Blue Bird D3RE 2014 - SCR System in Blue Bird Buses

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ROUTINE OPERATION
 • Securetheexhaustarea.
 •Ifbystanders mightenterthe area,set up barrierstokeep people
safely away from the exhaust outlet.
 •Iftheprocedureisperformedindoorsataservicefacility,attachan
exhaust discharge pipe rated for at least 1500°F.
 •Keepareextinguishernearby.
 • Checkexhaustsystemsurfacestoconrmthatnotools,rags,grease,debrisor
any other objects are on or near the exhaust system.
 • Starttheengine.
 • OperatetheRegenerationSwitchtobegintheregenerationprocess.
 • Monitortheprocess.Ifanyunsafeconditionoccurs,shutotheengineimme-
diately. During the regeneration process, the engine may change speed, and
the turbocharger may whistle. When the process is complete, the engine will
return to normal idle speed. Exhaust gas and exhaust surface temperatures
will remain elevated until they have had time to cool to normal levels.
SCR System in Blue Bird Buses
Selective Catalytic Reduction (SCR) is a Nitrous Oxide control technique for diesel
engine exhaust. The SCR system uses Diesel Exhaust Fluid (DEF) a nitrogenous com-
pound which readily decomposes into ammonia. The system process involves the
injection of DEF into the exhaust over a catalyst. The DEF converts to ammonia in the
exhaust stream. This ammonia then reacts with NOx and produces harmless nitrogen
(N) and water (HO).
The DEF-SCR system basically consists of three elements:
SCR Catalyst. The SCR is located in the exhaust stream rear of the Decomposition Re-
actor. It is similar in outward appearance to a small muffler. The device is comprised
of a canister containing the SCR catalyst which uses the amonia contained in the in-
jected DEF to react with NOx. This reaction is temperature dependent and transforms
the NOx into harmless nitrogen gas and water.