Regeneration

[MullenaxM]

There has been a lot of misconceptions and misinformation posted on different threads about the regeneration process on the Dodge Ram Pick-Up with the Cummins 6.7 liter engine. In an effort to try to correct this misinformation is the reason for this post.
This post will pertain to the Pick-Up with the Cummins ISB 6.7 liter. Although the Cab and Chassis model is similar, some of parameters for regeneration are different.
Regeneration is the process where soot particles trapped by the DPF (Diesel Particulate Filter) are burned into ash. This process involves a lot of different components as well as a program in the ECM triggered by the pressure differential sensor or by an internal counter. I’ll explain the different components and more about the counter later in this post.
First, there are three types of regeneration – Passive, Active and Manuel:

• Passive regeneration can occur when the engine is operating under load conditions that generate high enough exhaust temperatures to oxidize the soot particles trapped in the DPF
• Active Regeneration occurs when the exhaust temperature is insufficient to achieve passive Regeneration. Under certain conditions the ECM can automatically activate the fuel injectors to raise the exhaust temperature to achieve a successful Regeneration while the vehicle is in motion. The ECM activates the injectors post-combustion.
• Manuel Regeneration can be performed with a Scan tool or some of the Aftermarket performance programmers have the ability to perform Regeneration.
The ECM will start the Regeneration process of the DPF if the soot load exceeds a calibrated value. On Dodge Ram Pick-up that calibrated value is 47 grams of soot. The ECM determines the soot load of the DPF based on the voltage output of the pressure differential sensor. Or the ECM has an internal counter that runs anytime the engine is running. This counter is engine RPM and exhaust temperature dependent, so the more RPM the engine is turning or the higher the exhaust temperature, the faster the counter runs. When this counter reaches 24000, or the DPF reaches a soot load of 47 grams, the ECM will try to activate the Regeneration process. This is the Active part of the regeneration process.
There are four different diesel emissions, Oxides of Nitrogen (NOx), Oxides of sulfur (SOx), Particulate Matter (soot) and Hydrocarbons (in the form of unburned fuel). With a scan tool there are five modes of regeneration we can monitor:
• Normal : There engine is operating in normal condition,
• De-soot : The ECM is performing a regeneration of the DPF
• De-SOx: The ECM is in a regeneration event and is performing a sulfur oxidation process.
• De-NOx: The ECM is in the process of desorption and regeneration of the NAC, (Nox Absorber Catalyst) although a De-NOx event can happen shortly after regeneration, it is independent of regeneration.
• HC-Desorp: This is a process of the ECM to get rid of excess hydrocarbons, in the form of unburned diesel fuel, in the exhaust system. This is a process that most vehicles will not see very often.( I’ll address this process in another post, It is a issue in and of itself)
So with that said, the two processes that are involved in a regeneration event are, De-soot and De-SOx. Before we get into the regeneration processes I must mention the exhaust temperature is the main determiner of regeneration. The oxidation of diesel particulate matter (soot) begins at 1025 degrees Fahrenheit, oxides of sulfur (SOx) oxidation begins at 1185 degrees Fahrenheit. For this reason alone, since a lot of vehicles never get worked hard enough to raise the exhaust temperature high enough to reach the threshold, a passive regeneration will never be achieved. These vehicles will have to depend on the active regeneration process.

A De-NOx event, the process of NOx desorption, requires a exhaust temperature of approximately 500 degrees Fahrenheit. This process also requires the absence of oxygen in the exhaust system. For this reason the ECM will momentarily dump EGR gases and sometime fuel down the exhaust to displace the oxygen in the exhaust. This process only takes 5-10 seconds. The timing for a De-NOx event is based on an algorithm that takes engine run time, engine load, engine temperature and fuel rate to determine how often to perform a De-NOx event. This is the reason for the O2 sensors up-stream and down-stream of the NAC.

A De-SOx event during a regeneration process has a trigger of 4.5 grams of SOx. In other words when the ECM sees a SOx load of 4.5 grams, again based on an algorithm that uses engine run time, engine load, engine temperature, fuel rate and also ambient temperature, to determine the SOx load in the NAC.

When either of the triggers reach there threshold, 47 grams of soot or the internal ECM counter reaches 24000, the ECM will try to initiate regeneration. Once the engine reaches operating temperature and the vehicle speed is sufficient the ECM will enable the De-soot portion of the regeneration process. The internal counter will start at 24000 and continue to count up until the exhaust temperature reaches approximately 850 degrees Fahrenheit. Then the counter will start to count down. The ECM will set the VGT slide ring at 12% (88% boost), this is why you will feel a slight performance difference. Also the ECM will start to add fuel post combustion. The EGR valve will set closed. The DOC (diesel oxidation catalyst) will start the fuel burn and as it continues down the exhaust stream the NAC will aid in bringing the exhaust temperature up to approximately 1175 degrees Fahrenheit. The particulate matter will begin to oxidize and turn into ash. When the counter get to about 11000, depending on the soot load, the ECM will switch over to the De-SOx mode. In the De-SOx mode the EGR valve will open and resume normal operation. The VGT slide ring resumes normal operation and operates at the 50-70% position. The ECM will continue to try to raise the exhaust temperature with post combustion fuel injections until the exhaust temperature reaches approximately 1250 degrees Fahrenheit. All of this is variable, if the soot load is high and the SOx load is at the trigger point, the ECM will keep it in the De-soot mode longer and the De-SOx mode for less time. If the vehicle is stopped the ECM will try to start the regeneration process again when the vehicle is restarted. It will continue to try and do regenerations until the process is completed.

Next up…. When Stuff Goes wrong!! Mike