Why heavy pulling and high EGTs won't burn the soot out of your DPF

[wwillson]

I read years ago that a long pull up a steep grade with high EGTs will burn the collected soot out of your diesel particulate filter. I believed this until I pulled our Airstream (8,000 pounds with a GVCW of 17,000 pounds) from Denver to Breckenridge, which has two long and steep grades. Much to my surprise a DPF regen started just as we exited the interstate in Frisco. What! how could that be, I just pulled two long and steep grades with high EGTs?

Fast forward a couple years to the my new world of Banks iDash data.

The typical EGTs pulling our 5th wheel trailer cruising down the interstate at 60 MPH in 8th gear at 1880 RPMs is about 900°F at the turbo inlet. The boost is about 10 PSI and fuel burn is about 6.2 GPH. The turbo outlet temp will be about 750°F. So the reduction of pressure at the turbo (delta between inlet and outlet pressure) will drop the temperature about 150°F at this boost level.

When we pull a steep grade, like up to the Eisenhower tunnel on I-70 in Colorado the EGTs at the turbo inlet will be around 1200°F, the turbo outlet will be about 900°F. The boost will be about 25 PSI and the fuel burn will be about 15 GPH. In high boost and EGTs the temperature drop at the turbo is typically 300°F.

The strangest data I've seen is when you go from about 20 PSI boot to 25 PSI boost the turbo outlet temperature will actually decrease about 25°F despite the fact that the turbo inlet temperature increases. This is completely reproducible.

Let's look at the temperatures during a DPF regen.

During a regen the ECU attempts to keep the DPF inlet temperature at 1075°F by injecting fuel into the exhaust stream before the DPF. This is the temperature required to burn the soot out of the DPF. The regen typically takes about 30 minutes. Notice how 'cool' the exhaust is coming out of the turbo? 900°F is not hot enough to burn the soot out of the DPF. Pulling the grade up to the Eisenhower tunnel yielded about the same turbo outlet temperature, because there is so much temperature drop across the turbo at high boost levels.

There is so much heat lost at the turbo, you will never be able to keep the DPF hot enough to ignite the soot and burn it out. Hence, the need to burn fuel in the exhaust stream to get the exhaust hot enough clean the DPF.

The temps in the iDash display are defined below:

"EGT" = Turbo Inlet	"EGT1" = Turbo Outlet
"EGT2" = DPF Inlet	"EGT3" = DPF Outlet
"EGT4" = SCR Inlet	"EGT1/5" = SCR Outlet
"DPF RG" = ECU calculation of when to regen %	"REGEN" = OFF or ACTIVE

 

[xgmad]

Man, I didn't know turbo's got that hot!

 

[PiperOne]

Good data, luv my iDash too.

If your truck is a GM (looks like it) DPF RGN is not the soot load, DPF SL is. DPF RGN is the cumulative counter of all regen triggering events (miles, time, fuel used and soot loading). Active regens will always occur at 100 DPF RGN but the actual soot load can be anywhere from 40 to 70%.

I have a 22 L5P (iDash logging) and with the exception of 1, all my regens have occurred at exactly 807 miles (GM programmed mileage limit) with soot loads between 40 and 70.

Some passive regen does occur above 700F in the DPF, I've seen 20% drops, but only when the soot loads are under approx 50%. The higher the actual soot is the less effective passive regens are. You do need to have those temps for 10 plus minutes for a decent amount of passive to happen. Big trailers and wind do it for me.

I would bet your turbo temp drop after 20 psi boost is the variable geometry kicking in to start moderating boost. As it starts to flow more freely the temp changes.

It's awesome having an iDash and being able to see what's going on isn't it?

 

[wwillson]

f your truck is a GM (looks like it) DPF RGN is not the soot load, DPF SL is. DPF RGN is the cumulative counter of all regen triggering events (miles, time, fuel used and soot loading). Active regens will always occur at 100 DPF RGN but the actual soot load can be anywhere from 40 to 70%.

Thank you for the info, it's very hard to find online what the fields mean. I will correct my original post.

all my regens have occurred at exactly 807 miles

I've noticed the same thing, but in my 2018 Duramax there didn't seem to be a set mileage limit. I think the longest regen interval I saw in the 2018 was over 1,000 miles.

I would bet your turbo temp drop after 20 psi boost is the variable geometry kicking in to start moderating boost. As it starts to flow more freely the temp changes.

If that were the case, I would think the turbo out temps would significantly rise due to the smaller pressure drop. I can see that the boost limit is about 28 PSI. The book says 29 PSI, but the highest I've seen at WOT is 28.2.

