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Typical example (1) Diesel Exhaust Fluid (DEF) injector (2) Diesel Oxidation Catalyst (DOC) (3) Exhaust inlet connection from turbocharger (4) Flexible exhaust pipe (5) Flexible exhaust pipe (OEM supply) (6) Selective Catalytic Reduction (SCR) system (7) Exhaust outlet connection | |
The Clean Emissions Module (CEM) for the engine consists of the following components.
- Diesel Oxidation Catalyst (DOC)
- Selective Catalytic Reduction (SCR) system
The DOC oxidizes the carbon monoxide and the hydrocarbons that are not burnt in the exhaust gas into carbon dioxide and water vapor. The DOC also acts on the oxides of nitrogen to increase the nitrogen dioxide fraction for improved efficiency of the SCR system. The DOC is a through flow device that will continue to operate during all normal engine operating conditions.
A flexible exhaust pipe connects the engine to the Clean Emissions Module (CEM). Refer to Disassembly and Assembly for the correct procedure to install the flexible exhaust pipe.
After the DOC, the exhaust gases are injected with a Diesel Exhaust Fluid (DEF) by a Diesel Exhaust Fluid (DEF) injector. The exhaust gases and the DEF are mixed in a mixing chamber. The mixture decomposes to form ammonia and carbon dioxide. The mixture passes to the main Selective Catalytic Reduction (SCR) reaction chamber.
Exhaust gases and an atomized mist of ammonia and carbon dioxide enter the SCR reaction chamber. Together with the SCR catalyst inside the chamber, the mixture undergoes a chemical reaction that produces nitrogen gas and water vapor.
There is an oxidation catalyst after the SCR catalyst. The oxidation catalyst reacts with the excess ammonia to produce oxides of nitrogen and water vapor.
Refer to Systems Operation, Testing and Adjusting, "DEF Dosing Control System" for more information on the DEF system.