active regeneration occurs.

Exhaust gas recirculation is switched off to raise compustion temps
Extended injection of fuel occurs, with a secondary, smaller late injection to raise exhaust gas temps
Supply of intake air is adjusted with the electric "throttle" flap
Charge pressure is adapted (raised) so the driver feels no difference in power or driving


Also an interesting page on "over-run" operation in urban traffic.

In heavy traffic with strong changes in load, particular measures are required to maintain cleansing of the DPF. Normally no fuel is injected on over-run, but then the exhaust temps drop, and the DPF isn't regenerating.

If the car decides there is too much over-run happening:

A small amount of fuel is injected at over-run, approx 35 degrees after TDC
Since there is no main injection at TDC, there is no combustion and this extra fuel vaporises
This fuel then combusts in the DPF, and heat generated continues the regeneration cycle
The temp sender after the DPF controlls this process.

So it seems if you are a urban traffic driving rev head ( ie Mischa ) then the poor car will be doing this every time you back off the throttle at 4500rpms.

Perhaps this is why the lil wippersnapper had problems with his DPF early on.

I know I flog my car, but I stay between 2 and 4000 where the action is.

[Russ59]

Thanks Everyone,

I haven't started the beast yet this morning but I have to take it into the VW service dept. in a couple of weeks to get a new plastic door mould fitted on the passengers front door (double sided tape has lifted) so as I said in my previous post, I have mentioned to the sales guy that I would have to get it checked so I'll have to wait and see what they say ( I hope it's not the usual spiel - "oh that's normal sir " !!) God help them if they do . I may not be as lucky if it does it again and could end up being rear ended next time by some impatient wanker, I mean it's not like I ever hold anyone up in this thing !! They just have trouble keeping up !! Maybe that's what annoys them !!!

Russ

[Guy_H]

Now you can image what a "tuning box" does to your DPF cycle

[Russ59]

Now you can image what a "tuning box" does to your DPF cycle

Good or bad image ??

[Russ59]

Took the car out for a short run today and everything appears to be fine again, car is running normally and idling at the usual 800 rpm once at operating temp. I will still get the VW service dept. to check it out and see if they can find any errors, don't want to experience that again in a hurry, especially in traffic !!

Russ