Method for monitoring an ammonia slip catalyst
By using an ammonia cross-sensitive nitrogen oxide sensor upstream and downstream of the catalyst assembly, the method accurately detects ammonia slip catalyst defects, enhancing compliance with emissions regulations.
Patent Information
- Application Number
- CN201910145262.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Priority Date
- 2018-02-27
- Filing Date
- 2019-02-27
- Publication Date
- 2024-12-13
- Estimated Expiration
- 2039-02-27
AI Technical Summary
Existing ammonia slip catalyst monitoring methods are inadequate for accurately determining catalyst functionality and compliance with stringent emission regulations due to the use of cross-sensitive nitrogen oxide sensors that cannot differentiate between ammonia and nitrogen oxides, leading to potential errors and inefficiencies.
Implementing an ammonia cross-sensitive nitrogen oxide sensor upstream of the catalyst assembly, combined with a sensor downstream, to measure and compare nitrogen oxide levels, allowing for precise detection of ammonia slip catalyst defects by comparing values in specific engine operating phases.
Enables accurate determination of ammonia slip catalyst performance, ensuring compliance with legal emissions standards by identifying defects through value discrepancies, reducing sensor complexity and potential errors.
Smart Images
Figure CN110195635B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for monitoring an ammonia slip catalytic converter and a control system for implementing the method. Background Art
[0002] A method is known from DE 10 2012 211 705 A1, in which the functionality of an ammonia cross-sensitive nitrogen oxide sensor is checked. Summary of the invention
[0003] According to the method for monitoring an ammonia slip catalyst of the present invention, the ammonia slip catalyst is arranged in an exhaust aftertreatment device of a combustion engine, downstream of a catalyst component, and comprises the following steps: measuring the nitrogen oxide content in the exhaust gas with the aid of a sensor upstream of the ammonia slip catalyst, detecting a sensor signal of an ammonia cross-sensitive nitrogen oxide sensor arranged downstream of the ammonia slip catalyst, and checking whether the value measured by the ammonia cross-sensitive nitrogen oxide sensor is higher than the value measured by the sensor.
[0004] An ammonia cross-sensitive nitrogen oxide sensor according to the invention is a sensor which can measure both ammonia and nitrogen oxide, wherein the measured value is the sum of both measured values, so that it is generally not possible to accurately state the amount of ammonia alone or the amount of nitrogen oxide alone.
[0005] An ammonia slip catalyst is a component which is arranged downstream of the catalyst assembly and serves to convert ammonia slip, ie the part of the ammonia which leaves the catalyst assembly unconverted, so that the amount of ammonia emitted into the environment complies with legal regulations.
[0006] A possible advantage of the invention is that, in the case of a higher value measured by a nitrogen oxide sensor that is cross-sensitive to ammonia than the value measured by the sensor, it can be concluded that ammonia has left the ammonia slip catalytic converter. This makes it possible to detect whether the ammonia slip catalytic converter is functioning normally or has failed. This makes it possible to better comply with increasingly stringent ammonia emission limits.
[0007] Preferably, the sensor is arranged upstream of the catalyst assembly or upstream of the ammonia injector. Since no ammonia is present in the exhaust gas upstream of the catalyst assembly or the ammonia injector, an ammonia cross-sensitive nitrogen oxide sensor can preferably also be used at this location. This has the advantage that the same sensor type can be used for both sensors, so that only one type of sensor has to be provided. This saves storage space and eliminates possible sources of error due to mixed-up sensors.
[0008] In a preferred embodiment of the invention, the check is carried out in an operating phase in which the raw NOx emissions are essentially zero. Alternatively, the check is carried out in an operating phase in which the fuel injection rate is zero. Such a state occurs, for example, in a propulsion phase in which the combustion engine is towed by a motor vehicle. If the ammonia cross-sensitive nitrogen oxide sensor measures a higher value than the value measured by the sensor in a phase in which no ammonia injection is carried out and no NOx is present, then it can be concluded that the ammonia slip catalytic converter is defective, since it must be inferred from this that ammonia has left the ammonia slip catalytic converter. This has the advantage that the operation of the ammonia slip catalytic converter can be clearly stated in this phase.
[0009] In another preferred embodiment of the invention, the check is performed in an operating phase in which the actual ammonia loading of the catalyst component is higher than the required ammonia loading. In this phase, ammonia escapes from the catalyst component, so that the ammonia loading slowly adapts to the required ammonia loading. If the ammonia slip catalyst is defective in this phase, it is in this phase that the ammonia cross-sensitive nitrogen oxide sensor measures a higher value than the value measured by the sensor. As a result, the operation of the ammonia slip catalyst can be accurately described in this phase.
