EMISSION
CONTROL SYSTEM*
•CHNICAL
DESCRIPTION
Functional
description
The
emission control system effectively
reduces
the amount of pollutants in the
exhaust gas. The system is so designed
that
it requires no additional mainte-
nance.
With normal vehicle use, no
spe-
cial
operating instructions need be ob-
served
- apart from filling the tank
with
lead-free petrol. Only in certain excep-
tional
cases
is it necessary, for safety
reasons,
to note a few points - see page
90.
The
main parts of the emission control
system
are
• A mixture formation system which
guarantees very exact composition of
the air/petrol mixture at all engine speeds
• the catalytic converter
• the Lambda probe1
>
11 Lambda = Air/petrol relationship
The
catalytic converter is installed in the
exhaust pipe. It is a so-called three-way
catalytic converter and consists of a
steel-
cased
ceramic body containing a multi-
tude of longitudinal
passages
which are
vapour coated
with
a
thin
layer of platinum
or rhodium.
The
exhaust gas flows through the
catalytic converter and reacts
with
an af-
terburning process when it contacts the
noble metal coating. In this process
three pollutants (three-way catalytic
converter) are converted to harmless
substances
as follows
• Carbon monoxide to carbon dioxide
• Hydrocarbons to water
• Nitrogen oxide to nitrogen
(four
fifths
of the air we breathe is nitrogen).
A
stipulation for the proper functioning
of the catalytic converter, however, is
that
the exhaust gas has a certain
spe-
cific
composition and minimum tempera-
ture
when it enters the catalytic
con-
verter. To obtain this composition exact
regulation of the fuel/air mixture is
required.
A very exact regulation is
obtained on vehicles which are
fitted
at
the factory
with
a Lambda probe11.
117
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