Lean nitrogen oxide emission control system and method
View Patent ↗A control system comprising an NH 3 storage level determination module that determines an NH 3 storage level in an exhaust system, and a fuel control module that controls an air-to-fuel (A/F) ratio in an engine based on the NH 3 storage level. A method comprising determining an NH 3 storage level in an exhaust system, and controlling an A/F ratio in an engine based on the NH 3 storage level.
1. A control system, comprising:
an NH 3 storage level determination module that determines an NH 3 storage level corresponding to a level of ammonia absorbed in a selective catalytic reduction unit of an exhaust system; and
a fuel control module that controls an air-to-fuel (A/F) ratio of an engine based on said NH 3 storage level.
2. The control system of claim 1 further comprising a minimum NH 3 storage level determination module that determines a minimum NH 3 storage level based on an exhaust temperature.
3. The control system of claim 2 wherein said fuel control module sets said A/F ratio to lean when said NH 3 storage level exceeds said minimum NH 3 storage level.
4. The control system of claim 2 wherein said fuel control module sets said A/F ratio to rich when said NH 3 storage level does not exceed said minimum NH 3 storage level.
5. The control system of claim 1 further comprising a target NH 3 storage level determination module that determines a target NH 3 storage level based on an exhaust temperature.
6. The control system of claim 5 wherein said fuel control module sets said A/F ratio to lean when said NH 3 storage level exceeds said target NH 3 storage level.
7. The control system of claim 1 further comprising a NO x mass flow rate determination module that determines a NO x mass flow rate based on a NO x concentration.
8. The control system of claim 7 wherein said NH 3 storage level determination module determines a change in said NH 3 storage level based on said NO x mass flow rate.
9. The control system of claim 8 wherein said NH 3 storage level determination module determines said change in said NH 3 storage level further based on at least one of an exhaust temperature, a catalyst type, and said A/F ratio.
10. The control system of claim 8 wherein said NH 3 storage level determination module determines said NH 3 storage level based on a previous NH 3 storage level and said change in said NH 3 storage level.
11. A method, comprising:
determining an NH 3 storage level corresponding to a level of ammonia absorbed in a selective catalytic reduction unit of an exhaust system; and
controlling an air-to-fuel (A/F) ratio of an engine based on said NH 3 storage level.
12. The method of claim 11 further comprising determining a minimum NH 3 storage level based on an exhaust temperature.
13. The method of claim 12 further comprising setting said A/F ratio to lean when said NH 3 storage level exceeds said minimum NH 3 storage level.
14. The method of claim 12 further comprising setting said A/F ratio to rich when said NH 3 storage level does not exceed said minimum NH 3 storage level.
15. The method of claim 11 further comprising determining a target NH 3 storage level based on an exhaust temperature.
16. The method of claim 15 further comprising setting said A/F ratio to lean when said NH 3 storage level exceeds said target NH 3 storage level.
17. The method of claim 11 further comprising determining a NO x mass flow rate based on a NO x concentration.
18. The method of claim 17 further comprising determining a change in said NH 3 storage level based on said NO x mass flow rate.
19. The method of claim 18 further comprising determining said change in said NH 3 storage level further based on at least one of an exhaust temperature, a catalyst type, and said A/F ratio.
20. The method of claim 18 further comprising determining said NH 3 storage level based on a previous NH 3 storage level and said change in said NH 3 storage level.