OLEJOE
Well-Known Member
And less required torque means less pressure on the skinny pedal to maintain a certain speed.
And lower egt’s.
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Regen
- Thread starter Glassman
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And lower egt’s.
I don’t know if anyone will find this information useful, but I’ll throw it out anyway. Our 2022 3500 HO did a 24 hour regen today (unloaded on flat interstate). 0 on the DPF gauge at the start. We just got back from a 1,200 mile trip pulling 18,000 lbs over numerous mountain passes. It took almost exactly 20 miles at an average of 70 mph on a segment of road I drive frequently. Based on the fuel economy meter, I took about a 5 mile per gallon hit on fuel consumption during the region (15 instead of 20).
Do the 24 hour regens take longer depending on the DPF load at the start or does it not matter?
Do the 24 hour regens take longer depending on the DPF load at the start or does it not matter?
flan
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All of my regens (only have had 24hr ones) are about the same on the odo, 18-20 miles.
PRS
Active Member
Fuel dilution in the oil.
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In short, yes. But not the necessarily the load you’ll see on the dash gauge. When the 24 hour timer is reached the PID for regen % goes from 100 to whatever the spot loading is. The time it takes to compete the active regen is based on that.
Its time at temp to clean the DPF, so going 45 for the engine regen will do it in fewer miles that 65.
It does take longer for a 24 hour regen to heat the DPF to a cleaning temp based on speed too. If you’re driving in low load conditions it can take a while just to get it hot, but if you’re towing it can happen quick.
15-20 minutes is about what I’ve seen, on average, for a 24 hour regen to complete. I’ve also had them take hours when the driving conditions suck for active regen (short drives with 50% of the miles downhill without sufficient EGT’s to allow regen to initiate).
More frequent regens is not ideal. It means your driving style isn’t conducive to passive regen so the DPF fills up faster and requires more frequent active regens. More active regens means more fuel dilution in the oil. Soot based regens also last a lot longer than timer based regens, so there more time for fuel to get into your oil that way.
More frequent regens aren’t the good thing you think they are.
I’ll add that the active regeneration cycle is hard on the DPF’s internal media due to the higher heat cycles. Every active regeneration takes life off of the DPF. Trucks that run more regeneration cycles will require the DPF to be replaced far sooner than a truck that only sees them every 24 engine hours. This is exactly why passive regeneration is the preferred method for keeping the DPF cleaned out. Although passive regeneration is slower, it also requires less heat. The exact metric of how much life is lost on every active regeneration is hard to pin down, and some of it will change from one DPF to the next, it’s generally accepted that active regeneration cycles are a necessary evil for trucks that do not routinely passively regenerate on their own (primarily due to the duty cycles the truck and engine see). Active regeneration processes were added to DPF’s as a stop-gap measure in order to allow diesels to be operated in duty cycles that are less than ideal for emissions equipped diesels. They’re “good” in so far as they clean the DPF out and allow the truck to continue operating in a low-load duty cycle, but they’re not “good” for the DPF or the truck itself, especially in engines that utilize the primary fuel injectors as a means of introducing fuel into the emissions system for the purposes of regeneration.
I’ll say it before and I’ll say it again. When the emissions systems were forced onto these engines, we collectively lost the ability to leisurely drive these pickups like we did in the past. If you want max life out of the system and minimum headaches, the trucks need to be under at least a mild load at all times. Otherwise you’re on borrowed time.
I got lucky on the last active regen. It started just as I pulled onto the interstate for a 30 mile drive, instead of just as I was about to pull into the garage.
In the wishful thinking mode, I’ve wished for a couple of changes in regen logic. The truck should be smart enough to not do active regens when they are not necessary, such as when pulling a heavy load on a long trip. If the system is measuring soot loading in the DPF, why aren’t all active regens based upon soot loading (inlet/outlet pressure differential)?
