The latest U.S. EPA diesel emission regulations were designed to combat diesel pollution and obtain gasoline-like emissions standards from diesel-powered vehicles.
To achieve these goals, all diesel engines produced since 2007 must meet a reduction of nitrogen oxide (NOx) and hydrocarbons (HC) by 50% and particulate matter by 90+% over earlier 2004 emission standards.
In addition, Ultra-Low Sulfur Diesel (ULSD) fuel must have a 97% reduction in the sulfur content of highway diesel fuel. According to the EPA, some studies show that the use of ULSD alone can reduce particulate matter emissions by between 10-20%. However, of greater significance is that this cleaner fuel enables the use of advanced after-treatment technologies on new engines.
Emissions Control Technologies
Some of the emissions control technologies of the Duramax 6.6L diesel engine in Chevrolet and GMC light-duty trucks and vans and medium-duty trucks include a Diesel Oxidation Catalyst (DOC) and a Diesel Exhaust Particulate Filter (DPF). (Fig. 13)
(Fig. 13)
The DOC reduces hydrocarbons and oxides of nitrogen, carbon monoxide and odor-causing compounds. It also turns the majority of emissions into water and oxygen.
The DPF traps the particulate matter (solid particles that appear as black smoke) from the engine exhaust before they can be emitted into the atmosphere.
The DOC and DPF are installed in the exhaust system. To prevent clogging, particulate matter in the DPF is periodically burned off, leaving ash and yielding carbon dioxide and water. This process is called particulate filter regeneration.
DPF Regeneration
DPF regeneration may occur under several circumstances, called Active Regeneration, Passive Regeneration and Service Regeneration.
Active Regeneration - The regeneration operation is controlled by the engine control module (ECM), which keeps track of the mileage driven, the amount of fuel consumed, the hours of operation and the exhaust differential pressure.
When the conditions are met for regeneration to occur, the ECM enters a different engine calibration strategy that includes additional fuel injection pulses. This heats the DOC above its normal operating temperature and regeneration begins. For the process to complete satisfactorily and efficiently clean the filter, the vehicle must be operated continuously for approximately 18 minutes at speeds greater than 30 mph (50 km/h). If the engine is allowed to return to idle during this time, the idle speed may be elevated slightly and the operating sound may be different. This is normal, and the driver doesn't need to do anything.
During regeneration, the exhaust temperature increases (greater than 500° C), which converts the particulates into harmless gases and ash. The DPF is then clean and ready to filter particulates again.
If normal driving does not provide the necessary conditions for regeneration to occur, the pressure differential continues to increase across the exhaust filter. On some vehicles, a Clean Exhaust Filter message will be displayed or a warning lamp will illuminate. (Fig. 14)
(Fig. 14)
If the conditions necessary for regeneration do not take place, however, the ECM will eventually illuminate the MIL and the Reduced Power warning lamp. The engine enters the Reduced Power mode, which will require the vehicle to be serviced.
Passive Regeneration - Passive regeneration occurs when exhaust gas temperature is elevated above 300°C (575° F). These temperatures may be reached when the engine is under heavy load.
Service Regeneration - Service regeneration is performed with the scan tool and is used to clean a soot-loaded filter during a service visit.
Regeneration Temperatures
The exhaust system has been designed to deal with the temperatures involved in the regeneration process. On long wheelbase models, for instance, a heat shield protects the rear axle shock absorbers. All models have an exhaust cooler at the end of the tailpipe. A vacuum created by the exhaust passing through the openings draws in cool air, which mixes with the exhaust gases.
There are times when a DPF service regeneration must be performed in the service center. This must be conducted outdoors. The shop exhaust system will not handle the heat.
Diesel Fuel and Oil Requirements
The Duramax 6.6L diesel engine requires Ultra-Low Sulfur Diesel, which limits sulfur content to 15 ppm (parts per million).
It also requires oil that conforms to the CJ-4 standard established by the American Petroleum Institute. This oil offers lower oil consumption and reduces limits for phosphorus, sulfur and ash. Low ash oil is needed to extend the life of the DPF as well as to reduce the formation of engine sludge and deposits.
- Thanks to Frank Tornambe
Leave a comment