Attention: TDR Forum Junkies 
I was lucky enough to attend a class a few weeks ago on DPF's and thought I'd share part of what I learned... the guys putting on this class make them, and build the service equipment to service them on large trucks where the canister can be removed and cleaned. . They do not make the Cummins Dodge system but do understand how it works and functions, as they reviewed the bid process and either didn't bid or lost it... They are a Tier 1 supplier to the OEM truck builders... . The guy who taught the class was a mechanical engineer..... (SAE) There has been a lot said here in these pages that is not correct or miss understood... Please let me add my 5 cents worth... .
The DPF on your truck is the first to be designed and used so that it can be re-generated.....
The DPF is designed to hold and contain soot. At some point it must be cleaned or re-generated. The DPF is to reduce soot only, and the EGR system is there to reduce nox...
On larger trucks where space is not such a concern and the overall cost is not as important the DPF is several hundred lbs. , is a separate canister that can be removed and cleaned. And costs 2-3 times that of the light unit on our trucks...
On these larger trucks the canister that is the filter part of the DPF is designed to filter the soot from the air... in these cases this design of filter will glow red turning a great majority of the soot to ash... . something like a 50:1 reduction... sometime in the life of the canister it needs to be removed, placed in a shaker, and 800* air is forced through it in a time bake application... the heat turns more soot to ash, the forced air and shaking blows the ash from the canister and the canister is returned to service..... There is a flow test, and the DPF must pass this test to be returned to service... on a large truck the guess is several hundred thousand miles... yet to be determined on a large scale by fleets...
On our trucks, it was decided to make this filter so that it could be re-generated in the truck by adding raw fuel across a catalyst to generate about 800* F. of hot gases across the canister. This high temperature reduces the soot to ash, again about 50:1. The ECM monitors pressure before and after the DPF as well as the temperature. The design is such that when its sooted up and the back pressure is to a point the system goes into a re-gen. Thus the heating of the system to reduce soot to ash..... At this point you need to understand that ULSD has ultra-low sulfur because sulfur will contaminate the DPF... the engine doesn't care if it has LSD or ULSD it's to prevent the contamination of the DPF just like leaded fuel will contaminate a catalytic converter in gas engine.
This decision was made to reduce the size and cost of the DPF. At some point it will have to be replaced as from what I've been told its not designed as a separate canister to be removed and cleaned... .
It's my educated guess that the factory is still learning about the calibration of this system, (read NOT ENOUGH TESTING) and over coming the thousands of different driving habits of light truck owners... where in heavy trucks, the use and drivers use have been very well documented over the years with satelite information systems.
Just like in cars, if there is excessive fuel, the cat. over heats and plugs up and fails... thus the move from carburetors to fuel injection to better control the fuel... . plus improvements in cold starting and other systems...
I believe that there is something that has not been fully developed or predicted and the software is not refined enough to do the job... . but it will happen...
Of course the simple task would be to remove the complete DPF and re-install it when you sell the vehicle... do not throw this thing away... . it will cost several thousand to replace... . and remember that it is against fed emission laws to do so... . just like the half million farmers who remove the cat. so when driving in the field it won't burn the field down. . later to be re-installed at time of sale...
On a Cat. you can look in one end and see daylight through it (honey comb design), thus allowing raw gases to flow thru the cat. On a DPF there is NO CLEAR path from one end to the other... . all gases must pass through the membrane to be filtered, just like an air filter... it will clog up and will have to be re-generated to continue to function... .
With the EGR system, the EGR re-circulates exhaust gases to reduce temperatures and reduce NOX... but a by-product of reduced temperatures in a diesel engine is increased soot... .
OK this is an overview of what I've learned... . hope that its helpful...
The DPF on your truck is the first to be designed and used so that it can be re-generated.....
The DPF is designed to hold and contain soot. At some point it must be cleaned or re-generated. The DPF is to reduce soot only, and the EGR system is there to reduce nox...
On larger trucks where space is not such a concern and the overall cost is not as important the DPF is several hundred lbs. , is a separate canister that can be removed and cleaned. And costs 2-3 times that of the light unit on our trucks...
On these larger trucks the canister that is the filter part of the DPF is designed to filter the soot from the air... in these cases this design of filter will glow red turning a great majority of the soot to ash... . something like a 50:1 reduction... sometime in the life of the canister it needs to be removed, placed in a shaker, and 800* air is forced through it in a time bake application... the heat turns more soot to ash, the forced air and shaking blows the ash from the canister and the canister is returned to service..... There is a flow test, and the DPF must pass this test to be returned to service... on a large truck the guess is several hundred thousand miles... yet to be determined on a large scale by fleets...
On our trucks, it was decided to make this filter so that it could be re-generated in the truck by adding raw fuel across a catalyst to generate about 800* F. of hot gases across the canister. This high temperature reduces the soot to ash, again about 50:1. The ECM monitors pressure before and after the DPF as well as the temperature. The design is such that when its sooted up and the back pressure is to a point the system goes into a re-gen. Thus the heating of the system to reduce soot to ash..... At this point you need to understand that ULSD has ultra-low sulfur because sulfur will contaminate the DPF... the engine doesn't care if it has LSD or ULSD it's to prevent the contamination of the DPF just like leaded fuel will contaminate a catalytic converter in gas engine.
This decision was made to reduce the size and cost of the DPF. At some point it will have to be replaced as from what I've been told its not designed as a separate canister to be removed and cleaned... .
It's my educated guess that the factory is still learning about the calibration of this system, (read NOT ENOUGH TESTING) and over coming the thousands of different driving habits of light truck owners... where in heavy trucks, the use and drivers use have been very well documented over the years with satelite information systems.
Just like in cars, if there is excessive fuel, the cat. over heats and plugs up and fails... thus the move from carburetors to fuel injection to better control the fuel... . plus improvements in cold starting and other systems...
I believe that there is something that has not been fully developed or predicted and the software is not refined enough to do the job... . but it will happen...
Of course the simple task would be to remove the complete DPF and re-install it when you sell the vehicle... do not throw this thing away... . it will cost several thousand to replace... . and remember that it is against fed emission laws to do so... . just like the half million farmers who remove the cat. so when driving in the field it won't burn the field down. . later to be re-installed at time of sale...
On a Cat. you can look in one end and see daylight through it (honey comb design), thus allowing raw gases to flow thru the cat. On a DPF there is NO CLEAR path from one end to the other... . all gases must pass through the membrane to be filtered, just like an air filter... it will clog up and will have to be re-generated to continue to function... .
With the EGR system, the EGR re-circulates exhaust gases to reduce temperatures and reduce NOX... but a by-product of reduced temperatures in a diesel engine is increased soot... .
OK this is an overview of what I've learned... . hope that its helpful...