Also, within some time limit, like 1 hour, we should have the option to delay the active regen. This would apply to my “pulling into the garage” situation. We would be allowed to delay it one time, for no more than 1 hour, so we could plan a steady drive during the regen. I would even be OK if we could only delay it until the next engine start. I know that we can keep an eye on the time meter, but that can be ± an hour, not much help as to when it will actually start. I don’t think this kind of operating logic would be a problem for the processors in these vehicles. It’s just programming logic.
My final beef is with the location of the excess fuel injection. Injecting the excess fuel into one of the cylinders seems like an idiotic decision. One of the other brands injects it into the exhaust downstream of the engine. If you ask a ten year old car enthusiast, if such exists any more, where to inject the excess diesel, they would tell you to use downstream injection to prevent cylinder washdown or oil dilution. Is there any reason for Cummins/Ram’s approach I am not aware of?
In the wishful thinking mode, I’ve wished for a couple of changes in regen logic. The truck should be smart enough to not do active regens when they are not necessary, such as when pulling a heavy load on a long trip. If the system is measuring soot loading in the DPF, why aren’t all active regens based upon soot loading (inlet/outlet pressure differential)?
Also, within some time limit, like 1 hour, we should have the option to delay the active regen. This would apply to my “pulling into the garage” situation. We would be allowed to delay it one time, for no more than 1 hour, so we could plan a steady drive during the regen. I would even be OK if we could only delay it until the next engine start. I know that we can keep an eye on the time meter, but that can be ± an hour, not much help as to when it will actually start. I don’t think this kind of operating logic would be a problem for the processors in these vehicles. It’s just programming logic.
My final beef is with the location of the excess fuel injection. Injecting the excess fuel into one of the cylinders seems like an idiotic decision. One of the other brands injects it into the exhaust downstream of the engine. If you ask a ten year old car enthusiast, if such exists any more, where to inject the excess diesel, they would tell you to use downstream injection to prevent cylinder washdown or oil dilution. Is there any reason for Cummins/Ram’s approach I am not aware of?
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OLEJOE
Well-Known Member
Because they are able to do it without any additional hardware and it’s cheaper. No extra fuel line, pump or injector.
They might eventually change it though. They did do away with the in-cylinder EGR.
They might eventually change it though. They did do away with the in-cylinder EGR.
GM, at one time, used a standalone hydrocarbon injector (aka “ninth injector”) to fuel active regeneration cycles. I’m not familiar enough with their current arrangement to know if that it’s still the case. Larger commercial truck manufacturers do it both ways. Cummins is known for using the proprietary fuel injectors whereas Mack uses a dedicated HCI almost exclusively. There are pros and cons to both systems. The standalone HCI is more complex in materials, and warrants more maintenance as that injector has to be replaced, however it’s nice knowing that the excess fuel doesn’t go into the engine.
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Think of passive cleaning as regular cleaning and active regen as a deep clean. Even towing for 7 hours straight the DPF isn’t as clean as after an active regen, the temp difference does more cleaning. For example I towed to Yellowstone last Labor Day. My truck initiated an active regen as I drove by Madison towards Old Faithful. As the regen started the regen % PID only dropped to the 30-40 range, which is low for the end of a 24 hour cycle but not as low as it was after the active regen completed, which was in the teens instantly and around 6% after a power cycle at Old Faithful.
So, even if you’re towing all day an active regen does more cleaning and will extend DPF life by not letting the lower flow regions of the DPF fill up and become difficult to clean.
There may also be some emissions regulations requirements for frequency of regeneration.
Easy to delay it, just put it in Park. You then know to plan your drive next time for a longer route if you want to.
I have not seen any incomplete regen issues from interrupting a timer based regen. I don’t have much experience with interrupting a soot based regen, but from what I have seen that could lead to frequent regen issues.
So it comes down to what type of regen is happening. I have no concerns parking the truck in a 24 hour based regen, but prefer to drive soot based regens until completion.
