2017 2500 not using def

[kthaxton]

And that is called a passive regeneration

No, it isn't, DEF has NOTHING to do with regen. See my post above, or read this.

https://www.vehicleservicepros.com/...cle/12182599/dpf-regeneration-modes-explained

 

[MtnRider]

And that is called a passive regeneration

No, that is NOx reduction. Regen has ZERO to do with DEF and NOx reduction

 

[sag2]

OK, I'm pretty new to this stuff , but I'm going to take one last shot. Please look at the three attached descriptions. Notice that the SCR system is independent (and also downstream) of the DPF.

 

[MarkEagleUSA]

Forgive me as I'm a 3rd Gen'r that has no emissions on my 5.9, but my understanding of DEF/DPF is:

DEF: diesel exhaust fluid - injected into the exhaust stream to reduce NOx emissions.

DPF: diesel particulate filter - removes soot and other particulates from the exhaust stream. Regens heat the filter to burn them off.

 

[sag2]

Forgive me as I'm a 3rd Gen'r that has no emissions on my 5.9, but my understanding of DEF/DPF is:

DEF: diesel exhaust fluid - injected into the exhaust stream to reduce NOx emissions.

DPF: diesel particulate filter - removes soot and other particulates from the exhaust stream. Regens heat the filter to burn them off.

You are 100% correct.

 

[John Jensen]

kthaxton & MtnRider
We all agree that DEF is not employed with an active regen (DPF filter).

We are also in agreement that DEF is employed when, temps are right, into the SCR.
The difference is you are calling it one thing and I am calling it a passive regen. My terminology may be wrong, it comes from owning 2016 Ecodiesel where the forums and tuner (GDE) called it a passive regen.

 

[kthaxton]

kthaxton & MtnRider
We all agree that DEF is not employed with an active regen (DPF filter).

No, we are not in agreement on that, nobody has said that but you, therefore no agreement. DEF is always employed...it is always being dosed into the exhaust, regen or not. Did you see the part where everyone states that DEF has nothing to do with a regen, passive or active?

We are also in agreement that DEF is employed when, temps are right, into the SCR.

Well technically yes....because DEF is ALWAYS employed...just not only as you described!

The difference is you are calling it one thing and I am calling it a passive regen. My terminology may be wrong, it comes from owning 2016 Ecodiesel where the forums and tuner (GDE) called it a passive regen.

Well, it is wrong. The definition of what a passive regen is has already been provided, and it is not what you are saying.

 

[John Jensen]

No, we are not in agreement on that, nobody has said that but you, therefore no agreement. DEF is always employed...it is always being dosed into the exhaust, regen or not. Did you see the part where everyone states that DEF has nothing to do with a regen, passive or active?

Well technically yes....because DEF is ALWAYS employed...just not only as you described!

Well, it is wrong. The definition of what a passive regen is has already been provided, and it is not what you are saying.

I can understand why you say, "DEF is always employed...it is always being dosed into the exhaust, regen or not." However, saying "always" is not quite correct, it's only dosed when the engine reaches the prescribed temp, then the passive regen (SCR) takes place (using DEF).

I still say that DEF is not used with an active regen (DPF filter). Do you have any data that DEF is during an active regen? I have searched and found no such data, only that it used with the SCR to break down dangerous NOx emissions.

 

[MarkEagleUSA]

However, saying "always" is not quite correct, it's only dosed when the engine reaches the prescribed temp, then the passive regen (SCR) takes place (using DEF).

Regens affect the DPF, not the SCR.

 

[John Jensen]

Regens affect the DPF, not the SCR.

"The SCR technology allows for passive regeneration."
See https://otrperformance.com/pages/egr-dpf-scr

 

[kthaxton]

However, saying "always" is not quite correct, it's only dosed when the engine reaches the prescribed temp, then the passive regen (SCR) takes place (using DEF).

No sure why you don't believe us, or the linked information.....DEF is NOT used for regen, extra fuel is used for active regens, and nothing extra, special or different takes place for a passive regen. As said, passive regen just means enough heat is already generated by the combustion processes because the engine is being worked hard.

I still say that DEF is not used with an active regen (DPF filter).

