Diesel Particulate Filter

[Transporter]

AFAIK the DPF fills up because it captures the larger soot particles as you drive.

When flow through the DPF gets too restrictive (ie partially blocked with soot), the ECU "regenerates" (ie runs extra fuel to actually burn the soot). The burnt soot is reduced to a lesser volume of fine ash, which reduces the restriction.

Eventually the DPF gets full of the fine ash and can no longer be effectively regenerated, then it needs to be replaced.

I hope that there are some cheaper aftermarket alternatives when mine needs replacing, as I"m with cogdoc on this one, I can't imagine it will be a cheap fix.

I'd like to ad just a few more details about Gregozedobe DPF regenerating process.
The ECU runs extra fuel to burn the soot, but it is actually exhaust gas containg unburned diesel fuel from very rich mixture, that burns of the soot in DPF. By using DPF on engine to protect environment the engine's life is shortened by regenerating process, since the extra fuel washes of the oil film from cylinder walls and there is also more wear (pistons, turbocharger etc.) from extra heat from combustion process.

[gregozedobe]

I thought it wasn't so much a "very rich mixture", but rather the extra "DPF regeneration" fuel was injected very late in the combustion cycle (so that the extra fuel can make its way to the DPF where it is then burnt).

If it was simply extra fuel in the normal combustion cycle it would be burnt and produce large quantities of extra soot (pretty well the exact opposite affect of what you want). Excess fuel in the normal combustion cycle would also give a large amount of extra (unasked for) power, which could be dangerous.

DPF regeneration creates very high temperatures in the exhaust system, and uses a lot of extra fuel too.

I see current DPF technology as a crude, early attempt at pollution control for diesels. I hope that given time manufacturers will get much better at it, like they have with petrol cars. Does anyone remember some of the late 80s, early 90s attempts, particularly the low compression carbie versions ? Some were absolute shockers.

[Transporter]

" it is actually exhaust gas containg unburned diesel fuel from very rich mixture, that burns of the soot in DPF".

Yes, the mixture has to be rich in order to still burn in the DPF, if it was just soot particles you wouldn't burn anything with it.
Of course to achieve that you have to inject fuel later at the end of combustion stroke or at the start of the exhaust stroke. In the case of Unit Injector fuel system I'm not so sure that Unit Injector can inject during the exhaust stroke since the Unit Injector Pump is camshaft operated. Different to CR fuel system where the fuel injector can be activated by ECU at any phase of the piston stroke.
Thanks for making it more clear Gregozedobe,
I'm not a very good writer.

[gregozedobe]

Thanks for making it more clear Gregozedobe,
I'm not a very good writer.

I think you are plenty good writer, and make many good contributions. I'm just a bit (? ) pedantic, and wanted to make sure any newbies reading got a good undersatnding of how their DPF works.

BTW, I don't have any problems with my DPF at all, but that is because nearly all my driving is gentle highway and freeway cruising. I actually like the fact that when I give my van a bootfull it doesn't create a cloud of soot (which I know can irritate many motorists).

[Transporter]

Yes, the soot that what I hate on mine.
Even when you accelerate just a bit more than very slow take off with my T5 everybody around is probably thinking that you are belting the engine up.
How ever Touareg exhaust tips after 13,000 km are so clean that you don't get any dirt on your finger if you touch it inside.
Here is some link on deleting DPF and on DPF topic.

http://www.dieselpowermag.com/tech/general/0810dp_diesel_exhaust_dpf_delete/index.html

Great technical magazine highly recommend every body interested in auto technology, there is more similar magazines just browse the site. The negative is that they are very expensive and all of them are good so you may straggle to decide which one you want. I'm receiving ATZ Auto technology every month for free since I subscribed many years ago.

http://www.atzonline.com/index.php;do=edition/site=a4e/sid=68505503449405c1eb86ff114234158/ed=2008-11/mag=Autotechnology

[Oneofthegreats]

Just for interest sake, we had a 2.0TDI come in with 6000k & the DPF was believe it or not 90% blocked! Also a highway car & very well used car!

That mean's the regeneration process no longer work's & also it makes the service mode not work either due to the extreme chance that it may catch on fire, as stated in the service mode on the VASS!

Only thing to do is drive it & get it hot enough to burn some of it out to bring the blockage to an acceptible level where the service mode can work again.

Otherwise the DPF/Cat. has to replaced.

[Transporter]

Just for interest sake, we had a 2.0TDI come in with 6000k & the DPF was believe it or not 90% blocked! Also a highway car & very well used car!

That mean's the regeneration process no longer work's & also it makes the service mode not work either due to the extreme chance that it may catch on fire, as stated in the service mode on the VASS!

Only thing to do is drive it & get it hot enough to burn some of it out to bring the blockage to an acceptible level where the service mode can work again.

Otherwise the DPF/Cat. has to replaced.

What brand of fuel the customer use?
Does he/she use any fuel additives?
I would sample the fuel just to be sure.