Is there a data point for VGT position?

It's awesome having an iDash and being able to see what's going on isn't it?

Yes, that's how I figured out heavy pulling in 10th gear is a no no. Very high sustained exhaust temps was causing oil consumption.

 

[PiperOne]

There is a turbo vane position value in the data stream, not sure if the iDash will read it. Won't be near that truck till Tuesday but will check then.

Pulling in 10th caused oil use? Good to know. I've been dropping it into 8th on hills based in past experiences (would drop the 6 sp into 5th).
🍻

 

[Jetronic]

I read years ago that a long pull up a steep grade with high EGTs will burn the collected soot out of your diesel particulate filter. I believed this until I pulled our Airstream (8,000 pounds with a GVCW of 17,000 pounds) from Denver to Breckenridge, which has two long and steep grades. Much to my surprise a DPF regen started just as we exited the interstate in Frisco. What! how could that be, I just pulled two long and steep grades with high EGTs?

Fast forward a couple years to the my new world of Banks iDash data.

The typical EGTs pulling our 5th wheel trailer cruising down the interstate at 60 MPH in 8th gear at 1880 RPMs is about 900°F at the turbo inlet. The boost is about 10 PSI and fuel burn is about 6.2 GPH. The turbo outlet temp will be about 750°F. So the reduction of pressure at the turbo (delta between inlet and outlet pressure) will drop the temperature about 150°F at this boost level.

When we pull a steep grade, like up to the Eisenhower tunnel on I-70 in Colorado the EGTs at the turbo inlet will be around 1200°F, the turbo outlet will be about 900°F. The boost will be about 25 PSI and the fuel burn will be about 15 GPH. In high boost and EGTs the temperature drop at the turbo is typically 300°F.

The strangest data I've seen is when you go from about 20 PSI boot to 25 PSI boost the turbo outlet temperature will actually decrease about 25°F despite the fact that the turbo inlet temperature increases. This is completely reproducible.

Let's look at the temperatures during a DPF regen.

During a regen the ECU attempts to keep the DPF inlet temperature at 1075°F by injecting fuel into the exhaust stream before the DPF. This is the temperature required to burn the soot out of the DPF. The regen typically takes about 30 minutes. Notice how 'cool' the exhaust is coming out of the turbo? 900°F is not hot enough to burn the soot out of the DPF. Pulling the grade up to the Eisenhower tunnel yielded about the same turbo outlet temperature, because there is so much temperature drop across the turbo at high boost levels.

There is so much heat lost at the turbo, you will never be able to keep the DPF hot enough to ignite the soot and burn it out. Hence, the need to burn fuel in the exhaust stream to get the exhaust hot enough clean the DPF.

The temps in the iDash display are defined below:

"EGT" = Turbo Inlet	"EGT1" = Turbo Outlet
"EGT2" = DPF Inlet	"EGT3" = DPF Outlet
"EGT4" = SCR Inlet	"EGT1/5" = SCR Outlet
"DPF RG" = ECU calculation of when to regen %	"REGEN" = OFF or ACTIVE

View attachment 120454

That's why some manufacturers include a fuel borne catalyst, which reduces the temerature needed by nearly 200°F. I tried it in my car and could go up to 5x as far between regens. Also, the catalyst is active inside the engine aswell, likely reducing soot loading in the dpf.

 

[billt460]

Good God that's hot!

 

[Cujet]

Can your gauges determine how much fuel is used for a regen?

 

[wpod]

Man, I didn't know turbo's got that hot!

Too hot to run a turbo.

 

[PiperOne]

To answer a few questions,

Temps are fine, turbo is water cooled and fed a lot of oil. These temps are common on DPF equipped engines, since 2007 on GM stuff, and turbo failures on stock hp trucks are very rare.

Regen fuel use, I haven't seen a gauge that tracks it, and I'm not sure the truck has that data in it's stream.

Fuel borne catalysts,

I'd be very careful with those. Many use metallic agents, usually ferrocene, and while they may help with lowering passive regen temps, they are also leaving behind non combustible byproducts. Over time these plug a DPF. GM specifically is against their use. I have seen some of these catalysts contain so much metallic ingredient that it starts to show up on an engine oil sample. DPF's when removed will be rust colored instead of an ashy white and will usually not clean up even in an off vehicle clean process.

I was involved in some catalyst testing in 2008-9 and while the products did clean up combustion, the engine controls fought back and erased the benefits. It was determined that the engine was programmed to see certain levels of things (in this particular case oxygen) and when the cleaned up combustion altered it, it just contolled air intake to get things back to spec. It was during these tests I saw first hand the DPF long term fouling. It really stinks that engines are this picky now.

