2017 2500 not using def

[John Jensen]

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.

It's a semantics thing. I agree! You say "hot enough exhaust temps", I say "trigger". The passive regen takes place when the DPF inlet sensor sees 350c (662f). I call that a trigger. No matter pulling, carrying, high speed, stop & go, etc. the passive regen will not happen until that approx "trigger" temp is reached.
We are saying the same thing, just a bit differently.

Edit:
By the way, I still think you are wrong believing that an active regen uses DEF.

 

[AH64ID]

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?

Yes, it's used during active regen but NOT for a regen. It's used in the SCR not the DPF. They run independently and concurrently.

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?

SCR was added as a different means of reducing NOx output. Pre-SCR engines had to use more EGR to reduce the NOx, which is not good. SCR has allowed for less EGR and more cylinder pressure, both of which have positive impacts on longevity, and performance.

As it has been stated many times already in this thread they are not the same, don't don't the same things, and are 100% independent of each other.

SCR is always an active process. It has certain parameters to start and stop, but it's a contsant active process to redice NOx output from the engine.

Passive regen is always passive, there is no trigger, and no controls. This occurs when the DPF has enough heat to be self cleaning without any additional fuel. This is either while towing or running at interstate speeds. The more heat the faster the cleaning.

Regen occurs the same way regardless of if it's active or passive.

If they are two different processes they seem to use the same triggers, wouldn't they conflict?

They are in 2 different places in the exhaust, regen in the DPF and DEF in the SCR. In theory soot never enters the SCR and DEF never enters the DPF.

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?

Because it's two different chemical reactions. DPF's use high heat and precious metals, mainly platinum, to create a chemical reaction that cleans the DPF filter of accumulated soot.

SCR requires heat but not like a regen, the main process in the SCR is the reaction of UREA and the NOx to reduce the NOx gasses. The heat required here is minimal and achieved thru normal empty driving, basically it doesn't work when cold but it doesn't have to be as hot as the DPF does for a regen (active or passive).

It seems like SCR has replaced the passive regen, however, passive keeps appearing in artic;es and discussions.

No, No, No.... but if you don't get it by this point then I am not certain how else it can be explained to you. This thread has literally turned into everyone trying to explain to you that passive regen and SCR have nothing to do with each other.

 

[John Jensen]

Yes, it's used during active regen but NOT for a regen. It's used in the SCR not the DPF. They run independently and concurrently.

SCR was added as a different means of reducing NOx output. Pre-SCR engines had to use more EGR to reduce the NOx, which is not good. SCR has allowed for less EGR and more cylinder pressure, both of which have positive impacts on longevity, and performance.

As it has been stated many times already in this thread they are not the same, don't don't the same things, and are 100% independent of each other.

SCR is always an active process. It has certain parameters to start and stop, but it's a contsant active process to redice NOx output from the engine.

Passive regen is always passive, there is no trigger, and no controls. This occurs when the DPF has enough heat to be self cleaning without any additional fuel. This is either while towing or running at interstate speeds. The more heat the faster the cleaning.

Regen occurs the same way regardless of if it's active or passive.

They are in 2 different places in the exhaust, regen in the DPF and DEF in the SCR. In theory soot never enters the SCR and DEF never enters the DPF.

Because it's two different chemical reactions. DPF's use high heat and precious metals, mainly platinum, to create a chemical reaction that cleans the DPF filter of accumulated soot.

SCR requires heat but not like a regen, the main process in the SCR is the reaction of UREA and the NOx to reduce the NOx gasses. The heat required here is minimal and achieved thru normal empty driving, basically it doesn't work when cold but it doesn't have to be as hot as the DPF does for a regen (active or passive).

No, No, No.... but if you don't get it by this point then I am not certain how else it can be explained to you. This thread has literally turned into everyone trying to explain to you that passive regen and SCR have nothing to do with each other.

Got it - very clear, thanks. I got re-educated today. My previous teachers in the Ecodiesel world had led me astray. You have cleared it up - much appreciated.
And I apologize for turning this thread into everyone trying to explain to me, etc.
You and sag2 have taken the time to explain it.
Cheers from an 86 year old fart still learning.

 

[sag2]

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.


.

MtnRider is spot on on his explanation above. I don't think I could have said it any better. And by the way the temperature that you need for the SCR system to work is 362 degrees Fahrenheit. Once you get over that temperature the reaction occurs to turn the nitrous oxide into harmless nitrogen gas and water.
The only clarification and it might just be semantics is the EGR system doesn't remove the NOx, it prevents it from being created in the first place because it reduces combustion chamber temperatures.

 

[smittyd174]

Ok, I know this has been talked about but I can't find my situation. Here goes.. 2017Ram 2500, almost 50k miles. Everything was working properly before last service. Took approx 2500 mile trip last winter, burned 3/8 tank of def. Got service a couple months ago before going on a 2000 mile trip, and now almost 3k everyday miles and still no movement on def gauge. Tried topping off, took1 gal.. took to different dealership, did park regen (102 minutes), filter at 95%, Says everything looks good. Truck has never went this long on so little def. Any ideas?

Maybe the service fixed your high usage. My 2016 uses about a jug between oil changes 7500 miles. When towing def usage pretty well doubles.