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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.

This paper reports on the development of a new methodology for OBD-II catalyst efficiency monitoring. Temperature measurements taken from the center of the catalyst substrate or near the exterior surface of the catalyst brick were used in conjunction with macroscopic energy balances to calculate the instantaneous rate of exothermic energy generation within the catalyst. The total calculated rate of exothermic energy release over the FTP test cycle was within 10% of the actual or theoretical value and provided a good indicator of catalyst light-off for a variety of aged catalytic converters. Normalization of the rate of exothermic energy release in the front section of the converter by the mass flow rate of air inducted through the engine was found to provide a simple yet practical means of monitoring the converter under both FTP and varying types of road driving.