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Engine and aftertreatment models have been developed in support of gasoline direct injection (GDI) engine development and aftertreatment system design. A brief overview of the engine models that were used to project emissions and fuel economy performance for the GDI engine is presented. Additionally, the construction and validation of a NOx trap aftertreatment model is described in considerable detail. The insights and increased understanding which have been gained regarding the trade-offs between engine out emission targets, aftertreatment performance, and emission constrained fuel economy benefits for direct injection gasoline engines are reviewed and discussed.

Lean NOx traps were tested under various laboratory and engine dynamometer conditions to assess the effects of sulfur, temperature, and other exhaust gas parameters on their NOx efficiency and durability. Most recent vendor supplied NOx trap materials have shown significant temperature durability improvements, but sulfur tolerance has remained unchanged. Trap samples were subjected to sulfur poisoning and were desoxed at high temperatures and at various air to fuel ratios. It was found that a simple sulfate model of sulfur interaction with the NOx trapping specie is not sufficient to explain the sulfur interactions observed.

An improved process for determining oven aging times and temperatures for OBD-II threshold catalyst aging has been developed. The new process makes use of a catalyst model along with a kinetic data base in order to project vehicle tailpipe emissions for oven aged catalyst systems. The catalyst oven aging time and temperature required for a given vehicle can be specified such that the actual HC tailpipe emissions are within 15-20% of the desired threshold emission level. It is believed that this process could greatly reduce the need for much of the trial and error iteration which is currently associated with obtaining threshold catalysts for OBD-II calibration purposes.