FYI: DPF regen info from my '09 TDI
- Thread starter DoctorDawg
- Start date
MethylEster
Veteran Member
Nit pick time ? Ok ! Catalytic reactions concerning hydrocarbons are for the most part endothermic in nature, not exothermic as you state above.jvance said:
The extra fuel does indeed " burn " or go through a rapid oxidation.
TDIMeister
Phd of TDIClub Enthusiast, Moderator at Large
WRONG!MethylEster said:
MethylEster
Veteran Member
Hydrotreater desulfurizers using nickel/moly catalyst = endothermic
Reforming gasoline using platinum/rhenium catalyst = endothermic
Fluid Catalytic Cracking using rare earth catalyst = endothermic
How is this wrong ?
Reforming gasoline using platinum/rhenium catalyst = endothermic
Fluid Catalytic Cracking using rare earth catalyst = endothermic
How is this wrong ?
TDIMeister
Phd of TDIClub Enthusiast, Moderator at Large
As I understand it, we're simply talking in this thread about reactions inside an automotive catalytic converter, NOT reformation, hydrotreating, and fluid cracking using rare earth catalyst. In an automotive catalyst, HCs undergo oxidation, n * CxHy + O2 --> H20 + CO2 (unbalanced), which is exothermic. Other reactions involving other species may be endothermic, but the net reaction in the catalytic converter is still exothermic, which is why it gets hotter than the prevailing upstream gas.
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DoctorDawg
Veteran Member
Well, while you guys have been arguing about whether fire is hot or cold, I've been spending quality driving time with my TDI. Had 2 regens in the course of a 640 mile round trip at highway speeds. Once I have enough data I hope to be able to pretty accurately predict when my next regen will occur, so that I can be logging VAG-COM data during a regen; I really want to know how much additional fuel is consumed.
About the catalyst/endo-/exothermic debate, here's my story and I'm stickin' to it:
1. Thanks for pointing out that its a catalyst that oxidizes the fuel.
2. A catalyst has no influence on whether a chemical reaction will be endothermic or exothermic. All a catalyst does is speed up a chemical reaction...it affects the reaction's kinetics, but not its thermodynamics. Whether a chemical reaction is endo- or exothermic is determined solely by the difference in chemical potential between the reactants and products. Catalyzed or not, this difference will always be the same for a given chemical reaction.
3. Last time I checked, oxidation of hydrocarbons was exothermic. And thank goodness, says I. Life would be a LOT more boring if the oxidation of hydrocarbons was endothermic (for starters, we'd all be walking to work....).
We now return to our regularly scheduled thread....
About the catalyst/endo-/exothermic debate, here's my story and I'm stickin' to it:
1. Thanks for pointing out that its a catalyst that oxidizes the fuel.
2. A catalyst has no influence on whether a chemical reaction will be endothermic or exothermic. All a catalyst does is speed up a chemical reaction...it affects the reaction's kinetics, but not its thermodynamics. Whether a chemical reaction is endo- or exothermic is determined solely by the difference in chemical potential between the reactants and products. Catalyzed or not, this difference will always be the same for a given chemical reaction.
3. Last time I checked, oxidation of hydrocarbons was exothermic. And thank goodness, says I. Life would be a LOT more boring if the oxidation of hydrocarbons was endothermic (for starters, we'd all be walking to work....).
We now return to our regularly scheduled thread....
DoctorDawg
Veteran Member
Intervals between regens
Having now booked 4 regens since I started taking daily readings, my observed intervals between regens are:
1. 330 miles (70% hiway, 15% country, 15% city)
2. 279 miles (85% hiway, 7.5% country, 7.5% city)
3. 314 miles (100% hiway)
I still haven't figgered out what data the ECU uses to decide its time for a regen. Its pretty clearly not the Delta-P, as this is sometimes quite low when a regen happens. It makes some sense that the computer wouldn't use this, as the differential pressure sensor could break down and read zero, and failure to regenerate the DPF when it is obstructed would be pretty disasterous, I'd guess. Nor does the ECU seem to use (only) the Carbon mass (spec.) parameter, since right at this moment mine is at an all-time high (16.8 g) but it hasn't triggered a regen. There's another parameter visible to VAG-COM that I haven't been monitoring yet, called something like "Fuel used since last regen" (in liters). I'll need to start watching that too, I guess.
Having now booked 4 regens since I started taking daily readings, my observed intervals between regens are:
1. 330 miles (70% hiway, 15% country, 15% city)
2. 279 miles (85% hiway, 7.5% country, 7.5% city)
3. 314 miles (100% hiway)
I still haven't figgered out what data the ECU uses to decide its time for a regen. Its pretty clearly not the Delta-P, as this is sometimes quite low when a regen happens. It makes some sense that the computer wouldn't use this, as the differential pressure sensor could break down and read zero, and failure to regenerate the DPF when it is obstructed would be pretty disasterous, I'd guess. Nor does the ECU seem to use (only) the Carbon mass (spec.) parameter, since right at this moment mine is at an all-time high (16.8 g) but it hasn't triggered a regen. There's another parameter visible to VAG-COM that I haven't been monitoring yet, called something like "Fuel used since last regen" (in liters). I'll need to start watching that too, I guess.
