Method for adjusting a reductant used in an internal combustion engine to reduce NOx

A method for controlling reductant injection into a catalyst coupled to an internal combustion engine, the method comprising:

• determining a reductant fraction based on an amount of reductant used in the catalyst and an amount of the reductant passing through the catalyst, said fraction representative of a fractional amount of reductant used in a reaction in the catalyst, wherein the fractional amount is based on a desired ratio between ammonia in the supplied reductant and NOx exhausted from the engine;
• varying the reductant injection in accordance with both said determined reductant fraction and an amount of reductant exiting the catalyst, wherein said varying further comprises decreasing said amount of reductant injection when said reductant concentration passing from the catalyst is greater than an allowable level or said reductant fraction is greater than an allowable reductant fraction, decreasing said amount of reductant injection when said reductant concentration downstream of the catalyst is greater than an allowable level of post-catalyst reductant, and decreasing said amount of reductant injection when said reductant fraction is greater than an allowable reductant fraction;
• and
• wherein said engine is a diesel engine in a vehicle.

A method for controlling reductant injection into a catalyst coupled to an internal combustion engine, the method comprising:

• determining a reductant fraction based on an amount of reductant used in the catalyst and an amount of the reductant passing through the catalyst, said fraction representative of a fractional amount of reductant used in a reaction in the catalyst, wherein the fractional amount is based on a desired ratio between ammonia in the supplied reductant and NOx exhausted from the engine;
• varying the reductant injection in accordance with both said determined reductant fraction and an amount of reductant exiting the catalyst, wherein said varying comprises increasing said amount of reductant injection when said amount of reductant passing from the catalyst is less than an allowable level of post catalyst reductant and said reductant fraction is less than an allowable reductant fraction, and further comprising increasing said amount of reductant injection by a predetermined amount;
• and
• wherein said engine is a diesel engine in a vehicle.