5-8
Fundamentals
Carbon Dioxide (CO
2
)
CO
2
is a combustion product formed when one carbon atom bonds
with two oxygen atoms, and by the oxidation of CO in the catalytic
converter. Unlike CO, CO
2
is comparatively harmless.
CO
2
is a good indicator of combustion efficiency because its
volume in the exhaust peaks just before the stoichiometric air-fuel
ratio.
CO
2
peaks when the combustion chamber fuel mixture approaches
about 15:1, and decreases when the mixture becomes more lean
or more rich. CO
2
level is used to check exhaust system integrity,
since significant leaks lower CO
2
.
Figure 5-6
: Carbon Dioxide Versus Air-Fuel Ratio
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