Enhanced real-time ammonia slip detection

Patent metadata

Field	Value
Publication number	US-9429059-B2
Application number	US-201313859435-A
Country	US
Kind code	B2
Filing date	Apr 9, 2013
Priority date	Apr 9, 2013
Publication date	Aug 30, 2016
Grant date	Aug 30, 2016

Abstract

Various systems and methods are described for detecting ammonia slip. In one example method, an exhaust system with two NOx sensors uses transient responses of the NOx sensors to allocate tailpipe NOx sensor output to NOx and NH 3 levels therein. An ammonia slip detection counter with gains is included that determines a probability of NOx and NH 3 based on the measured sensor activities that are further processed by a controller to adjust one or more parameters based on the allocation and changes of sensor output.

First claim

The invention claimed is:

1. A method for an engine comprising:
allocating a NOx sensor output to each of NH 3 and NOx based on calculating upstream and downstream NOx rates of change relative to an SCR emission device,
determining an expected downstream NOx rate of change,
generating an envelope surrounding the expected downstream NOx rate of change, and
comparing the calculated downstream NOx rate of change to the expected downstream NOx rate of change and the envelope surrounding the expected downstream NOx rate of change, where the expected downstream NOx rate of change is determined based on the calculated upstream rate of change; and

adjusting reductant delivery into engine exhaust via an injector based on the allocation.

2. The method of claim 1 wherein more of the NOx sensor output is allocated to NOx than NH 3 when the calculated downstream NOx rate of change is within the envelope.

3. The method of claim 1 wherein a first portion of the NOx sensor output is allocated to NOx and a second, remaining portion of the NOx sensor output to NH 3 , wherein reductant delivery is based on each of the first and second portions, with different adjustments for the first portion as compared to the second portion.

4. The method of claim 1 wherein a portion of the NOx sensor output is allocated to NH 3 when the calculated downstream NOx rate of change is outside of the envelope.

5. The method of claim 1 wherein the upstream NOx rate of change is determined based on a sensor.

6. The method of claim 1 wherein the allocating is further based on a counter that quantifies the comparison of the calculated downstream NOx rate of change and the envelope.

7. The method of claim 6 wherein the counter ramps negative to a lower level that indicates NOx slip when the calculated downstream NOx rate of change is within the envelope and ramps positive to an upper level that indicates NH 3 slip when the calculated downstream NOx rate of change is outside of the envelope.

8. The method of claim 7 wherein the allocation is based on the counter relative to the lower level and upper level.

9. The method of claim 8 wherein an additional operating parameter is adjusted based on the allocation.

10. A method for performing real-time control of ammonia slip in an engine exhaust system, comprising:
allocating an output of a NOx sensor arranged downstream of an SCR emission device to each of NH 3 and NOx based on:
predicting a a rate of change of NOx downstream of the

SCR emission device,
generating an envelope that surrounds the predicted rate of change, and
comparing an actual rate of change of NOx downstream of the SCR emission device to the predicted rate of change and the envelope, the actual rate of change based on the output from the NOx sensor downstream of the SCR emission device; and

adjusting delivery of a reductant to engine exhaust upstream of the SCR emission device via an injector based on the allocation.

11. The method of claim 10 further comprising, if the actual rate of change is outside of the envelope surrounding the predicted slope, determining there is an NH 3 slip condition.

12. The method of claim 11 wherein the predicted rate of change is based on an upstream NOx rate of change.

13. The method of claim 12 wherein the predicted rate of change is further based on a current output of the NOx sensor arranged downstream of the SCR emission device and a current output of a NOx sensor arranged upstream of the SCR emission device.

14. The method of claim 10 wherein the allocation is further based on a counter that quantifies the comparison of the actual rate of change and the predicted rate of change.

15. The method of claim 10 wherein the envelope surrounding the predicted rate of change is comprised of a positive envelope offset from the predicted rate of change in a positive direction, and a negative envelope offset from the predicted rate of change in a negative direction.

16. A system, comprising:
an engine with an exhaust system;
an exhaust treatment system disposed in the exhaust system and including an SCR emission device, a urea injector disposed upstream of the SCR emission device, a NOx sensor disposed downstream of the SCR emission device, and a NOx sensor disposed upstream of the SCR emission device; and
a control system in communication with the exhaust treatment system, where the control system includes non-transitory instructions for NH 3 slip detection based on a transient NOx signal, wherein the NH 3 slip detection includes:
allocating an output of the NOx sensor disposed downstream of the SCR emission device to each of NH 3 and NOx and
adjusting injection of reductant via the urea injector to engine exhaust gas upstream of the SCR emission device based on the allocation, where the allocation is based on:
a comparison of an envelope which surrounds an expected rate of change of NOx downstream of the SCR emission device and a calculated rate of change of NOx downstream of the SCR emission device,
wherein if the calculated rate of change of NOx downstream of the SCR emission device is within the envelope, determining there is a NOx slip condition.

Assignees

• Ford Global Tech Llc

Inventors

• Riffle Chris
• Korpics Frank M
• Van Nieuwstadt Michiel J
• Upadhyay Devesh
• Nader David Robert

Classifications

• Y02T10/12

  Improving ICE efficiencies · CPC title

• B01D53/9495

  Controlling the catalytic process · CPC title

• F01N2610/02

  the substance being ammonia or urea · CPC title

• B01D53/9409

  Nitrogen oxides · CPC title

• F01N2900/1616

  NH3-slip from catalyst · CPC title