FYI: DPF regen info from my '09 TDI
- Thread starter DoctorDawg
- Start date
DoctorDawg
Veteran Member
You're making my head hurt, NoSmo. I guess twenty years ago I coulda thought your argument through, but an ill-spent youth full of recreational neuron abuse has left me incapable (or, at least, unwilling) of pursuing such trains of thought for more than about 3.4 seconds, which I find insufficient time to think your argument through carefully. That, plus I've been running a chainsaw all day, so I'm pretty blissed out on exhaust fumes. So I'll just concede your point, but with prejudice.
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.
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.
You're right I think. The effects of n would be minimized in terms of soot, but all the other particulate matter would count too. As I remember, in a gas composed of many elements we had to figure P V for each of them. So I think that might account for the heat farther back in low loads.
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GoFaster
Moderator at Large
I don't have one of these cars to play with, but could "thermal inertia" explain higher post-DPF temperature upon reducing engine load?
Also, if the DPF is oxidizing some of the soot (which will happen if the exhaust stream has excess oxygen even if it is not in an official "regen" cycle) then that will raise the post-DPF temperature. It is a plain ordinary exothermic oxidizing reaction. Boyle's law (which has to do with the relationship between temperature and pressure and volume - but the absolute pressure is essentially identical within measurement error before and after the DPF) and that's not relevant to this case.
Also, if the DPF is oxidizing some of the soot (which will happen if the exhaust stream has excess oxygen even if it is not in an official "regen" cycle) then that will raise the post-DPF temperature. It is a plain ordinary exothermic oxidizing reaction. Boyle's law (which has to do with the relationship between temperature and pressure and volume - but the absolute pressure is essentially identical within measurement error before and after the DPF) and that's not relevant to this case.
DoctorDawg
Veteran Member
Yeah, that's my position. However it must be said that 'my position' usually involves having a major body part up a major orifice...i.e., I'm just guessing.GoFaster said:
Yeah, I'm thinking that it is a matter of degree for several factors operating at once, each contributing more or less depending on engine load. My Boyle point probably has a varying effect but it may be microscopic. We would have to break down the composition of the exhaust gases and analyse all contributing factors.
I agree that soot combustion at and behind the catalyst probably would be a partial factor. There is probably some "element" in there that preserves heat. I think ceramic does that exact thing.
The major question is why does it heat farther back in low load situations? Maybe its good old "backpressure".
The DPF gets more clogged with soot under load. Heated exhaust will have a tendency to backup because of this. Therefore heat readings are higher in the front. When the load comes off laminar flow improves and the heat registers farther back because it can flow better, and pick up the stored heat in the ceramic of the catalyst and the heat from passive soot burning. Whataya think?
I agree that soot combustion at and behind the catalyst probably would be a partial factor. There is probably some "element" in there that preserves heat. I think ceramic does that exact thing.
The major question is why does it heat farther back in low load situations? Maybe its good old "backpressure".
The DPF gets more clogged with soot under load. Heated exhaust will have a tendency to backup because of this. Therefore heat readings are higher in the front. When the load comes off laminar flow improves and the heat registers farther back because it can flow better, and pick up the stored heat in the ceramic of the catalyst and the heat from passive soot burning. Whataya think?
Here's an interesting and easily read link on Diesel Catalysts from the Washington State University.TDIMeister said:
http://search.yahoo.com/search;_ylt=A0geu6BKSkVJEh0ANn1XNyoA?p=diesel+oxidation+catalysts&y=Search&fr=yfp-t-501&ei=UTF-8
It has a nice first paragraph:
"A diesel oxidation catalyst (DOC) is a flow through device that consists of a canister containing a
honeycomb-like structure or substrate. The substrate has a large surface area that is coated with an active
catalyst layer. This layer contains a small, well dispersed amount of precious metals such as platinum or palladium. As the exhaust gases traverse the catalyst, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles (unburned fuel and oil) are oxidized, thereby reducing harmful emissions."
So, it could be that passive regeneration involves only the smaller microscopic particles listed above. Active burnoff is for clumps of accumulated soot or "liquid hydrocarbon particles".
honeycomb-like structure or substrate. The substrate has a large surface area that is coated with an active
catalyst layer. This layer contains a small, well dispersed amount of precious metals such as platinum or palladium. As the exhaust gases traverse the catalyst, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles (unburned fuel and oil) are oxidized, thereby reducing harmful emissions."
So, it could be that passive regeneration involves only the smaller microscopic particles listed above. Active burnoff is for clumps of accumulated soot or "liquid hydrocarbon particles".
