Browse Publications Technical Papers 2007-24-0106
2007-09-16

Control-Oriented Modeling of NOx Aftertreatment Systems 2007-24-0106

The Lean NOx Trap (LNT) is an aftertreatment device used to attain a reduction in nitrogen oxide emissions for Diesel and lean burn engines. The LNT is typically used as a storage device, capturing NOx during lean engine operation. The trap can be regenerated by controlling the exhaust air-fuel ratio to create a rich gas mixture. Under rich conditions, the stored NOx is released and catalytically converted. This way, tailpipe emissions can be significantly reduced by properly modulating the lean (storage) and rich (regeneration) periods.
To maintain the LNT operate with high conversion efficiency, an optimized control of the regeneration scheduling is required. In addition, LNT systems require fault diagnostic schemes to detect and isolate failures, typically related to sulphur and thermal damages.
The paper presents a control-oriented model of a Lean NOx Trap which captures the most relevant phenomena driving the storage and regeneration dynamics. In addition, the model includes a simplified characterization of the LNT fault modes.
The model is experimentally validated from data collected on a Diesel LNT system and integrated with a quasi-steady engine and vehicle simulator to estimate tailpipe emissions during driving cycles.

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