This paper presents an after-treatment architecture combining a close coupled NOx trap and an under floor NOx trap. Instead of simply increasing the volume of the catalyst, we propose to broaden the active temperature window by splitting the LNT along the exhaust line.
In order to design this architecture, a complete 1D model of NOx trap has been developed. Validated with respect to experimental data, this model has been useful to define the two volumes of LNT, making significant savings on the test bench exploitation.
However, one of the main difficulties to operate the proposed architecture is the NOx purge and sulfur poisoning management. In order to optimize the NOx and sulfur purge launches, we have developed a control strategy based on an embedded reduced LNT model. These strategies have been validated on different driving cycles, by the means of simulation and of vehicle tests using rapid prototyping tools.
Finally, the architecture has reached the target of 70% NOx efficiency on NEDC cycle while respecting the specifications on the penalty associated with NOx purge (fuel consumption, oil change interval and acoustics constraints). Moreover, we have proved that it is possible to use NOx trap in highly transient conditions, showing that this LNT architecture could be also a good challenger of classical SCR technology for heavy applications.