US20130213008A1

US20130213008A1 - Method and system for improving the robustness of aftertreatment systems

Info

Publication number: US20130213008A1
Application number: US13/401,737
Authority: US
Inventors: Shankar Kumar; Krishna Kamasamudram
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2012-02-21
Filing date: 2012-02-21
Publication date: 2013-08-22
Also published as: WO2013126202A1

Abstract

A method for treating a catalyst in an internal combustion engine is disclosed. The method comprises detecting the efficiency of a catalyst; sending the catalyst efficiency to a threshold monitor; and heating the catalyst when the detected catalyst efficiency is below a predetermined percentage.

Description

FIELD OF THE INVENTION

The present invention relates generally to diesel engines and more specifically to improving the robustness of aftertreatment systems of diesel engines.

BACKGROUND OF THE INVENTION

Diesel engines are known to emit pollutants such as sulphur, nitrous oxide (NO_x), particulate matter, and unburned hydrocarbons. Despite new technologies and modern electronic control devices that aid in reducing engine-out exhaust emissions, these pollutants remain a subject of concern. In addition to adversely affecting the environment, these contaminants also hinder the overall performance of the diesel engine aftertreatment systems they are linked with. The most commonly used catalytic converter in today's modern diesel engines is the Diesel Oxidation Catalyst (DOC), which uses oxygen (O₂) in the exhaust gas stream to convert carbon monoxide (CO) and unburned hydrocarbons to water and to carbon dioxide (CO₂). The DOC however, does not effectively treat the nitrous oxide (NO_x) emissions from the diesel engines.
In addition to the DOC, selective catalytic reduction converter (SCR) and ammonia oxidation (AMO_x) catalysts are both copper-zeolite and iron-zeolite based catalysts used in diesel engine aftertreatment systems which decrease NO_xand ammonia (NH₃) emissions to help achieve near-zero emissions standards. However, a loss in oxidation functionality of the SCR and AMO_xcatalysts often leads to a decrease in the intended catalyst functions. The loss of catalysts' oxidation functionality, can some times be linked to long idling periods of the diesel engine, or exposure of the catalyst to ambient conditions for extended periods of time.
The decrease in the catalyst's oxidation functionality (also referred to as catalyst degradation) can adversely impact the performance of the diesel engine aftertreatment system. For example, in the SCR catalyst, a decrease in oxidation functionality would lead to a decrease in the catalyst's ability to convert NO_xto NO₂and to adsorbed nitrogen oxides and also a decrease in the catalyst's ability to convert unburned hydrocarbons to CO₂. The AMO_xand DOC catalysts would be similarly affected since each of these catalysts often have zeolite-based components in its formulation. Therefore, the SCR, DOC, and AMO_xcatalysts having copper-zeolite- or iron-zeolite based catalysts that would experience a decline in the aftertreatment system's feed gas quality while experiencing an increase in the diesel exhaust emissions output. Each of these undesired affects result from a loss of oxidation functionality of the copper-zeolite or iron-zeolite catalysts.
Accordingly, what is needed is a system and method of regenerating diesel engine aftertreatment catalysts in an internal combustion engine.

SUMMARY OF THE INVENTION

The present invention satisfies this need, and presents a method and system for treating a catalyst in an internal combustion engine. To achieve the above object, the present method is described as detecting the efficiency of a catalyst; sending the catalyst efficiency to a threshold monitor; and heating the catalyst when the detected catalyst efficiency is below a predetermined percentage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a typical diesel engine aftertreatment system 10.

FIG. 2 is a graphical illustration of an SCR model-based treatment of sulphur on an SCR catalyst.

FIG. 3 is a graphical illustration of the adsorption of sulphur entering the SCR.

FIG. 4 illustrates nitric oxide (NO_x) oxidation to nitrogen dioxide (NO₂).

FIG. 5 illustrates NO_xconversion of a copper-zeolite SCR catalyst in a selected temperature region.

FIG. 6 illustrates the logic flow for the proposed deSO_xcontroller.

