On an engine with exhaust gas recirculation (EGR), the air intake system and exhaust system components work together to provide the correct amount of intake charge-air flow into the engine. This overview covers the major components of the exhaust system.
The exhaust manifold is a three-piece design with a sealed slip-joint to allow for thermal expansion.
Depending on the application, the exhaust manifold used can vary, to enable the turbocharger to be located in various positions.
The exhaust manifold has an additional port that connects to the EGR cooler inlet (1).
The exhaust manifold sections are sealed by a metallic exhaust seal (2), which is replaceable in the event the seal malfunctions and leaks exhaust gas.
The seal requires a special installation tool to be properly installed to the exhaust manifold. Use the following procedure for additional information on the exhaust manifold seal installation. Refer to Procedure 011-007 in Section 11.
The EGR cooler (1) cools the exhaust gases flowing to the EGR valve. The EGR cooler is mounted above the exhaust manifold and is supported by the EGR valve mounting bracket (not shown), attached to the rocker housing.
Because the EGR valve is mounted after the EGR cooler, the EGR cooler is subject to the same exhaust temperatures and pressures as the exhaust manifold.
The EGR cooler has a coolant vent (3) near the exhaust inlet of the EGR cooler. This vent prevents air from being trapped in the cooler during coolant filling and engine operation by continuously flowing coolant to the top tank of the vehicle cooling system.
Exhaust pressure in the exhaust manifold (which determines the position of the variable geometry turbocharger and the EGR valve) is measured by an exhaust pressure sensor.
To maximize the durability of the exhaust pressure sensor, the sensor does not mount directly into the exhaust manifold. The exhaust pressure sensor is connected by a tube to the exhaust manifold.
The exhaust pressure sensor is located on the EGR cooler coolant outlet connection for additional cooling of the sensor.
Passive regeneration occurs when the exhaust temperatures are naturally high enough to oxidize the soot collected in the aftertreatment diesel particulate filter faster than the soot is collected.
Passive regeneration typically occurs when the temperature of the aftertreatment diesel particulate filter is above 316°C [601°F]. This occurs during highway driving or driving with heavy loads.
Since passive regeneration occurs naturally, it is considered to be normal engine operation. No fuel is added to the exhaust stream during passive regeneration.
Active regeneration occurs when the exhaust temperatures are not naturally high enough to oxidize the soot collected in the aftertreatment diesel particulate filter faster than it is collected.
Active regeneration requires assistance from the engine in order to increase the exhaust temperature. This is typically done by injecting a small amount of diesel fuel into the exhaust stream (called aftertreatment injection) which is then oxidized by the aftertreatment diesel oxidation catalyst. The oxidation of this additional fuel creates the heat needed to regenerate the aftertreatment diesel particulate filter.
For active regeneration to occur, the electronic control module (ECM) must detect that the aftertreatment diesel particulate filter restriction has reached a specified limit. Once this limit is reached, the engine will alter its operation in order to create exhaust temperatures high enough to actively regenerate the aftertreatment diesel particulate filter.
The SCR uses diesel exhaust fluid (DEF) in order to convert nitrogen oxides from the exhaust stream into nitrogen and water.
During an initial cold start, the engine will go into SCR warm up condition. This condition will sound and act like an active regeneration. The SCR catalyst will need to have a temperature of over 250°C [482°F] in order to properly convert NOx in the exhaust stream.
The NOx sensor at the outlet of the SCR will monitor the NOx output in the exhaust system and relay the information back to the ECM.
The purpose of the aftertreatment diesel exhaust fluid controller is similar to the engine ECM. It will control and monitor the dosing system for the necessary ambient conditions and DEF dosing rates.
Electrical connection point for the 86-pin and 53-pin connectors.
The aftertreatment diesel exhaust fluid dosing control valve is controlled by the DEF controller. The DEF controller sprays the correct amount of DEF into the exhaust stream. Because the dosing control valve is mounted directly to the exhaust system, it will encounter high temperatures. Engine coolant is supplied to the DEF control valve to keep the valve cool and operable.
Gasket
Injector/DEF inlet port
Electrical connection to the aftertreatment DEF controller
The DEF control valve is mounted to the aftertreatment decomposition tube. The aftertreatment decomposition tube contains a mixer to help the DEF mist distribute evenly in the exhaust stream.
When the aftertreatment DEF dosing unit is activated, it pulls DEF from the DEF tank, filters the DEF, and then pressurizes the DEF to the DEF control valve. Any DEF that is not used is returned to the DEF tank
When a driver turns the key OFF, the dosing system will run a purge cycle during shutdown to prevent DEF from being left in the system and freezing in cold climates. An audible click and pumping sound will be heard from the DEF dosing unit when it is in the purge cycle. The DEF dosing unit will move its reverting valve, changing the direction of flow for the DEF. The DEF dosing unit will pull all of the DEF out of the DEF dosing control valve and line, and return the unused DEF to the DEF tank. After a complete purge, the system will be free of any remaining DEF.
If ambient conditions are below -4°C [25°F], the DEF controller will turn ON the DEF dosing unit internal heater to defrost itself and prepare to prime the system with DEF. The DEF dosing unit will not prime until it is completely defrosted.
The main components of the aftertreatment DEF dosing unit.
Aftertreatment DEF dosing unit filter cap
Electrical connector to the aftertreatment DEF dosing unit
The aftertreatment DEF tank is designed to store DEF for the SCR aftertreatment. A sensor detects DEF tank level and DEF tank temperature and sends a signal to the aftertreatment DEF controller.
If the DEF tank level becomes too low, the ECM will register a fault and derate engine power.
