Lean NOx trap desulfation process

1. A process for desulfation of a NOx adsorber in an internal combustion engine exhaust system, said process comprising an active phase including:

determining an amount of post fuel (Q 2 ) required to reach a rich target exhaust air fuel ratio (AFR rich ) on the basis of a measured air flow;

determining a heating-contributing fuel value (ηQ 2 ) required to reach or maintain a target desulfation temperature in said NOx adsorber by way of an exothermal reaction;

calculating a target air flow (Air tgt ) corresponding to an air flow required for a stoichiometric combustion of a torque-contributing main fuel quantity (Q 1 ) together with said heating-contributing fuel value (ηQ 2 );

causing the engine to inject said post fuel amount (Q 2 ) and said main fuel quantity (Q 1 ) while controlling the air flow to meet said target air flow (Air tgt ).

2. The process according to claim 1 , wherein said NOx adsorber has an associated oxidation catalyst function.

3. The process according to claim 2 , wherein said heating-contributing fuel value (ηQ 2 ) is determined with respect to the exothermal reaction occurring in said associated oxidation catalyst function.

4. The process according to claim 2 , wherein said heating-contributing fuel value is determined based on a steady state model of said NOx adsorber with associated oxidation catalytic function.

5. The process according to claim 2 , wherein the NOx adsorber and the associated oxidation catalyst function are combined in a single housing.

6. The process according to claim 1 , wherein said target air flow is controlled by adjusting one or more of a throttle valve position, a boost pressure or a position of an exhaust gas recirculation valve.

7. The process according to claim 1 , wherein said process further comprises enabling said process when an estimator of the sulfur mass trapped in the NOx adsorber exceeds a predefined threshold or when the observed NOx efficiency is too low.

8. The process according to claim 1 , wherein said active phase is operated in a predetermined engine speed range and a predetermined load range.

9. The process according to claim 8 , wherein said predetermined engine speed range is 1,200 to 2,500 rpm.

10. The process according to claim 8 , wherein said predetermined load range is 20% to 50% of maximum engine torque.

11. The process according to claim 1 , wherein an exhaust air-fuel ratio is monitored in closed loop by means of an oxygen sensor located downstream of the NOx adsorber and the post fuel amount is adapted when the monitored air-fuel ratio deviates from the rich target exhaust air fuel ratio (AFR rich ).

12. The process according to claim 1 , wherein said process further comprises a heat-up phase, prior to said active phase, wherein the post fuel amount is controlled to bring the NOx adsorber to a predetermined desulfation temperature range.

13. The process according to claim 1 , wherein said active phase is disabled in case the temperature of the NOx adsorber exits a desulfation temperature range and/or the engine load and/or speed exit(s) predetermined ranges.

14. The process according to claim 1 , wherein said process further comprises disabling said process is based on the status of a desulfation indicator.