# Passive regen?



## MP81 (Jul 20, 2015)

The diesel regens on its own, yes.


----------



## johnmo (Mar 2, 2017)

I don't think anything short of driving it WOT for 10 minutes or so would sustain regen temperatures in the DPF. In general, though, I think highway speeds add less soot to the DPF than stop-and-go, low-speed driving, so there's that.

Why would you want to fire off a manual regen? It automatically regens more often than I like already.


----------



## Taxman (Aug 10, 2017)

johnmo said:


> Why would you want to fire off a manual regen?


I'd want to trigger it when it was getting near time to regen and I was driving 75-80mph, preferably at the bottom of a long grade. I believe that would be the way to get the regen done swiftly with minimum waste of fuel.


----------



## ProDigit (Aug 31, 2015)

Taxman said:


> I'd want to trigger it when it was getting near time to regen and I was driving 75-80mph, preferably at the bottom of a long grade. I believe that would be the way to get the regen done swiftly with minimum waste of fuel.


Yes, it should also add turbo boost, as the exhaust should be running more stoic.


----------



## LiveTrash (May 24, 2015)

johnmo said:


> I don't think anything short of driving it WOT for 10 minutes or so would sustain regen temperatures in the DPF..


I've had it initiate a regen while I was driving and then complete it while I was parked numerous times. I just held the RPMs at 1,500 - 2,000 and it maintained the engine temp and what ever else it needs to complete. Mind you, I do notice quicker soot accumulation after completing a parked regen. It probably isn't burning it off as well as if I were driving.


----------



## johnmo (Mar 2, 2017)

LiveTrash said:


> I've had it initiate a regen while I was driving and then complete it while I was parked numerous times. I just held the RPMs at 1,500 - 2,000 and it maintained the engine temp and what ever else it needs to complete. Mind you, I do notice quicker soot accumulation after completing a parked regen. It probably isn't burning it off as well as if I were driving.


Right, because the engine computer is dumping extra fuel independent of your input on the throttle.

The original question was will soot burn off passively under mostly normal driving conditions? I don't have the specifics, but my guess is that the computer dumps more raw fuel into the exhaust and thereby creates a higher exhaust temperature than what could easily be achieved under any normal driving conditions with the possible exception of running WOT and even then not a lot of raw fuel is going to make it into the DPF. I think I've read that the VW system even sends a little raw fuel through an injector while an exhaust valve is open to feed the DPF fire. The GM system likely does the same thing.


----------



## Rivergoer (Mar 30, 2017)

At higher speeds, rather than burning soot in the DPF (passive Regen) the higher EGT just slows down soot accumulation. 

DPF Soot Mass readings never drop/reduce at any speed unless the car is in active Regen mode.


----------



## Barry Allen (Apr 18, 2018)

To a certain extent, I'm sure the engine does passive regen. My understanding is the ECU monitors DPF backpressure. Every time you are driving the car hard enough to get exhaust temperatures high enough, some of the trapped soot is likely being burnt off. Only when the DPF accumulates enough to cause high backpressures does the active regen have to occur.


----------



## ProDigit (Aug 31, 2015)

It would be nice if the fuel was injected BEFORE the turbo.
That way it would act as an 'afterburner'; rather than injecting the fuel after the turbo, where no performance gains are noticed.


----------



## johnmo (Mar 2, 2017)

It would be nice if fuel was never wasted on regens.

We have to make a fire in the DPF and that takes fuel. The products of a combustion cycle are fuel-poor. More fuel ahead of the combustion cycle is never going to feed the fire in the DPF enough fuel.


----------

