SPRING 6F6677 - Caterpillar

Retrofit SCR System
The Retrofit SCR System must have the following components:
Diesel Oxidation Catalyst (DOC) or Diesel Particulate Filter (DPF)
SCR catalyst
Pre/Post NOx sensors
Mixing section
Dosing cabinetEngine exhaust flows into the Retrofit SCR System reactor housing through the exhaust inlet. Exhaust flows through the DOC or DPF. Once sufficient exhaust temperature is reached, and a boost signal indicating engine load is present, DEF is injected into the exhaust stream. Exhaust and DEF flow through a series of stationary fans to ensure a uniform mixture is disbursed across the SCR catalyst section. Precise DEF injection is monitored and controlled by an electronic controller in the dosing cabinet. The following components provide signals to the controller to control DEF injection for emission reduction:
Boost pressure sensor located in the inlet manifold.
Thermocouple located in the reactor housing.
Post NOx sensor located in the outlet of the reactor.
Pre NOx sensor installed in the inlet to the reactor.
Illustration 1 g03669976
Aftertreatment system components (1) Catalyst housing (2) Exhaust outlet (Not supplied) (3) NOx Sensor outlet (4) Back pressure sensor (5) NOx Sensor inlet (6) DEF injection lance (7) DEF supply from dosing control cabinet (8) Air supply from dosing control cabinet (9) Exhaust gas temperature sensor (10) Tube assembly (11) Cable assembly (12) Dosing control cabinet (13) Ball valves (14) Air supply to dosing control cabinet (Not supplied) (15) DEF supply to dosing control cabinet (16) Air source (May be supplied) (17) Air coalescing filter (May be supplied) (18) DEF tank (Not supplied) (19) DEF tank vent (Not supplied) (20) DEF tank fill pipe (Not supplied)Machine Operating Temperature Range
The standard system configuration begins DEF dosing and NOx reduction at an exhaust temperature of 300° C (572° F) within the reactor housing. Optimal NOx reduction occurs above 350° C (662° F). Maximum allowable exhaust temperature is 550° C (1022° F). Special configurations for different exhaust temperatures or operating conditions may be available. Consult your Cat dealer for additional information on special configurations of your SCR system.Reactor Housing
Illustration 2 g03669980
The reactor housing contains a NOx sensor located on the inlet and outlet piping. These sensors communicate values to the SCR Controller for DEF management. The values can be viewed by use of a computer interfaced with SCR Controller. Refer to this Operation and Maintenance Manual, "Model Views" sensor location diagram for the correct location of the sensors. Control of the SCR system requires six inputs that are external to the SCR Controller.
Boost pressure sensor
Boost temperature sensor
Exhaust back pressure sensor
Exhaust temperature sensor
Pre NOx sensor
Post NOx sensorDiesel Oxidation Catalyst
Illustration 3 g03398644
Flow through substrate used for diesel oxidation catalystsThe Diesel Oxidation Catalyst (DOC) oxidizes hydrocarbons contained in the exhaust gas. The DOC is a flow-through device. A chemical reaction takes place that reduces the amount of hydrocarbons and carbon monoxide when the exhaust gas flows through the cells that are coated with precious metals located within the DOC.The temperature of the exhaust is an important factor to activate the catalyst. Below 200° C (392° F) little to no catalyst activity is occurring. This means that emissions from