For the VW Touareg TDI or Audi Q7 TDI, see 1000q: 3.0L engine DPF FAQ page 1. There are substantial differences from the 2.0L emissions system.
The passive regeneration occurs with no action taken by the car's computer. It occurs with higher sustained engine loads like freeway driving or fast acceleration onto the highway when exhaust gasses are hotter. These types of loads will produce exhaust gas temperatures (EGT) of about 350-500oC which thoroughly heat up and burn the DPF. If the car has only short stop-go trips, the exhaust doesn't have a chance to have a good passive burn off and will have more active regens or clog.
The active regeneration "self clean" occurs when filter soot loading is beyond 45% or every 466-621 miles (750-1000 kilometers), whichever is sooner. EGR is shut off and the fuel injectors squirt a little fuel into the engine cylinders after combustion (post combustion injection) that travels to the oxidation catalytic converter and oxidizes to raise EGT to around 600-650oC. The gasses travel to the DPF and burn up the trapped particulates.
During an active regen the car's computer also temporarily increases turbo boost about 2-4 psi to make up for any lost power. Engine rpm also goes up around 200 rpm on the 2.0L engine. A cycle lasts about 10 minutes and if you shut the engine off in the middle of an active regen cycle, you'll hear the radiator fans in the front of the car running fast (even after the car is shut off) and you may smell a burning rubber type odor. It will resume once you exceed 38 mph after the next engine start (and the exhaust is warm enough).
If the car still can't do an active regen and soot loading reaches 50-55%, it will try to force a 15 minute regen cycle. If you interrupt it by shutting the engine off, the active regen cycle won't finish. There is normally no light or indicator to show when the car is doing an active DPF cycle. If the cycle was interrupted by engine shut off, it'll try again before lighting the DPF warning light on the dashboard (pictured right). If that happens, drive at about 40 mph for at least 10 minutes in 4th or 5th gear at 2000RPM (Disclaimer: faster would be fine as long as you don't exceed the speed limit).
At 75% loading, the glow plug light will also come on. If you see the warning, go to have the car service or go to the dealer so they can explain the warning lights to you. It's still possible to do a service regeneration, a manually started active DPF regen.
In the 2.0L engine, the automatic active regen is blocked by the car's computer once DPF loading reaches 40 grams. The service regen must be manually initiated using the procedure below. I'm not sure if the service regen is the same as the emergency 95% regen so try both methods below.
If clogging reaches 95% (45 grams) it must be manually removed and cleaned since all that combustion could damage or melt the filter due to extreme heat and pose a fire risk. There's a chance the repair would not be covered by the car warranty (maybe the federal emissions warranty) if you ignored the warning light or if the clogging is caused by your driving style.
The newer common rail TDI engines (CRD) in VW Jetta TDI or other models with DPF will run as well on biodiesel as older TDI engines ran fine on biodiesel. However, using biodiesel has three main problems. During the post injection combustion, it can collect in the cylinder instead of vaporizing and raising the EGT to heat up the DPF, preventing normal active DPF regenerations. By not vaporizing, biodiesel works its way into the engine oil much more than diesel. Because biodiesel has a higher distillation and boiling point, once it's in the oil, it accumulates and dilutes the engine oil.
There's always greater engine oil dilution during a post combustion injection cycle but regular diesel can evaporate more easily than biodiesel out of the engine oil. Once it evaporates, it's recycled into the air intake by the crankcase ventilation system and consumed by the engine. Biodiesel accumulates because it doesn't evaporate as easily. At a 2008 biodiesel conference, a VW representative said the engine could tolerate up to 50% fuel mix in the oil but no more. (source) This level could be exceeded after 10,000 miles with just B5. B10 would definitely exceed this level.
Some possible solutions are to delete the DPF on your VW or Audi TDI or install a DPF bypass kit. The engine tuning must also be adjusted to account for the removal of post combustion injection of fuel and DPF removal. It might be possible to tune the post combustion injection to have bio produce the same results as regular diesel.
