Identifying ammonia slip conditions in a selective catalytic reduction application
A system includes a filtering module that filters a first signal that indicates an amount of nitrogen oxides (NOx) in exhaust gas upstream from a catalyst, and that filters a second signal that indicates amounts of NOx and ammonia (NH3) in exhaust gas downstream from the catalyst. A slip determination module determines whether NH3 is present in exhaust gas downstream from the catalyst based on a frequency response of the first and second signals.
1. A system comprising:
a filtering module that filters a first signal that indicates an amount of nitrogen oxides (NOx) in exhaust gas upstream from a catalyst, and that filters a second signal that indicates amounts of NOx and ammonia (NH 3 ) in exhaust gas downstream from the catalyst; and
a slip determination module that determines whether NH 3 is present in exhaust gas downstream from the catalyst based on a frequency response of the first and second signals.
2. The system of claim 1 , wherein the filtering module passes first frequency components of the signals that indicate only NOx and attenuates second and third frequency components of the signals that indicate NOx and NH 3 .
3. The system of claim 2 , wherein the first frequency components include frequencies that are greater than a frequency threshold and the second and third frequency components include frequencies that are less than or equal to the frequency threshold.
4. The system of claim 2 , further comprising a conversion ratio module that determines a NOx conversion ratio of the catalyst based on the first frequency components.
5. The system of claim 4 , wherein the slip determination module determines an estimated magnitude of the second signal based on a magnitude of the first signal and the NOx conversion ratio.
6. The system of claim 5 , wherein the slip determination module determines NH 3 is present when a difference between the estimated magnitude and a magnitude of the second signal is greater than a threshold.
7. A system comprising:
an injector control module that adjusts a flow rate of a dosing agent, wherein the adjusted flow rate controls an amount of ammonia (NH 3 ) in exhaust gas upstream from a catalyst;
a comparison module that compares first and second samples of a signal based on the adjusted flow rate, wherein the signal indicates an amount of nitrogen oxides (NOx) and an amount of NH 3 in exhaust gas downstream from the catalyst; and
a slip determination module that determines whether NH 3 is present in the exhaust gas downstream from the catalyst based on the adjusted flow rate and the comparison,
wherein the slip determination module determines whether a slip in the amount of NH 3 in the exhaust gas has occurred based on whether the signal indicates a change in the amount of NOx by more than a predetermined amount.
8. The system of claim 7 , further comprising a sampling module that samples the first sample when the injector control module adjusts the flow rate and that samples the second sample at a predetermined time after the first sample.
9. The system of claim 7 , wherein the slip determination module determines:
NH 3 is present when the adjusted flow rate decreases the amount of NH 3 and the second sample is less than the first sample; and
NH 3 is present when the adjusted flow rate increases the amount of NH 3 and the second sample is greater than the first sample.
10. The system of claim 7 , wherein the slip determination module:
determines a slip in the amount of NH 3 in the exhaust gas has occurred when the signal indicates a decrease in the amount of NOx by more than a first predetermined amount; and
determines a slip in the amount of NH 3 in the exhaust gas has not occurred when the signal indicates an increase in the amount of NOx by more than a second predetermined amount.
11. A method comprising:
filtering a first signal that indicates an amount of nitrogen oxides (NOx) in exhaust gas upstream from a catalyst;
filtering a second signal that indicates amounts of NOx and ammonia (NH 3 ) in exhaust gas downstream from the catalyst; and
determining whether NH 3 is present in exhaust gas downstream from the catalyst based on a frequency response of the first and second signals.
12. The method of claim 11 , further comprising:
passing first frequency components of the signals that indicate only NOx; and
attenuating second and third frequency components of the signals that indicate NOx and NH 3 .
13. The method of claim 12 , wherein the first frequency components include frequencies that are greater than a frequency threshold and the second and third frequency components include frequencies that are less than or equal to the frequency threshold.
14. The method of claim 12 , further comprising determining a NOx conversion ratio of the catalyst based on the first frequency components.
15. The method of claim 14 , further comprising determining an estimated magnitude of the second signal based on a magnitude of the first signal and the NOx conversion ratio.
16. The method of claim 15 , further comprising determining NH 3 is present when a difference between the estimated magnitude and a magnitude of the second signal is greater than a threshold.
17. A method comprising:
adjusting a flow rate of a dosing agent, wherein the adjusted flow rate controls an amount of ammonia (NH 3 ) in exhaust gas upstream from a catalyst;
comparing first and second samples of a signal based on the adjusted flow rate, wherein the signal indicates an amount of nitrogen oxides (NOx) and an amount of NH 3 in exhaust gas downstream from the catalyst;
determining whether NH 3 is present in the exhaust gas downstream from the catalyst based on the adjusted flow rate and the comparison; and
determining whether a slip in the amount of NH 3 in the exhaust gas has occurred based on whether the signal indicates a change in the amount of NOx by more than a predetermined amount.
18. The method of claim 17 , further comprising:
sampling the first sample when the flow rate is adjusted; and
sampling the second sample at a predetermined time after the first sample.
19. The method of claim 17 , further comprising;
determining NH 3 is present when the adjusted flow rate decreases the amount of NH 3 and the second sample is less than the first sample; and
determining NH 3 is present when the adjusted flow rate increases the amount of NH 3 and the second sample is greater than the first sample.
20. The method of claim 18 , further comprising:
determining a slip in the amount of NH 3 in the exhaust gas has occurred when the signal indicates a decrease in the amount of NOx by more than a first predetermined amount; and
determining a slip in the amount of NH 3 in the exhaust gas has not occurred when the signal indicates an increase in the amount of NOx by more than a second predetermined amount.