3.0L Duramax DPF regen graphs

[wwillson]

Ever wondered what the temperatures, delta P, and fuel flow look like during a GM 3.0L Duramax regen?

The first graph is the Exhaust temperatures at the exhaust manifold and at the sensor just before the DPF. The high EGTs burn off the soot in the DPF. The second graph is the fuel flow and the DPF delta P. The soot is mostly burned out by about 6 minutes into the regen. The addition fuel flow sprayed into the exhaust is about 1 gallon/hr. This regen was entirely cruising at highway speed.

 

[DemoFly]

Great data

 

[OneLonelyBurrito]

Was this entire regen steady-state highway driving?

 

[BobsArmory]

Nice

 

[Jetronic]

Ever wondered what the temperatures, delta P, and fuel flow look like during a GM 3.0L Duramax regen?

The first graph is the Exhaust temperatures at the exhaust manifold and at the sensor just before the DPF. The high EGTs burn off the soot in the DPF. The second graph is the fuel flow and the DPF delta P. The soot is mostly burned out by about 6 minutes into the regen. The addition fuel flow sprayed into the exhaust is about 1 gallon/hr.

View attachment 261153

View attachment 261154

Pretty consistent with the findings on my own car, a regen takes 10 minutes, and though it never took longer for me, I believe its possible this gets extended. 0.5l of fuel was dumped into the cat, so that works out to 3l per hour, slightly less than yours but smaller engine with smaller cat and dpf. If the regen was able to run at least half a cycle, the proces would not restart on the next drive, and I'd get almost a normal distance between regens. If I could I let the engine idle if I reached my destination before a regen was finished, don't believe I interrupted it more than 5 times in it's life.

if you can monotor the turbo pressures during a regen, mine limited turbo pressure to the bare minimum during regen, so that naturally increased the egt aswell.

also interesting to see is that the process doesn't stop just because you are off the throttle, or at a stop 'n go light, like a lot of people believe. if it does stop, your catalyst has issues.

 

[fantastic]

From 700F before Regen, then to 1100F shortly after Regen starts, & ending at 1200F. Good to see for this particular engine.

 

[Opelman]

Interesting, is there a way to add DEF consumption in the graph? With EGT that high, Nox will be forming and DEF needed to knock it out.

 

[wwillson]

Was this entire regen steady-state highway driving?

Yes, 77 MPH the entire time.

if you can monitor the turbo pressures during a regen, mine limited turbo pressure to the bare minimum during regen, so that naturally increased the egt aswell.

No change in boost pressure other than going up and down grades, that's what the power changes were.

Interesting, is there a way to add DEF consumption in the graph? With EGT that high, Nox will be forming and DEF needed to knock it out.

There is a field on the iDash, but unfortunately there is no data. It does make sense that more DEF (Diesel Exhaust Fluid) would be used during the regen, as there is more fuel burned and there would be more NOx. Some people erroneously believe that DEF is used to burn the soot out of the DPF, this is untrue. Fuel is used to heat the DPF which burns built up soot and DEF is used to react with NOx and a catalyst in the SCR to reduce NOx.

 

[burbguy82]

Yes, 77 MPH the entire time.


No change in boost pressure other than going up and down grades, that's what the power changes were.


There is a field on the iDash, but unfortunately there is no data. It does make sense that more DEF (Diesel Exhaust Fluid) would be used during the regen, as there is more fuel burned and there would be more NOx. Some people erroneously believe that DEF is used to burn the soot out of the DPF, this is untrue. Fuel is used to heat the DPF which burns built up soot and DEF is used to react with NOx and a catalyst in the SCR to reduce NOx.

so drive it hard?

 

[AZjeff]

Does the Delta P trigger the regen? It went from about 1.3 to 0.5 psi after. Do you see the same psi after regen every time?

 

[OneLonelyBurrito]

There is a field on the iDash, but unfortunately there is no data. It does make sense that more DEF (Diesel Exhaust Fluid) would be used during the regen, as there is more fuel burned and there would be more NOx. Some people erroneously believe that DEF is used to burn the soot out of the DPF, this is untrue. Fuel is used to heat the DPF which burns built up soot and DEF is used to react with NOx and a catalyst in the SCR to reduce NOx.

Interesting, is there a way to add DEF consumption in the graph? With EGT that high, Nox will be forming and DEF needed to knock it out.