The future of DPF systems might substitute an extra injector in the exhaust to inject the post combustion fuel downstream of the engine instead of right in the engine cylinder. This type of system is required if the DPF is downstream of the Adblue or NOx catalyst. Modern systems which don't use post combustion injection at the engine use this type of injection. In fact, when TDI was first introduced to North America, the VW Passat TDI used a low pressure injector in the exhaust to burn up fuel in the catalyst. It was discontinued because it didn't work very well, see 1000q: VW Passat 5th injector for details. Technology has improved since 1994-1995 so it's possible this type of system might return. The main obstacle is additional complexity and cost vs. an extra squirt at the existing fuel injectors.
Trace metals in the biodiesel from processing can also accumulate and foul SCR catalysts. On Adblue equipped cars like the Touareg or Q7 TDI, (see below for a detailed system description), most contaminants will be trapped by the upstream DPF. The level of trace metals are also so small that the SCR should be more tolerant of contamination and last the "real" lifetime of the car, or over 400,000 miles.
For more basic information about biodiesel and VW, see 1000q: intro to biodiesel.
Plug the VCDS cable into the OBD2 port and start
the software. The Ross
tech VCDS tool or dealer tool is required to view this info. Click on "Engine" and you'll see the screen
Click on "Meas. Blocks" and select group 075. The 3rd number block is the particle filter load. You can also see the soot load in the screenshots below.
Shown below is the procedure to manually start an active DPF regeneration. This is not required under normal circumstances. Use VCDS to enter the engine module as shown earlier. Click on "Security Access" and enter the security code 12233. Go back to the screen below and click on "Long Adaptation".
Click "Up" or enter 13 in "Channel" to get to channel 13 - DPF Regeneration. The value for active regen is 0 for off. Enter 1 in the "New value" box highlighted below and click "Save". This will start the active regen. The test conditions are: the vehicle must be driven between 80-120 kilometers per hour and no shutting off the ignition.
The screenshots below show calculated and measured soot loading
in the DPF before and after the last active regen. The right screen shows
0km since last regen because it just finished. Note - 2010 and later
appear to have changed their electronics and as of this writing, VCDS software
shows milliliters loading as 0 and never moves. Soot load calculated and measured
also show 0. 2010 TDI don't have label files yet and because the
values never move, I don't believe it shows any
actual values in this screen.
As stated earlier, do not attempt an emergency regen if loading is above 95%. For the 2.0L engine this is 45 grams. Enter the engine module as shown before. Ross tech VCDS shows the following procedure but it didn't work for me.
Enter "Coding II" instead of adaptation. Enable regeneration by entering 21295 and hit "do it". Go back to the engine module and enter "Meas. Blocks". Select both groups 070 and 075. Block 3 of group 70 is the timer. In group 75, block 1 is EGT before turbo, block 2 is EGT before DPF, block 3 is particle filter load, and block 4 is EGT after DPF. During the test, keep driving between 20-37 mph and keep engine RPM around 1500-2500.
I would personally just keeping driving it until active or driver initiated regens don't work anymore or become so frequent that it bugs you into replacing or cleaning the DPF. Engine power will also feel low once the DPF is clogged. Since the DPF is a filter, as it becomes clogged the exhaust backpressure will increase to the point of the engine also losing efficiency. VW and Audi's recommendation is to replace the DPF once it's clogged but it's a common procedure to remove and clean the filters used with heavy duty trucks. Again, I'm told this isn't possible with the combined DPF/cat unit on the 2.0 North American engines because the DPF has to be separated and open for cleaning. The EPA requires DPF systems on heavy duty trucks to have a minimum life of 435,000 miles (with regular filter cleaning and maintenance). If you decide to remove the system due to clogging, you should pick up noticeable mpg gain if you delete it due to the increased effiency of the engine. Don't throw the deleted DPF out because it has precious metals inside. Below are the suggested service intervals for Volkswagen and Audi DPF systems.
