Blue Bird VISION 2011, Руководство водителя

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VISION
D R I V E R S H A N D B O O K
104
• 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 fire extinguisher nearby.
• Check exhaust system surfaces to confirm 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 off 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
The Selective Catalytic Reduction (SCR) system uses diesel exhaust fluid (DEF) as a
chemical reactant. The DEF converts to ammonia in the exhaust stream. This ammo-
nia reacts with NOx over a catalyst to form harnless nitrogen gas and water.
In an SCR system, the rate at which DEF is sprayed must be tightly controlled. If
the rate is too high, not all of the ammonia will react with the NOx and some ammo-
nia will “slip” through the catalyst. If the rate is too low, the desired NOx reduction will
not be achieved. Both situations are undesirable and must be avoided.
The DEF-SCR system basically consists of three elements:
scr catalyst. The catalyst is mounted in the exhaust stream. It is similar in outward
appearance to a small muffler. It contains chemical compounds which, in the pres-
ence of ammonia, help transform nitrogen oxides into harmless nitrogen and water.
deF dosing system. The DEF dosing system and the decomposition reactor spray a
fine mist of DEF under all environmental conditions. The DEF amount has to be care-
fully controlled so that the availability of ammonia is closely matched to the amount
of NOx being produced by the engine in real time.