Systems and methods for diagnosing selective catalytic reduction systems

1. An aftertreatment system, comprising:

a selective catalytic reduction system structured to decompose constituents of an exhaust gas produced by an engine;

an engine out NOx (EONOx) adjustment system; and

a controller configured to:

when the selective catalytic reduction system is in a diagnostic enabling condition, instruct the engine out NOx adjustment system to adjust an EONOx amount between a high EONOx level for a first predetermined time and a low EONOx level for a second predetermined time, the EONOx amount comprising an amount of NOx gases included in the exhaust gas emitted by the engine;

determine a selective catalytic reductions system out NOx (SONOx) amount, the SONOx amount comprising an amount of NOx gases included in the exhaust gas after passing through the selective catalytic reduction system;

determine an efficiency parameter of the selective catalytic reduction system from the SONOx amount when the EONOx amount transitions from the low EONOx level to the high EONOx level;

determine if the efficiency parameter satisfies a predetermined threshold; and

in response to the efficiency parameter not satisfying the predetermined threshold, determine that the selective catalytic reduction system has failed.

2. The aftertreatment system of claim 1 , wherein the controller is further configured to determine if the diagnostic enabling condition is satisfied,

wherein the controller instructs the EONOx adjustment system to adjust the EONOx amount in response to the diagnostic enabling condition being satisfied.

3. The aftertreatment system of claim 2 , wherein the diagnostic enabling condition comprises an EONOx amount mass flow rate being within a predetermined EONOx mass flow rate range corresponding to the high EONOx level.

4. The aftertreatment system of claim 2 , wherein the diagnostic enabling condition comprises at least one of a selective catalytic reduction system temperature being within a predetermined temperature threshold range, and a selective catalytic reduction system temperature rate being within a predetermined temperature rate range.

5. The aftertreatment system of claim 2 , wherein the diagnostic enabling condition comprises at least one of an exhaust gas mass flow being within an exhaust mass flow range, and an exhaust gas mass flow rate being within an exhaust mass flow rate range.

6. The aftertreatment system of claim 2 , wherein the diagnostic enabling condition comprises an ammonia to NOx ratio of the exhaust gas being within a predetermined ratio range.

7. The aftertreatment system of claim 1 , wherein the efficiency parameter comprises the SONOx amount, and wherein not satisfying the predetermined threshold comprises the SONOx amount being above the predetermined threshold.

8. The aftertreatment system of claim 1 , wherein the efficiency parameter comprises a conversion inefficiency comprising a ratio between the SONOx amount and the EONOx amount, and wherein not satisfying the predetermined threshold comprises the conversion inefficiency being above the predetermined threshold.

9. The aftertreatment system of claim 8 , wherein the efficiency parameter comprises a normalized conversion inefficiency comprising the conversion inefficiency normalized with respect to at least one of an ammonia to NOx ratio of the exhaust gas, a selective catalytic reduction system temperature, and an exhaust gas flow velocity.

10. The aftertreatment system of claim 1 , wherein the EONOx adjustment system comprises an exhaust gas recirculation system.

11. The aftertreatment system of claim 1 , further comprising:

a reductant insertion assembly fluidly coupled to the selective catalytic reduction system, the reductant insertion assembly operatively coupled to the controller,

wherein the controller is further configured to adjust an amount of reductant inserted during at least one of the first predetermined time and the second predetermined time so as to adjust an amount of ammonia stored in the selective catalytic reduction system.

12. The aftertreatment system of claim 1 , wherein the first predetermined time is equal to the second predetermined time.

13. The aftertreatment system of claim 1 , wherein the second predetermined time is smaller than the first predetermined time.

14. A control circuitry for diagnosing a catalytic conversion efficiency of a selective catalytic reduction system of an aftertreatment system, comprising:

a controller configured to be operatively coupled to the aftertreatment system, the controller comprising:

an engine out NOx (EONOx) adjustment circuitry configured to instruct an engine out NOx adjustment system of the aftertreatment system to adjust an EONOx amount between a high EONOx level for a first predetermined time and a low EONOx level for a second predetermined time when the selective catalytic reduction system is in a diagnostic enabling condition, the EONOx amount comprising an amount of NOx gases included in the exhaust gas emitted by the engine;

a NOx determination circuitry configured to determine a selective catalytic reduction system out NOx (SONOx) amount, the SONOx amount comprising an amount of NOx gases included in the exhaust gas after passing through the selective catalytic reduction system; and

an efficiency parameter determination circuitry configured to:

determine an efficiency parameter of the selective catalytic reduction system from the SONOx amount when the EONOx amount transitions from the low EONOx level to the high EONOx level;

determine if the efficiency parameter satisfies a predetermined threshold;

in response to the efficiency parameter not satisfying the predetermined threshold, determine that the selective catalytic reduction system has failed; and

indicate to a user that the selective catalytic reduction system has failed.

