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Understanding Regeneration
- Thread starter Wolfy
- Start Date
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I think what this posting is really telling us is that, the new 6. 7 motor isn't a good option for someone who drives short trips, and or empty all the time. short trips may include anything under say 20 miles. Yes the Active regen should work, and it seems to, but millage may allways be low for someone driving this truck. I would be interested in a poll of people who tow all the time, and others who drive empty most of the time. Also I wonder if transmission choices play a part in all of this. We are also assuming that the fuel we get is ULSD, I would venture an educated guess that people who drive short trips, no loads, are the people with all of the issues. And that these people may be in areas of older tanks, smaller fuel stations, and or Questionable LSD VS ULSD avaiablility. This is all a guess from what I have learned on this post, I do apreciate the work people have put into getting this info, Honestly it changes my opinion of the new EPA stuff
Do you mean to tell me that if I replace the color on the face of my gauge with a darker green, my engine will not run cooler? You're kidding, right?
Golly Gee Merrick, ... you've got me intimidated right off the bat. Imagine how difficult it is for me to dare to question someone whose intellect (and "dyno reading"!) dwarfs my own. (Let's not even mention any particular body part. )
See if you can say this with me; "Duh".
Try again,... "DUH!".
That's it. Now,... slap yourself on the forehead as you say it ... "Duh!"(slap).
Perfect!
Now keep doing that as you think about the fact that you accused another TDR member of thinking that some colors on a gauge face are the secret to safe engine operation.
(I think I could almost be starting to get ready to begin to feel nearly %!$$^&-off!, any minute now!)
Now stop slapping, so you can think more clearly, and consider this. There are inferior beings on the planet who know little about these engines. Some of them even admit this up front, ... while they turn to others whom they believe they have some reason to trust, for learning.
They look at the fact that someone presumably more knowledgable, like a gauge maker offering his products to a bunch of experienced truckers, has attempted to INDICATE, by the use of color, a generally safe operating temperature range. He picks green. Cleverly, he uses a DIFFERENT color, maybe yellow, to indicate that the next-color range is getting a bit "iffy", and may not be the best thing for the average engine, but is still probably ok.
Then, he chooses still another color(he picks red) to indicate a range where there may begin to be a likelyhood of some sort of heat damage, if the engine is operated for too long a time at those temperatures.
Now,... that "newby" we were considering, notices that the temperature at the upper limit of what the gauge-maker has decided to indicate as the "safe" temperature zone, is right around 1050 degrees. The foolish newby reasons that the gauge maker should be one of those "trust-able" people, who presumably knows his business,... so he assumes, poor naive dolt, that perhaps it is reasonably safe to operate his engine at those temperatures.
Now get this surprising-to-you part -- The idiot newby KNOWS that it isn't the color the gauge-maker has selected that makes a difference. He thinks he understands that it is the temperature that matters. He imagines that the same zone could have been colored chartreuse, brown, or purple, without effecting things for better or worse.
He also observes that the somewhat hotter range, colored, as it happens, (but not neccesarily, our slowly-brightening newby understands) yellow, extends from 1050 degrees, up to about 1250 degrees. Still foolishly willing to trust the more experienced maker, he assumes that operating his engine in this range MAY be of some concern, so he should at least take some notice when doing so.
Lastly, of course, he stares intently and realizes that the "red"(arbitrarily, of course) range begins at approximately1250 degrees and runs off the scale somewhere around 1500 degrees,... and suspects that the experienced, knowledgable maker is trying to suggest that some damage may occur to the engine when it is operated at these temperatures, ... and so it would probably be best NOT to do so.
Now the newby has spent a little time finding out that different experts have different opinions on just what is-or-is-not "safe", "questionable" or "dangerous" when it comes to engine exhaust temperatures, ... but he is willing, in the absence of expertise of his own, to go along with what seems to be the general consensus.
Interestingly, the newby sees the logic in the maker having chosen colors already familiar to almost everyone who has seen a traffic light, to indicate, in a general but not-exactly-true-in-every-case sense, "safe", "caution", and "danger".