A 7th injector would be nice, but after 18 model years you would think they are sticking without one for a good reason.
Good Info. I guess it makes sense. The temps are much higher during an active regen than during passive.
I've tried not to interrupt (and restart) the 24 hour regens if I could avoid it, but sometimes it is just not possible.
What is the name of the PID you are using for "regen %"?
I'm pretty sure GM still uses the downstream injector in the Duramax.
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I think it’s %-regen stat.
Jackrabbit
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Wondering about how the Ram active Regen works. Does it inject fuel on the exhaust stroke on one cylinder? Is it always the same one cylinder?
Not much good info from Ram / Cummins on this but based on what I’ve discussed / read, I believe it’s the front three injectors that are used to inject the fuel. The fuel is injected during the exhaust stroke so that it is pushed downstream to the DOC / DPF.
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Interesting, I would have thought it used all 6…. But that’s a thought, I’ve got nothing to back that up.
I am fairly certain it’s the front three but definitely not 100% positive on this. I have a vague memory of discussing this or reading it in a technical document, but I don’t remember when or where. I’ll see what I can dig up. Again, Ram is so poor about providing this kind of info a lot has to come from the Cummins side, and even that gets tricky because we don’t really know how much proprietary stuff stays Cummins or what Ram sees fit to meddle with or change on these engines.
For some reason, I thought it was cylinder 6 but I don’t remember where I picked that up so I could be way off base. It seems that less fuel in each of more cylinders would be better. In thinking about this, if the fuel is injected during the exhaust stroke and everything is working correctly, it should be unlikely that fuel would get into the crankcase. The air movement out of the cylinder should be carrying the fuel with it. The one case we have been following about excessive fuel dilution may be from another cause or defect.
I’m trying to find that document I was reading but sifting through years worth of data sheets and stuff I’ve collected isn’t easy. One day I’ll get time to organize better. In my mind, I would think using the front three would space out the fuel pulses enough to keep temps up in the DPF, without needing to flood any one cylinder with fuel. I don’t necessarily think the engine would need fuel from all six but I’m not certain. The firing order would provide enough fuel with the front three to maintain the 1,100°F or so but again, this is only my hypothesis. I’ll keep digging.
As for the fuel dilution, I agree with you that it theoretically wouldn’t cause much but it doesn’t seem to be the case. Common sense would lead you to believe that the fuel should be getting pushed out pretty much completely. However the fuel dilution analyses I’m seeing on frequent regeneration trucks is much higher than I would expect. In my own truck, my fuel dilution was at 3.6% after about 12,700 miles. This is at the limit of what amsoil recommends as “safe”, which is why that’s about as far as I’ll go on an oil change interval with my given duty cycles. I’ll see if that number continues to improve as I move further and further away from my frequent regeneration problem. This next oil change should have only 24 hour regenerations on it, which would be the bare minimum these trucks would experience, so I’m excited to see what my fuel dilution looks like.
I would suspect that some of the fuel dilution showing up may be attributed to “when” the regen cycle kicks in, and “how” the truck is being driven. Often these are trucks that are getting stuck in stop and go traffic. Regen cycles are less effective in these scenarios and I would suspect that due to the decrease in rpm and engine load / temp, some more fuel may find its way to the cylinder walls and wash down. Also have to consider the operators that like to interrupt the cycles and let it start up the next day. The truck will go into regeneration almost as soon as the truck is moving. The engine isn’t at full operating temperature then, and I could see it very likely that some more fuel may make it past the rings if everything isn’t up to temp.
That all makes good sense to me, particularly regarding the engine condition during the extra regen fuel injection. If the regen system injects the same amount at idle as at highway cruise, I cold see more likelihood for dilution. There have been a couple of situations where I had to shut down during an auto regen. Sometimes you can’t avoid it. I’ve started keeping better track of the hours and planning around an expected regen.
Are you checking dilution between oil changes? If so, how are you drawing a sample? Where do you get it tested?