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EMISSION CONTROL SYSTEM*
Functional description
The e m i s s i o n control s y s t e m effectively
r e d u c e s the amount of pollutants in the
exhaust gas. The s y s t e m is so d e s i g n e d
that it requires no additional mainten-
a n c e . With normal vehicle use, no s p e -
cial operating instructions need be ob-
s e r v e d - apart from filling the tank with
leadfree petrol. Only in certain e x c e p -
tional c a s e s is it n e c e s s a r y , for safety
reasons, to note a few points - s e e
page 83.
The main parts of the e m i s s i o n control
s y s t e m are
an electronically controlled fuel me-
tering s y s t e m (fuel injection)
the catalyst
the L a m b d a probe
The catalyst is installed in the exhaust
pipe. It c o n s i s t s of a s t e e l - c a s e d c e r a m i c
body containing a multitude of longitu-
dinal p a s s a g e s which are vapour c o a t e d
with a thin layer of platinum or rhodium.
The exhaust gas flows through the c a t a -
lyst and reacts with an afterburning pro-
c e s s w h e n it c o n t a c t s the noble metal
coating. In this p r o c e s s the c a r b o n m o -
noxide and h y d r o c a r b o n s are c o n v e r t e d
to harmless c a r b o n dioxide and water
and the o x i d e s of nitrogen are c o n v e r t e d
to nitrogen
(four fifths of the air w e
breathe is nitrogen).
A stipulation for the proper functioning
of the catalyst, however, is that the
exhaust gas has a certain specific c o m -
position and minimum temperature w h e n
it enters the catalyst. To obtain
this
c o m p o s i t i o n e x a c t regulation of the fuel/
air mixture is required. O n vehicles w h i c h
are fitted at the factory with a e m i s s i o n
control s y s t e m this is d o n e with the aid
of a L a m b d a probe.
The L a m b d a probe is fitted in the ex-
haust pipe in front of the catalyst and
m e a s u r e s the exhaust gas c o m p o s i t i o n
continuously. The information signal is
fed to an electronic control unit w h i c h
in turn regulates the fuel injection s y s -
tem s o that the mixture is kept c o n -
stantly correct.
106
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