 

[AZjeff]

Wayne, you're gaining an in depth understanding of this engine, pretty cool. How much does instantaneous fuel usage change during regen? Does the soot box have to be serviced?

 

[RobbyDawg]

Interesting. Makes sense if you think about it…boost created by the turbo is not “free” energy, instead it is a reflection of the heat absorbed by the turbo.

For those saying 1200F is too hot, that’s actually about right for pre-turbo temps under full load. Part of my work involves load testing diesel generators under full load, so I am often measuring this.

Once you start seeing 1300F+, it’s time to back off.

 

[wwillson]

How much does instantaneous fuel usage change during regen?

Not pulling it will cost you about 3 MPG, while pulling it will be about 1.5 MPG.

Does the soot box have to be serviced?

I have no experience with this yet, thankfully. I think there are many factors that determine how long your DPF will last, including fuel quality, idle time, puttering around town, incomplete regens, etc.

Maybe one of our semi mechanics will comment.

 

[wwillson]

Good God that's hot!

I wrote before that the torque race between the big three with their diesel trucks is silliness. If you are WOT you will see 1500+°F the computer will defuel the engine fairly quickly to EGTs around 1350°F, but these temps are way too hot for longevity.

Cummins 6.7 Variations

My uncle was telling me about his new Isuzu F-Series class 6 box truck he has on order. His current Isuzu truck is powered by a 4 cylinder diesel and the new truck will have a 6.7 Cummins. Research revealed that the 6.7 in the Isuzu has 260 HP and 440 lbs of torque. The 6.7 in a Ram truck has...

bobistheoilguy.com

 

[c502cid]

A minor point in this discussion but really I'm just curious. When you say two long grades going from Denver to Breckenridge are you talking Floyd Hill and Eisenhower approach or did you go over the original Loveland Pass too?

 

[PiperOne]

With proper care (correct oils, fuel, no goofy additives) a DPF on a Duramax should go past 300,000 miles without issue.

On a semi, 300,000 plus depending on how the truck is used. Highway only trucks can go 800k sometimes, more city use and the number drops. The saving grace is semi DPF's you can remove just the core of the filter and send them out for serious cleaning or just buy a pre cleaned replacement.

If you're paying attention to things like @wwillson is, long happy life is fairly easily obtained.

 

[wwillson]

A minor point in this discussion but really I'm just curious. When you say two long grades going from Denver to Breckenridge are you talking Floyd Hill and Eisenhower approach or did you go over the original Loveland Pass too?

Yes, Floyd Hill and the Eisenhower approach. Not the original Loveland Pass (US-6), no way would I voluntarily pull that road. I see fuel tankers pulling that and those guys have special skillz. I have driven it in the truck without the trailer and was imagining it with the trailer. Nope.

 

[mobilnissan1991]

Good friend of mine has a 2019 6.7 Cummins, the DPF capacity display on his dash rarely shows the DPF full, hes always hooked to a 10,000 pound skid steer or a heavy camper. When not loaded and on the interstate hes doing 85-90 mph. Truck rarely regens. 77k no issues

 

[Majsmith]

With proper care (correct oils, fuel, no goofy additives) a DPF on a Duramax should go past 300,000 miles without issue.

On a semi, 300,000 plus depending on how the truck is used. Highway only trucks can go 800k sometimes, more city use and the number drops. The saving grace is semi DPF's you can remove just the core of the filter and send them out for serious cleaning or just buy a pre cleaned replacement.

If you're paying attention to things like @wwillson is, long happy life is fairly easily obtained.

What do you think of using TDR-FL from Amalgamated Inc ? I took a gander at the SDS and saw no mention of ferrocene as an ingredient.

 

[Bailes1992]

How far away is the turbo from the DPF in these units?

I've seen with both my (now sold) 2021 Vauxhall Insignia 1.5 Turbo D and my Wifes 2017 Dacia Logan 1.5DCi that the DPF 'load' will drop when the engine is being worked hard enough. I do run Archoil 6900D-Max in all my diesel engine'd vehicles which contains Ferrocene, not sure if this makes a difference. Another thing worth mentioning, in both vehicles, the DPF is literally bolted directly to the turbo and tucked deep down between the back of the engine and bulkhead with little to no airflow, so I suspect this makes a difference.

One thing that used to irritate me with the Vauxhall, it would initiate a DPF regen every ~200miles or so regardless of the DPF state. Often when towing our caravan long distances on the motorway, I could get the DPF 'load' down to 3% but it would still regen every 200miles.