Regeneration Strategies for NOx Adsorber Catalysts

The successful commercialization of lean burn gasoline engines is dependent upon development of an effective emission aftertreatment system which can provide HC, CO, and NOx control not only under lean operating conditions, but also when the engine operates at the stoichiometric point under conditions of high engine speed and/or load. NOx adsorber catalysts (NOx traps) are capable of storing NOx under lean condition, and subsequently releasing and catalyzing its reduction under conditions rich of the stoichiometric point. Aftertreatment systems based on these types of catalysts show great potential for reaching current and future emission standards. Key to the successful application of NOx adsorber catalysts is the development of engine control strategies which maximize NOx conversion while minimizing the fuel economy penalty associated with adsorber regeneration.

In this paper limitations associated with NOx trap adsorption and regeneration strategies are discussed. Results of synthetic gas and engine bench tests demonstrate relationships between adsorption conditions and NOx trap capacity, the richness and duration of the regenerative pulse, and HC, CO, and NOx conversion efficiencies. These results are then used as the basis for development of models of two extremes in regeneration strategy. Fuel economy penalties associated with each strategy are discussed.