Reduction of Particulate, NOx, and Ammonia Emissions

A method for controlling emissions from an engine, comprising:

• reducing trapped nitrogen oxides to ammonia on a lean nitrogen-oxide trapping (LNT) catalyst while concurrently oxidizing soot accumulated on the LNT catalyst including flowing exhaust from the engine over the LNT catalyst;
• flowing the ammonia to a selective catalytic reduction (SCR) catalyst;
• and
• adjusting a duration of said flowing in response to an amount of soot oxidized on the LNT catalyst.

A method for controlling emissions from an engine, comprising:

• reducing trapped nitrogen oxides to ammonia on a lean nitrogen-oxide trapping (LNT) catalyst while concurrently oxidizing soot accumulated on the LNT catalyst including flowing exhaust from the engine over the LNT catalyst;
• flowing the ammonia to a selective catalytic reduction (SCR) catalyst;
• and
• adjusting a duration of said flowing in response to an amount of soot oxidized on the LNT catalyst;
• increasing the air-to-fuel ratio of the exhaust when the amount of soot increases and decreasing the air-to-fuel ratio of the exhaust when the amount of soot decreases, wherein increasing and decreasing the air-to-fuel ratio of the exhaust comprises adjusting at least one of a fuel-injection amount and a throttle valve opening amount of the engine, wherein an amount by which the at least one of an air-to-fuel ratio of the exhaust and a duration of said flowing is adjusted is based on exhaust temperature, and wherein said amount is increased with increasing exhaust temperature and decreased with decreasing exhaust temperature

A method for controlling emissions from an engine, comprising:

• reducing trapped nitrogen oxides to ammonia on a LNT catalyst while concurrently oxidizing soot accumulated on the LNT catalyst including flowing exhaust from the engine over the LNT catalyst;
• flowing the ammonia to a SCR catalyst;
• and
• adjusting an air-to-fuel ratio of the exhaust in response to an accumulated soot amount on the LNT catalyst and a pressure differential across a locus of the LNT catalyst.