Engine Emission Control
Engine Emission Control - 6.7L Diesel
EGR System
System Overview
NOTICE: Do not use silicone based sprays or lubricants on any components installed onto or around the diesel exhaust system or intake air distribution and filtering system. Silicone reacts with the Nitrogen Oxides (NOx) sensor and may cause permanent damage to the NOx sensor.
The EGR recirculates some of the engine exhaust gases into the engine at a lower temperature. The cooled exhaust gases have a higher heat capacity and contain less oxygen than air, lowering combustion temperatures and reducing the formation of Nitrogen Oxides (NOx).
Component List
The EGR system consists of the following components:
- EGR valve is mounted to the EGR bypass
- EGR bypass is mounted to the EGR cooler
- EGR cooler is mounted to the RH valve cover
System Components
The EGR valve controls the amount of exhaust gases introduced into the intake manifold.
The EGR bypass directs exhaust gases straight into the air intake system when the engine is cold during startup to get EGR working as soon as possible to lower NOx levels. At normal operating temperatures and above engine idle speeds the bypass reverts back to normal operation.
The EGR cooler is a floating core design, allowing the EGR coolers to independently move within their housings as they thermally expand and shrink. The EGR cooler also uses both engine and the powertrain secondary cooling systems to maintain EGR temperatures.
System Operation
The EGR system reduces the peak combustion temperatures and NOx emissions by 90 %. All of the engine EGR comes from the right exhaust manifold. EGR gases pulled from a single bank instead of both sides of the engine, reducing the plumbing required. It also eliminates airflow balance issues that can occur when using EGR gases from two cylinder banks.
The EGR system also has a bypass feature that skips the EGR cooler to allow the engine to warm up faster.
The EGR system uses two EGR coolers, but it introduces a hot-side valve at the front of the first cooler that controls the volume of air allowed into the system instead of using a conventional cool-side valve behind the second cooler.
Closed Crankcase Ventilation (CCV) System
System Overview
The Closed Crankcase Ventilation (CCV) system uses intake manifold vacuum and crankcase pressure to ventilate blow-by gases from the crankcase and return the gases to the intake manifold for combustion. Additionally, the separator removes oil from the blow-by gas and returns it to the engine.
Do not permanently remove or render inoperative any part of the vehicle emission control system including related hardware. Failure to comply may violate applicable state and federal law.
Component List
The diesel CCV system consists of the following components:
- CCV oil separator is located on the LH valve cover
- CCV tube is connected from the CCV oil separator to the lower intake manifold
System Components
The CCV oil separator varies the amount of blow-by gases returned to the intake manifold based on available engine vacuum. It also prevents excessive vacuum from the intake system from reaching the crankcase.
The CCV tube carries the blow-by gases from the crankcase to the lower intake manifold.
System Operation
As the engine runs, high pressure gases are contained within the combustion chamber. Piston rings seal against the cylinder preventing the high pressure gases from passing into the crankcase between the side of the piston and the cylinder bore. Some amount of gas always leaks past the piston rings into the crankcase. If this blow-by gas could not escape, pressure would build up within the crankcase. The CCV oil separator pulls oil out of the blow-by gas and delivers the blow-by gas back to the intake system.
It is critical to keep the parts of the CCV system clean and open; otherwise gas flow will be insufficient. A plugged or malfunctioning CCV system eventually damages an engine. A poorly maintained CCV system eventually becomes contaminated with sludge, causing serious engine problems.
Reductant System
System Overview
NOTICE: Do not use silicone based sprays or lubricants on any components installed onto or around the diesel exhaust system or intake air distribution and filtering system. Silicone reacts with the NOx sensor and may cause permanent damage to the NOx sensor.
The reductant system uses a selective reduction catalyst to improve exhaust emissions and fuel efficiency by injecting a reductant into the exhaust system. The reductant, also referred to as diesel exhaust fluid, is a 32.5% solution of urea in deionized water. The reductant system reduces Nitrogen Oxides (NOx) present in the exhaust stream to nitrogen and water.