Looking at what I've written, I'm imagining that these 40-50 word sentences may be a bit confusing to you, ... let's change the subject back to your first comments.
First, ... as to the idea of putting gauges all over my engine just so I can maybe get a better idea of what to accurately say when discussing some theoretical possibilities on the inter-net,... I think I will pass. (I should probably feel guilty for not following your ever-so-practical suggestion, but I have such an undeveloped personality that I do not. ) If you, on the other hand will or have done so, I expect that there would be a gradient, - hot,- hotter,- hottest, in that order, from the gauges you place at the EGT sensor, the turbo, and the catalyst.
Meanwhile, let's assume you are prepared, if not really eager, to engage in a bit of idea-exploration.
I will put forth the reasons I think that the turbo may be in a hotter environment than the upstream pyro sensor,... and then, no doubt, you will easily provide lucid and convincing reasoning proving that this is not so. I am trainable.
Here goes:
As you point out, the already hot exhaust temperature is raised by the catalyst by its chemical action on the exhaust gases ( and the newly introduced raw fuel, during "active regeneration"). This takes place (Duh!, again) AT the catalyst.
Contrary to something else you point out, however, the temperature is NOT "raised by" the filter. (Please explain this phenomena, if you insist it is so. )
But until you do,... we will stick to the catalyst, as the source of the "raised" temperature. (Coincidentally, Cummins describes it this way too. ) The hotter gases are IN the filter, but they were raised to their new higher temperature by the catalyst.
So we have exhaust gas coming out of the manifold at a certain temperature, passing by the sensor at about the same temperature, and proceeding to the catalyst, passing the turbine on the way. (That was an important detail,... "passing the turbine on the way". )
This means that the turbine is closer (than the sensor)to the gas which will have been heated-up even more after reaching the catalyst. The gas at the catalyst is hotter than the gas at the sensor. The turbo is closer to the catalyst than the sensor is. The hot gases are moving away from the sensor, towards the catalyst. This means that one means of heat transfer, convection, is being restricted in its ability to heat the sensor from the catalyst's location. It is also restricted in reaching the closer turbo. (Convection is heat transfer by movement of the heated substance,... gases, in this case. You can see that hot gases are not going to move backwards, or "upstream" against the continuing stream being expelled through the exhaust system. So that form of heat transfer is not going to work. )
Another form of heat transfer, radiation, is effected by distance, ... you know this because a person standing closer to a fire is warmer.
So if the turbo is "standing closer" to the catalyst than the sensor is, the turbo will be "warmer".
The third and last means of heat transfer is conduction, but there is no excellent means of conduction from the catalyst to either the turbo or the sensor, ... and whatever conduction may occur(through metal pipe,housings, etc. ,) will heat the turbo more than the sensor, because conduction is also less when a greater distance is traveled through the conductor (resistance loss).
So, if the turbo is closer to the catalyst, which is the source of the hotter gas, it will be "warmer", by radiation and possibly conduction, with convection playing no part. I believe physics says so.
But I am not Einstein. You speak quite authoritatively, if condescendingly, so perhaps you are related. Surely your counter-presentation will be fascinating.
I must apologize. At first I almost thought that rather than actually being here in the spirit of a mutual effort to increase understanding, you were jumping in to play "I'm smart,... you're dumb!"
But then I saw your helpful contribution about the marine engine, which all of us certainly should have known. Well now we do, thanks to you. At least if you are correct, we do.
I will lie awake tonight, to see if I can understand how that info proves your point about the turbo not being in a hotter environment than the sensor.
I would have preferred a bit of explanation about your claim, to just hearing you make it so adamantly. But everyone has their own style.
If you come back to play some more,... I will try to find something I can teach you. (Don't feel bad about your spelling, mine isn't perfect either. )
Perhaps some members (or moderators) will think I have been a tad less than gracious in responding to you.
"I won't even begin to compare how I feel about that. " (???)
Since I don't understand what I just said, I'll add that I don't feel any obligation to take $%!# from anyone, whatever the venue. (... and at least I didn't say you had done anything ludacris
I should probably wait and look this over in the morning,... but I'm sending it and going to bed.
I'll be nicer tomorrow.
