DPF regeneration random speculations

Edit by GoFaster because I can't make a new "post #1" so this is a place-holder.

I had to split a thread in two because it was an important topic but was going in two directions at once.

This other thread ...
http://forums.tdiclub.com/showthread.php?t=229303
... has measurements and discussion about how the original-equipment, bone-stock, DPF regeneration system works. Measurements. Facts. Stuff that has reference material to back it up. That sort of thing. For someone coming into this fresh, read that other thread first, then come back here.

The thread that you are reading now, contains everything that was split off from the other thread, and concerns discussions about improvements, speculations, off-topic banter, people beating their heads with a stick (okay I'm probably going to delete that stuff).

The other thread is the neat and tidy one (as best we could), this thread is the messy left-over stuff. Be that as it may. Carry on and go where you want with it ...

NosmoKing said:

That's what we need to find out. Is it better to have the engine running and the car moving during an active regeneration because of the heat buildup?

Click to expand...

I don't think its quite a question of "better" or not. If your engine ain't running, you're not regen'ing any more. When you shut down and hear your fans, the ECU is merely trying to keep your car from turning into a puddle of molten metal. At this point the regen is over; either interrupted, or completed, and the fans are just dumping the remaining accumulated heat.

I suspect, but do not know and cannot prove, that an interrupted regen is probably fairly wasteful, in terms of burning extra fuel to little effect.

Exactly! Great point! That is why we need to find out how to predict the active regeneration event to save our engines and exhaust systems. The fan keeps running but the coolant is no longer circulating and the heat is going both ways. Burning paper towels at on one end and heating back into the engine on the other. That sucker is hot; why waste a cycle? It seems destructive!!

If we can find out what sensor(s) kick off a regen and what values they have when they do, then we can find a way to rig an indicator light or sumtin for a regeneration alert and drive till its done. Don't you think that would be worth knowing? I guess VW will cluck sympathetically when our exhausts melt down and other stuff turns up damaged and gleefully charge us a mint?

Boyle's Law and Soot

DoctorDawg said:

But I will say this: PV=nRT is the "Ideal Gas Law" (of which Boyle's law is a derivative). It applies perfectly to 'ideal gases' (where the particles are infinitely small, and there is no form of interaction between particles, and particles collide elastically). It applies less and less well as a gas becomes less and less ideal (i.e., where the particles are big, or stick to each other, or don't collide elastically. Soot particles are sooooo big (by ideal gas standards), and soooooo sticky, and soooooo non-elastic that I am confident they do not contribute to 'n' at all in calculations based on the ideal gas law.

Click to expand...

The chainsaw fumes aren't doing you much good. The DPF is a fancy name for a soot filter. Soot is a solid, a particulate of carbon perhaps, but a solid never-the-less. It does not diffuse or follow any gas law at temperatures and pressures found on Earth. In addition, if soot was a gas, we would not be using a physical filter to remove it from the exhaust. Only diffusion based filters can seperate gases and that is not what we have.

Fundamentally, it is the job of a regenerative cycle to change soot to a gas (CO2) so the carbon particles can finally pass through and come out of the exhaust pipe in a form that allows the carbon, should we breath it in, to diffuse in and out our lung membranes rather than become embedded as carbon particles.

When one thinks of it, our lungs are another DPF that cannot regenerate.


Jack

NosmoKing said:

That's what I ws trying to say before. I called RossTech today and verified that the VAGCOM will record the universe of parameter values in snapshots each set according to a preset time up to the storage limits of the hard drive.

So if someone were to hook up and drive around with the laptop on, then eventually a regen will occur and a before and after analysis of the sensor readings can be done.

Maybe a more simple solution will be just to get the 09 manual on ebahn.com. Maybe it will be clear in there what exactly is going on.

Click to expand...

Tell me what parameters need to be monitored and I'll gladly do some recording with VAG-COM. I've only experienced one active regen cycle that I'm aware of so I think I'm safe in assuming that the others are passive regens that are happening while I'm cruising on the highway in the morning or the evening, to and from work.

