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Old 08-12-2021, 03:48 PM   #1
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Is DEF fluid used to regen DPF?

I have had some diesel owners (not particularly experts in the field) say that the DEF fluid is injected to exhaust to burn off soot in the DPF.

It was my understanding that they are completely different systems, the DPF does regenerations using diesel fuel to create heat to bake dpf, as it was even before def, and def injected after the dpf into a catalyst that simply makes a chemical change in exhaust (not related to DPF and filters).

Does anyone here know which is true or have info from a knowledgeable authority as to how this works exactly? Or could it vary by individual engine make?
I dont have a DEF engine, but just curious about how it works.

Interested to hear your thoughts.
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Old 08-12-2021, 04:02 PM   #2
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It's part of the SCR system. DPF is still used upstream. They are both used in newer emissions vehicles.

Here's a good explanation: https://mmm-freight.com/def-how-does-it-works/

To answer your question "Is DEF fluid used to regen DPF?" The answer is 'NO'

I recommend everyone runs a fuel based catalyst as well. Mixed with your diesel. It will help minimize regens and reduces DEF usage. It will also increase fuel economy and extend DPF life.
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Old 08-12-2021, 04:14 PM   #3
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Quote:
Originally Posted by caleb1 View Post
I have had some diesel owners (not particularly experts in the field) say that the DEF fluid is injected to exhaust to burn off soot in the DPF.

It was my understanding that they are completely different systems, the DPF does regenerations using diesel fuel to create heat to bake dpf, as it was even before def, and def injected after the dpf into a catalyst that simply makes a chemical change in exhaust (not related to DPF and filters).

Does anyone here know which is true or have info from a knowledgeable authority as to how this works exactly? Or could it vary by individual engine make?
I dont have a DEF engine, but just curious about how it works.

Interested to hear your thoughts.
You are correct in your understanding, but there are a couple of area where confusion might arise.


To be clear, DEF is used only in the catalytic converter to reduce NOx emissions. it does not get injected into any other component of the system.



The DPF reduces soot. Period. Regnerations are to increase exhaust temperatures in order to burn off the soot inside the DPF, if necessary. Increased exhaust temperature is done through increase injection of fuel, not DEF. The additional fuel is injected into the exhaust stream before the DPF. Increased exhaust temps will require more DEF in the SCR (catalytic converter) to keep the NOx numbers within spec, so in that sense, DEF is used more during a regeneration.


In short, both fuel and DEF are injected during a regeneration, but not in the same parts of the system. More specifically, DEF is only used in the SCR, not anywhere else.
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Old 08-12-2021, 05:09 PM   #4
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The purpose of DEF (a urea and water solution) is only to reduce nitrous oxides that are created by the high temperatures in the combustion chamber. Power plants have been using ammonia (basically a stronger form of urea) injection into their flue gas for years and it has proven very effective. It has nothing to do with the particulate filter.
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Old 08-13-2021, 04:24 PM   #5
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Thanks for the clarification everyone!
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