FEITCTAJ
Am awaiting arrival of my Mega at dealer on July 9th. Was supposed to be
shipped June 20, but was shown to be modified to June 13. How can I be sure
that it has the latest flash for regen and do you think I should request it
before taking delivery? Dealership has just changed ownership and I don't
know the quality of their service department yet... ... .
shipped June 20, but was shown to be modified to June 13. How can I be sure
that it has the latest flash for regen and do you think I should request it
before taking delivery? Dealership has just changed ownership and I don't
know the quality of their service department yet... ... .
I have never seen any regen indication in 8k miles, My understanding and personal observation is that if the DPF reaches 80% full and continues filling you will see MIL, 80% then 90%, 98% and 100% full on the overhead, if regen does not occur then 2 chimes a code will be set the display changes to "Requires Service" and the engine is de-rated. If any time before the "Requires Service" / De-rating, regen conditions are met the percent full counts back down. Mine never counted down and thus it remains in the shop on it's third week out of service spread over 1 month.
Try not to read my words so seriously. If you were to meet me, you'd think differently of me. I don't come across very well on the 'boards. (apparently)
I see where you are going with this, but, the first item after the turbine is the nOX filter, and as I have learned from you, the filters do not raise the temperature of the gasses passing them, they only filter out what they are designed to filter. As the gasses travel down the exhaust they are cooling off, so the turbine should experience almost no additional heating. The downpipe and nOX filter bend sharp enough to remove the worry of heat radiation. Please feel free to correct me. I do not have any schooling on this subject except for my 24yrs of "hard knocks" schooling, of which I am still a student.
I bet you can be very punny in person. Maybe we can meet up at rally somewhere. You made me laugh. If I let my hair grow out, I do show a resemblance of Einstein, LOL. Maybe not, but you are funny anyway.
By no means. I'm here for the same reason you are. I'm not saying I'm smarter, but, it honestly did sound like you were trying to say that the gauge turning red at 1250 indicated engine damage at that temperature. You didn't show any eveidence that you thought otherwise, so I took you at face value. What temperatures can the 6. 7L ISB-e operate at safely?
I think you responded accordingly. You are very smart.
Cheers,
Merrick
I see where you are going with this, but, the first item after the turbine is the nOX filter, and as I have learned from you, the filters do not raise the temperature of the gasses passing them, they only filter out what they are designed to filter. As the gasses travel down the exhaust they are cooling off, so the turbine should experience almost no additional heating. The downpipe and nOX filter bend sharp enough to remove the worry of heat radiation. Please feel free to correct me. I do not have any schooling on this subject except for my 24yrs of "hard knocks" schooling, of which I am still a student.
I bet you can be very punny in person. Maybe we can meet up at rally somewhere. You made me laugh. If I let my hair grow out, I do show a resemblance of Einstein, LOL. Maybe not, but you are funny anyway.
By no means. I'm here for the same reason you are. I'm not saying I'm smarter, but, it honestly did sound like you were trying to say that the gauge turning red at 1250 indicated engine damage at that temperature. You didn't show any eveidence that you thought otherwise, so I took you at face value. What temperatures can the 6. 7L ISB-e operate at safely?
I think you responded accordingly. You are very smart.
Cheers,
Merrick
Cumminz, There is no indication on the dash or overhead that shows the truck is in the regen cycle. I know when a regen begins by watching the pyrometer increase to 1200 degrees and staying there for a period of time.
It would have been pretty handy if Dodge would have made it so we could see the % before it got to the 80% figure so we could take action before the engine derating started... it sounds like once it gets to 80% it goes fast from there to 'Service Required'. I would rather be able to see something like that than how many miles I got until the fuel tank is empty... after all I got a fuel gauge that tells me how much I got left. It sounds like it's about as functional as the idiot light for low oil pressure... it's too late #@$%!
Alright,... a sense of humor. ( and if you actually read the lengthy reply I wrote last night, you deserve points for perseverance. )
"punny" is a funny word. But I believe I get your point.