15. The control circuitry of claim 14 , wherein the controller further comprises an enabling condition determining circuitry configured to determine if the diagnostic enabling condition for diagnosing the selective catalytic reduction system is satisfied,

wherein the EONOx adjustment circuitry is configured to adjust the EONOx amount in response to the diagnostic enabling condition being satisfied.

16. The control circuitry of claim 15 , wherein the diagnostic enabling condition comprises an EONOx amount mass flow rate being within a predetermined NOx mass flow rate range corresponding to the high EONOx level.

17. The control circuitry of claim 15 , wherein the diagnostic enabling condition comprises at least one of a selective catalytic reduction system temperature being within a predetermined temperature threshold range, and a selective catalytic reduction system temperature rate being within a predetermined temperature rate range.

18. The control circuitry of claim 15 , wherein the diagnostic enabling condition further comprises at least one of an exhaust gas mass flow being within an exhaust mass flow range, and an exhaust gas mass flow rate being within an exhaust mass flow rate range.

19. The control circuitry of claim 15 , wherein the diagnostic enabling condition further comprises an ammonia to NOx ratio of the exhaust gas being within a predetermined ratio range.

20. The control circuitry of claim 14 , wherein the efficiency parameter comprises the SONOx amount, and wherein not satisfying the predetermined threshold comprises the SONOx amount being above the predetermined threshold.

21. The control circuitry of claim 14 , wherein the efficiency parameter comprises a conversion inefficiency comprising a ratio between the SONOx amount and the EONOx amount, and wherein not satisfying the predetermined threshold comprises the conversion inefficiency being above the predetermined threshold.

22. The control circuitry of claim 14 , wherein the efficiency parameter comprises a normalized conversion inefficiency comprising the conversion inefficiency normalized with respect to at least one of an ammonia to NOx ratio of the exhaust gas, a selective catalytic reduction system temperature, and an exhaust gas flow velocity.

23. A method for diagnosing a conversion efficiency of a selective catalytic reduction system of an aftertreatment system receiving an exhaust gas from an engine, the method comprising:

determining if a diagnostic enabling condition is satisfied;

in response to the diagnostic enabling condition being satisfied, adjusting an engine out NOx (EONOx) amount between a high EONOx level for a first predetermined time and a low EONOx level for a second predetermined time, the EONOx amount comprising an amount of NOx gases included in the exhaust gas emitted by the engine;

determining a selective catalytic reduction system out NOx (SONOx) amount, the SONOx amount comprising an amount of NOx gases included in the exhaust gas after passing through the selective catalytic reduction system;

determining an efficiency parameter of the selective catalytic reduction system from the SONOx amount when the EONOx amount transitions from the low EONOx level to the high EONOx level;

determining if the efficiency parameter satisfies a predetermined threshold;

in response to the efficiency parameter not satisfying the predetermined threshold:

determining that the selective catalytic reduction system has failed, and

indicating to a user that the selective catalytic reduction system has failed.

24. The method of claim 23 , wherein the diagnostic enabling condition comprises a first NOx amount mass flow rate being within a predetermined NOx mass flow rate range corresponding to the high EONOx level.

25. The method of claim 23 , wherein the diagnostic enabling condition comprises at least one of a selective catalytic reduction system temperature being within a predetermined temperature threshold range, a selective catalytic reduction system temperature rate being within a predetermined temperature rate range, an exhaust gas mass flow being within an exhaust mass flow range, an exhaust gas mass flow rate being within an exhaust mass flow rate range, and an ammonia to NOx ratio of the exhaust gas being within a predetermined ratio range.

26. The method of claim 23 , wherein the efficiency parameter comprises the SONOx amount, and wherein not satisfying the predetermined threshold comprises the SONOx amount being above the predetermined threshold.

27. The method of claim 23 , wherein the efficiency parameter comprises a normalized conversion inefficiency comprising a ratio between the SONOx amount and the EONOx amount, and wherein not satisfying the predetermined threshold comprises the conversion inefficiency being above the predetermined threshold.

28. The method of claim 27 , wherein the efficiency parameter comprises a normalized conversion inefficiency comprising the conversion inefficiency normalized with respect to at least one of an ammonia to NOx ratio of the exhaust gas, a selective catalytic reduction system temperature, and an exhaust gas flow velocity.

29. The method of claim 23 , further comprising:

adjusting an amount of reductant inserted during at least one of the first predetermined time and the second predetermined time so as to adjust an amount of ammonia stored in the selective catalytic reduction system.