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CTD&TDI
Veteran Member
doctordawg, is there a way you can pinpoint on your mpg chart what tank had the regen in it? i know in my truck, regen flat out destroys my mileage...im real curious as to what it does to overall mileage.
unless, of course, as you state a regen occurs ~300 miles...which would be every tank correct?
unless, of course, as you state a regen occurs ~300 miles...which would be every tank correct?
It adds another injection event for 15 minutes, during which the engine would normally burn about a quart of diesel. Let's be generous and say that it throws an additional cup of fuel into the exhaust. So two events a tank, that's an additional pint of fuel not associated with movement - an eighth of a gallon or about 5 miles not traveled. 595 miles in 14 gallons instead of 600 miles in 14 gallons - three tenths of an MPG.CTD&TDI said:
CTD&TDI
Veteran Member
I would seriously love to believe you, but i dont. no offense meant, but if you have an article i can look at, then kewl. I just know the chug-a-lug my truck does in regen (yes i know, a 408 c.i. I-6 is a little different than a 2.0l tdi) but the regen cycle is handled the same...my truck regens approx every 600 miles which is about every other tank. so, in recording my fuel consumption, i notice a mileage difference of 11.2 w/o regen compared to 10.2 (sumtimes even lower) w/ regen. so, 1mpg difference loses me approx 50 miles on a tank. 50 miles @ 11.2/g =4.46 gal lost to regen...
thats a big difference than .125 gal (again, i know, diff size dpfs and the like) or even .25gal (if the tdi is @ approx 300 mile avg regen compared to my 600 mile avg)
my math is crude but i hope that explains my view of it
thats a big difference than .125 gal (again, i know, diff size dpfs and the like) or even .25gal (if the tdi is @ approx 300 mile avg regen compared to my 600 mile avg)
my math is crude but i hope that explains my view of it
jvance said:
TDIMeister
Phd of TDIClub Enthusiast, Moderator at Large
The frequency of regens encountered is right in the ballpark as published in a VW paper:DoctorDawg said:
Source: The New 2.0-l-4V-TDI Engine with Common Rail Modern Diesel Technology from Volkswagen
Authors: Jens Hadler, Falko Rudolph, Hermann-Josef Engler and Sven Röpke
MTZ 11|2007 Volume 68
Let me take a crack at explaining why your truck uses more fuel to regen.
To go 600 miles, you use roughly 60 gallons of diesel. A tdi uses about 15. Right there, it would appear the truck would need 4 times the fuel for a 600 mile regen as the tdi. Now the tdi also has alot less exaust blowing through the dpf during a regen than the truck. The exaust flow cools the dpf below the point needed for burnoff, so there's even more fuel wasted. The regen probably also has to be longer to account for the vastly larger accumulation, when things burn, only their surface area goes. When you have 4 times the carbon (not accounting for the difference in air mixtures and soot discharge rates/size of particles), for twice as long, a total of 8 times the volume. Good luck interpreting that for your own uses heh, I'm going to bed now.
To go 600 miles, you use roughly 60 gallons of diesel. A tdi uses about 15. Right there, it would appear the truck would need 4 times the fuel for a 600 mile regen as the tdi. Now the tdi also has alot less exaust blowing through the dpf during a regen than the truck. The exaust flow cools the dpf below the point needed for burnoff, so there's even more fuel wasted. The regen probably also has to be longer to account for the vastly larger accumulation, when things burn, only their surface area goes. When you have 4 times the carbon (not accounting for the difference in air mixtures and soot discharge rates/size of particles), for twice as long, a total of 8 times the volume. Good luck interpreting that for your own uses heh, I'm going to bed now.
Jack Frost
Veteran Member
DPF regen and 507 oil
Castrols claims that their 507 vw approved oil reduces long term blocking prolonging the life of the particulate filter.
So how is the engine oil involved? I remember reading somewhere (cant find the link) that the key feature of 507 oil is its tolerance to the presense of unburnt diesel fuel in it as a result of the injection of fuel in the exhaust stroke. Another link I saw mentioned that the 507 oil helps keeps the oil film intact on the cylinder wall when this occurs.
It sounds like when vw specifies 507 oil for the 2009 tdi, they really mean it.
Any comments?
http://www.castrol.ae/TDS_SDS/Edge5W-30_TDS.pdf
Castrols claims that their 507 vw approved oil reduces long term blocking prolonging the life of the particulate filter.
