Optimized NOx reduction system
View Patent ↗An exhaust after-treatment system for an internal combustion engine includes a lean NOx catalyst having an exhaust stream from the internal combustion engine flowing therethrough. A NOx absorber catalyst is downstream of the lean NOx catalyst. The NOx absorber is selectively regenerated to increase a NOx reduction efficiency of the exhaust after-treatment system.
1. An exhaust after-treatment system for an internal combustion engine, comprising:
a lean NOx catalyst receiving an exhaust stream from said internal combustion engine;
a NOx absorber catalyst downstream of said lean NOx catalyst, wherein said NOx absorber is selectively regenerated to increase a NOx reduction efficiency of said exhaust after-treatment system; and
a control module that determines a NOx reduction demand, that initiates regeneration of said NOx absorber catalyst when said NOx reduction demand is greater than or equal to a first threshold, and that introduces hydrocarbons (HC) into said exhaust stream when said NOx reduction demand is less than said first threshold and greater than or equal to a second threshold.
2. The exhaust after-treatment system of claim 1 wherein said lean NOx catalyst reduces NOx in said exhaust stream when said NOx reduction demand is less than said second threshold.
3. The exhaust after-treatment system of claim 1 wherein said HC is introduced via at least one of post-combustion in-cylinder fuel injection and in-exhaust injection downstream of said internal combustion engine.
4. The exhaust after-treatment system of claim 1 further comprising a hydrocarbon (HC) dosing unit disposed upstream of said lean NOx catalyst.
5. A method of reducing a NOx content of an exhaust stream exiting an internal combustion engine, comprising:
directing said exhaust stream through a lean NOx catalyst to reduce said NOx content of said exhaust stream;
directing said exhaust stream through a NOx absorber catalyst that is disposed downstream of said lean NOx catalyst;
determining a NOx reduction demand;
initiating regeneration of said NOx absorber catalyst when said NOx reduction demand is greater than or equal to a first threshold; and
introducing hydrocarbons (HC) into said exhaust stream when said NOx reduction demand is less than said first threshold and greater than or equal to a second threshold.
6. The method of claim 5 wherein said lean NOx catalyst reduces said NOx content in said exhaust stream when said NOx reduction demand is less than said second threshold.
7. The method of claim 5 wherein said step of introducing said HC is achieved via at least one of post-combustion in-cylinder fuel injection and in-exhaust injection downstream of said internal combustion engine.
8. The method of claim 5 further comprising selectively injecting hydrocarbon (HG) into said exhaust stream using a dosing unit that is disposed upstream of said lean NOx catalyst.