If the DEF tank temperature drops below -5°C [23°F], the DEF tank coolant valve will be commanded open by the aftertreatment DEF controller. Hot engine coolant will flow though the tank to defrost the frozen DEF. The DEF dosing system will not prime until the DEF tank is defrosted.
DEF tanks will vary in size and shape. Refer to the OEM service manual for additional information.
The aftertreatment DEF lines carry the DEF to and from the aftertreatment DEF tank as well as to the DEF control valve.
The aftertreatment DEF will fill the lines during a prime or operating state and be removed in a purge state to prevent freezing of the DEF.
If the ambient temperature is below -5°C [23°F], the DEF fluid controller will command the heated lines ON. The dosing system will not prime until the DEF lines are completely defrosted.
DEF line connectors, length, and design will vary upon vehicle manufacturer. Refer to the OEM service manual for additional information.
Aftertreatment injection requires temperatures in the aftertreatment system to reach approximately 288°C [550°F]. At this temperature and above, the small quantities of fuel injected into the exhaust will properly oxidize across the aftertreatment diesel oxidation catalyst, creating the additional heat required to actively regenerate the aftertreatment diesel particulate filter.
During active regeneration, the engine ECM monitors the exhaust temperatures before and after the aftertreatment diesel particulate filter, and maintains the temperatures in a range of approximately 482 to 649°C [900 to 1200°F]. The quantity of fuel used for aftertreatment injection will vary as the temperature is controlled within these limits.
The temperatures achieved during active regeneration are typically higher than those achieved during passive regeneration. The conversion of soot to carbon dioxide occurs much faster as temperatures increase.
A typical active regeneration event will take approximately 20 to 40 minutes to complete while the vehicle is operating. The vehicle operator may notice additional turbocharger noise during this time, along with an illuminated high exhaust temperature lamp, if equipped.
The frequency at which an engine will require an active regeneration varies greatly from application to application. In general, vehicles with a low vehicle speed, such as urban vehicles, or a low-load duty cycle, will require more active regeneration events than a heavily loaded vehicle or a vehicle with a highway speed duty cycle.
The engine ECM also contains a time-based feature for active regenerations that is used to verify correct aftertreatment operation when the vehicle duty cycle is typically high enough that active regeneration events are not necessary.
If the engine has not completed an active regeneration within the last 96 hours of operation, the engine ECM will call for a time-based active regeneration event.
The timer resets each time the ECM detects that an active regeneration event has completed.
Under some operating conditions, such as low speed, low load, or stop and go duty cycles, the engine may not have enough opportunity to regenerate the aftertreatment diesel particulate filter during normal vehicle operation. When this occurs, the engine illuminates the aftertreatment diesel particulate filter lamp to inform the vehicle operator that assistance is required, typically in the form of a stationary (parked) regeneration.
Stationary (parked) regeneration is a form of active regeneration that is initiated by the vehicle operator when the vehicle is not moving. Refer to Procedure 014-013 in Section 14.
The vehicle manufacturer has the option of installing two switches (the start switch and the permit switch) that control aftertreatment functions.
The start switch (known as the Diesel Particulate Filter Regeneration Start Switch in INSITE™ electronic service tool) is used to start a stationary (parked) regeneration. The vehicle manufacturer can also reference this switch as a stationary regeneration switch, start switch, or parked regeneration switch.
The permit switch (known as the Diesel Particulate Filter Permit Switch in INSITE™ electronic service tool) is used to allow the vehicle operator to disable active regeneration, if necessary. The vehicle manufacturer can also reference this switch as an inhibit switch, stop switch, or disable switch.
The Minimum Vehicle Speed for Automotive Mobile Regeneration parameter in INSITE™ electronic service tool allows the vehicle manufacturer to program a minimum vehicle speed at which active regeneration is allowed.
This parameter is controlled by the vehicle manufacturer and can be protected by an OEM password. Do not change the value of this parameter without written consent of the vehicle manufacturer. This parameter can be set between 0 to 40 km/h [0 and 25 mph].
When this parameter is set to 0 km/h [0 mph], the engine is allowed to activate an active regeneration event at any vehicle speed.
If the engine needs to initiate an active regeneration event, but the vehicle speed is 0 km/h [0 mph] and the engine is at low idle speed, the engine will not immediately enter an active regeneration event. The ECM will wait until the engine speed increases to begin the active regeneration event. Once the active regeneration begins, and the exhaust temperatures have increased, the engine will maintain the active regeneration event, even if the vehicle speed returns to 0 km/h [0 mph] and the engine speed returns to idle.
When the vehicle speed is greater than 0 km/h [0 mph] and the engine speed is above idle speed, an active regeneration event can occur at any time.
When this parameter is set to any speed other than 0 km/h [0 mph], the triggers for active regeneration change.
In order for an active regeneration event to start, the vehicle speed must exceed 64 km/h [40 mph], regardless of minimum vehicle speed parameter setting. Once the vehicle speed exceeds 64 km/h [40 mph], an active regeneration event can begin.
Once the vehicle speed has exceeded 64 km/h [40 mph] and the active regeneration event has started, the active regeneration event will continue until the vehicle speed drops below the minimum speed parameter. Once the vehicle speed drops below the minimum speed parameter, the active regeneration stops.
The vehicle must once again exceed 64 km/h [40 mph] to begin the active regeneration event again.
If a vehicle will not achieve 0 km/h [0 mph] minimum vehicle speed for mobile active regeneration, and has a low vehicle speed, or stop and go duty cycle (such as a transit bus, delivery vehicle, or school bus), the engine may not have enough opportunity to perform or complete an active regeneration event. An engine in this situation can illuminate the diesel particulate filter (DPF) lamp on a frequent basis, signaling the need for a stationary regeneration.