So how is the engine oil involved? I remember reading somewhere (cant find the link) that the key feature of 507 oil is its tolerance to the presense of unburnt diesel fuel in it as a result of the injection of fuel in the exhaust stroke. Another link I saw mentioned that the 507 oil helps keeps the oil film intact on the cylinder wall when this occurs.
It sounds like when vw specifies 507 oil for the 2009 tdi, they really mean it.
Any comments?
http://www.castrol.ae/TDS_SDS/Edge5W-30_TDS.pdf
DoctorDawg
Veteran Member
Bunch of great posts here, guys...thanks!
Jack Frost: my understanding is that 507.00 oil has an extremely low ash content. Like soot, ash can clog the DPF. Unlike soot, ash can't be burned off during the regen (since its composed of inorganic minerals, not carbon). So by using 507.00 oil, we avoid clogging the DPF with stuff it can't burn off.
CTD&TDI: you are correct in concluding that since regens occur every 300 miles or so, I am experiencing 1-2 regens per tank. So every tank you see in my sig graph reflects one or more regens. I'm sorry to hear how much fuel your truck is gulping during regen. I think that, for all the reasons put forth by others here, the TDI is a very different beast: smaller engine sipping a lot less fuel, and not working as hard = more fuel-efficient regens. Plus (dare I say it?) superb German engineering and an appreciation for efficiency. Much as I love my ole Dodge Cummins (a '95), I wouldn't dream of buying a new one with a DPF; I'd buy a used one from before DPFs were introduced on the Dodge...and then I'd take care of it so it would last longer than I will. My ol' '95 Cummins reliably books 20-22 MPG; not bad for a 3/4 ton 4x4 horse-haulin' machine. Actively regenerated DPFs are a good strategy on small, efficient, light-duty diesels. But for heavy-duty hard-workin' diesels like your CTD, I just don't buy it. I think Dodge fumbled the ball there. Much as urea injection doesn't appeal to me, I'd prolly go with urea in a big-@ss truck, thus enabling passive regeneration.
TDIMeister: I'm sure many of us would love to read that Hadler et al. paper you cite. I guess it would be a copyright violation for you to make it more readily accessible to us.....(?)
Jack Frost: my understanding is that 507.00 oil has an extremely low ash content. Like soot, ash can clog the DPF. Unlike soot, ash can't be burned off during the regen (since its composed of inorganic minerals, not carbon). So by using 507.00 oil, we avoid clogging the DPF with stuff it can't burn off.
CTD&TDI: you are correct in concluding that since regens occur every 300 miles or so, I am experiencing 1-2 regens per tank. So every tank you see in my sig graph reflects one or more regens. I'm sorry to hear how much fuel your truck is gulping during regen. I think that, for all the reasons put forth by others here, the TDI is a very different beast: smaller engine sipping a lot less fuel, and not working as hard = more fuel-efficient regens. Plus (dare I say it?) superb German engineering and an appreciation for efficiency. Much as I love my ole Dodge Cummins (a '95), I wouldn't dream of buying a new one with a DPF; I'd buy a used one from before DPFs were introduced on the Dodge...and then I'd take care of it so it would last longer than I will. My ol' '95 Cummins reliably books 20-22 MPG; not bad for a 3/4 ton 4x4 horse-haulin' machine. Actively regenerated DPFs are a good strategy on small, efficient, light-duty diesels. But for heavy-duty hard-workin' diesels like your CTD, I just don't buy it. I think Dodge fumbled the ball there. Much as urea injection doesn't appeal to me, I'd prolly go with urea in a big-@ss truck, thus enabling passive regeneration.
TDIMeister: I'm sure many of us would love to read that Hadler et al. paper you cite. I guess it would be a copyright violation for you to make it more readily accessible to us.....(?)
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Jack Frost
Veteran Member
Ashes to Ashes
I found a link from vw almighty ...http://http://www.volkswagen.co.uk/assets/common/content/owners/Longlife_servicing.pdf ... that states that the use of non 507 oils will half the life of a particulate filter. It is especially interesting that this was published in 2007. Obviously this has been known for a long time.DoctorDawg said:
Nit pick number two - you're conflating two different regeneration events here. Burning off soot, which requires heat, and clearing out the nitrogen oxide trap, which is done under normal exhaust temperatures. Urea doesn't do anything for burning off soot. It's only used for getting rid of nitrogen oxides.DoctorDawg said:
DoctorDawg
Veteran Member
Dang but you fellers surely do love tuh pick my nits (ya buncha monkeys)! Credit is due, jvance...I mis-spoke. Urea nukes NOx, not particulate matter. I guess I was thinking about other fuel-borne chemicals which some systems use to lower the soot burn-off temperature. Not to claim Wikipedia as the ultimate authority on anything, but its article on "Diesel particulate filter" refers to these alternatives thus:jvance said:
"Diesel particulate matter combusts when temperatures above 600 degrees Celsius are attained. This temperature can be reduced to somewhere in the range of 350 to 450 degrees Celsius by use of a fuel borne catalyst. The actual temperature of soot burn-out will depend on the chemistry employed."
