Advanced NOx Aftertreatment System Performance Following 150 LNT Desulfation Events

An advanced exhaust aftertreatment system is being developed using a fuel dosing system, mixing elements, fuel reformer, lean NOx trap (LNT), diesel particulate filter (DPF) and a selective catalytic reduction (SCR) catalyst arranged in series for both on- and off- highway diesel engines to meet the upcoming emissions regulations. This system utilizes a fuel reformer 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 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 LNT and SCR catalyst degradation as these were subjected to 150 desulfation events using a pre-production 2007 medium heavy-duty, on-highway diesel engine. Catalyst performance was characterized at six engine operating conditions (B50, A50, A100, B100, C75 and C35) to quantify catalyst degradation. Results indicate that there was no apparent degradation on the fuel reformer catalyst. LNT catalyst performance stabilized by 100 desulfation cycles at medium load operating conditions and by 30 desulfation cycles at high load operating conditions. Testing results showed very good temperature control at any single thermocouple location during desulfation; however, more work is needed to reduce the radial temperature spread.