Abstract: An experimental and model-based study of the effect of rich air/fuel ratios (AFRs) and temperature on the NO_x slip of a lean NO_x trap (LNT) was conducted in a lean-burn gasoline engine with an LNT after-treatment system. The emissions of the engine test bench and the inlet temperature of the LNT were used as the major inlet boundary conditions of the LNT. The engine periodically operated between a constant lean AFR of 23 with alterable rich AFRs of 10, 11, 12, 13, and 14. A decrease in the rich AFR of the engine strengthened the desorption atmosphere in the LNT, an effect closely related to the number of reductants, and further heightened the NO_x desorption of the LNT, but with a penalty in fuel consumption. To eliminate that penalty, the inlet boundary conditions of the LNT were varied by adjusting the inlet temperature within a range between 200 °C and 400 °C. An increase in inlet temperature heightened the NO_x desorption of the LNT, and a NO_x breakthrough occurred after the inlet temperature exceeded 390 °C. To control NO_x breakthrough, the inlet temperature can be adjusted to offset the strong desorption atmosphere in the LNT commonly created by a rich AFR.

Key words: Lean NO_x trap (LNT), Air/fuel ratio (AFR), Temperature, NO_x adsorption, NO_x desorption

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