I'm trying to figure out this passive regen process. From what I've read here it sounds like the passive regen is something that is turned ON and OFF. If the passive regen uses the exhaust temperatures naturally created under heavy loads then what is turned ON and OFF?

I also understand that this is unique to the 6.7 engine. Didn't the 6.4 engine generate high enough exhaust temps to burn off the soot?

Thanks guys.

Rob

 

I may get corrected here, but from what I have observed passive regen is what you are suggesting. When pulling loads and generating higher exhaust temps my soot concentration dropped (I monitor that on a Dashdaq). But I did notice that even with this there was still a regen triggered at a lower soot concentration.
I think what you are asking about going on and off is an active regen, this starts when the soot concentration reaches a certain amount and fuel is pumped in to burn and create enough heat to burn up the soot.

 

Passive regen (DPF Regeneration) occurs naturally at high exhaust temps. Like when you have a trailer attached and you're working the truck. Active regen happens when the DPF fills up and the exhaust temps alone are not enough to burn off the soot. This is when the truck goes into "regen mode" or and active regen and injects raw diesel fuel into the exhaust system which burns at high temperatures in front of the DPF. Active regens turn on and off automatically and the user has no control as to when it will begin.

 

Not unique to the 6.7L. Passive regeneration happens whenever the DPF temperatures reach high enough temperatures (typically 700+ degrees). Driving under average load will create those conditions continuously.

The 6.4L worked the same way (as in passive regen). The active regeneration is significantly different between the two engines. Maybe the main reason why the 6.4L had a less effective passive regeneration is due to the fact that it required a lot more EGR (causing lots more soot, but reduces NOX) than the new engine. The new engine requires less EGR because it is using an SCR (DEF) to reduce NOX - Less EGR = better engine efficiency!

 

As Whiteline and Epic explained, active regen's are what turn on/off.
This occurs at or near a 2.66 soot GPL.
Passive regen occurs any time EGT's are high enough to burn off the soot so there isn't exactly an on or off mode.
I see passive regen begin to slowly work when post DPF EGT's are above 550 degrees and becomes decently effective above 650 degrees (and continues to work better with higher EGTs).
Active regenerations force post DPF temps into the 1,150-1,200 degrees range.

 

Thanks guys, that's how I thought passive regen worked. In earlier posts some had mentioned that passive regen was unique to the 6.7 engine. But the regen takes place at a given temperature whether that temp is reached through heavy work (passive) or burning fuel (active) and this would apply to any DPF system on Ford or GM or Dodge pickups

Thanks again.

Rob

 

Good info . . ken

 

This is an old thread, but it answered a lot of questions that I had about regen on my still-on-order 2015 F250 PSD. I live in the heights and a lot of my commute will be from sea level to 600' MSL (moderate to steep grade) without a load. Would driving in a lower gear to raise RPMs increase EGT to where passive regen would take place?
- Ken

 

Seems odd but higher get temps actually occur when you're heavy on the throttle, doesn't matter what the rpms are. To make heat it needs fuel so I think you'd be better off in a higher gear with full throttle rather than a low gear with light throttle.

If you're curious enough you can buy a monitoring device that will,show you exactly what your temps are.

 

I doubt that you will be able to make the exhaust hot enough for passive regens. Towing is what usually is required to make things hot enough.


The exhaust system does pretty good at retaining the heat to allow the passive regen but you need the load to get it there.

 

Constant highway speeds over a long stretch will do a very effective job of getting the exhaust hot enough for passive regen. That is why you sometimes get that message that says to drive at least 55 mph for 45 mins.

 

+Thanks, all for the replies. Increases my knowledge of how the 6.7L works. I used to be a standardization heli instructor so I like to discuss and understand big, heavy, powerful, complex machines. My only hands-on experience with diesels is the 2005 VW Golf TDI that I drove for a while before giving it to my daughter to commute to college. She loves her diesel and short-shifts through 3 gears from a stop sign to the other side of the intersection. I'm proud of her. Sorry for going off on a tangent. I just upgraded my membership today.
-Ken

 

Passive Regens happen ANY time you have egt over 572° Of course the hotter the EGT temps, the more passive regen that takes place. Towing usually puts you up in that 800-900° range. So you have constant passive regen going on while towing. Of course the added work load, produces more soot, So it's always a trade off.

EGT temps jump when you have turbo pressure and you increase the combustion taking place in the combustion chamber.

If you had one of the older 7.3L trucks for example. We used to chip them and install a pyro. If we saw the pyro temps climbing to a level we didn't want. We could downshift, increase the RPMs, and the increased air flow through the engine cooled the EGTs right down, While we still maintained the same speed.

Same is true with the 6.7L Increasing the RPM without a load, will usually decrease the EGT temps. If you want higher EGT's just lug the engine, where you stay at lower rpms, but have more turbo boost.

It's the same conversation I see with folks wanting to warm up their trucks on cold morning. You will get your coolant warmed up faster and get your heater blowing hot air faster if you get your turbo pressure ups. Idling at 1100 rpm vs 700 rpm really doesn't produce much heat, Since there is no turbo pressure or load at idle.