1981 Emission Control Technology

The catalytic converters used on most 1981 model year vehicles fall into two general categories: three-way converters and dual-bed converters. (Some manufacturers employ dual converters. The distinction between dual-bed and dual converters is whether the two catalysts are housed in the same container or in separate containers.) Both contain a three-way catalyst, but with the dual-bed converter (and dual converter) the three-way catalyst is followed by an oxidation catalyst to provide increased oxidation capability. Supplemental air is added to the exhaust ahead of the oxidation catalyst. The pellet type dual-bed catalytic converter used by General Motors is shown in Figure 2. Both the three-way catalyst and oxidation catalyst are enclosed in the same converter, separated by the air plenum. Operation of the three-way catalyst requires that the exhaust A/F be controlled close to the stoichiometric composition. A diagram which illustrates the relationship between conversion efficiency and A/F for the two converter types is presented in Figure 3. A closed-loop feed-back control system holds the A/F in a narrow region near stoichiometry.