DPF Operation

[rory]

Hi all
Can anyone steer me onto info regarding the nitty gritty of PDF operation on my TDI? With thanks in anticipation.

[jayjay]

DPF per chance?
Diesel Particulate Filter (DPF)

[rory]

OOps. DPF of course!! (Now that I have your attention)

[Greg Roles]

I've promised to make a sticky on DPF's, but in a nutshell:

The "DPF" in a typical modern VW is a cannister right off the back of your turbo, at the start of the exhaust system. Here's one without the rest of the tailpipe:




In the 2.0 TDI cars it's situated like this, behind the engine:



The DPF functions like a cat converter to reduce pollution, but where a cat is basically straight through, with a large number of small channels like a stack of drinking straws, a DPF has dead end channels. The exhaust is forced to travel across the silicon matrix to a nearby exit channel, thus leaving the solid "soot" particles behind. Other emission reducing reactions also take place like in a cat, but the main task is trapping the visible soot you see old 4x4's and trucks spewing out, to be burnt off later.

[Greg Roles]

So the upside to a modern diesel with a DPF is having already lower CO2 emissions than a petrol car AND no visible soot. Diesels do produce more Nitrogen Oxide than petrol cars, but this is reduced somewhat by the precious metals in the DPF.

The downside is the DPF will eventually clog for good. Oil, introduced mainly into the inlet via crankcase blowby gas, burns to a non removable ash that is the main source of DPF clogging. Add to that the simple fact that no reaction is 100%, and each regeneration there is always some soot left behind, and this slowly builds up.

Regeneration happens both automatically, and dependant on your driving. You will notice a DPF regen when the idle is sitting at 1000rpm instead of the usual 800, and if you stop during a regen the car smells "hot" and will most likely want to resume the regen next time you start the car. During a regen the injection cycle is prolonged, and fuel is burnt late in the combustion cycle purely with the aim of making the exhaust system, specifically the DPF, extra hot. The DPF has both pressure and temp sensors before and after it, and once the restriction reaches a certain level, a regen is begun. If you drive in a manner that doesn't produce much soot, and the pressure sensors don't register a pressure buildup, the car will automatically force a regen after specified km range.

I've found if you avoid the sub 1800rpm range during normal driving, and make sure to get some open road / flowing driving in during the week, you raise the exhaust temps sufficiently to burn off the soot trapped, you rarely notice any regens happening. If you drive in start stop traffic, do lots of short trips, or labour the engine below the 1800 "boost" range, you generate a lot of soot, and you'll notice frequent regens. At first I was getting a regen about once a fortnight, now it's several weeks between each one I notice, as I've changed how I drive. Keep the revs up above 2000, and if you do find yourself off boost, don't plant the foot, change down, or use gradual accelerator to minimise the soot the engine is producing. I often drive in 3rd at 60kph, especially in traffic, and the net result is hopefully my DPF will last as long as possible. Watch those nasty old diesels, and notice the times they are belching smoke, and when they aren't. Your modern diesel is doing the same, just your DPF is catching it all.

With a few DPF's already beginning to fail below 100k, and VW saying 150k is the expected lifespan, coupled with a genuine price beyond $4k, I'd highly suggest you take steps to reduce the load you put on this expensive piece of pollution gear!

The second best thing to do for prolonged DPF lifespan apart from watching your driving style, is to install some sort of aftermarket secondary oil blowby filter, such as the Mann and Hummell Provent mentioned in several threads in this section. It will only reduce the amount of oil your inlet sees, but dramatically so, and in my mind is a must do mod for any modern Silicon Carbide DPF equipped diesel vehicle. The Provent filter only lasts approx 25-30k before it becomes oil soaked, but it's cheap insurance. I routinely remove a lot more condensed oil than you'd expect from it's drain hose. Scary amounts actually!

And yes, before anyone else asks the MK V TDI has a very impressive stock oil blowby filteration system including a cyclonic step, but the bottom line is that it's still letting a lot more oil vapour by than I'd like to see. My DPF is going to last a long time hopefully, and I've taken every step I can to make sure it does so.

[Transporter]

There are fuel additives that can extend the life of the DPF and help it with regeneration process. http://www.cdti.com/pdf/PP%20DFX-DPF%20Data%20Sheet.pdf

[kaanage]

From the sounds of it, an ECU remap would shorten the DPF life, since most of them will increase the injected fuel at most points of the map.

[Transporter]

There is not such thing as a free lunch.

Sent from my HTC Desire using Tapatalk

[Greg Roles]

In my opinion a chipped TDI with a good catchcan running OEM low ash engine oil would have the DPF last as long if not longer than a stock TDI. Oil ash seems to be the biggest blocker of DPF's as unlike soot it can't be regenerated at all. Also driving style plays a big part in soot production, and someone lugging the car around in peak hour traffic would be more likely to produce more soot overall than an enthusiast with a chipped car who would spend more time on boost and producing DPF regenerating heat.

[kaanage]

Greg, you mentioned that you had pulled apart the clogged DPF from someone's car and couldn't see distinct cat and dpf sections and it all looked like a lump of cinders.
So did it look at all like the picture 1/2 way down this page?