Optimization of purge air-to-fuel ratio profiles for enhanced Lean NOx Trap control

Lean NOx Traps (LNT), as a critical aftertreatment device for lean burn engines, require active control to manage its storage and purge cycles. In this paper, optimal air-to-fuel ratio profiles are pursued in LNT operation cycles with focus on the purge phase in which the stored NOx is neutralized by a rich air-to-fuel ratio mixture. It is shown that allowing the AFR to vary during the purge phase can provide a substantial leverage in improving LNT performance, in comparison to the fixed AFR purge strategy. Our findings also demonstrate a fundamental trade-off between the NOx and HC emissions and the fuel consumption with different purge AFR profiles.