Cool. Problem is we don't know what parameters to monitor yet.

So the idea is take sequential recordings or snapshots of all the parameters until we can pin point a before and after scenario. From that we should be able to see most likely suspect sensors and what signal levels trip off an active reneration. Doc has already pointed out some that may be involved.

I'm wondering if there aren't two possible scenarios:

1. A firmwear initiated active regen that is nonnegotiable - it kicks off at time or mileage intervals.

2. One that activates according to engine load parameters.

VW cut our warranty from 2006, 5 years 60k to 3 years 36k. I smell a potential screwjob and I want to head it off.

Like Doc said: Fans are screaming and the thing stinks like its trying to meltdown. We're in new territory here folks and we need to be alert or it could cost us a lot of money. That thought originates with the owner of the diesel shop/machine shop I use: Paul.
I need the manual. Who wants to split the cost of an online subscription to ebahn, IF ITS LEGAL TO DO SO?

NosmoKing said:

Who wants to split the cost of an online subscription to ebahn, IF ITS LEGAL TO DO SO?

Click to expand...

As others have previously advised, you might consider taking a quick look at the licensing agreement before making further solicitations.

NosmoKing said:

Cool. Problem is we don't know what parameters to monitor yet.

So the idea is take sequential recordings or snapshots of all the parameters until we can pin point a before and after scenario. From that we should be able to see most likely suspect sensors and what signal levels trip off an active reneration. Doc has already pointed out some that may be involved.

I'm wondering if there aren't two possible scenarios:

1. A firmwear initiated active regen that is nonnegotiable - it kicks off at time or mileage intervals.

2. One that activates according to engine load parameters.

VW cut our warranty from 2006, 5 years 60k to 3 years 36k. I smell a potential screwjob and I want to head it off.

Like Doc said: Fans are screaming and the thing stinks like its trying to meltdown. We're in new territory here folks and we need to be alert or it could cost us a lot of money. That thought originates with the owner of the diesel shop/machine shop I use: Paul.

Click to expand...

The powertrain warranty is still 5 yrs/60,000 miles; however, I'm not sure if the DPF falls under that or the bumper-to-bumper. Also, I'm pretty sure the DPF falls under the emissions equipment warranty, which may be longer than even the powertrain warranty in some states.

NosmoKing said:

If we can figure out what triggers the ECU that it's time to burn out soot we can get two valuable pieces of info from that.

1. Who has the best fuel - least soot producing.

2. How to drive most economically and really know what your doing because the computer tells you.

Click to expand...

Soot production doesn't have much (if anything?) to do with fuel quality. Soot happens...all the time...but in greatest abundance when your air/fuel ratio falls too low because you're driving like a crazed monkey (see my thread, Invisible Smoke).
From doing a lot of poking around logging stuff with VAG-COM I'm now convinced that it will be quite difficult to figger out how the ECU decides when to do a regen. I'd be kind-of amazed if ebahn covers this...its kinda 'inside baseball'. Techs just want to know how to unbolt the old DPF and bolt on a new one.

But I do agree with you that the ECU could do a better job of telling you what's what. I would love to have an idiot light that lights up when a regen is in progress. Might-could just slap a thermocouple on the outside of the DPF with a relatively simple circuit that would light an LED on the dash when the temp goes above some limit, maybe 500* or so.

Well that's probably a good start and maybe eliminates one possibility. I want that light too. All 09 owners need it maybe more than we think.

We have a difficult problem here, but we agree that understanding it is important probably for the longevity of our cars. By dissecting this problem and studying it we will solve it. And we will acquire in depth knowledge that will help new generations of TDIers. We might find that spinoffs of this study will have profound implications for performance. We're standing at the beginning of a new geneation of diesel performance.

It just hit me. I think this is the answer: If we can find a way to record/measure the ECU regeneration signal to one or all of the cylinders(?) then we may find a separate pin on the ECU and measure when voltage comes out of that location.

