Method and device for periodically desulphating a nitrogen oxide or sulphur oxide storage vessel with rich/lean engine cylinder distribution

A device for periodically desulphating at least one of a nitrogen oxide storage vessel and a sulphur oxide storage vessel of an exhaust emission cleaning system of a multi-cylinder internal combustion engine, comprising:

• a common throttle valve for all the cylinders;
• and
• a control arrangement for feeding an engine exhaust emission containing a reducing agent and oxygen to the at least one of the nitrogen oxide storage vessel and the sulphur oxide storage vessel during a desulphation period, the control arrangement setting a first rich fuel/air ratio for a first subset of the engine cylinders and setting a second leaner fuel/air ratio for a second, remaining subset of the engine cylinders, the control arrangement controlling the quantity of fuel injected for the first subset of the engine cylinders according to a first manner and controlling the quantity of fuel injected for the second subset of the engine cylinders according to a second manner different from the first manner;
• wherein during an initial storage vessel heating-up phase, the control arrangement sets a difference between the first rich fuel/air ratio and the second leaner fuel/air ratio to a first level;
• and
• wherein after a predefined desulphation temperature is reached, the control arrangement sets the difference between the first rich fuel/air ratio and the second leaner fuel/air ratio to a second level, the second level being lower than the first level.