I'll proceed under the assumption that we are going to be friends. [Yes, inter-net comms. can result in misperception. With this in mind, I respectfully suggest simply assessing ideas on their merits, or lack-thereof, without "characterizing" either the statements or the poster.
Apparently neither of us has had formal engineering training,... most specifically not at Dodge/Cummins. Perhaps we can ferret-out some understanding despite that lack. [ We are both students in the school you mention. ]
"As the gasses travel down the exhaust they are cooling off, so the turbine should experience almost no additional heating. The downpipe and nOX filter bend sharp enough to remove the worry of heat radiation. Please feel free to correct me. "
I believe additional heating is evidenced by two facts:
1. Cummins says that during "active regeneration" an injection of raw fuel is made during the exhaust stroke, to supply the DOC (part of the Diesel Particulate Filter System,) with additional "diesel" to "oxidize", a chemical process which generates ADDITIONAL HEAT in the DOC and the DPF. [Note the descriptive title of the DOC - "Diesel Oxidation Catalyst" - it is NOT A FILTER. It is a catalyst. A catalyst is something which supports/enhances a chemical reaction, ... and this one, unlike filters, which "only filter out what they are designed to filter". . effects a chemical reaction which releases HEAT. ]
Cummins emphasizes that this extra diesel is "NOT burned", ... a statement which I do not understand, as the common term used to describe rapid oxidation is,... "burning".
[I am tempted to assume that whomever wrote that Cummins statement meant that the extra diesel is not burned in the conventional manner, during the power stroke, creating the explosive gas-expansion which propels the truck. ]
In any case, the design-function is that this oxidation of the extra diesel, beginning as this raw fuel is acted-upon by the catalytic action of the DOC, DOES CREATE ADDIONAL HEATING,... that is the whole point. This increases temperatures in the DOF(immediately next in the exhaust path), which then is suffiently hot to enable oxygen in the catalysed-mix to combine with soot previously trapped in the filter, after which both exit the system as CO2 gas.
This is the purpose of "active regeneration"(AR),... to initiate a temperature INCREASE because the operating temperature reached during the particular vehicle's normal operation is not high-enough, or not high-enough a sufficient percentage of the time, to enable the changing of soot to a gas. Thus, if driving practice does not change, and without AR, soot will build-up and clog the system.
Now there is much we do not yet understand about this action,... illustrated by the following point -
2. Some owners report seeing a noticeable , sudden, increase of exhaust gas temperatures, to more than 1200 degrees, during AR. This increase is measured by a sensor upstream from the DOC.
How/why this temperature increase, supposedly originating from catalyzed fuel AT THE DOC, is measurable upstream from the catalyzation,... is the not-yet-understood part of things. It suggests that the catalysed reaction is intense enough and rapid enough, that the heat is exchanged between the downstram gas molecules and the on-coming upstream molecules, FASTER than the downstream movement of the gas stream.
Regardless, the increase is showing on the gauge, and it is being reported to the gauge from an upstream sensor,... so it IS being somehow "transmitted" to that sensor, whether against the flow, and around curves, ... or not.
Now we are back to my original thought: If the source of the heat increase is the DOC, and the turbo is closer to the DOC than the sensor is,... then it is to be expected that the temperature at the turbo will be even higher than that which effects the further-upstream sensor.
Frankly, I am surprised and a bit disappointed (although I will live
, that no one has shown up in these threads who has a more definitive understanding and can explain these things to us. (I believe the existence of the NOX filter(sensor) which you mention in the line ahead of the turbine is beside the point we have been discussing, as explained above. It changes nothing which I have said. )
Enlightening comment, hypothesized OR knowledge-based, is always welcome.
Best wishes,
All power systems for ’94-04 Ford Power Strokes, ’94-04 Dodge/Cummins 5. 9L turbo-diesels, and ’93-02 Cummins 5. 9L and 8. 3L motorhome turbo-diesels feature the Banks OttoMind fuel calibration system to correctly add fuel to match increased airflow in such a manner as to keep peak EGT below 1300º F. Every power system has its own specifically calibrated OttoMind for the power level of the system on that particular vehicle. The calibration is engineered to coincide with the engine manufacturer’s EGT recommendation and Banks’ extensive testing. Power systems for the ’98-04 Dodge/Cummins 24-valve 5. 9L pickups
Wolfy, I think your info from Banks is a little outdated. Starting with the 04. 5 some of the metals in the engine were changed to withstand higher heat levels. You might still be able to find some info by doing a search in the in the 5. 9 forums. It was talked about early on. The Cummins site may still have some info also.
