Closed loop temperature control of a lean NOx trap during desulfation

The design of a temperature control system for a lean NO_x trap (LNT) during a desulfation event is described. Lean NO_x traps store NO_x during lean (fill) A/F operation and release harmless N₂ and O₂ during rich A/F (purge) operation. The presence of sulfur in the fuel poisons the LNT and reduces its NO_x storage capacity. The NO_x capacity can be restored through desulfation. The desulfation method used here involves sequential A/F ratio modulation of the engine cylinders. This process generates an exotherm in the LNT. The exotherm must be accurately controlled to avoid over temperature and damage to the LNT and under temperature to avoid ineffective desulfation. The control system described contains both feedforward and feedback elements. Values for the control parameters were determined through system identification