NOx release index

Method of monitoring the adsorptive capacity of a NOX adsorber of an internal combustion engine, comprising the following steps: 1) identification of O2 moles released from the adsorber during rich pulse regeneration, 2) calculation of NO2 moles released during rich pulse regeneration using the value from step 1 in a release model based on lambda deviation across the adsorber and the release chemistry of NO2 from said adsorber 3) optional storage of successive results of steps 1 and 2 4) use of the results of step 2 and/or 3 to update an adaptative capacity model to control the duration of the lean phase and/or of the rich pulse.