I would expect the same heat resistant capabilities to hold true for the 6. 7L design. At least once the DPF software is functioning properly.
Wolfy, I think your info from Banks is a little outdated. Starting with the 04. 5 some of the metals in the engine were changed to withstand higher heat levels. You might still be able to find some info by doing a search in the in the 5. 9 forums. It was talked about early on. The Cummins site may still have some info also.
I would expect the same heat resistant capabilities to hold true for the 6. 7L design. At least once the DPF software is functioning properly.
Hi Jim,
I'm uncertain what you mean by "my" Banks info, unless you are referring to this link:
http://bankspower.com/Tech_whyegt.cfm
... which I have posted previously, quoted statement(s) from (one, I believe), and still suggest as recommended reading.
This is "current" info in the sense that it is being presented today on Banks' web-site.
I am aware that this info may not be revised regularly, and your comment that higher limits have been tolerable since '04 (3 years ago), would suggest that it IS out-dated or at least incomplete regarding our new rigs.
Newly-developed/utilized metals aside for the moment, ISSPRO's designation of the 1250 degree point as the beginning of their "red" zone(as previously over-discussed in this thread
, taken together with Banks' advice to keep things under the "1300 deg. limit", would seem to indicate a consensus that following this advice would be generally a safe approach. BUT: The situation has a new ingredient, not previously a factor, ... "active regeneration(AR)".
During this event, Brad has reported (pre-REV A. flash), temperatures of 1400 deg. for +/- 5% of driving, and you have reported 1200 deg. for 20-25%.
These types of reported GAUGE readings have raised what I think is a reasonable question as to what the temperatures are AT THE DOC, when increased by AR,... and how these presumably higher-than-gauge temperatures may effect metals in the turbine, etc. (including any "new" metals, since we do not know what the increased temperatures actually are. )
It seems to me that the main (possible!)concerns center around two points, both previously discussed:
1. IS(??) the temperature in the turbine area higher than that at the EGT sensor? ( I have postulated that it may be,... and no one has yet argued convincingly to the contrary. Taking Brad's 1400 deg. (gauge) as a worst-case scenario, this would mean that temps. at the turbine are high indeed. )
2. The AR raises too-low exhaust temps to a higher level in order to effect regeneration,... which is its sole purpose, when operating correctly.
If operating INCORRECTLY (because of ECM mis-programming or malfunction), when exhaust temperatures are ALREADY HIGH ENOUGH, ... do the higher-still temps. caused by AR reach "dangerous" or damaging levels, ... new metals or not?
The last point is behind my strong feeling that anyone experiencing AR that may be occurring too-frequently or when NOT really called-for, ... get the situation corrected ASAP. So far The "REV. A" flash, performed correctly, seems to be a fix.
My computer is extremely slow to download pages, especially, for reasons unknown to me, on the TDR site. I am spending too-much time here already. So I hesitate to go on a general search for metal heat tolerances in the 5. 9L forum. Besides, if found, they would not address what the temperatures may be raised-to in the DOC and turbine sections,during OFF-DESIGN OPERATION as described in point 2, above.
A further area calling for exploration is the idea, presented by previous posters, that time-at-various service-levels(idle vs. highway/hauling/towing), pedal pressure(what about no-pedal-pressure-"cruise-controlled" operation?), and who-knows-what other factors may be involved in the ECM triggering AR.
D/C could sure help a lot with owner understanding if they would make available a COMPREHENSIVE description of this whole system, addressing these and other questions.
Meanwhile, we are left to batter this still-twitching horse with whatever sticks we can find.
You and I are still confounded by our different experience with supposedly similarly- set-up trucks, and with no authority avaiable to definitively sort things out, we are left to our own devices.
I appreciate the participation and contributions of those willing to continue wrestling with these questions.
