Virtual diesel exhaust fluid (DEF) quality monitor

1. A diesel engine exhaust aftertreatment system comprising:

an entrance through which untreated diesel engine exhaust enters and an exit through which treated diesel engine exhaust exits, a first sensor which, when the engine is operating, measures quantity of NOx in diesel engine exhaust entering the aftertreatment system and a second sensor which, when the engine is operating, measures quantity of NOx in diesel engine exhaust exiting the aftertreatment system, an SCR catalyst for converting NOx in diesel engine exhaust passing through the aftertreatment system into nitrogen (N 2 ) and water (H 2 O) by selective catalytic reduction, a diesel exhaust fluid (DEF) injector for injecting DEF into diesel engine exhaust upstream of the SCR catalyst, and an engine control system comprising a controller for controlling quantity of DEF injected by the DEF injector and a virtual DEF quality monitor operable to monitor DEF quality;

the virtual DEF quality monitor being operable with the engine operating 1) to repeatedly perform an intrusive test which comprises successive first, second, and third phases, the first phase comprising preventing the DEF injector from injecting DEF until measurements from the first sensor and the second sensor disclose that the SCR catalyst has been sufficiently purged of stored ammonia for allowing the second phase to proceed, the second phase comprising causing the DEF injector to inject DEF in quantity which, for DEF whose formulation is compliant with a DEF performance standard, has been predetermined to enable the SCR catalyst to reduce quantity of NOx in engine exhaust to a quantity not less than a first NOx reduction target which is greater than a second NOx reduction target below which failure of the SCR catalyst is indicated, and the third phase comprising processing measurements obtained from the first sensor and the second sensor during the second phase to calculate quantity of NOx reduced during the second phase, 2) when the third phase discloses that quantity of NOx reduced during the second phase is less than the first NOx reduction target but greater than the second NOx reduction target, to log the event as an indication of the formulation of injected DEF having been non-compliant with the DEF performance standard, and 3) when the third phase discloses that quantity of NOx reduced during the second phase is not less than the first NOx reduction target, to log the event as an indication of the formulation of injected DEF having been compliant with the DEF performance standard.

2. The diesel engine exhaust aftertreatment system as set forth in claim 1 in which the monitor is further operable to calculate % dilution of DEF injected during the second phase using quantity of DEF injected and NOx measurements obtained from the first sensor and the second sensor during the second phase.

3. The diesel engine exhaust aftertreatment system as set forth in claim 1 in which the monitor is further operable to cause the intrusive test to purge the SCR catalyst of ammonia after completion of the second phase.

4. The diesel engine exhaust aftertreatment system as set forth in claim 1 in which the monitor is operable to repeatedly perform a succession of intrusive tests.

5. The diesel engine exhaust aftertreatment system as set forth in claim 4 in which the monitor is operable to condition performance of an intrusive test on at least one condition precedent.

6. The diesel engine exhaust aftertreatment system as set forth in claim 4 in which the monitor is operable to condition performance of an intrusive test on the immediately preceding intrusive test having disclosed quantity of NOx reduced during the second phase being no less than the first NOx reduction target.

7. A method for distinguishing use of diesel exhaust fluid (DEF) whose formulation is compliant with a DEF performance standard from use of DEF whose formulation is non-compliant with the DEF performance standard in a diesel engine exhaust aftertreatment system having an entrance through which untreated diesel engine exhaust enters and an exit through which treated diesel engine exhaust exits, an SCR catalyst for converting NOx in diesel engine exhaust passing through the aftertreatment system into nitrogen (N 2 ) and water (H 2 O), a DEF injector for injecting DEF into diesel engine exhaust upstream of the SCR catalyst, a first sensor for measuring quantity of NOx in diesel engine exhaust entering the aftertreatment system, a second sensor for measuring quantity of NOx in diesel engine exhaust exiting the aftertreatment system, and an engine control system comprising a controller for controlling quantity of DEF injected by the DEF injector and a virtual DEF quality monitor operable to perform a method for disclosing DEF quality;

the method comprising:

with the engine operating, 1) repeatedly performing an intrusive test having successive first, second, and third phases, the first phase comprising preventing the DEF injector from injecting DEF until measurements from the first sensor and the second sensor disclose that the SCR catalyst has been sufficiently purged of stored ammonia for allowing the second phase to proceed, the second phase comprising causing the DEF injector to inject DEF in quantity which, for DEF which is compliant with a DEF performance standard, has been predetermined to enable the SCR catalyst to reduce quantity of NOx in engine exhaust to a quantity not less than a first NOx reduction limit which is greater than a second NOx reduction limit which, if exceeded, would disclose failure of the SCR catalyst, the third phase comprising processing measurements obtained from the first sensor and the second sensor during the second phase to calculate quantity of NOx reduced during the second phase, 2) when the third phase discloses that quantity of NOx reduced during the second phase is less than the first NOx reduction limit but greater than the second NOx reduction limit, logging the event as an indication of the formulation of injected DEF having been non-compliant with the DEF performance standard, and 3) when the third phase discloses that quantity of NOx reduced during the second phase is not less than the first NOx reduction target, logging the event as an indication of the formulation of injected DEF having been compliant with the DEF performance standard.

