SwRI IRD 2003--Protection of Aftertreatment Systems from Sulfur, PASS 2™ - Advanced System Design Evaluation, 08-9358

Protection of Aftertreatment Systems from Sulfur, PASS 2™ - Advanced System Design Evaluation, 08-9358

Background - Recent developments in diesel aftertreatment systems have led to a number of important technologies. These technologies, while critical to meeting future diesel engine emissions legislation requirements, are easily deactivated by sulfur in the exhaust gas resulting from sulfur in the fuel and oil. Despite future diesel fuel sulfur levels below 15 ppm, the technologies are still sensitive to even small levels of sulfur. The authors conceived the original PASS system that is now covered by two U.S. patents. That system used an in-exhaust bypass line and valve arrangement that were system complexities unattractive to industry.

For this work, the authors conceived of a different system design that dramatically simplifies the PASS system, making it more commercially practical. It works on the principle that sulfur passing through the aftertreatment system under reducing conditions will not adversely interact with it. This SwRI Internal Research and Development program was performed to evaluate the effectiveness of the advanced system design.

Approach - A Cummins ISB, in-line, 6-cylinder diesel engine was selected for this project. A Lean NO_xTrap (LNT) was selected as the sulfur-sensitive emissions reduction device. A Lean Sulfur Trap (LST) was formulated, prepared, and installed between the engine and the LNT. A Rich Sulfur Trap (RST) was formulated, prepared, and installed downstream of the LNT. The LNT was exposed to high sulfur fuel to measure the time to deactivation. Then the LST was installed, and the experiment repeated to determine how much longer the LNT functioned with the LST protection. Finally, the LST was regenerated on-line to determine if the high sulfur levels emitted during regeneration would pass through the LNT without adversely effecting its performance.

Accomplishments - The project successfully demonstrated that an LST upstream of an LNT does provide protection for the LNT from the adverse effects of fuel-borne sulfur. The work also demonstrated that the LST could be regenerated on-line, with all of the product sulfur species passing through the LNT, without adversely affecting the LNT's performance. These two results validate the PASS-2™ advanced system design.

The data obtained suggest that an LST could be effective at storing sulfur from diesel exhaust at very high efficiency for at least 50,000 miles. A single regeneration of the LST could release most of the stored sulfur in less than five minutes, with only a minor impact on fuel economy. A temporary deactivation of the LNT was reversed within five minutes, so the NO_x emission impact would also be very minor. The lack of high temperature required to regenerate the LNT would result in significantly increased durability of the LNT. In essence, the PASS 2™ system could be used to maintain emissions efficiency over 435,000 miles for heavy-duty applications, with an estimated nine regenerations of the LST during that period.

PASS 2™ System Design

PASS 2™ System Sulfur Storage and Regeneration Effect on LNT Performance