Is diesel added from all cylinders during active DPF regen?

[Alphonse]

From CumminsHub regarding the DPF:

"Two regeneration modes clean the filter when it nears maximum capacity - passive and active regeneration. Passive regeneration occurs naturally anytime the exhaust gas temperature reaches the required threshold to burn the collected particulates from the filter (950+ degrees F). Since the conditions that allow for passive regeneration don't always occur during everyday use, the engine enters the active regeneration state to periodically burn off particulates that have accumulated in the filter. A differential pressure sensor measures the pressure difference between the inlet and outlet of the DPF in order to monitor the filter's capacity. An exhaust gas temperature and oxygen sensor mounted in the inlet of the DPF provide additionally information to the engine control module. During active regeneration, commonly referred to as "reburn" or "regen", diesel fuel is introduced into the exhaust stream by an injection event occurring late in the power stroke and/or through the exhaust stroke."

How does Cummins juice up the regen diesel fuel? Some of you may know that Ford is struggling a bit at the moment with the MY 15 and 16's because they are juicing from one bank only and creating exhaust valve problems. So on our trucks are all cylinders adding diesel to the exhaust stream during active regeneration?

 

[sag2]

It is added to all cylinders as an after injection event on the exhaust stroke, or at least well after the power stroke point of peak torque.

 

[Alphonse]

Active generation on a short trip daily driver

Thanks sag2 for the confirmation.

Side note, the description in CumminsHub regarding active vs. passive regeneration is a good one with an interesting data point.

"Passive regeneration occurs naturally anytime the exhaust gas temperature reaches the required threshold to burn the collected particulates from the filter (950+ degrees F)."

This appears to be the primary cause of more active regenerations on continued short trip use of the truck. I am assuming short trips do not reach and sustain the temperatures high enough to passively regenerate the DPF and it eventually triggers a "cook off". Using one of these beasts as a daily driver running short trips comes with a price of the number of active generations it will cause. It certainly would not help the fuel economy.

So watching the temperatures into and out of the DPF would be an interesting tell tale of what is going on. Now to try to figure out how to do that via some monitor. I am sure someone has done this. I am going to make this a topic for a separate thread.

 

[AH64ID]

Even long trips may not reach sufficient temps in the DPF for passive regeneration. The frequency and efficiency of passive regen will depend on the engine load. Towing at GCWR across the Rockies will likely yield some passive regen, while cruising at 75 thru Kansas may not.

 

[Alphonse]

Even long trips may not reach sufficient temps in the DPF for passive regeneration. The frequency and efficiency of passive regen will depend on the engine load. Towing at GCWR across the Rockies will likely yield some passive regen, while cruising at 75 thru Kansas may not.

Thanks, makes sense. I think I have seen indications of that towing vs. daily driver use but I have no data.

It would be very interesting to watch/monitor the temps in and out of the DPF to really understand what is happening.

 

[Jim W]

On my 2008; truck I could tell when the DPF went into regen two ways. The first one and this was not to accurate was to watch the MPG on the over head display. The mileage would drop off when the truck went in to regeneration mode. If the truck was towing a load this could occur almost every 200 miles or so. My MPG would be between 10.5 and 12 when towing, depending if I was in hilly terrain or flat. Also when I added an EGT gage to the truck, I could tell when the truck would go into regeneration. The EGT's would start to climb up to 1450F max and cycle between 1200F and 1300F for 20 min's or so, than returning to 850F. So an EGT gage could work for your truck too.

Now I member and writer for TDR Joe Donnelly; bought a new fourth gen truck and he wrote about using the Edge Insight CTS display in issue 85 and 86. In issue 86 on page 108 he discuss the different parameters of the insight and which ones he uses to monitor the engine when it was operational. This article may help you.

Jim

 

[Alphonse]

Thanks Jim for the TDR issue numbers, I will dig in.

Secondly, when you mention the EGT that you added, I assume you put it in the exhaust manifold near the exit to the turbo. Correct?

 

[sag2]

If you were looking to add an EGT sensor instead of buying one of the monitors to determine when regeneration was happening, a more accurate location would be before or after the DPF. You do not need one in the manifold on a stock truck for monitoring EGT as the stock fueling will not allow the engine EGT to get high enough for damage to occur.

