System for assisting the regeneration of an exhaust gas purifying device

The system has a sensor (11) that determines dilution level of a lubricating oil of an engine, and a monitoring unit (12) that monitors increase in dilution level. The unit changes the operation of the engine into degraded rich mode, when the level reaches a high dilution threshold. The unit changes the operation of the engine into nominal rich mode, when the level reaches a low dilution threshold.