DPF regeneration..according to Audi

[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

[Guy_H]

Well a tuning "box" tricks the ECU into supplying more fuel & edits the feedback sent back to the ECU to say everything is normal, therefore on a DPF cycle, the system is trying to inject an "exact" quantity of fuel for the DPF burn, it gets an undesired extra amount of fuel. When I was last in Germany I was shown several burnt out DPF boxes that were the victims of over fuelling - not pretty & not cheap!

[gerhard]

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

Good to see I was wrong, and your problem is not really a problem

[Russ59]

Good to see I was wrong, and your problem is not really a problem

Cheers mate, yeah providing it doesn't do it too often I won't consider it a real problem either, but if it does it again under the same circumstances and someone runs up the back of me I won't be impressed at all. I think I might be doing a few nice day trips on a regular basis to keep the DPF flowing clean !!

Russ

[Russ59]

Well a tuning "box" tricks the ECU into supplying more fuel & edits the feedback sent back to the ECU to say everything is normal, therefore on a DPF cycle, the system is trying to inject an "exact" quantity of fuel for the DPF burn, it gets an undesired extra amount of fuel. When I was last in Germany I was shown several burnt out DPF boxes that were the victims of over fuelling - not pretty & not cheap!

So are you talking about chipping (ie tuning box) causing problems with the actual DPF filter ?? Hence meaning it would be safer not to chip the vehicles fitted with the DPF ??

Russ

[Greg Roles]

That's what the Guy man is saying. Makes sense to me, no way I'd risk a $40k plus vehicle with a tuning box over a properly integrated tune.

Thanks also Russ for being the DPF regen on cold guniea pig. Moral of the story is if you think the car is doing a regen cycle, drive it till it's done! If that happened to me cold, I'd pull over and let it idle for the 10 mins till it was back to normal!

Scary experience all the same russ!