GoFaster
Moderator at Large
If recollection is correct, the DOC and DPF are in the same housing in this engine. Is the exhaust temperature sensor in front of the DOC? If that's the case then the temperature sensors are measuring the temp diff across not only the DPF but also the DOC, which is oxidizing CO and HC all the time.
(p.s. Earlier in this thread, there was a request to un-sticky this thread. Request denied! Too interesting)
(p.s. Earlier in this thread, there was a request to un-sticky this thread. Request denied! Too interesting)
I tried to prepare a short discussion of how a catalytic reaction takes place so there will be a better understanding of passive and active regeneration. Please chew on it.
Diesel is a long chain hydrocarbon and catalysis is explained like this:
1. Each carbon atom has a potential of 4 single bonds which are the most attractive to hydrogen and other carbons. The Methyl molecule forms the simplest carbon bond: 1 C and 4 H. Forming methylene gas, CH4. The "H's" are supposed to be attached to the "C".
H
l
H - C – H
l
H
2. So ethyl is the next step up: C2H6. The "H's" are supposed to be attached to the "C's".
H H
l l
H - C – C - H
l l
H H
Diesel is a long chain hydrocarbon and catalysis is explained like this:
1. Each carbon atom has a potential of 4 single bonds which are the most attractive to hydrogen and other carbons. The Methyl molecule forms the simplest carbon bond: 1 C and 4 H. Forming methylene gas, CH4. The "H's" are supposed to be attached to the "C".
H
l
H - C – H
l
H
2. So ethyl is the next step up: C2H6. The "H's" are supposed to be attached to the "C's".
H H
l l
H - C – C - H
l l
H H
- So imagine a simple diesel molecule: C12 to C16 with all these hydrogens attached, say C16H34. These bonds are based on plus or minus charges and each represents stored energy which has a recorded specific value. In ULSD 15 or less out of a million diesel molecules will have a S or sulfer molecule attached. Or some form of Sulfer like H2S will be present.
- In active regeneration, the vaporized charge of Diesel fuel and Air which is sent as an extra injection to the engine by the ECU on a down stroke will be exhausted to the DPF. Then it will stick to the honeycombed ceramic element inside the DPF housing and come in contact with the palladium or platinum catalyst coating on the ceramic and the sticky soot.
- What the catalyst does is attract either the C or the H or both and cause the attractive forces between them to weaken. This lowers the flash point because it allows the surrounding O2 or Oxygen to become more attractive to each atom in the long chain molecule and pulls it apart causing oxidation or burning. When the bonds break, the bond energy is released and the reaction is exothermic causing the soot to burn off.
- The flash point of Diesel is about 184 degrees F depending on additives. That of pure Biodiesel is above 300 degrees F. The catalytic material in the DOC/DPF aids the passive/active regeneration processes for diesel, but apparently can’t support Biodiesel.
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rodneyh1
Well-known member
Based on the symptoms I've read here (very hot smell, fan running on shutdown, etc), I believe my '09 when through at least a few active regen cycles when using B99. No VAG COM info, however, so I can't be certain. I ran B99 for 4K miles, ULSD for 3.5K miles, and will switch back to B99 in a month or so (at 10K).NosmoKing said:
Pelican18TQA4
Veteran Member
I didn't try burning a paper towel, but the other day when I experienced the first active regen cycle, I could see the heat coming out the back of the car in my rearview mirror.CTD&TDI said:
Blue91
Veteran Member
Link or more info?jharrison said:
Pelican18TQA4
Veteran Member
Here's some interesting regen info. Tonight, after leaving work (34 ambient temperature), after less than a mile of driving and with the coolant gauge still showing "full cold", I hear the fans running at a traffic light. I look down and the idle speed has come up. Sure as Sh!t, my car is doing an active regen not more than 5 minutes after being started with a cold engine! By the time I got to the next traffic light, maybe 5 minutes later, coolant temp had come all the way up. I snapped a pic with my phone to show the higher idle speed that occurs during an active regen.
DPM
Top Post Dawg
the fans are likely under ECU control and that control will be based on road speed, coolant temp, A/C, and perhaps other variables. But I can't see the ECU telling you *why* it's choosing to run one or more fans at one of their (perhaps three) speeds...
GoFaster
Moderator at Large
Thread clean-up done.
Jack Frost
Veteran Member
For anyone's info, I have nearly 6000 km on my 2009 tdi and never heard the fan come on at all ... ever. I drive about 130 km per day and most of that is on the highway, but still, I feel as if my car has not grown up. Perhaps it needs to see a counselor.
Maybe its the cold weather.
Maybe its the cold weather.
