Diesel Tuner's Blog

How does REGEN work in an LML Duramax?

Posted by Paul Wilson on Jul 6, 2016 10:30:43 AM

REGEN is the burning of soot built up in a DPF. 

 The Emissions Equipment for diesel trucks has changed quite a bit through out the years. In 2004.5 all heavy duty diesel pickups had to install EGR's which is the exhaust gas recirculation system. Basically it turns exhaust into inert gas and directs the gas back into the combustion process. Then in 2007.5 the EPA required pickups to use a DPF. The DPF, or Diesel Particulate Filter, is a filter that catches soot, or unburnt fuel from the exhaust. Once the soot builds up, the exhaust heats up to burn the soot off. Starting in 2011 Diesel Exhaust Fluid is used to treat NOx emissions, in addition to the EGR and DPF treating the carbon emissions. 

The DPF is a crucile part of treating diesel emissions and each OEM utilizes and operates their DPF a little differently. Below, the DPF in the 2011-2016 LML Duramax is explained.


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Before discussing how Regen works, there are a few things you will need to know:

Soot is a byproduct of unburnt fuel, it is also called "particulate matter".

DPF Diesel Particulate Filter,  traps soot in the exhaust. 

Regen The process of burning off accumulated soot in the DPF.  The soot is converted to ash.   The process of burning off accumulated soot in the DPF.  The soot is converted to ash.  

EGR Exhuast Gas Recirculation, located in the engine bay, redirects exhaust gas to the intake converting exhaust into inert gas and reducing NOx emissions.

SCR Selective Catalyst Reduction, located in the exhaust after the DOC and before the DPF, converts NOx into nitorgen gas and water.

DOC Diesel Oxidation Catalyst, located in the exhaust after the 9th injector and before the SCR, produces heat for DPF Regen while converting hydrocarbons and carbon monoxide into water and carbon monoxide.

9th Injector Fuel injector, located in the exhaust before the DOC, raises exhaust gas temperatures during Active Regen.

DEF Deisel Exhaust Fluid, used to treat NOx emissions, sprayed in the exhaust after the DOC and before the SCR.

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1. Exhaust flows from from the engine, through the downpipe into the exhaust.

2. The exhuast enters the DOC and is treated to convert hydrocarbons and carbon monoxide into water and carbon dioxide.  The DOC is also responsible for producing extra heat for DPF Regen.

3. As the exhaust exits the DOC, DEF is sprayed into the exhuast, heat from the exhaust converts DEF to amonia and carbon dioxide.

4. DEF is required for the SCR process to convert NOx into nitrogen gas and water.

5. Next the DPF traps soot.

6. During some truck operations the exhuast is hot enough to burn off soot while driving with no fuel sprayed through the 9th injector, this process is called Passive Regen.  Passive regen is happening any time temperature in the DPF is above 800 deg F.  

7. Differential pressures before and after the DPF help the ECM determine when enough soot has built up to trigger an Active Regen.  Active Regens require fuel to be sprayed through the 9th injector to raise exhuast temperatures high enough to burn the accumulated soot.  On an LML the active regen process initiates once 42 grams of soot have collected in the DPF or after 700 miles without active regen (whichever comes first).  DPF temperatures during an active regen will quickly climb to 1000 deg F in order to quickly burn collected soot off and allow the DPF differential pressure to come back down.  Temperatures during active regen can reach as high as 1300 deg F.  Driving the truck you'll notice a different engine pitch, and higher idle while stopped.  You may feel extra heat underneath the truck during active regen and will occasionally catch a funny smell out of the exhaust.  





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