For example: Honda has a lot of charts out for ECU pinouts. I built my own adaptor harness to convert from OBD2 to OBD1 on my Honda just for chipping so I'm a little bit familiar with the thought process.

My pre cat O2 sensor went bad, so all I did was switch to the post O2 cat pin on my fabricated harness and the CEL went out. The OBD1 ECU thought that the signal from post cat O2 sensor was the right one! Point: distinct functions are usually on separate pins.

If we can find the pinout chart for the US 09 ECU its probably clearly labeled. An electrical guru will be able to tap into that wire and rig it to a light on the dash. So it should flash briefly. Maybe they can set up a trigger switch activated by the brief signal?

So the problem may be simpler than we thought. Who do you know would know where to get info on the ecu pinouts. I'm a black sheep around here so if you wanted to post a thread or whatever you need to do we might knock this problem out fast. Nice!

Meanwhile I'll ge the ebahn manual and make some calls. I have some friends who are Ubermeister mechanics. Anyone else out there that can help?

That thermocoupler Idea is probably the easiest to implement

Nosmo, you are a true Enthusiast. God bless ya.

DoctorDawg said:

Soot production doesn't have much (if anything?) to do with fuel quality. Soot happens...all the time...but in greatest abundance when your air/fuel ratio falls too low because you're driving like a crazed monkey (see my thread, Invisible Smoke).

Click to expand...

Certainly biodiesel reduces soot production. There's plenty of data on that. http://www1.eere.energy.gov/vehicles...r07_sappok.pdf or http://www1.eere.energy.gov/vehicles...r07_sappok.pdf

I assumed there would also be lots of variation in soot production with different batches of ULSD. Not true???

NosmoKing said:

Thanks old friend. You don't know how much that does for me. No else one seems to understand my enthusiasm. These cars are so cool! You push the accelerator and they effortlessly and smoothly begin to fly. Esp with the Diesel power module. I'm a Dieselfreakforlife.

The thermocoupler idea might be easier to implement though, but not as technical and we wont learn as much. Just a matter of locating the right one and hooking it up. Have you ever been on the Manhattan Supply Corp website? They might have one. They have an incredible array of stuff. Switches, electrical parts, brass rods, steel etc.

We need to break this down though. The Module when I turn it up is incredible with the amount of acceleration it produces. The tach buries in a heartbeat. It reminds me of the built smallblock we put in a Toyota 4x4 while we still had the stock 15" tires. Instant acceleration.

The only problem with the module on the 09 is that it will throw a MIL on the higher settings and go into limp mode beyond that. Page 238 of the manual states that it is an emissions problem. I think it overwhelms the DPF with soot. Maybe a DPF off a big dodge would do better? When you turn the mod back down or remove it the cel goes out after about 8 starts and moving the car. One thing I noticed is I can go 1 setting higher with a high flow airfilter. I'm using KN right now, but am getting an Amzoil cause of the MAF oil problem.

I don't know how anyone can improve on that module and it is removable and adjustable for economy and/or power. I think after we get the MIL problem solved the module would actually cause engine damage just from sheer power! The engine roars! I wish I had the manual tranny.

Click to expand...

Keep in mind that limp mode can be triggered by a multitude of engine conditions; e.g. overboost, high EGT, high intake temps, emissions, etc. I have a feeling that overboost and/or high intake temps are what are causing your limp mode when you have the module turned up. Have you scanned your car with VAG-COM after it enters limp mode? If you do, you'll find out exactly what caused it.

Nosmo, one of the things I love about the internet it that virtually all knowledge can now be found on it. The other thing is that when knowledge cannot be found on the net, it can be created. Let's create some knowledge, eh?

NosmoKing said:

It just hit me. I think this is the answer: If we can find a way to record/measure the ECU regeneration signal to one or all of the cylinders(?) then we may find a separate pin on the ECU and measure when voltage comes out of that location.

Click to expand...