Component List
The reductant system consists of the following components:
- Reductant tank - located on the inside or outside of the frame rail depending on the vehicle wheelbase
- Reductant tank filler hose - located near the fuel filler
- Reductant pressure line, with integrated heater - located on the frame rails
- Reductant pump assembly - located on the reductant tank
- Reductant heater and sender assembly - located below the reductant pump assembly in the reductant tank
- Reductant injector - located on the catalyst and particulate filter assembly
- Catalyst and particulate filter assembly - located in the exhaust system
- NOx sensor - located on the catalyst and particulate filter assembly
- NOx sensor module - located on the frame rail
System Diagram
Reductant System
System Components
The reductant tank stores the reductant.
The reductant tank filler hose is a 2-piece design consisting of a filler hose and a vent hose.
The reductant pressure line supplies the reductant from the reductant pump assembly to the reductant injector. There are different reductant pressure lines for different vehicle wheelbases. The reductant pressure line is heated to prevent freezing.
The reductant pump assembly pumps reductant to the reductant injector. It contains a diaphragm pressure pump, pressure sensor, purge valve, outlet filter, and internal heating element.
The reductant heater and sender assembly contains the pickup tube for the reductant pump module, electric heating element, temperature sensor, and electrode-type level sensor.
The reductant injector is a Pulse Width Modulated (PWM) solenoid controlled directly by the PCM. The injector receives reductant from the reductant pressure line and sprays it into the exhaust stream, where it is mixed into the exhaust gases before entering the catalyst.
The NOx sensor detects levels of NOx in exhaust gases and sends input to the NOx sensor module. For additional information, refer to Electronic Engine Controls - Diesel Engine Electronic Engine Controls.
The NOx sensor module receives input from the NOx sensor and sends it to the PCM. For additional information, refer to Electronic Engine Controls - Diesel Engine Electronic Engine Controls.
System Operation
The NOx sensor detects the level of NOx in the exhaust gas and sends that input to the NOx sensor module. The NOx sensor module sends that input to the PCM which commands a reductant injection. The reductant injector opens and the reductant pump operates, filling the reductant pressure line and the reductant injector to purge the air out of the system. When all of the air is purged, the reductant injector closes, allowing the reductant pump pressure to build to 500 kPa (73 psi). With the system fully primed, the reductant injector provides the reductant to the catalyst as commanded by the PCM. The catalyst contains a copper catalyst washcoated on a zeolite substrate. At the inlet of the catalyst is a port for the reductant injector, followed by a grate diffuser and a twist mixer. When the reductant is introduced into the system, it atomizes in the grate diffuser and mixes evenly with exhaust gases in the twist mixer. During this time, the heat of the exhaust gases causes the urea in the reductant to split into Carbon Dioxide (CO2) and ammonia. As the ammonia and NOx pass over the catalyst, a reduction reaction takes place and the ammonia and NOx are converted to nitrogen and water. This reaction takes place at up to 95% efficiency, allowing the engine to run leaner and more efficiently. The high levels of NOx that are produced under lean conditions are now eliminated.
The PCM commands the Glow Plug Control Module (GPCM) to provide voltage to the reductant pump assembly internal heating element, reductant pressure line heater and the reductant heater and sender assembly when the reductant temperature approaches its freezing point of -11°C (12°F). The reductant heater and sender assembly heating element is located directly above the pickup tube inlet filter. When the reductant heater and sender assembly temperature sensor detects the reductant temperature dropping to its freezing point, the reductant heater and sender assembly heating element thaws and maintains a pool of liquid reductant within the reductant heater and sender assembly reservoir.
The reductant heater and sender assembly level sensor incorporates four stainless steel electrodes. Three electrodes arranged vertically provide a high, middle, and low level signal and the fourth electrode runs the length of the level sensor and acts as a ground. The reductant is a good conductor of electricity. When the reductant tank is full, the reductant closes a circuit between all three level electrodes and the ground electrode, indicating the tank is full. As the reductant is consumed, the level drops and uncovers each electrode in sequence. The PCM calculates the reductant level based on these signals.
When the vehicle is shut down, the PCM closes the reductant injector and actuates the reductant pump purge valve, causing the reductant pump to reverse the pump flow and bleed down the pressure from the reductant pressure line. The PCM then opens the reductant injector to allow air to enter the reductant pressure line, which in turn allows the reductant pump to purge all remaining reductant from the system and return it to the reductant tank. The PCM then closes the reductant injector and returns the reductant pump purge valve to the forward pump position.