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| Illustration 1 | g06166725 |
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(1) Turbocharger compressor
(2) Turbocharger turbine (3) Diesel Exhaust Fluid (DEF) injectors (4) Clean Emissions Module (CEM) (5) Mixer (6) Selective Catalyst Reduction (SCR) (7) Exhaust out (8) Pump Electronic Tank Unit (PETU) (9) DEF pump 1 (10) DEF pump 2 (11) DEF Tank (12) Heating element (13) Coolant to and from the DEF injectors (14) Electrical connection (15) Coolant to and from the PETU (16) DEF fluid to DEF injectors (17) Ground fill system | |
Note: The tool to measure the DEF concentration is the 431-7087 Tool Gp (Refractometer (DEF)). Refer to Testing and Adjusting, "Diesel Exhaust Fluid Quality - Test" for additional information.
Selective Catalyst Reduction (SCR) refers to a method of treating engine exhaust to reduce the undesired oxides of nitrogen compounds (NOx). SCR uses a catalyst which promotes a desired chemical reaction over other possible chemical reactions. The catalyst remains unchanged. DEF is mixed into the exhaust, and reacts with the NOx in the presence of the catalyst to form harmless compounds (water and nitrogen). In this system, urea ((NH2)2CO) is injected into the exhaust, which quickly decomposes into ammonia under the heated conditions. Urea is used because urea is inexpensive, and does not need the special handling that ammonia requires.
DEF is an aqueous urea solution (urea salt dissolved in water).
A 32.5 percent (by weight) solution of DEF is required for the system.
A 32.5 percent concentration has the lowest freezing point possible,
A 32.5 percent concentration of urea keeps a constant concentration through freezing and thawing.
DEF must be stored below
Use only DEF that meets quality properties per ISO 22241-1. Using DEF that does not meet ISO 22241-1 can result in clogging of the injection nozzle.
DEF is a non-toxic source of ammonia.
DEF is corrosive. Do not store DEF in a tank or use supply lines that are made of the following materials: aluminum, brass, and steel. Use only corrosion resistant materials such as PVC or stainless steel. Any O-rings must be Ethylene Propylene Diene Monomer (EPDM).
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| Illustration 2 | g06166762 |
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(1) Inlet NOx sensor
(2) Urea injector (3) Diffuser plate (4) Catalyst brick (5) Outlet NOx sensor (6) Outlet temperature (7) Exhaust out (8) Miser (9) SCR catalyst inlet pressure sensor (10) Exhaust in (11) SCR catalyst inlet temperature sensor | |
The exhaust gas exits the engine and enters the mixing tube, where the DEF is injected into the exhaust stream.
The DEF decomposes into ammonia and carbon dioxide.
The mixture of exhaust and ammonia travels through the SCR.
The ammonia reacts with the NOx in the exhaust stream at the SCR catalyst to produce water vapor and nitrogen.
Pump Electronic Tank Unit (PETU)
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| Illustration 3 | g06168713 |
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(1) Coolant diverter valve
(2) Manual fill (3) Diesel Exhaust Fluid Control Unit (4) Ground level fill valve (5) Ground level fill hose (6) Selective Catalyst Reduction Controller (7) Drain plug (8) DEF header (9) DEF header (10) Back flow valve (11) DEF pump | |
CEM Identification Number Module
The identification number module outputs a 10 character alphanumeric serial number for the CEM to the Selective Catalytic Reduction System ECM.
The Selective Catalytic Reduction System ECM transmits this data to the engine ECM over the local CAN data link.
The engine ECM compares the first 3 letters of the serial number (the prefix) to a value programmed into the engine software.
The NOx sensor communicates to the Selective Catalytic Reduction System ECM over the CAN data link. The sensor has built-in diagnostics to indicate sensor failure modes.
The Selective Catalytic Reduction System ECM controls the power supply to the NOx sensors.
Aftertreatment #1 Intake NOx Sensor #1
The aftertreatment #1 intake NOx sensor #1 is monitored to control the DEF dosing rate based on engine out emissions levels.
Aftertreatment #2 Intake NOx Sensor #2
The aftertreatment #2 intake NOx sensor #2 is monitored to control the DEF dosing rate based on engine out emissions levels.
Aftertreatment #1 Outlet NOx Sensor #1
The aftertreatment #1 outlet NOx sensor #1 is monitored to control the DEF dosing rate based on catalyst out emissions. The Selective Catalytic Reduction System ECM monitors the sensor to calculate the necessary DEF flow rate to meet emission targets.
Aftertreatment #2 Outlet NOx Sensor #2
The aftertreatment #2 outlet NOx sensor #2 is monitored to control the DEF dosing rate based on catalyst out emissions. The Selective Catalytic Reduction System ECM monitors the sensor to calculate the necessary DEF flow rate to meet emission targets.
Aftertreatment #1 SCR Catalyst Intake Gas Temperature Sensor
The aftertreatment #1 SCR catalyst intake gas temperature sensor is monitored for dosing control and system protection.
The temperature indicates the capability of the Selective Catalytic Reduction System ECM to calculate the DEF dosing rates. The temperature is monitored to indicate temperatures that are too low or too high.
Aftertreatment #1 SCR Catalyst Outlet Gas Temperature Sensor
The aftertreatment #1 SCR catalyst outlet gas temperature sensor is also monitored for dosing control and system protection.
The temperature indicates the capability of the SCR system to calculate the DEF dosing rates. The temperature is monitored to indicate temperatures that are too low or too high.
The Selective Catalytic Reduction System ECM monitors the sensor for system protection. The pressure is monitored to indicate pressures that are too low or too high.
The pressure is measured at the inlet to the CEM. A pressure that is too high can indicate a restriction in the CEM exhaust stream. A pressure that is too low could indicate missing SCR catalyst bricks, or a sensor that has been removed from the exhaust stream.