Exhaust emission control system and method for internal combustion engines

摘要

An NO_x storage-and-reduction type catalyst is used which exhibits a saturated NO_x storage amount of 5 g or more as NO₂ with respect to 1 liter of a catalyst volume at 500° C., and rich spiking is controlled so that an actual NO_x storage amount of the NO_x storage-and-reduction type catalyst becomes 50% or less of the saturated NO_x storage amount. Since the saturated NO_x storage amount is large, the NO_x storage amount is large even when it is 50% or less, it is possible to prolong intervals of the rich spiking. Then, since NO_x storage component stores NO_x preferentially into the sites which are likely to store and release NO_x, a reduction efficiency is high. Therefore, while prolonging the intervals of the rich spiking and sustaining an effect of mileage improvement, it is possible to improve the reduction efficiency of NO_x.