[0010] Here, the control system according to the invention for an exhaust gas aftertreatment device having a catalytic converter assembly, an ammonia slip catalytic converter arranged downstream of the catalytic converter assembly, a sensor, and at least one ammonia injector arranged upstream of the ammonia slip catalytic converter, and an ammonia cross-sensitive nitrogen oxide sensor arranged downstream of the ammonia slip catalytic converter is adapted to carry out the method according to the invention for monitoring an ammonia slip catalytic converter. Here, the control system has the advantage that it can be indicated whether the ammonia slip catalytic converter is functioning properly or defective based on the measured values of the ammonia cross-sensitive nitrogen oxide sensor and the sensor recorded and evaluated according to the method according to the invention. This provides a control system by means of which legal regulations for ammonia emissions can be complied with. BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Further advantages of the invention are apparent from the following description of the drawings of preferred embodiments. In the drawings:
[0012] Figure 1 An embodiment of an exhaust gas aftertreatment device of a combustion engine with a control system for implementing the method according to the invention is shown.
[0013] Figure 2 A method for monitoring an ammonia slip catalyst according to a first embodiment of the present invention is shown.
[0014] Figure 3 A method for monitoring an ammonia slip catalyst according to a second embodiment of the present invention is shown, and
[0015] Figure 4 A method for monitoring an ammonia slip catalyst according to a third exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION
[0016] Figure 1 An embodiment of an exhaust gas aftertreatment device 10 of a combustion engine with a control system 14 for implementing the method according to the invention is shown. The exhaust gas aftertreatment device 10 comprises a catalyst assembly 18, wherein the catalyst assembly 18 comprises a diesel oxidation catalyst (DOC) 22, an SCR-coated particle filter (SCRF) 26 and an SCR catalyst (SCR) 30. In addition, the exhaust gas aftertreatment device 10 comprises an ammonia slip catalyst (ASK) 34, which is arranged downstream of the catalyst assembly 18; an ammonia cross-sensitive nitrogen oxide sensor 38, which is arranged downstream of the ammonia slip catalyst (ASK) 34 in the flow direction 42; and a sensor 46, which is arranged upstream of the ammonia slip catalyst (ASK) 34, in particular upstream of the catalyst assembly 18. A first ammonia injector 50 is arranged upstream of the ammonia slip catalyst (ASK) 34, between the diesel oxidation catalyst (DOC) 22 and the SCR coated particle filter (SCRF) 26, through which ammonia is injected into the exhaust line. A second ammonia injector 54 for injecting ammonia into the exhaust line is arranged upstream of the ammonia slip catalyst (ASK) 34, between the SCR coated particle filter (SCRF) 26 and the SCR catalyst (SCR) 30. In order to implement the method according to the invention, the control device 14 is connected to the ammonia cross-sensitive nitrogen oxide sensor 38, the sensor 46, the ammonia injectors 50, 54, the SCR coated particle filter (SCRF) 26, the SCR catalyst (SCR) 30 and the ammonia slip catalyst (ASK) 34 (the connection is not shown).
[0017] In another embodiment of the present invention, a diesel particle filter (not shown) is provided instead of the SCR coated particle filter (SCRF) 26. In addition, in this embodiment, only a single ammonia injector can be provided, which is arranged between the diesel particle filter and the SCR catalyst (SCR).
[0018] Figure 2A first embodiment of the method according to the invention for monitoring an ammonia slip catalyst (ASK) 34 is shown. In the figure, the NOx concentration is plotted over time. In the method according to the invention, the nitrogen oxide content in the exhaust gas upstream of the ammonia slip catalyst (ASK) 34 is first determined with the aid of a sensor 46. This value is displayed in the figure as "NOx upstream of ASK". After this, the sensor signal of an ammonia cross-sensitive nitrogen oxide sensor 38 arranged downstream of the ammonia slip catalyst (ASK) 34 is detected. This value is displayed in the figure as "NOx downstream of ASK". Based on these two values, in a next step it is checked whether the value measured by the ammonia cross-sensitive nitrogen oxide sensor 38 is higher than the value detected by the sensor 46. In Figure 2 The curve shown in FIG. 1 represents the exhaust gas value when the ammonia slip catalyst (ASK) 34 fails, that is, the ammonia slip catalyst (ASK) 34 is defective. Figure 2 In the measurement range, a range is obtained (see dashed box) in which the value determined downstream of the ammonia slip catalytic converter (ASK) 34 is greater than the value determined upstream, so it can be inferred that the ammonia slip catalytic converter (ASK) 34 is defective. Using the method according to the invention, a defect of the ammonia slip catalytic converter (ASK) 34 can be detected.