Sorry for the mis-statement. A feller's gotta get up purty early in the mornin' to sneak anything past you guys....
DoctorDawg
Veteran Member
For me, the best reason for occasionally monitoring yer DPF (both Delta-P and regen frequency) is so that, once 120K rolls around and the dealer tells me "she needs a new DPF" I can say either "oh no she don't," or "yep, she sure seems to." Without baseline data from a still-new(ish) DPF, I'd have no way of knowing whether to believe them or not.
beetle98
Veteran Member
This is interesting thread. Two things i noticed last weekend not sure if related to regen or not but seemed like it. With cruise control set no diff. on flat or up hills but when going down hills the RPM's would jump around a few hundred rpm's. When i noticed this I was close to getting off interstate anyway and make a stop when i shut the car off the fans stayed on. This is the second time this has happened. I restarted car and shut off again and fans went off. Will the fans go off automatically after a certain amount of time? Is any of this related to regen?
DoctorDawg
Veteran Member
Beetle98, I would guess that the fan was involved in a regen. I know that when I've shut down during a regen, after starting and stopping the engine again the fan would go off (just like you report).
I haven't mentioned this before, but my nose can detect a very slight, but quite distinct smell associated with regens. Smells like the tiniest whiff of bleach - not strong, just subtle. Maybe its just 'hot metal' smell, I don't know, but its distinctive.
I haven't mentioned this before, but my nose can detect a very slight, but quite distinct smell associated with regens. Smells like the tiniest whiff of bleach - not strong, just subtle. Maybe its just 'hot metal' smell, I don't know, but its distinctive.
beetle98
Veteran Member
I agree now that you mentioned it I remember smelling like something was hot also. Chad
moondawg
Veteran Member
Delta-pressures are generally more accurate during times of high exhaust flow.DoctorDawg said:
PM models are generally more accurate during steady-state operation, rather than times of transient operation.
So, depending on your duty-cycle, the ECU will trust one measurement more than the other.
Sometimes, regens are done purely as a prophylaxis.... something like "Do a regen after X hours of operation, or after X amount of fuel burned."
Jack Frost
Veteran Member
I would hope that the ECU uses more than one measurement. For example, a fuel consumption sensor could be just as likely to fail as a mileage or a exhaust pressure sensor. If I were writing software for a ECU, I would monitor at least two seperate sensors and if one appeared to have failed (it wasn't changing at the usual or expected rate) then it would turn on one of the "get your butt into the dealership" lights on the dashboard.moondawg said:
The trick is determing the difference knowing between a reading obtained from a sensor that is out of calibration and a reading that is the result of unusual driving habits or operating conditons.
At any rate, as DrDawg states, the failure to do a regen could be disasterous. Given this potential, maybe one day, there will be some extra instrumentation put into the TDI that will provide some feedback. Personally I would like to preemptively request the engine to do a regen if I know that I have an unbroken highway trip ahead of me.
DoctorDawg
Veteran Member
+1! This thought occurs to me often. I want a button on the dash I can press to tell the ECU "now would be a great time to do a regen if you feel the need," for when I know I'm going to be on the highway for at least 15 minutes. It seems to me that an interrupted regen is prolly a total waste of fuel. I'd like to be able to minimize 'em.Jack Frost said:
As for the likelihood of a fuel consumption sensor failing, in the '09 you'd know about that long before it affected the DPF. The '09 very precisely monitors fuel consumption...it doesn't just guess, as in previous years...and that parameter influences everything the ECU does. If one of your glow-plug pressure sensors failed (its my understanding that this is how it monitors fuel consumption) I'm sure you'd throw a CEL right quick.
CTD&TDI
Veteran Member
I believe it has something to do w/ the catalyst in the dpf...i notice the same thing in my truck...Have you noticed how hot your exhaust gas is @ the tailpipe? ive burnt a paper towel w/ mine during regen...lolDoctorDawg said:
Jack Frost
Veteran Member
How about that! Our Jettas have "afterburners" in every sense of the word except these ones don't produce any extra thrust or power.
It seems obvious that "regeneration interruptus", i.e., shutting down during a regeneration, is a potentially wasteful process that was allowed by the VW engineers to provide a seamless user interface.DoctorDawg said:
It bothers me on an intuitive level because:
1. Seems like the DPF has to deal with much more heat passively than with the engine running and car moving. The first time it happened was on a hot day and my first impulse was to get in and drive to aid the cooling process.
2. The potential reduction in overall efficiency. If shutdown occurs during regen, is the proper completion of the process decreased adding to the burden of the next regen cycle?
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