[bluey]

It's just a matter of time before VW might decide to wash its hands of DPF cars running fuel less than 51CN as recommended - well at least in the brochure - what does the manual and fuel flap sticker say??

Maybe they will even take the hard line on bio blends too - any trace of bio, no dpf warranty.

I read in the AA article that there are also "regeneration additives" typically used by design for cars with a colder DPF at the rear of the car. Presumably they would also help a car with a colder DPF at the front of the car.

[Oneofthegreats]

What brand of fuel the customer use?
Does he/she use any fuel additives?
I would sample the fuel just to be sure.

It's an ex demo & only used BP Diesel. Owner only picked it up a couple of week's ago, so they've probably one put in one tank of fuel from where ever.

That's not going to clog up a DFP 90% in a couple of week's!

[gregozedobe]

Sounds like something to be added to the list of things to be checked when buying a s'hand TDI - "What is the current level of soot in the DPF ? "

IIRC it can be displayed on the dealer tool at least, maybe on VCDS as well.

In the demo car above, I would have thought that it should have been complaining (error msgs etc) about being blocked well before it was sold. Maybe it has DPF sensor problems ? Either that or the new owners have been flooring it at every opportunity in heavy traffic without any longer highway runs. I have heard of one TDI that regenerates every 150-200Km (but I think there is something wrong with it).

[DutchAussie]

Spot on about the regeneration cycle mate, as this is the only reason given in all the VW manuals I recently printed off ErWin. VW also suggests an upgraded fuel heater on their "bio" models.

250 downunder, go look up "dutchaussie" in the Caddy section, he's a bio burner from way back, and is currently doing a lot of research and fact finding about the VW's, most probably for his bio e-book he is due to complete in the next few months.

I'm on his "want one" list!

cogdog,

Is there any information about fuel heaters in erWin?
You mentioned my "Australian Biodiesel Handbook".
It is in the shop!
You will find more information on my Website below:

http://biodiesel-handbook.synthasite.com/

[bluey]

It's an ex demo & only used BP Diesel. Owner only picked it up a couple of week's ago, so they've probably one put in one tank of fuel from where ever.

That's not going to clog up a DFP 90% in a couple of week's!

Why not? (There would have to be a regeneration problem.)

Only high cetane diesel is low soot. Only BP ultimate or Caltex Vortex Diesel are commercially available as high cetane diesel fuels. Or you have to use a cetane improving additive.

On my non-DPF car, I have seen huge clouds of soot behind. Watch any commercial diesel vehicle - huge clouds of soot.

The DPF is a ceramic filter - exhaust gas has to flow *through* the ceramic material. It would be easy for clouds of soot to clog up the ceramic.

Perhaps the carbon residue burning fuel additives (eg Techron 5000) could be used to help burn out the soot from a DPF.

[gregozedobe]

Bluey is correct - I've heard of DPFs getting "full" after only a couple of hundred Kms of driving in heavy traffic. The VAG 125Kw TDI engine seems to be one of the most prone to DPF issues (particularly faulty sensors).

The DPF is more of a "trap" than a "filter". It captures most of the soot in the exhaust gases, then when it gets near full it goes into a special burn-off mode to burn the accumulated soot particles (IIRC you need to drive at a steady speed with the revs between 2,000 and 3,200 rpm). This uses more fuel, makes the engine run roughly and the exhaust gets hotter.

There are lots of threads around which go into great detail about DPFs, what they do and what sort of problems they have.

[mtaoz3]

Black Smoke from Eos with DPF

Yesterday whilst driving in Melbourne, an Eos pulled in front of me from a freeway on-ramp. The driver floored it to get up to speed and a cloud of black smoke belched from the exhaust. I noticed that the whole back of the car had an oily black residue on it. It was my understanding that all TDI Eos had the Common Rail DPF engines. If so, then this one had a major problem. I would have thought that the DPF would clog up and the car would stop running if it was this bad. I suppose it could be the petrol TSI engine with a badly modified engine map (I have seen Nissan 200SX and similar belch black smoke from poor remaps).
Can any of the "VW Techies" comment on this? This EOS had the "straight out" exhausts as distinct from the turned down exhaust on the non DPF cars like non GT Golf V/Jetta.
Thanks, as I am curious about how this could happen.

[gldgti]

no matter what emissions equipment is fitted to a diesel vehicle - if you catch the engine off boost and give it the right throttle/load, you'll make it blow smoke. it could EASILY be down to the drivers habits. for instance, i can drive my car smoke free and fast. someone who doesnt 'know' my car will hop in and not know how to 'massage' the throttle in just the right way so as to keep from blowing smoke, and hey presto, theres a big cloud behind. its not that hard.

in order to make boost and eliminate smoke, you need to burn more fuel in a diesel.... theres no throttling, its all about how much fuel you add. if you step on hte gas, even the most sophisticated engine management CANT wait around forever for boost to come up a little bit so it can add fuel. it has to dump some fuel in there to get things moving. theres no way a DPF will cath it all, and theres no way around this without making a car dangerously slow in a situation created by the driver like that....

basically, whoever was driving should have been in a lower gear