The EGR cooler seen in the video reduces the oxides of nitrogen entering the intake system by cooling the exhaust using coolant that flows around the exhaust passing through the cooler core from the exhaust manifold. After exiting the EGR cooler the exhaust goes through the EGR Valve which is controlled by the engine ECU allowing the cooled exhaust gases into the combustion chamber reducing NOx levels.
Methods To Reduce Emissions
Cooled EGR working alongside an exhaust filter that catches particulate matter is the typical 2 stages of emission reduction in diesel engines 2007 and newer. There is a second way to reduce emissions and that is the SCR (selective catalyst reduction) and the DOC (diesel oxidation catalyst).
The Cummins ISB 6.7 diesel has all of the above to reduce emissions to Final Tier 4 regulations. Lower combustion temperatures created by the EGR cooler causes an increase in particulate matter. The diesel oxidation catalyst and DPF (diesel particulate filter) capture the particulate matter. The DOC causes a reaction with exhaust gases to cut down PM including carbon monoxide and hydrocarbons.
Exhaust heat during normal operation oxidizes the particulate matter in the DPF turning it into nitrogen gas and carbon dioxide which is the final product flowing out the tail pipe. This process is regeneration commonly called a “parked regen” which requires the operator to push the “regen” button on the dash when the regen light on the dash stays on.
Different Ways To Clean PM Out Of The System
There is also the “passive regen” which happens while the vehicle is working and controlled by the engine ECU. The third option is the “forced regen” that is controlled by the technician using engine software on a laptop computer. A forced regen is necessary if the soot level indicator in the software is high or if the regen light is coming on. Most times the operator can start a parked regen but the option is always there to force it with the laptop if the dash button does not start up the process.
The SCR System
The SCR that Cummins uses also requires DEF diesel exhaust fluid that causes the chemical reaction required to reduce NOx. The engine operates at higher exhaust temperatures and delayed timing to improve combustion. This reduces particulate matter but increases NOx levels. Using diesel exhaust fluid injected into the exhaust downstream combining with the SCR catalyst the NOx is broken down into nitrogen gas and water vapor.