And you'd still be wrong.

Do you have any data that DEF is during an active regen? I have searched and found no such data, only that it used with the SCR to break down dangerous NOx emissions.

Here's a tip, sag2, whom posted a couple times above, is a factory trained, retired service writer for Chrysler (correct me if I am wrong Stan, on the title and retired part ). He knows a thing or two.


Simplified explanation:
The DPF gets regened when too much soot builds up. Active regen adds fuel on exhaust stroke to increase heat. Passive regen occur without adding additional fuel.

The SCR uses DEF to remove NOx after the DPF. It does not get regened nor does DEF have anything to do with a regen.

 

[sag2]

OK, I'll clarify a couple of things, but then I'm going to respectfully bow out of this discussion. I don't think we are going to change his mind.

John is correct on one point, SCR is not always employed. There are a couple of situations where it isn't. When the exhaust temp is low like after a cold start, or on a long decel with no fueling there is no need to dose DEF because NOx levels are low and do not need to be cleaned up. The other major time is when the DEF is frozen. In that situation the EPA has issued a waiver to exceed NOx emissions, because the system is not operational until the heater can thaw the DEF. Other than that, the SCR system is dosing DEF based on the NOx sensor input. NOx too high, DEF added to SCR CAT to reduce NOx.
Again, there is no relationship between a DPF regeneration event and the SCR system. If there are folks on the Ecodiesel forums telling you there is, they are grossly misinformed.

 

[sag2]

"The SCR technology allows for passive regeneration."
See https://otrperformance.com/pages/egr-dpf-scr

I'm sorry, reputable company or not, that statement they have listed is just not correct. Perhaps they should attend a class or the factory training to find out how the system works.

 

[sag2]

Here's a tip, sag2, whom posted a couple times above, is a factory trained, retired service writer for Chrysler (correct me if I am wrong Stan, on the title and retired part ). He knows a thing or two.

Well, close enough. I don't know everything, but I'm pretty sure I know more than the average truck owner on aftertreatment and emissions. After all, I fixed the trucks the dealers couldn't. And it wasn't because I was smarter than them, it was because I learned from the engineers who designed it how they worked. I tell my students all the time, "if you don't know how it works, you can't fix it". That is true for any system, automotive or your toaster.

 

[Wayne M.]

Poor Tommid. Do you think he will ever peek in here again?

 

[kthaxton]

John is correct on one point, SCR is not always employed. There are a couple of situations where it isn't. When the exhaust temp is low like after a cold start, or on a long decel with no fueling there is no need to dose DEF because NOx levels are low and do not need to be cleaned up. The other major time is when the DEF is frozen. In that situation the EPA has issued a waiver to exceed NOx emissions, because the system is not operational until the heater can thaw the DEF. Other than that, the SCR system is dosing DEF based on the NOx sensor input. NOx too high, DEF added to SCR CAT to reduce NOx.

Thanks, I didn't consider those situation.

 

[John Jensen]

sag2,
Thanks for your posts #32 & 33.

I respect your, "I'm sorry, reputable company or not, that statement they have listed is just not correct." Thus, I concede and stand corrected. I have 2 subjects that still bother me:

! - Can you confirm whether or not DEF is used during an Active Regeneration?
2 - I'm' confused. I believe SFT was added after DPF first started to allow for higher HP engines. Ever since when I read about emissions, passive regens are always mentioned but SCR not as much.
Are SCR and Passive regens two different processes or the same?
If they are two different processes they seem to use the same triggers, wouldn't they conflict?
If SCR requires heat and DEF to reduce NOx, how does a passive regen do it with heat but, as the other posters are saying, no DEF?
It seems like SCR has replaced the passive regen, however, passive keeps appearing in artic;es and discussions.

Thanks for your input, I'm hoping you can straighten me out on passive and SCR.

 

[MtnRider]

sag2,

Are SCR and Passive regens two different processes or the same?
If they are two different processes they seem to use the same triggers, wouldn't they conflict?
If SCR requires heat and DEF to reduce NOx, how does a passive regen do it with heat but, as the other posters are saying, no DEF?
It seems like SCR has replaced the passive regen, however, passive keeps appearing in artic;es and discussions.