I think this isn't going to work the way you'd like. My bet is that a regen isn't triggered by a single signal on a single wire. What actually happens is that the ECU is controlling the timing of the individual fuel injection events. It will cause the injectors to squirt a tiny quantity of fuel into the cylindar at precise moments in the engine cycle, I think as many as 4 injections per combustion. When it's time to do a regen, the ECU simply adds more injections that happen a few milliseconds later, post-combustion. To detect this externally, you'd need a pretty smart sensor.

Cool! Just for the sheer joy of thinking and learning would be enough, but we have a lot more at stake than that. We'll be able to do stuff with this knowledge.

Points are well taken. Something triggers the ECU to send signals to load the cylinder on the down firing stroke so that the exhaust stroke is loaded with hot burned gases and unburned CHARGE. We should be able to find out what it is.

So that really makes sense that multiple tiny spurts would join the exhaust stream and head back to the DPF. So its a long burn situation and if you stop in the middle its wasted as Doc says and actually tries to melt down.

Catalysis causes the carbon hydrogen bonds to weaken faster and become more attractive to oxygen, so that the potential heat is higher than fuel burning in an uncatalysed state.

While I'm driving sometimes my car gives a jerk and the tack jumps briefly. I'm going to pull over and shut down next time and see if that is a precursor to a regen. Sorry if I missed anything. BKMetz lifted my editing function and its hard to remember everthing you said precisely. That's his perogative.

VAG engines microsquirt 5 times during a cycle. So maybe 5 additional appear after the firing event.

what i would find extremely useful would be, not an idiot light showing when a regen is occuring, but a small lcd module that has a % soot level in the dpf, along w/ a button to force regen when it would be useful for me...i.e. as i leave for a 30 minute drive or sumthing.... that would be awesome.

just think, youre leaving for a small trip ( i mean medium drive, not putting around town) and you see 95% dpf...so, you push a button b4 the ecm tell the engine to regen so that upon your destination arrival, its finished regen instead of just beginning...

hows that sound? forced regen is definately doable, cuz the techs can do for diagnostic purposes (well, i know at least dodge does...i would assume vag can too)

There is A LOT of speculation going on regarding regen cycles in this thread. We know what requests a regen cycle - DPF sensors. What actually triggers a regen cycle is most likely a combination of readings from many different sensors; coolant temp, intake temp, MAP sensor, exhaust temp, RPM, engine load, fuel temp, fuel pressure, etc. Trying to figure out the exact combination of these readings that actually causes a regen cycle to happen is probably a futile effort. Consequently, other than by VAG-COM telling you that a regen is happening, it might be impossible to figure out exactly when a passive regen is taking place (an active regen is accomanied by several factors that you can see and/or hear; i.e. coolant fans running, increased idle, increased boost pressure, etc.). You'd have to be able to pinpoint exactly how all of the involved sensors behave when a passive regen is taking place. Not saying it's impossible, but I'm guessing it will prove very difficult to determine.

I am curious though, why is there so much concern about regen cycles? The engine, exhaust system and the emissions system were all designed to function in this manner, and to do so as passively as possible. If a regen cycle isn't being carryed out correctly or if something happens to one of the components involved, a CEL will be thrown. The code should be specific enough to determine what component isn't functioning since it's emissions-related.

Personally I want to know because I don't want to shut my engine off during the cycle. As Doc pointed out, it seems destructive - like a meltdown is tryng to happen and a wasted cycle. What if something happened to the power and no fans would run? THink about all that heat - this is new technology; we don't know how long these systems will last or how to make them last longer.

Second, if we want to change this for of road use, we need to know how to bypass. Third, I want to know how it works period. If you don't understand it you can't fix it or modify it. Maybe a larger DPF would give more performance yet stay legal for on road use.

Dodge has had this technology out since 2007. I wonder how their's works. If it's a combination of factors surely one or two of them are constant and can be measured.

No I haven't need to buy. Debating Hex or Micro CAN. Only have an 09 right now.