FIG. 7 illustrates a feedforward block diagram of a proposed deSO_xcontroller 700 for use in a diesel engine aftertreatment system.

FIG. 8 illustrates a feedforward block diagram of a proposed desorb controller for use in a diesel engine aftertreatment system.

DETAILED DESCRIPTION

The present invention relates generally to diesel fuel engines and more specifically to the improved robustness of aftertreatment catalysts.
The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.
A method and system in accordance with the present invention improves the robustness of Cu-zeolite aftertreatment catalysts by using a controller for predictive and corrective actions, and also to detect and remove poisoning species from aftertreatment catalysts.
FIG. 1 is an illustration of a typical diesel engine aftertreatment system 10. The aftertreatment system 10 includes a DOC catalyst 12, an SCR catalyst 14, an AMO_xcatalyst 16, a diesel particulate filter (DPF) 18, and a diesel exhaust fluid valve 20. In some diesel engine aftertreatment systems, a DPF 18 is not utilized, which makes the overall system 10 more susceptible to sulphur, humidity, and other contaminants which would otherwise be prevented from entering the SCR catalyst 14. In addition, non-DPF diesel aftertreatment engines have greater reliance on the DOC catalyst 12 to provide the NO₂/NO_Xratios for the aftertreatment system 10 to adhere to the emissions design target. As discussed above, there are several contaminants which can adversely impact the aftertreatment system 10 including humidity, sulphur, and unburned hydrocarbons.
FIG. 2 is a graphical illustration of an SCR model-based treatment of sulphur on an SCR catalyst although sulphur is described as the contaminant, one of ordinary skill in the art recognizes that other contaminants such as humidity and unburned hydrocarbons could be present and addressed in a similar manner. In the SCR model 200, temperature 202 is an input variable. Sulphur 204 is an inlet gas feed measured in kg/s. The stored sulphur 206 is an output of the SCR model 200. The outlet rate 208 is the rate at which the sulphur is removed (desorbed) from the SCR model 200 and is measured in kg/s. The SCR model 200 shows that the storage capacity 210 (y-axis) and the outlet rate 208 are both a function of temperature. For example, the higher temperatures of 400° C. and 600° C. show a lower storage capacity 210 (y-axis) and a faster rate of sulphur removal (illustrated by the incrementally larger control valves) than the 200° C. temperature.
FIG. 3 is a graphical illustration of the normalized adsorption of sulphur entering the SCR catalyst as a function of normalized pre-stored sulfur on the catalyst. The curve 300 depicted in FIG. 3 illustrates that the sulphur entering the SCR is adsorbed (300) exponentially depending on the amount of sulfur already present on the SCR catalyst. As discussed above in FIG. 2, sulphur is a contaminant which adversely impacts the diesel engine aftertreatment system 10. Humidity is described as another example of a contaminant which adversely impacts the diesel engine aftertreatment system 10.
FIG. 4 illustrates nitric oxide (NO_x) oxidation at selected temperatures on an SCR catalyst. Unused copper-zeolite catalysts oxidation functionality (dotted curve) can be increased (solid curve) by treating the catalyst to high temperatures, such as 650° C. In addition, further exposure of the 650° C. which currently has active oxidation functionality (solid curve), to humidity at low temperatures such as 80° C., decreases the Cu-zeolite oxidation ability (dashed curve). Finally, the oxidation functionality change (dotted curve) is reversible where the degrade Cu-zeolite is treated at high temperatures such as 650° C., which fully recovered the oxidation performance (dashed curve) of the Cu-zeolite catalyst.
FIG. 5 illustrates NO_xconversion with NH3 reductant on a copper-zeolite SCR catalyst in a selected temperature region. The Cu-zeolite catalyst lost its oxidation functionality due to extended periods of storage under ambient conditions, humidity exposure, or due to long idling conditions. Accordingly, the performance of the Cu-zeolite catalyst decreases in the case of the SCR reactions such asNOx reduction with NH3 (dotted curve) and NH3 oxidation reaction in the case of AMOx catalyst (not shown). Finally, the NO_xconversion of the degraded Cu-zeolite catalyst can be recovered by high temperature treatment such as 600° C. (solid curve and dashed curve). Cu-zeolite catalyst regeneration can be achieved through various means of auxiliary or engine management techniques.