[0019] In another embodiment according to the invention, the detection is performed during an operating phase in which the NOx emissions are substantially zero. This allows the range to be determined more accurately (see Figure 2 ), in which a defect of the ammonia slip catalytic converter (ASK) 34 can be determined. Therefore, it is no longer necessary to evaluate a large measuring range.
[0020] Figure 3 A second exemplary embodiment of the method according to the invention for monitoring an ammonia slip catalyst (ASK) 34 is shown. In this figure, the ammonia loading of the catalyst component 18 is plotted over time. In this exemplary embodiment according to the invention, the detection is performed in an operating phase in which the actual ammonia loading of the catalyst component 18 is higher than the required ammonia loading (see dashed box). In this range, the ammonia released from the catalyst component 18 increases, so that in the case of a defect in the ammonia slip catalyst (ASK) 34, this ammonia can be measured by the ammonia cross-sensitive nitrogen oxide sensor 38. As a result, defects in the ammonia slip catalyst 34 can be better determined in this range.
[0021] Figure 4A third embodiment of the method according to the invention for monitoring an ammonia slip catalytic converter 34 is shown. In the figure, the fuel injection rate or the accelerator pedal position is plotted over time. In the method according to the invention, the detection is carried out in an operating phase in which the fuel injection rate is zero. In this phase, it can be inferred that no combustion takes place and thus no nitrogen oxides are released. If the ammonia cross-sensitive nitrogen oxide sensor 38 measures a higher value than the value measured by the sensor 46 in such a phase, it can be inferred that the ammonia cross-sensitive nitrogen oxide sensor 38 only measures ammonia, so that the conclusion that the ammonia slip catalytic converter (ASK) 34 is defective must be drawn. Such an operating phase is therefore particularly suitable for determining a defect in the ammonia slip catalytic converter (ASK) 34.
[0022] In other embodiments, Figures 2 to 4 The methods for monitoring the ammonia slip catalyst 34 shown in the figure can be combined with each other. Figure 2 and Figure 3 Another preferred embodiment is according to Figure 3 and Figure 4 This combination of methods allows for a more precise and better determination of ammonia slip.
Claims
1. A method for monitoring an ammonia slip catalyst (34) arranged in an exhaust gas aftertreatment device (10) of a combustion engine, downstream of a catalyst component (18), wherein the method comprises the following steps: - measuring the nitrogen oxide content in the exhaust gas by means of a sensor (46) upstream of the catalytic converter component (18) and the ammonia injector (50), - detecting a sensor signal of an ammonia cross-sensitive nitrogen oxide sensor (38) arranged downstream of the ammonia slip catalytic converter (34), and - Check whether the value measured by the ammonia cross-sensitive NOx sensor (38) is higher than the value measured by the sensor (46), The check is performed during an operating phase in which the raw NOx emissions are essentially zero, and if the value measured by the ammonia cross-sensitive nitrogen oxide sensor is higher than the value measured by the sensor (46) during a phase in which no ammonia injection is performed and no NOx is present, it can be concluded that the ammonia slip catalytic converter is defective.
2. The method for monitoring an ammonia slip catalyst (34) according to claim 1, characterized in that This check is carried out during an operating phase in which the fuel injection rate is zero.
3. The method for monitoring an ammonia slip catalyst (34) according to claim 1 or 2, characterized in that: The check is carried out during operating phases in which the actual ammonia loading of the catalyst component (18) is higher than the required ammonia loading.
4. A control system for an exhaust gas aftertreatment device (10), the exhaust gas aftertreatment device having: a catalyst component (18); an ammonia slip catalyst (34) arranged downstream of the catalyst component; a sensor (46); and at least one ammonia injector (50, 54), which are arranged upstream of the ammonia slip catalyst (34); and an ammonia cross-sensitive nitrogen oxide sensor (38), which is arranged downstream of the ammonia slip catalyst (34), wherein the sensor (46) is upstream of the catalyst component (18) and the ammonia injector (50, 54), wherein the control system (14) is adapted to perform the method according to any one of claims 1 to 3.