 

[Alphonse]

If you were looking to add an EGT sensor instead of buying one of the monitors to determine when regeneration was happening, a more accurate location would be before or after the DPF. You do not need one in the manifold on a stock truck for monitoring EGT as the stock fueling will not allow the engine EGT to get high enough for damage to occur.

Sag2, aren't there two there already (in and out on the DPF) feeding info into the ECM on a 4th generation (2016)?

 

[zetatre]

I would suspect there is more than two. I'm not familiar with the exhaust system with SCR, but my 2012 with the LNT has a total of 4 EGT probes.

In my case there's the DOC (diesel oxidation catalyst to process HC and CO), the LNT (lean NOx trap) and the DPF last.

In your case with have the DOC, the DPF and the SCR (selective catalyst reducer). The DOC and DPF are "close coupled" so the look like one canister, but it is actually 2 separate after treatment devices. I admit that I have only seen picture of this, but looking at the "second canister" where the SCR resides, I see a bung in the middle which could be the post-SCR NOx sensor. Some SCR systems have an ammonia reducer after the selective catalyst reducer that threats NOx to process any unused ammonia (urea is injected, it converts into ammonia and CO2 through an intermediate process, and ammonia is docked in the SCR and used to reduce the NOx back to N2 and H2O)

In any case, you recognize the EGT probes because they are very small diameter. Oxygen sensors look like the ones in car and connect directly to the harness. NOx sensors look like oxygen sensor but connect to a processing module that then connects to the harness. You also have 2 pickups for the DPF differential pressure that are just hoses attached to the exhaust (one before and one after the DPF) and going to an individual module.

There's a lot of misunderstanding and misinformation around about diesel after-treatment so your best option if you're really after the truth is either find official Cummins/Ram documentation (probably not available) or crawl under your truck and see what's what.

 

[zetatre]

I would suspect there is more than two. I'm not familiar with the exhaust system with SCR, but my 2012 with the LNT has a total of 4 EGT probes.

In my case there's the DOC (diesel oxidation catalyst to process HC and CO), the LNT (lean NOx trap) and the DPF last.

In your case with have the DOC, the DPF and the SCR (selective catalyst reducer). The DOC and DPF are "close coupled" so the look like one canister, but it is actually 2 separate after treatment devices. I admit that I have only seen picture of this, but looking at the "second canister" where the SCR resides, I see a bung in the middle which could be the post-SCR NOx sensor. Some SCR systems have an ammonia reducer after the selective catalyst reducer that threats NOx to process any unused ammonia (urea is injected, it converts into ammonia and CO2 through an intermediate process, and ammonia is docked in the SCR and used to reduce the NOx back to N2 and H2O)

In any case, you recognize the EGT probes because they are very small diameter. Oxygen sensors look like the ones in car and connect directly to the harness. NOx sensors look like oxygen sensor but connect to a processing module that then connects to the harness. You also have 2 pickups for the DPF differential pressure that are just hoses attached to the exhaust (one before and one after the DPF) and going to an individual module.

There's a lot of misunderstanding and misinformation around about diesel after-treatment so your best option if you're really after the truth is either find official Cummins/Ram documentation (probably not available) or crawl under your truck and see what's what.

The very first EGT probe, right past the turbocharger is the one used for fueling and the one you should observe. All others are there monitor chemical reactions.

 

[Alphonse]

I would suspect there is more than two... ... ...

Zeta, there are several - I was referring to those on the inlet and outlet of the DPF. See page 14 of the pdf that sag2 posted for us in this thread, fourth post down.
https://www.turbodieselregister.com/threads/253836-Sensor-list-and-or-schematic

Also take a look at CumminsHub under exhaust emissions for a fairly decent description, albeit without too much detail.
http://cumminshub.com/emissions.html

 

[zetatre]

Zeta, there are several - I was referring to those on the inlet and outlet of the DPF. See page 14 of the pdf that sag2 posted for us in this thread, fourth post down.
https://www.turbodieselregister.com/threads/253836-Sensor-list-and-or-schematic

That is a schematic of the exhaust system up to 2012 when the LNT was used to process NOx. Your exhaust is different and has different sensors in different positions.

