The aim of the present work is to analyse and compare the energetic performances and the emissions conversion capability of active and passive aftertreatment systems for lean burn engines. To this purpose, a computational one-dimensional transient model has been developed and validated. The code permits to assess the heat exchange between the solid and the exhaust gas, to evaluate the conversion of the main engine pollutants, and to estimate the energy effectiveness.The response of the systems to variations in engine operating conditions have been investigated considering standard emission test cycles.The analysis highlighted that the active flow control tends to increase the thermal inertia of the apparatus and then it appears more suitable to maintain higher temperature level and to guarantee higher pollutants conversion at low engine loads after long full load operation. Conversely, the unidirectional flow is preferable when a rapid heating (i.e., cold start, warm up phase, etc.) is required. Depending on the engine load and the requested converter thermal level, the coupled operation of active and passive flow represents the possible strategy apt to improve the system performances.