Fundamentals
5-7
Carbon Monoxide (CO)
CO is an exhaust by-product formed when combustion occurs with
less than the ideal volume of oxygen (rich fuel mixture). This
combines a carbon atom with an oxygen atom. Carbon in the
combustion chamber comes from the HC fuel, and oxygen from
inducted air.
When the fuel mixture in the combustion chamber is richer,
meaning more HC and less air, the concentration of CO in the
exhaust is higher. Therefore, anything causing a rich air-fuel ratio
results in high CO concentrations in the exhaust.
Figure 5-5
shows that the CO level decreases as the air-fuel ratio
approaches about 15:1, and maintains this low level even while the
mixture is further leaned out. Because of this, CO is a good
indicator of fuel mixture richness, but a poor indicator of leanness.
This makes the HC and CO content in the exhaust a good measure
of engine performance, besides being important for compliance
with clean air laws.
Figure 5-5
: Carbon Monoxide Versus Air-Fuel Ratio
To Next Page
Loading...