Exhaust After Treatment System - Volvo 9700 Manual

Exhaust after treatment system

System description
Exhaust gases go through the silencer,
(1) it integrates a diesel oxidation
catalyst (DOC) (2) which oxidises carbon
monoxide and hydrocarbon, generates
heat for the active regeneration and
creates a favourable gas composition for
the selective catalytic reduction (SCR)
catalyst.
Then exhaust gases pass further through
the diesel particulate filter (DPF) (3)
which removes particles. Before the SCR
catalyst, the urea solution is sprayed (via
a nozzle) and mixed with exhaust gases
in the mixing chamber (4). The heat
decomposes urea into ammonia and
carbon dioxide.
As the mixture passes through the SCR
catalyst (5), nitrogen oxide is converted
into harmless nitrogen and steam.
Before exhaust gases leave the silencer
they pass through the ammonia slip
catalyst (ASC) (6), where any residual
ammonia oxidation is eliminated.
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