BOLT 4M6424 - Caterpillar

The Caterpillar Clean Emissions Module (CEM) houses catalytic converters that treat exhaust gas from the engine.System Block Diagram
Illustration 1 g06077530
(1) Clean Emissions Module (CEM)
(2) Dosing control cabinet
(3) Diesel Exhaust Fluid (DEF) customer supply tank
(4) Compressed air supply
(5) Separate circuit aftercooler (SCAC)
(6) Air cleaner
(7) Turbocharger compressor
(8) Turbocharger turbine
(9) Mixing tube
(10) Selective Catalyst Reduction (SCR)
(11) Exhaust outDiesel Exhaust Fluid (DEF)
Note: Two tools are available to measure the DEF concentration. The two tools are the 431-7087 Tool Gp (Refractometer (DEF)) and the 360-0774 Refractometer (Brix). 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. Ammonia (NH3) 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 or 40 percent (by weight) solution of DEF is required for the system.A 32.5 percent concentration has the lowest freezing point possible, −11 °C (11 °F), for this solution.A 32.5 percent concentration of urea keeps a constant concentration through freezing and thawing.DEF must be stored below 50 °C (122 °F) to delay decomposition.Note: The customer is responsible for providing primary filtering of the DEF from the site tank to the buffer tank. The system requires a 40 micron primary filter.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.Refer to Operation and Maintenance Manual, "Maintenance Section" to obtain locations for DEF suppliers.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).Clean Emissions Module (CEM)
Z Style CEM
Illustration 2 g03776497
(1) Exhaust in
(2) Catalyst brick
(3) Service door
(4) Outlet mixer
(5) Exhaust out
(6) Flute
(7) Deflector plate
(8) Flapper mixer
(9) Swirl mixer
(10) Mixing tube
(11) Urea injectorU Style CEM
Illustration 3 g03776498
(1) Exhaust in
(2) Urea injector
(3) Mixing tube
(4) Swirl mixer
(5) Flapper mixer
(6) Service door
(7) Catalyst brick
(8) Outlet mixer
(9) Flute
(10) Exhaust outCEM Operation
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.Dosing Control Cabinet
Illustration 4 g03773465
(1) SCR controller
(2) Wiring harness connector to main DEF tank
(3) Wiring harness connector to CEM
(4)