Marine Selective Catalytic Reduction (SCR) Retrofit Aftertreatment Caterpillar

Retrofit SCR System

The Retrofit Selective Catalytic Reduction (SCR) System may have the following components:

Common Arrangement Identification Number

Illustration 1	g06145370

As supplied from the factory, the dosing cabinet and CEM are serialized together under one product Common Arrangement - AFTM.

When installed, the Common Arrangement - AFTM serial number of the CEM and of the Dosing Cabinet must match. If the two components are not paired correctly, a fault code will be activated.

The Common Arrangement - AFTM serial number can be found on the CEM to the left of the SCR catalyst access hatch. The corresponding Common Arrangement - AFTM dosing cabinet-mounted serial number plate is just off center of the dosing cabinets front connection face. The Common Arrangement - AFTM Part Number, Serial Number, and Config Group must all match in order that the system work correctly. If the labels do not match, contact your dealer for assistance.

Note: The Common Arrangement 8-digit Serial number should be referenced when contacting your Caterpillar dealer for service in addition to the engine serial number. This action will indicate to the Caterpillar dealer that there is an aftertreatment unit installed in addition to the engine. There may be other serial numbers present on the CEM and dosing cabinet. For manufacturing use only and will most likely be 10 digits in length.

CEM Identification

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Typical location of the CEM identification plate. The identification plate is on top of the CEM housing. The specific location may be different depending on CEM configuration.

Selective Catalytic Reduction Substrate

Caterpillar offers two SCR catalyst formulations. (Vanadia Based and Copper Zeolite Based). Your Cat dealer can provide details on the type of catalyst being used in your application. Catalyst array size and Catalyst formulation are selected at the time of order to match the engine and emissions site requirements. The system requires liquid Diesel Exhaust Fluid (DEF) to be sprayed into the system and allowed to evaporate into water vapor and ammonia. The ammonia reacts with exhaust gas and catalyst to convert oxides of nitrogen to harmless water and nitrogen.

Aftertreatment System Description

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Caterpillar supplied aftertreatment components are illustrated with dashed line rectangles.

Selective Catalyst Reduction (SCR) catalyst technology is used to reduce NO_x emissions and particulate matter.

The aftertreatment system is composed of the following components:

• Air compressor

• Bulk Urea Transfer Pump

• DEF Dosing cabinet

• DEF Filter

• DEF Mixing tube

• DEF Nozzle

• DEF Supply tank

• SCR catalysts

• SCR reactor housing

Engine exhaust flows into the SCR System reactor housing through the exhaust inlet. Once sufficient temperature is achieved, the DEF is injected into the exhaust. Exhaust flows through a mixer assembly in the mixing tube to ensure that exhaust is not stratified for uniformity. This mixing will ensure complete disbursement across 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:

• Thermocouple located in the reactor housing.

• Inlet NO_x sensor located in the exhaust before the inlet to the SCR catalyst reactor housing.

• Outlet NO_x sensor located in the exhaust at the outlet of the SCR catalyst reactor housing.

When engine operating conditions dictate, DEF fluid is injected into the exhaust stream before entering the SCR. When injected into the exhaust stream, the DEF is atomized into droplets. The atomized droplets are then sent through the mixer. The mixer disrupts the exhaust flow and allows DEF to be distributed throughout the exhaust gas. Water evaporates due to the high temperature of the exhaust. This process will cause the DEF to decompose and release ammonia (NH₃) that was bound to the DEF. NH₃ is free to react with the NO_X and the oxygen present in the exhaust system stream. This reaction occurs on the SCR catalyst. NH₃ and NO_X are converted into gas particles of nitrogen and water. The inlet and outlet NO_X sensors read the levels of NO_X and determine how much DEF needs to be injected into the exhaust.

Dosing Cabinet

The dosing control cabinet controls the following:

• Rate of DEF flow to the injector

• Compressed air pressure

• Urea purges shut down cycle

The aftertreatment ECM located in the dosing cabinet and theCat ECM is designed to communicate with each other. This communication controls the complete engine/emission system to meet emission levels.

DEF Tank

There are two separate DEF tanks in the dosing system.

• DEF tank 1 is the customer installed DEF tank. DEF tank 1 is the bulk DEF tank. A DEF high and low-level switch in tank 1 will notify the operator when the tank requires refilling.

• DEF tank 2 is the buffer tank located in the dosing cabinet. Tank 2 is a small DEF tank that is filled from DEF tank 1. Tank 2 provides DEF to the DEF pump to be injected into the exhaust.

Reactor Housing

The reactor housing contains the following:

• SCR catalyst substrates

• DEF nozzle

• DEF mixing tube

• SCR catalyst temperature and pressure sensors

• NO_x sensors

The aftertreatment ECM uses the sensors on the module to determine how much DEF needs to be injected into the exhaust system.

Selective Catalytic Reduction Substrate

The Selective Catalyst Reduction (SCR) substrates are located in the reactor housing. These catalysts allow exhaust to flow through the substrate converting the NO_x into N2 and H20.

The exact chemical formulation of the catalyst has been engineered for this engine to provide optimal system performance and durability.