This exhaust aftertreatment system is applied to direct injection engines (leanburn engines). During the lean operation of the engine, the NOx emissions are adsorbed on the NOx trap catalyst. The loading level is monitored by the NOx sensor.

If the NOx loading level increases, less NOx absorbs at the catalyst. This means that the passing NOx increases. If a certain threshold of detected NOx emissions is exceeded, the regeneration phase starts. The engine combustion conditions change from lean burn to rich air/fuel-ratio conditioned and the NOx trap catalyst is regenerated. The engine is then operated again under lean air/fuel-ratio conditions.