FIG. 6 illustrates the logic flow for the proposed deSO_xcontroller 600. A deSO_xis a thermal event where the engine control levers (not shown) are manipulated to achieve a catalyst temperature of approximately 550° C. or above. The engine control levers are activated by one of three triggers: a contaminant load trigger 602, a timer-based trigger 604, or a catalyst efficiencybased trigger 606. The contaminant load trigger 602 is activated when the amount of sulphur estimated by the model exceeds a predetermined threshold. The timer-based trigger 604 is activated when a predetermined time occurs. The catalyst efficiency trigger 606 is activated when a drop in the catalyst's efficiency is noted by the catalyst monitor (not shown). Long exposure of the catalysts to low temperatures for example ambient conditions or extended periods of idling could lead to poisoning of the catalysts, for example Cu-zeolite. As illustrated with FIG. 4 and FIG. 5, poisons arising from humidity cause loss of oxidation function and could also lead to loss of NOx conversion efficiency. A controller, similar to the one described in FIG. 6, that work based on humidity contaminant load trigger, for example idling time, timer based trigger and performance based trigger.
FIG. 7 illustrates a feedforward block diagram of a proposed deSO_xcontroller 700 for use in a diesel engine aftertreatment system 10′. In this instance, sulphur is the contaminant to be removed by the aftertreatment system 10′. The proposed deSO_xcontroller 700 comprises a DOC catalyst 12′, an SCR catalyst 14′ and an AMO_xcatalyst 16′. First, engine-out sulphur 702 at a predetermined temperature setpoint enters the DOC storage estimator. In step 704, the amount of stored sulphur is calculated as a function of the inlet exhaust temperature and mass flow rate. The stored sulphur is then sent to the DOC release estimator in step 706, which calculates the amount of sulphur released based on the stored sulphur from 704, and also temperature, and timing variables.
Next, in step 708, the amount of accumulated sulphur is calculated as the difference between the sulphur stored (via step 704) and the amount of sulphur released (via step 706). The accumulated sulphur from step 708 is then sent to the threshold comparator via step 710, and is also the input variable 711 for the SCR storage estimator in step 714. In step 710, the threshold comparator compares the accumulated sulphur to a predetermined threshold that is based upon NO₂/NO_x. The output of the threshold comparator in step 710 is then sent to the deSO_xthreshold monitor 712. In step 714, the inlet sulphur's temperature and mass flow rate are utilized by the SCR storage estimator to calculate stored sulphur, which is then sent to the SCR release estimator via step 716. In step 716, the SCR release estimator calculates the amount of sulphur released as a function of temperature, storage, and timing variables. The sulphur released in step 716 is then sent to step 718. In step 718, the amount of accumulated sulphur is calculated as the difference between the stored sulphur from step 714 and the released sulphur from step 716. The accumulated sulphur from step 718 is then sent to a threshold comparator via step 720, and is also the input variable 721 for the AMO_xstorage estimator in step 722. In step 720, the threshold comparator compares the accumulated sulphur to a predetermined threshold that is based on SCR catalyst efficiency. The output of the threshold comparator in step 720 is then sent to the deSOx threshold monitor 712. Note that for aftertreatment systems that do include a DPF, a suitable block needs to be included to accommodate the storage, release dynamics of sulphur on the DPF. The basic structure of the DPF block would remain the same as that of the DOC or the SCR ones.
Next, in step 722, the AMO_xstorage estimator calculates the amount of sulphur stored as a function of the inlet sulphur temperature, and the mass flow rate. The stored sulphur from step 722 is then sent to step 724, where the AMO_xrelease estimator calculates the amount of sulphur released as a function of stored sulphur (from step 722), temperature, and timing variables. The sulphur released from step 724 is then sent to step 726, where the accumulated sulphur is calculated as the difference between the stored sulphur from step 722, and the sulphur released from step 724. The accumulated sulphur of step 726 is then output as system-out sulphur 728, and secondly, the accumulated sulphur of step 726 is also input to the threshold comparator in step 730, which compares the accumulated sulphur to a predetermined threshold based upon performance of the AMO_xcatalyst.
