5-14
Fundamentals
Figure 5-12
shows NO
x
versus air fuel ratio after being treated by
a three-way catalytic converter. NO
x
levels are typically low when
the air-fuel ratio is more rich than stoichiometric. When the air-fuel
ratio is near stoichiometric and more lean than stoichiometric, NO
x
levels increase, then fall to slightly lower values as the air-fuel
mixture continues to get leaner.
Catalytic converters oxidize HC, CO and NO
x
producing H
2
O, CO
2
and N
2
. Therefore, monitoring HC and CO does not give an
accurate picture of engine performance because the catalytic
converter alters these gases. Using the analyzer to monitor O
2
,
CO
2
, HC, CO and NO
x
provides a more accurate method of
monitoring engine operation on vehicles with a catalytic converter.
Figure 5-12
: NO
X
Vs. Air Fuel Ratio After Three-Way Converter Treatment
To Next Page
Loading...