3-Way Catalyst Conversion Efficiency
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A TWC requires a stoichiometric fuel ratio, 14.7 pounds of air to one pound of fuel (14.7:1), for high conversion efficiency. In order to achieve these high efficiencies, air/fuel ratio must be tightly controlled with a narrow window of stoichiometry. Deviations outside of this window will greatly decrease conversion efficiency. See Fig 1. For example, a RICH mixture will decrease HC and CO conversion efficiency, while a LEAN mixture will decrease NOx conversion efficiency.
