Operation
9270−1/A1
Winterthur Gas & Diesel Ltd.
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2.6 SCR System − Stop and Vent (Tier II)
If the operation conditions are not in the limits, the SCR system can be set to off while
the engine operates. The SCR system automatically deactivates (see Fig. 8)
When SCR operation stops, valve V3 opens. Subsequently, valves V1 and V2 close
to isolate the SCR system. No exhaust gas can go through the SCR reactor.
Air between valves V1 and V2 is used to remove exhaust gas that flows through the
SCR reactor. This prevents exhaust gas condensation and thus corrosion in the SCR
reactor and pipes. The air, which flows for some minutes, moves the exhaust gas
through the exhaust pipe through valve V7. Subsequently, the SCR and the catalyst
system control activates and purges the urea solution pipe.
After valve V7 is closed during engine operation, the vent unit keeps air pressure in
the SCR reactor and pipe. This makes a seal against the exhaust gas.
You can manually activate the external heating unit of the SCR reactor if the engine
operates in Tier III mode. This helps to keep the SCR reactor temperature stable. The
external heating system helps to decrease the time necessary to increase the
temperature of the SCR reactor.
Engine
V1
V2
V3
V7
V4
Turbocharger
SCR Reactor
Air pipes − flow
Exhaust pipes − no flow
Exhaust pipes − flow
WCH03726
Fig. 8: SCR System − Stop and Vent
2016−11
Selective Catalytic Reduction System
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