8. The method as set forth in claim 7 further comprising calculating % dilution of DEF injected during the second phase using quantity of DEF injected and NOx measurements obtained from the first sensor and the second sensor during the second phase.

9. The method as set forth in claim 7 further comprising causing the intrusive test to purge the SCR catalyst of ammonia after completion of the second phase.

10. The method as set forth in claim 7 comprising repeatedly performing a succession of intrusive tests.

11. The method as set forth in claim 10 comprising conditioning performance of an intrusive test on at least one condition precedent.

12. The method as set forth in claim 10 comprising conditioning performance of an intrusive test on the immediately preceding intrusive test having disclosed that quantity of NOx reduced during the second phase is greater than the first NOx reduction target.

13. A motor vehicle comprising:

a diesel engine for propelling the vehicle, the diesel engine having an engine exhaust aftertreatment system having an entrance through which untreated diesel engine exhaust enters and an exit through which treated diesel engine exhaust exits, the system comprising a first sensor which, when the engine is operating, measures quantity of NOx in diesel engine exhaust entering the aftertreatment system and a second sensor which, when the engine is operating, measures quantity of NOx in diesel engine exhaust exiting the aftertreatment system, an SCR catalyst for converting NOx in diesel engine exhaust passing through the aftertreatment system into nitrogen (N 2 ) and water (H 2 O), a diesel exhaust fluid (DEF) storage tank for storing DEF, an injector for injecting DEF from the storage tank into diesel engine exhaust upstream of the SCR catalyst, and an engine control system comprising a controller for controlling quantity of DEF injected by the DEF injector; and

a virtual DEF quality monitor which is operable with the engine operating 1) to repeatedly perform an intrusive test which comprises successive first, second, and third phases, the first phase comprising preventing the DEF injector from injecting DEF until measurements from the first sensor and the second sensor disclose that the SCR catalyst has been sufficiently purged of stored ammonia for allowing the second phase to proceed, the second phase comprising causing the DEF injector to inject DEF in quantity which, for DEF whose formulation is compliant with a DEF performance standard, has been predetermined to enable the SCR catalyst to reduce quantity of NOx in engine exhaust to a quantity not less than a first NOx reduction target which is greater than a second NOx reduction target below which failure of the SCR catalyst is indicated, and the third phase comprising processing measurements obtained from the first sensor and the second sensor during the second phase to calculate quantity of NOx reduced during the second phase, 2) when the third phase discloses that quantity of NOx reduced during the second phase is less than the first NOx reduction target but greater than the second NOx reduction target, to log the event as an indication of the formulation of injected DEF having been non-compliant with the DEF performance standard, and 3) when the third phase discloses that quantity of NOx reduced during the second phase is not less than the first NOx reduction target, to log the event as an indication of the formulation of injected DEF having been compliant with the DEF performance standard.

14. The motor vehicle as set forth in claim 13 in which the monitor is further operable to calculate % dilution of DEF injected during the second phase using quantity of DEF injected and NOx measurements obtained from the first sensor and the second sensor during the second phase.

15. The motor vehicle as set forth in claim 13 in which the monitor is further operable to cause the intrusive test to purge the SCR catalyst of ammonia after completion of the second phase.

16. The motor vehicle as set forth in claim 13 in which the monitor is operable to repeatedly perform a succession of intrusive tests.

17. The motor vehicle as set forth in claim 16 in which the monitor is operable to condition performance of an intrusive test on at least one condition precedent.

18. The motor vehicle as set forth in claim 16 in which the monitor is operable to condition performance of an intrusive test on the immediately preceding intrusive test having disclosed that quantity of NOx reduced during the second phase is greater than the first NOx reduction target.

19. The motor vehicle as set forth in claim 13 in which the controller is operable to detect a vehicle event which provides a potential opportunity for DEF in the DEF storage tank to be diluted and to cause the monitor to perform an intrusive test in consequence of detection of such a vehicle event.

20. The motor vehicle as set forth in claim 19 in which the controller is operable to detect the vehicle having been stopped for more than a predetermined length of time before resuming travel and to cause the monitor to perform an intrusive test after the vehicle has resumed travel after having been stopped for more than the predetermined length of time.