I feel that we already know much more than we did when concerns were first raised.
PS,... Do you have/not-have the "modification" label?
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Wolfy, thanks for taking the time and effort to research / post all this information. There are some pretty complex chemical / physics processes involved and in my estimation, what you have written makes sense, logically speaking. Although I am not a chemical engineer or physicist either, I do have a technical background and I think you have a pretty good understanding of the processes involved here and your thoughts have certainly improved my understanding of the system.
My sense of logic tells me that those events of high EGT (pre turbo) that some have experienced are caused by burning in the exhaust manifold of the "extra" fuel injected to support Active Regeneration. There is obviously already a fire close by to ignite it and I would guess plenty of oxygen to support combustion (supplied by the turbo). With all three necessary conditions present to cause combustion (fuel, oxygen, ignition source), what would prevent combustion? That may not be an intended consequence but I have a hard time understanding why that fuel doesn't burn in the manifold, rather than waiting until it reaches the DOC to undergo the catalyzed oxidation process which is not burning.
George
My sense of logic tells me that those events of high EGT (pre turbo) that some have experienced are caused by burning in the exhaust manifold of the "extra" fuel injected to support Active Regeneration. There is obviously already a fire close by to ignite it and I would guess plenty of oxygen to support combustion (supplied by the turbo). With all three necessary conditions present to cause combustion (fuel, oxygen, ignition source), what would prevent combustion? That may not be an intended consequence but I have a hard time understanding why that fuel doesn't burn in the manifold, rather than waiting until it reaches the DOC to undergo the catalyzed oxidation process which is not burning.
George
Which sensor are we getting these readings from? Aftermarket gauge? or an OBD scanner?
I think we need to take several readings all over the exhaust and see how much and where the EGT's cool off and heat up.
I think we are assuming that because we see higher exhaust temperatures at the EGT probe, that the higher temps are coming back from the DOC, but when the temperatures could possibly be highest in the manifold, and continually cool off until gasses get to the DOC...
? Maybe ?
I think the ECM modulates the butterfly valve in the intake, the EGR valve, and the post injection events to raise EGT, and jumpstart the DOC by raising the temperatures high enough for the DOC to maintain regeneration without additional help from extra exhaust gasses.
Propane Catalyst heater comes to mind...
Merrick
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Hi Merrick.
Yes. "Maybe".
George Shelton suggested this (post #34, above), and I replied in agreement and discussed the point in a post that I now cannot find. (I'm guessing that I clicked "preview" rather than send. I will check my "history", and see if I can find it. )
The fly in this ointment is Cummins' emphatic statement that the extra injected fuel IS NOT BURNED(!). This limits the cause of the temperature-raising to catalytic action, which should not occur until the fuel reaches the DOC. My current supposition is that this was a somewhat misleading statement from Cummins.
It is unfortunate that we are forced into all this conjecture because of a lack of complete customer-accessible info from D/C.
Hi George,
Thanks for the appreciative comment.
I typed a somewhat longer reply last night, but apparently stopped at the "preview' stage, mistakenly believing I had clicked "send". I am unable to find it.
I agree that the manifold burning is "logical", and share your "hard time understanding" Cummins' statement that the fuel does not burn, as mentioned in my last post to Merrick, above. My guess is that the writer intended to communicate that the fuel was not "burned" conventionally, during the power stroke, ... but whatever his intent, the statement seems questionable and ambiguous.
I had a reservation about the three conditions-for-combustion being present, i. e. , there being "plenty" of oxygen remaining in the exhaust gases, ... wondering whether this would mean the mix would have had to be "too lean" to be that desired for the original combustion process.
Let's keep thinkin',... while looking for more system info.
Let's keep thinkin',... while looking for more system info.
Regarding "triggers: for "active regeneration":
I'm wondering why such factors as "pedal pressure", and "idle time" are needed to tell the ECM when the particulate matter (soot)has accumulated to the point where the filter must be cleaned by active regeneration.
Are not the readings from the before-and-after pressure sensors sufficient indicators? (... or is this measure too "coarse", maybe only serving as a rough guide, which is only adequte to indicate severe clogging,... rather than being able to monitor the accumulation in smaller increments?)