Thanks for your input, I'm hoping you can straighten me out on passive and SCR.

Regens (of any kind) are a different process then SCR, period. They have nothing to do with each other. 2 different technologies for solving 2 different problems.

They do not use the same triggers. SCR/DEF is triggered by NOx emissions (a NOx sensor), active regens are triggered by differential pressure across the DPF (pressure sensors) ie: when it starts getting clogged.
Now a passive DPF regen will start to occur anytime the exhaust temp goes over 600 degrees (at the DPF) but I would argue at that temp it is not burning much "off" but holding it's own. Active regens (where additional fuel is injected) it will reach around the 1100 degree mark and really burn off the soot. Again, nothing to do with the SCR, DEF, or NOx.

The SCR does not require any "extra" heat for the DEF to work, it works with the standard exhaust temps. NOx is a byproduct of the fuel/heat produced in the combustion chamber so the hotter the truck is running (under load, towing etc) the more NOx it will produce, and the more DEF it will consume to get those NOx levels down. Again, nothing to do with regens.
As far as cold starts and not using DEF, again this is triggered by the NOx sensor. When the engine is cold it is not producing as much NOx so DEF is not needed as much. (remember heat in the combustion chamber causes NOx, more heat more NOx produced. Less heat less NOx produced)

Now to throw another wrench on the works you have the EGR which also helps by reducing the NOx emmsions. It takes some of that hot NOx filed exhaust, cools it and recirculates it to remove the NOx. Prior to DEF and SCR this was the main method for reducing NOx in these trucks, hence the pre-DEF trucks get worse mpg.


.

 

[John Jensen]

Regens (of any kind) are a different process then SCR, period. They have nothing to do with each other. 2 different technologies for solving 2 different problems.

They do not use the same triggers. SCR/DEF is triggered by NOx emissions (a NOx sensor), active regens are triggered by differential pressure across the DPF (pressure sensors) ie: when it starts getting clogged.
Now a passive DPF regen will start to occur anytime the exhaust temp goes over 600 degrees (at the DPF) but I would argue at that temp it is not burning much "off" but holding it's own. Active regens (where additional fuel is injected) it will reach around the 1100 degree mark and really burn off the soot. Again, nothing to do with the SCR, DEF, or NOx.

The SCR does not require any "extra" heat for the DEF to work, it works with the standard exhaust temps. NOx is a byproduct of the fuel/heat produced in the combustion chamber so the hotter the truck is running (under load, towing etc) the more NOx it will produce, and the more DEF it will consume to get those NOx levels down. Again, nothing to do with regens.
As far as cold starts and not using DEF, again this is triggered by the NOx sensor. When the engine is cold it is not producing as much NOx so DEF is not needed as much. (remember heat in the combustion chamber causes NOx, more heat more NOx produced. Less heat less NOx produced)

Now to throw another wrench on the works you have the EGR which also helps by reducing the NOx emmsions. It takes some of that hot NOx filed exhaust, cools it and recirculates it to remove the NOx. Prior to DEF and SCR this was the main method for reducing NOx in these trucks, hence the pre-DEF trucks get worse mpg.
.

Thanks for your partial reply. You say, "The SCR does not require any "extra" heat for the DEF to work". Yes, it doesn't require "extra" induced heat but it requires that the exhaust temps (heat) at the DPF inlet and the NOx Ratio to soot ratio are high enough to oxidize the particulate matter. That tells me that passive regens and SCR do have the same triggers but maybe not the same parameters. Passive needs 662 degrees, they don't say what degrees are "high enough" for SCR.

I'll await sag2's reply as well.

 

[kthaxton]

THERE IS NO "TRIGGER" FOR PASSIVE REGENS!
Passive regens just happen when the truck works hard. Nothing is actively occurring (hence "passive"), in fueling, programming or anything else....the engine is just producing hot enough exhaust temps, on its own, to burn off soot in the DPF.

As soon as you start pulling a prolonged grade with a trailer.....that alone results in a passive regen....and this occurs whether the DPF needs it or not, and there is no trigger.