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	Graph showing LNT performance degradation after 20 fast aging cycles
	LNT NOx adsorption capacity evaluation results

To evaluate the effect of aged lean NOx trap (LNT) on emissions, an accelerated aging cycle consisting of sulfur loading and desulfation processes is needed. Southwest Research Institute (SwRI) researched fast lean/rich switching to achieve LNT desulfation.

Approach

Sulfur loading on LNT can deactivate LNT NOx adsorption capacity. A desulfation process can release sulfur from LNT and restore the NOx adsorption capacity. Desulfation requires a high temperature exhaust (e.g., 650°C) and rich A/F ratio condition.

However, the high desulfation temperature may cause severe thermal degradation of LNT performance. Due to the sulfur poisoning and thermal degradation, durability becomes a major concern for LNT application.

To evaluate LNT durability, an accelerated aging cycle was developed to age a selected LNT to the end useful life condition (120,000 miles—Tier II, Bin 5) in a short time. The cycle consisted of fast sulfur loading and desulfation. Before and after each desulfation, LNT NOx adsorption capacities were evaluated, respectively. The capacity evaluation method is shown in the lower right figure.

Before the evaluation, NOx adsorped in LNT was fully purged with rich LTC combustion. Then, engine operation condition was changed to conventional diesel combustion with an engine-out NOx around 600ppm and LNT catalyst temperature about 300°C .

Outcome

The capacities were evaluated by comparisons between tailpipe and engine-out NOx at levels of 20, 100, and 200 ppm. The upper right figure shows the comparison of LNT performance between a fresh LNT and an aged LNT.

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Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

December 28, 2012