I do believe that the system has at least 3 EGT probes, possibly more. You have one downstream from the turbo, before any aftertreatment system. You then have one before the DPF and one after the DPF. Since the DOC and the DPF are closed coupled you probably have a probe in the middle of the first canister that houses the DOC and the DPF. I'm unsure if more EGT probes are used after that but like I said they are very easy to spot because they are small in diameter.

 

[Alphonse]

That is a schematic of the exhaust system up to 2012 when the LNT was used to process NOx. Your exhaust is different and has different sensors in different positions.

Okay! Sincere thanks for the clarification. This document is a training document and while it does refer to DEF (2013 introduction), it obviously has a mixture of different vintage stuff in it.

Do you have any idea where to get a schematic of the latest configuration? I have been reluctant to do an experiment on TechAuthority to see if it is there since the 2016 information is not yet available. Perhaps it would be worth it to see if the schematic is there for 2015's, I would gladly spend the $35 for a three day subscription.

 

[zetatre]

Actually at a closer look, there is schematic in the page 26 that referes to the chassis cab exhaust which was fitted with SCR earlier than the pickups. That's how your DOC & DPF should look like Notice that there's a DOC inlet sensor, a DOC outlet/DPF inlet and a DPF outlet. Unfortunately there is no schematic of the "second canister".

Here's a couple of pictures of the second canister:

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In the first picture all you see is the metering unit which inject the urea solution.

The second picture shows several sensors. Upon close inspection I'm tempted to believe that the canister is not two devices. The reason why a set of sensor is placed in the middle is simply because the initial section of the canister may contain a mixer element that ensure that the urea/ammonia is properly mixed with the exhuast gasses.

You can clearly see 2 small sensors that are the EGT probes before and after the SCR. You also see two other sensors that look like oxygen sensors, but are not, certainly the second one is a NOx sensor (you see the processing unit I spoke about earlier). I believe the first sensor it is also a NOx sensor (specifically the pre-SCR sensor) that has been disconnected from the processing unit which I believe is mounted on the frame.

The only thing that is a little odd is that NOx sensor are usually placed before the urea is injected. NOx sensors are incapable of distinguishing NOx from NH3 (ammonia) so I'm not convinced that my description above is entirely accurate.

In summary there should be 5 EGT probes:
1) at the inlet of the DOC
2) between the DOC and the DPF
3) after the DPF
4) before the SCR
5) after the SCR

 

[Alphonse]

Thanks ZetaTre for the insights, the photos, and the list you have taken the time to generate.

Now to figure out if I can get to the data these sensors generate via a monitor.

 

[zetatre]

Thanks ZetaTre for the insights, the photos, and the list you have taken the time to generate.

Now to figure out if I can get to the data these sensors generate via a monitor.

Of course it can be done.

Those parameters are published by the PCM via the OBD port. They are called PID and SAE has standardized several of them.

You need to find an OBD monitor that has them programmed (like the EDGE gadget). I don't know if the Torque Pro app for smartphones has them.

 

[finallycummins]

Even long trips may not reach sufficient temps in the DPF for passive regeneration. The frequency and efficiency of passive regen will depend on the engine load. Towing at GCWR across the Rockies will likely yield some passive regen, while cruising at 75 thru Kansas may not.

I can vouch for this. Even pulling the 24' enclosed across windy Kansas in july, post dpf temps were only 800*. Still did the active regen about every 200 miles.

 

[Alphonse]

Of course it can be done.

Those parameters are published by the PCM via the OBD port. They are called PID and SAE has standardized several of them.

You need to find an OBD monitor that has them programmed (like the EDGE gadget). I don't know if the Torque Pro app for smartphones has them.

I have been studying the Edge Insight CTS2 and also read up on Joe Donnelly's articles, pointed out by Jim W., on the Edge monitor. I have one on order and am expecting that it will work fine. I also have Torque Pro and KIWI 2BT but don't like tying my phone up for such things. I am betting that the CTS2 does exactly what I am after. Thanks again for your replies.

 

[Newsa]

I always thought an active regen would only occur after the truck engine reaches operating temps. But i had what seemed like an active regen with a newly started cold engine this week.