VW: you're supposed to check it at 120,000 miles and check ash loading. If it's OK, check it every 10,000 miles afterwards. If it's replaced it's good for another 120,000 miles. As mentioned above, 45 grams is the limit for the 2.0L engine.
Audi: check the DPF at 125,000 miles for ash loading. If it has more than 45 grams of ash it must be replaced. Inspect it every 20,000 miles afterwards until it needs replacement. Since the A3 TDI uses the same engine as the VWs, I don't know why the inspection isn't at 120k then every 10k afterwards like theirs.
This reduces NOx and sulfur, the stinky part of the exhaust. The amount of NOx generated and the effectiveness of the NOx converter is what separates Adblue systems found in the 3.0L TDI engine vs. the non Adblue systems. The smaller engines don't use Adblue because the NOx cat converter can handle the emissions generated and use an exhaust valve and EGR system for sufficient reduction. The larger engines use Adblue as a reducing agent to reduce all the NOx. The NOx catalyst is placed last so that the high EGT from the DPF has a chance to cool down a little. Unlike the DPF, it's a pass through converter and not a filter.
The engine converter acts in 2 modes: DeNOx and DeSOx. DeNOx captures NOx during cooler operation and burns it off during hotter operation. To burn it off, the air intake throttle and the exhaust valve partially close to reduce the amount of O2 available and to provide sufficient backpressure to the low pressure EGR. When the O2 sensor detects a rise in the reduction agents (HC, CO, and H2), the NOx are burned off and it returns to capturing NOx. You can view some data on the NOx converter in channel 18 of long adaptation using the procedure shown above. Details of the 3.0L catalyst are shown below since they use Adblue.
As a side note, the exhaust valve (shown below) is an electric motor and spring.
My guess is that the spring acts as a helper for the electric motor. Because the spring is on the outside of the
shaft, it's possible road salts
could rust the spring and cause problems over the life of the car. NOTE: In March 2013, VW issued an extended warranty on this part and has a new part number. See this thread in the forum for details.
DeSOx mode removes sulfur buildup which slowly deactivates the DeNOx mode by burning it away at about 620oC and is done at the end of a DPF regen. It's calculated from fuel consumption so non ULSD can result in excess sulfur in this component. The H2S converter reacts H2S formed during DeSOx mode completely into SO2. H2S is a colorless poison gas with a rotten egg odor. Don't remove the H2S converter. SO2 has a sulfur smell like a match which was just lit and can irritate the nose and eyes. Although the exhaust meets all emissions standards, don't inhale the exhaust gasses!
The H2S converter is visible in the picture below.
First, make sure to check and comply with any applicable emissions regulations regarding the DPF system and modifying the exhaust. See the TOS Agreement for the full legal disclaimer. Deleting the system will increase power and efficiency but you may not pass vehicle inspections without this system. You can immediately tell if a TDI has a DPF or not because without the DPF, the tailpipe will have soot on the inside. With the DPF, even after high miles, the inside of the tailpipe is clean. This means it makes even less particulates than almost all gasoline cars.
Then, you need an engine tune. Now that you've read the previous sections about how the system works, you can see the car will not run as intended without the system in place. The check engine light will immediately come on but the car will still run. One person who removed the system before getting the engine tuned reported that the bumper reflector light above the exhaust melted when the car tried to do a DPF regen without the system in place. The service manual says that the front subframe has to be lowered for clearance but according to ToeBall "Just undo the passenger side CV from the trans. Manual says the subframe needs to come out, it doesn't. You'll have to rotate the DPF as it comes out and pry up on the heat shield on the floorboard but it'll come out. I've already done two this way."
Again, you need a tune from Malone tuning for the car to run as normal with no check engine lights. This is the only company that does DPF delete tunes for North American spec TDI.
Here are some thumbnail pictures (click to enlarge) from ToeBall's downpipe and exhaust replacement. For more on DPF delete, see this thread in the forum. and this thread
Here are some videos of what the car will sound like (chipped car)
If you have more questions or comments about Adblue or why a DPF delete or DPF bypass is illegal, feel free to ask in the myturbodiesel.com forums