Stoichiometry and Catalyst Efficiency

The accompanying graph represents the efficiency of a three-way catalyst system at varying air/fuel ratios. As the graph clearly shows, the catalyst is most efficient in a narrow air/fuel ratio range.

The theoretical or ideal air/fuel ratio at which all tail pipe emissions are best converted is referred to as stoichiometry. The stoichiometric air/fuel ratio occurs around 14.7 to 1 (14.7 pounds of air for each pound of fuel).

It is important to note that the primary reason for using a closed loop fuel control system is to satisfy the requirements of the three-way catalyst system.

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Air/Fuel

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Richer --- Leaner

Air/Fuel Ratio

Richer --- Leaner

Air/Fuel Ratio

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