Pelican18TQA4 said:

Keep in mind that limp mode can be triggered by a multitude of engine conditions; e.g. overboost, high EGT, high intake temps, emissions, etc. I have a feeling that overboost and/or high intake temps are what are causing your limp mode when you have the module turned up. Have you scanned your car with VAG-COM after it enters limp mode? If you do, you'll find out exactly what caused it.

Click to expand...

Hex or Micro CAN

One of those options features an on-board processor on the interface cable that allows faster sampling. I can't remember which one.

Jack

Thanks! I didnt remember seeing that. That's the one we need.

I just checked Ross-Tech's web site .. http://www.ross-tech.com/vag-com/interfaces.html, it is the Hex+CAN version.

It has to be used with the Windows XP to get the faster sampling rates. I imagine you should also ask for the USB cable as the USB is a faster protocol than what the serial.

It is also a bit more expensive but not exhorbitantly so if the faster sampling speed is something you need only once.

Jack

Here's a great article on DPFs. For some reason I typed in "onboard dpf regeneration" and it popped up.
http://www.google.com/search?hl=en&rlz=1T4ADBR_enUS256US257&q=onboard+dpf+regeneration
It covers it all.

Pelican18TQA4 said:

There is A LOT of speculation going on regarding regen cycles in this thread. We know what requests a regen cycle - DPF sensors. What actually triggers a regen cycle is most likely a combination of readings from many different sensors; coolant temp, intake temp, MAP sensor, exhaust temp, RPM, engine load, fuel temp, fuel pressure, etc. Trying to figure out the exact combination of these readings that actually causes a regen cycle to happen is probably a futile effort. Consequently, other than by VAG-COM telling you that a regen is happening, it might be impossible to figure out exactly when a passive regen is taking place (an active regen is accomanied by several factors that you can see and/or hear; i.e. coolant fans running, increased idle, increased boost pressure, etc.). You'd have to be able to pinpoint exactly how all of the involved sensors behave when a passive regen is taking place. Not saying it's impossible, but I'm guessing it will prove very difficult to determine.

I am curious though, why is there so much concern about regen cycles? The engine, exhaust system and the emissions system were all designed to function in this manner, and to do so as passively as possible. If a regen cycle isn't being carryed out correctly or if something happens to one of the components involved, a CEL will be thrown. The code should be specific enough to determine what component isn't functioning since it's emissions-related.

Click to expand...

Choose the "Selection Guide". I think we are going to experience steady performance degradation due to ASH accumulation. It is supposed to be inevitable and it can't be burned off. That is the main reason for 507 oil. Other stuff in the fuel might cause ash too. Any metal containing fuel additives too. They discuss cleaning the DPFs of ash though and using larger ones and backpressure and using backpressure for monitoring soot levels to stimulate regeneration. MAP sensor! There might be electric ignitors on ours. I'm going to crawl under mine tomorrow and look.

From the Article: Active-Passive Regeneration [FONT=KFCKKO+Arial,Arial][FONT=KFCKKO+Arial,Arial]– In some cases, the exhaust temperatures are sufficient to combust most, but not all, of the soot during normal equipment operation. This has been seen to occur in systems incorporating a fuel borne catalyst and/or base metal catalyzed DPFs. In this case, the active regeneration of the DPF is required only after extended periods of operation, say, for example, after 250 or 500 hours and can be performed during the regularly scheduled maintenance. Active-passive regeneration of the DPF uses the same methods as those for Active Regenerating systems described above. [/FONT][/FONT]
[FONT=KFCKKO+Arial,Arial][FONT=KFCKKO+Arial,Arial][/FONT][/FONT]
[FONT=KFCKKO+Arial,Arial][FONT=KFCKKO+Arial,Arial]***Monitoring of back pressure is critical for these systems, because a slight reduction in the operating cycle load can significantly lower the soot burn off rate and reduce the operating time before active regeneration is required.***
[/FONT][/FONT]