I'm not sure engine out NOx would be higher as the EGT in the manifold isn't significantly higher. As far as I'm aware, NOx typically aren't formed in the DOC during the oxidation process that happens in the DOC. NOx typically change from NO to NO2 inside the DOC. The NO2/NO ratio is an important factor in setting up the SCR for maximum NOx conversion.

 

[wwillson]

Does the Delta P trigger the regen? It went from about 1.3 to 0.5 psi after. Do you see the same psi after regen every time?

Good question to which I don't think anyone outside of GM knows the complete answer. There seems to be a maximum mileage allowed between regens. When on a long trip, the regens seem to be 650 miles apart. I've read that when the 3.0L is short tripped or idled the regen mileage can be a low is 300 miles, so soot loading of the DPF is certainly part of the calculation.

 

[Jetronic]

Yes, 77 MPH the entire time.


No change in boost pressure other than going up and down grades, that's what the power changes were.


There is a field on the iDash, but unfortunately there is no data. It does make sense that more DEF (Diesel Exhaust Fluid) would be used during the regen, as there is more fuel burned and there would be more NOx. Some people erroneously believe that DEF is used to burn the soot out of the DPF, this is untrue. Fuel is used to heat the DPF which burns built up soot and DEF is used to react with NOx and a catalyst in the SCR to reduce NOx.

there's less oxygen left over if more fuel (and soot is burned) so there would be less NOx. In fact, part of the dpf regen is turning off EGR (on my old car)

 

[AZjeff]

Any feel from the forums how long the DPF lasts? Dependent on useage?

 

[dnewton3]

Looks like the overall strategy and effect are achieving the intent.

Good thing they have the tech sorted out, because GPFs are on their way ...

 

[AZjeff]

GPFs are here.

 

[OneLonelyBurrito]

Good question to which I don't think anyone outside of GM knows the complete answer. There seems to be a maximum mileage allowed between regens. When on a long trip, the regens seem to be 650 miles apart. I've read that when the 3.0L is short tripped or idled the regen mileage can be a low is 300 miles, so soot loading of the DPF is certainly part of the calculation.

I believe I read a TSB somewhere that is could be trigger by miles, engine hours, and amount of fuel burned in addition to the pressure differential across the filter. According to certification data, it looks like the LM2 regens every 454 miles on the FTP72 drive cycle.

I wouldn’t be surprised if GM also has a mathematically model in the PCM of engine soot out minus any passive regeneration that is happen along with expected pressure delta vs actual pressure delta to try and mitigate plugging the filter.

 

[wwillson]

so drive it hard?

It doesn't matter how hard you drive, because there is so much EGT temperature drop at the turbo that you can't burn the soot out of the DPF without more heat. To burn the soot out requires about 1150°F at the DPF, which would require exhaust manifold temperatures of around 1550°F, because at very high boost the heat loss at the turbo is about 400°F. Sustained EGTs of 1550°F will melt pistons and hurt other parts in pretty short order, hence the need to inject fuel post turbo to heat things back up.

 

[wwillson]

According to certification data, it looks like the LM2 regens every 454 miles on the FTP72 drive cycle.

Hmm, my average miles between regens is > 600, maybe because I do so much steady state highway driving?

 

[OneLonelyBurrito]

Hmm, my average miles between regens is > 600

The FTP72 drive cycle is mostly slow speed driving. The average speed is 19mph, so if you have a significantly higher average speed with steady state engine load i.e. highway driving. Regen can be much longer.

It doesn't matter how hard you drive, because there is so much EGT temperature drop at the turbo that you can't burn the soot out of the DPF without more heat. To burn the soot out requires about 1150°F at the DPF, which would require exhaust manifold temperatures of around 1550°F, because at very high boost the heat loss at the turbo is about 400°F. Sustained EGTs of 1550°F will melt pistons and hurt other parts in pretty short order, hence the need to inject fuel post turbo to heat things back up.

Soot can also be oxidized by NOx. Oxidation of soot from NOx occurs at much lower temperatures , if I remember correctly it’s about 300-350C, than thermal oxidation of soot. I don’t exactly know how the SCRoF used on this engine affects passive regeneration using NOx, but it should still be happening some, unlike when the DPF is behind the SCR. Then regeneration relies entirely on thermal oxidation of the soot.