Performance of a Fuel Reformer, LNT and SCR Aftertreatment System Following 500 LNT Desulfation Events 2009-01-2835
An advanced exhaust aftertreatment system is characterized following end-of-life catalyst aging to meet final Tier 4 off-highway emission requirements. This system consists of a fuel dosing system, mixing elements, fuel reformer, lean NOx trap (LNT), diesel particulate filter (DPF), and a selective catalytic reduction (SCR) catalyst. The fuel reformer is used to generate hydrogen (H2) and carbon monoxide (CO) from injected diesel fuel. These reductants are used to regenerate and desulfate the LNT catalyst. NOx emissions are reduced using the combination of the LNT and SCR catalysts. During LNT regeneration, ammonia (NH3) is intentionally released from the LNT and stored on the downstream SCR catalyst to further reduce NOx that passed through the LNT catalyst. This paper addresses system durability as the catalysts were aged to 500 desulfation events using an off-highway diesel engine. Catalyst performance was characterized at three engine operating conditions to quantify catalyst durability. The LNT catalyst performance stabilized after 250 desulfation events. The downstream SCR catalyst yielded stable performance across all desulfation events. Results confirm that NOx conversions required for meeting final Tier 4 off-highway emissions are feasible with catalysts aged to the end of the emissions useful life using this fuel reformer, LNT and SCR based aftertreatment system.