This from the article too: Its important

Exhaust back pressure
[FONT=KFCKKO+Arial,Arial][FONT=KFCKKO+Arial,Arial]As the DPF collects soot, the passage of exhaust gas through the pores of the filter element is progressively blocked and the pressure required to maintain the exhaust flow increases. This pressure that the engine exhaust must work against is called "back pressure." Engine manufacturers place limits on the exhaust back pressures for their engines. Beyond a certain limit, excess exhaust back pressure increases engine exhaust temperature, CO, and particulate matter (soot) emissions. The additional soot emissions loads the DPF up even faster. Because of detrimental effects of excessive exhaust back pressures on both engine and DPF (discussed below), a back pressure monitoring system must be installed with the DPF. The exhaust back pressure increases for two reasons:
• short term build up of soot, remedied in the short term by regeneration; and
• long term build up of ash, the noncombustible component of soot, remedied by cleaning.
[/FONT][/FONT]
Need for back pressure monitoring
[FONT=KFCKKO+Arial,Arial][FONT=KFCKKO+Arial,Arial]Overloading the DPF with soot can be detrimental to the life of the DPF. When the DPF is overloaded, spontaneous regeneration in passive DPFs becomes difficult to control and may become too vigorous causing the filter media to melt or crack. For both the protection of the engine and the DPF, all DPF installations [/FONT][/FONT][FONT=KFCLGI+Arial,Italic,Arial][FONT=KFCLGI+Arial,Italic,Arial]require [/FONT][/FONT][FONT=KFCKKO+Arial,Arial][FONT=KFCKKO+Arial,Arial]a system to monitor engine exhaust back pressure continuously during engine operation. Back pressure monitoring systems can range from those consisting of a simple mechanical gage with the high level marked on the dial to systems using electrical pressure sensors in a sophisticated electronic data loggers and a display multiple alarm set points. Some can incorporate an exhaust pressure measurement into the electronic engine control system to cut back the fueling rate when exhaust back pressures exceed the safe level. Back pressure monitoring systems are offered by most DPF manufacturers as part of the DPF installation and is one criteria to be used for selecting a DPF supplier. Exhaust back pressure monitoring is also a must because of the slow increase of the back pressure in a regenerated DPF caused by the build up of ash. At some point in the service life of any DPF, the regenerated DPF back pressure will be too high to allow the normal build up of soot without exceeding the back pressure allowed by the engine. When this happens the ash must be removed from the DPF by following the manufacturer's instructions for cleaning. The ash build up will not occur if the regeneration process includes an ash removal step in the routine regeneration process.
[/FONT][/FONT]

That's a good find!

And here's the relevant concern: Biofuel users may wish to inquire as to the ash content of their fuel. Sodium and potassium salts are "ash" as far as a DPF is concerned ...

Wolfshund: VWVortex

"Not that I would do this, but if the traps plugged, they could be disconnected from the exhaust system and the core bashed through with a pipe and dumped just like any other cat converter. The empty housing would then be reinstalled without the core. The delta p sensors would show no pressure drop and the engine would not enter regeneration mode. The theory could easily be tested by connecting the upstream and downstreem pressure points together and taking a test drive."

NosmoKing said:

Wolfshund: VWVortex

"Not that I would do this, but if the traps plugged, they could be disconnected from the exhaust system and the core bashed through with a pipe and dumped just like any other cat converter. The empty housing would then be reinstalled without the core. The delta p sensors would show no pressure drop and the engine would not enter regeneration mode. The theory could easily be tested by connecting the upstream and downstreem pressure points together and taking a test drive."

Click to expand...

Except that the regeneration is scheduled based on mileage too. You'd be injecting fuel into the exhaust every 300 miles.

I'd be very careful with speculation on the Whoretex.

EDIT: here's another not implausible thought. Knock out the filter media, and the sensors detect too small a delta p, and puts the car in limp mode. Also, since the low pressure EGR feeds off of the clean end of the DPF, maybe there'd be a nice array of other side effects.