Any ideas?
My understanding of the fuel / air relationship in diesel engines is that you can stuff as much air in it as possible all the time and regulate power / acceleration by controlling fuelling. Unlike gas engines which require a (14 to 1?)fixed fuel / air ratio for proper combustion. There should always be enough oxygen in a turbocharged diesel's exhaust to support combustion, unless the intake manifold butterfly valve 'seriously' restricts airflow. I believe the stipulation that the excess fuel does not burn might refer only to the process in the DOC, which is catalytic oxidation, not burning. I still believe that all the elements required for combustion in the exhaust manifold are present if fuel is injected during or just before the exhaust stroke.
George
George
George, I agree that this sounds quite reasonable,... if there is in fact no "ideal" combustion mix for diesel/oxygen. ( I assume this means so long as there is "enough" oxygen to combine explosively with the supplied amount of diesel fuel. In other words, there is no "maximum" permissible oxygen %, ... but there certainly must be a "minimum". )
But, there is still a fly struggling in the ointment
Fuel that has burned as you suggest in the manifold can hardly be described as reaching the DOC as "unburned" or "raw" fuel, upon which the catalyst is to do its work.
Here are some words, directly quoted from Cummins' literature:
" ACTIVE REGENERATION occurs when there is not sufficient heat in the exhaust. Exhaust temperatures are raised by injecting a small quantity of fuel upstream of the diesel oxidation catalyst.
The resulting chemical reaction OVER THE DIESEL OXIDATION CATALYST raises exhaust temperatures high enough to oxidize the carbon from the filter. " [ Emphasis mine - Wolfy. Note that it does not say temps are "raised by burning in the manifold" PLUS "chemical reaction". ]
Then, again, in the same document:
" An aftertreatment injector, also known as a 'dosing' injector, introduces a small amount of fuel into the exhaust stream ahead of the DPF, which increases the temperature of the exhaust but DOES NOT BURN. "
[I have added the capitalization to the last 3 words, whereas Cummins provided emphasis by printing them in red - as opposed to the black of the other text. ]
If we assume that in our 6. 7 engine a post-combustion injection "event" replaces the function of the "dosing" injector, but operating principles are the same, then we can assume the "DOES NOT BURN" description still holds.
The above is followed by this note, in its own box :
"Note: There is no actual flame or burning of the fuel that is injected into the system".
To me, the implication of this/these statement(s) is clear,... UN-BURNED fuel is provided to the DOC, which raises temperatures in the gases subsequently passing throught the DPF sufficiently to accomplish regeneration of the DPF.
Should we not take this repeated emphasized statement to mean what it says? Should the presumed high-temperature in the exhaust stream right after exiting the exhaust valve(in the 6. 7 situation) be imagined to be sufficient to "ignite" the mix,... but the still extremely-hot mix only a bit further downstream at the point of "dosing" injection (in a system with such an injector,) be imagined to be so cool that such ignition will not occur?
And if ignition, thence "burning", occurs in either case,... then how are we to make sense of Cummins' "does not burn"/"no actual flame or burning" statements?
The statements, if taken to be literally true, do not even allow for the situation where "burning" DOES occur, but catalytic action upon unburned hydrocarbons STILL remaining in the mix are catalyzed in the DOC, raising the temperature even higher.
If we ignore the Cummins statements, IMO the best indicator of any "manifold burning" is the increased EGT reading, ... but I am not satisfied to make-do with a "best guess".
If this is NOT the case, and the temps are indeed "raised by" DOC action, "OVER" the DOC, ... then even-higher-than-gauge-reading turbo temperatures would seem a reasonable concern.
Still mud, IMO.
As I may have said previously, if we are to benefit from careful reading, ... someone has to provide us with careful writing.
Let's hope that some info specific-to-the-6. 7L becomes available to us, with a clearer explanation of things.
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The Perfect Collection
The Perfect Collection Vol. II
TSB Updates
Dodge/Cummins Historical Overview
Cameron Collection
What Makes Us Tick?
Product Showcase
Advertising
