A new diesel engine is available for 2007Â (fig. 1). It's the Duramax 6.6L (RPO LMM). This engine is being released to conform with 2007 US EPA diesel emission regulations, which require a 60% reduction of NOx and a 90% reduction of particulate matter.
This new engine has been designed to be the most powerful and cleanest Duramax Diesel ever offered in the Chevrolet (Silverado, Express, Kodiak) and the GMC (Sierra, Savanna, Top Kick) models.
A number of design strategies have been put in place to meet these new emission regulations. These include both software and hardware:
- Exhaust particulate filter
- Intake air valve
- Revised EGR
- Exhaust tailpipe cooler
- ECM calibration
- Revised injector nozzle flow
- More robust internal engine components and a more efficient turbocharger
EMISSION CONTROL COMPONENT HIGHLIGHTSÂ (fig. 2)
A Diesel Oxidation Catalyst (DOC)
B Exhaust Particulate Filter (DPF)
Diesel Oxidation Catalyst (DOC) --Â Reduces hydrocarbons (HC) and oxides of nitrogen (NOx), carbon monoxide (CO) and odor-causing compounds. It also turns the majority of emissions into water and oxygen.
Exhaust Particulate Filter (DPF) --Â Traps the particulate matter (solid particles that appear as black smoke) from the engine exhaust before they can be emitted into the atmosphere.
During the regeneration process (explained later), the DOC is heated above its normal operating temperature by a different engine calibration strategy that includes additional fuel injection pulses. The extra heat created by the DOC is used to increase the temperature of the exhaust particulate filter (DPF). The DOC helps obtain and sustain the required temperatures during regeneration.
EXHAUST PARTICULATE FILTER (DPF) OPERATION
The DPF is installed in the exhaust system behind the catalytic converter, and its appearance resembles the catalytic converter. The filter element (fig. 3) is made of porous, catalytically coated silicon carbide, which allows the exhaust gases to pass through, while trapping the solid matter from the exhaust. This decreases particulate matter (soot) and eliminates exhaust smoke. The DPF collects particulates while the engine is running.
To prevent clogging, particulate matter is periodically burned off, leaving ash and yielding carbon dioxide and water. This process is called particulate filter regeneration.
DPF REGENERATION CONTROLÂ (fig. 4)
A Pressure sensor
B Exhaust differential pressure sensor
C Temperature sensor
D Particulate filter
The ECM keeps track of operating conditions to determine the amount of particulate accumulation, and periodically initiates a regeneration process.
Pressure Sensors --Â The exhaust differential pressure sensor (EPS) measures the pressure difference between the inlet and outlet of the DPF filter. When the pressure difference has increased above a calibrated threshold, it indicates a high particulate loading condition. The ECM then commands a regeneration event in order to restore the DPF.
The exhaust pressure differential sensor is also used to monitor the filter for cracks or holes in the filter substrate.
Exhaust Gas Temperature Sensors --Â During regeneration, two temperature sensors are used to monitor the process. One sensor, located ahead of the DPF, measures the temperature of the exhaust gases leaving the Diesel Oxydizing Catalyst and entering the DPF. This temperature measurement is used by the ECM to control fuel injector flow that is used to maintain temperatures necessary for regeneration. A second temperature sensor, located after the DPF, helps the ECM monitor and regulate the regeneration temperatures and helps protect the system.
DPF REGENERATION OPERATION
Regeneration may occur under several circumstances, called Active Regeneration, Passive Regeneration and Service Regeneration.
Active Regeneration
The regeneration operation is controlled by the 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 is above its normal operating temperature and regeneration begins.
For the process to complete satisfactorily, the vehicle must be operated continuously for approximately 18 minutes at speeds greater than 30 mph (50 km/h) to efficiently clean the filter. 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 different.
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.
Driver Notification --Â If normal driving does not provide the necessary conditions for regeneration to occur, the pressure differential continues to increase across the exhaust filter. The ECM will illuminate a CLEAN EXHAUST FILTER message on the instrument panel Driver Information Center (C/K only).
When this occurs, the owner manual and a label placed by the driver's sun visor instruct the customer to drive the vehicle under the conditions necessary for a regeneration to take place until the CLEAN EXHAUST FILTER message no longer appears on the DIC.
Reduced Power --Â However, if the CLEAN EXHAUST FILTER message is ignored, the ECM will eventually illuminate the MIL and the Reduced Power 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 Tech 2, and is used to clean a soot loaded filterduring a dealership service visit.
DEALING WITH 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
(fig. 5). A vacuum created by the exhaust passing through the openings draws in cool air, which mixes with the exhaust gases. Cooled exhaust exits the tailpipe.
A Exhaust cooler
B Exhaust flow
C Air flow
D Cooled exhaust
IMPORTANT --Â There are times when a DPF service regeneration must be performed at the dealership. THIS MUST BE CONDUCTED OUTDOORS. The shop exhaust system will not handle the heat.
DIESEL FUEL AND OIL REQUIREMENTS
The LMM diesel engine requires ultra low sulfur fuel, which limits sulfur content to 15 ppm (parts per million). It also requires use of oil which conforms to the CJ-4 standard established by the American Petroleum Institute (API). 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 Engine Particulate Filter, as well as to reduce the formation of engine sludge and deposits.
IMPORTANT
Use Ultra Low Sulfur Diesel Fuel (ULSF) only (fig. 6). The emission control hardware may be damaged if high sulfur level fuels are used.
Do not use Low Sulfur Diesel Fuel.
Do not use Off Road Diesel Fuel.
Use only engine oil that has the API classification of CJ-4, which is formulated to work properly with the Diesel Particulate Filter.
Vehicle Modifications --Â DO NOT modify any exhaust systems or engine control components, unless it's GM approved.
- Thanks to Frank Tornambe