DoctorDawg
Veteran Member
If most of your driving is highway, then most of your regens are highway, so the fans aren't needed, so they don't come on. My '09 is going on 10K miles (mostly highway), and I've only caught the fans running 3 times, despite the fact that I have had about 30 regens now (based on my observed 300 mi/regen rate).Jack Frost said:For anyone's info, I have nearly 6000 km on my 2009 tdi and never heard the fan come on at all ... ever. I drive about 130 km per day and most of that is on the highway, but still, I feel as if my car has not grown up. Perhaps it needs to see a counselor.
Maybe its the cold weather.
At highway speeds there's really no way to tell you're having a regen, unless you're an auto-psychic.
DPM
Top Post Dawg
see if you can monitor boost, egr throttle settings, and coolant temp while expecting a highway-driven regen. I've noted in the Subaru that extreme amounts of EGR seem to be applied at this time, the throttle valve closing right over to the point of strangling boost.
GoFaster
Moderator at Large
That is what one would expect ... but also, in the case of the North American spec models, expect to be confused, because there are three different "regenerations". See chart in post #42 of this thread.
DPF regeneration gets initiated by high exhaust temperature (to ignite the catalyst) and that's done by injecting fuel late, but the overall exhaust stream still has to be lean (to provide the oxygen for oxidizing the soot).
De-NOx regeneration is initiated by running the engine close to stoichiometric by using very high EGR. This provides a reducing stream, for taking the oxygen out of the stored NOx. This happens much more frequently than DPF regen.
I don't know how the H2S catalyst gets regenerated.
DPF regeneration gets initiated by high exhaust temperature (to ignite the catalyst) and that's done by injecting fuel late, but the overall exhaust stream still has to be lean (to provide the oxygen for oxidizing the soot).
De-NOx regeneration is initiated by running the engine close to stoichiometric by using very high EGR. This provides a reducing stream, for taking the oxygen out of the stored NOx. This happens much more frequently than DPF regen.
I don't know how the H2S catalyst gets regenerated.
DoctorDawg
Veteran Member
Nosmo, I bought a single copy PDF of this article a while back from the publisher's web site. It really wasn't worth the $25...lots of generalities, very little technical info. Since it is copyrighted I'm afraid I can't offer to share it. You can buy a copy yourself, but I would recommend you save your money.NosmoKing said:
HumbleSmoker
banned, trolling, using aliases
Noticed some discussion in this thread about how to know when active regen is going on. Well, when I go to shut off and I hear the industrial grade fans going and usually in 300 mile intervals, I know that active regen is going on. I popped the hood last time and looked at the top of the DOC and it was snap crackle popping!
I never shut down in the first part of an active regen. Last night I was coming in the garage talking on the brain cancer stimulator with another TDIclub member and I heard the fans, so I took a ride. Stopped, to water some roadside vegetation, and while I was standing there enjoying the view noticed that heat was just rolling out from under the car. Put my hand behind the tailpipe and the exhaust was hOt!
Think you should try to continue driving if you notice the fans roaring. That puppy needs all the help it can get. Any thoughts?
I never shut down in the first part of an active regen. Last night I was coming in the garage talking on the brain cancer stimulator with another TDIclub member and I heard the fans, so I took a ride. Stopped, to water some roadside vegetation, and while I was standing there enjoying the view noticed that heat was just rolling out from under the car. Put my hand behind the tailpipe and the exhaust was hOt!
Think you should try to continue driving if you notice the fans roaring. That puppy needs all the help it can get
. Any thoughts?CMB430
Veteran Member
I wish I knew when it was...I have only noticed it twice when, like you, I heard the fans. Except I was already stopped. I have hearing loss, and that frequency does not catch my attention with background noise. I knew when my Ford was in a regen...this car does not give me any power loss or issues...and I have over 7600 miles on it.
I think it would be good to let it finish the regen cycle...for the sake of the emission components and your MPGs...get that crap out in one regen.
I think it would be good to let it finish the regen cycle...for the sake of the emission components and your MPGs...get that crap out in one regen.
bigman111387
Veteran Member
Pelican I was looking over this thread again today and I just thought of something from ur last post with pic of higher idle. My car when really cold would do the same thing so it may not have gone through a regen. It could have Im just saying I think there are other reason the engine idles that high. But I dont know much so let me know what you think.
HumbleSmoker
banned, trolling, using aliases
Prolly could run a wire off one of the three fan switches to a light. Have to find out which one.CMB430 said:
Pelican18TQA4
Veteran Member
Yes, one thing about the CBEA that I don't recall experiencing on other TDIs is the raised idle after a cold start. When I leave in the morning the tach will read about 1100 RPM anytime the engine is idling for at least the first few miles I drive. Generally after that the idle RPMs settle back to their normal reading. The increased idle during regen is noticeable because it will happen after the idle RPMs have returned to normal.bigman111387 said: