Robustness of a LNT-SCR System to Aging Protocol 2007-01-0469
Experiments were conducted to determine the effect of accelerated aging on LNT-SCR system performance. The systems were aged and evaluated on an engine dynamometer using a DW12 2.2L I4 Diesel. The aging consisted of three modes, including sulfur exposure, desulfation (deSOx), and DPF regeneration conditions. Two systems were aged using different desulfation protocols and then evaluated over steady-state cycling conditions. The sulfur release characteristics were measured.
Overall system gross NOx conversion was robust to the aging protocol; however, there were significant differences in the individual component performance depending on the nature of the aging conditions. LNT NOx conversion was significantly lower for the case where maximum temperatures reached only 730°C, as opposed to the more severe aging where temperatures reached 800°C. NOx conversion over the SCR was higher for the 730°C maximum temperature aging, resulting in nearly equal overall system gross NOx conversion for the two systems.
Possible reasons for the differences in component performance are examined, including precious metal sintering on the DOC and LNT, HC and sulfur poisoning of the catalysts, and catalyst feedgas composition that resulted from the different aging protocols.