FIG. 8 illustrates a feedforward block diagram of a proposed desorb controller 800 for use in a diesel engine aftertreatment system 10′ without a DPF. In this instance, unburned hydrocarbons is the contaminant to be removed by the aftertreatment system 10′. The proposed desorb controller 800 comprises a DOC catalyst 12′, and SCR catalyst 14′ and an AMO_xcatalyst 16′. First, engine-out hydrocarbon 802 at a predetermined temperature setpoint enters the DOC storage estimator. In step 804, the amount of stored hydrocarbon is calculated as a function of the inlet hydrocarbon's temperature and mass flow rate. The stored hydrocarbon is then sent to the DOC release estimator in step 806, which calculates the amount of hydrocarbon released based on the stored hydrocarbon from 804, and also temperature, and timing variables.
Next, in step 808, the amount of accumulated hydrocarbon is calculated as the difference between the hydrocarbon stored (via step 804) and the amount of hydrocarbon released (via step 806). The accumulated hydrocarbon from step 808 is then sent to the threshold comparator in step 810, and is also the input variable 811 for the SCR storage estimator in step 814. In step 810, the threshold comparator compares the accumulated hydrocarbon to a predetermined threshold that is based upon NO₂/NO_x. The output of the threshold comparator in step 810 is then sent to the desorb threshold monitor 812. In step 814, the inlet hydrocarbon's temperature and mass flow rate are utilized by the SCR storage estimator to calculate stored hydrocarbon, which is then sent to the SCR release estimator via step 816. In step 816, the SCR release estimator calculates the amount of hydrocarbon release as a function of temperature, storage, and timing variables. The hydrocarbon released in step 816 is then sent to step 818. In step 818, the amount of accumulated hydrocarbon is calculated as the difference between the stored hydrocarbon from step 814 and the released hydrocarbon from step 816. The accumulated hydrocarbon from step 818 is then sent to a threshold comparator via step 820, and is also the input variable 821 for the AMO_xstorage estimator in step 822. In step 820, the threshold comparator compares the accumulated hydrocarbon to a predetermined threshold that is based on SCR catalyst efficiency. The output of the threshold comparator in step 820 is then sent to the desorb threshold monitor 812, and is also the input variable 821 for the AMO_xstorage estimator.
Next, in step 822, AMO_xstorage estimator calculates the amount of hydrocarbon stored as a function of temperature, and mass flow rate. The stored hydrocarbon from step 822 is then sent to step 824, where the AMO_xrelease estimator calculates the amount of hydrocarbon released as a function of temperature, storage, and time. The released hydrocarbon in step 824 is then sent to step 826, where the accumulated hydrocarbon is calculated as the difference between the stored hydrocarbon from step 822, and the hydrocarbon released from step 824. In addition, the hydrocarbon released in step 824 also goes to the exotherm predictor in step 827. The accumulated hydrocarbon of step 826 is then output as system-out unburned hydrocarbon via step 830, and secondly, the accumulated hydrocarbon of step 826 is then input to the threshold comparator in 832, which compares the accumulated hydrocarbon to a predetermined threshold based upon performance of the AMO_xcatalyst.
One advantage of a system and method in accordance with the present invention is that the system robustness is improved due to the predictive and corrective actions produced by the proposed controller.
A second advantage of a system and method in accordance with the present invention is that the proposed controller enables the virtual sensing of the catalyst poisons, which allows for removal of the poisons from the aftertreatment system.
A third advantage of a system and method in accordance with the present invention is that the proposed controller works complementary to the existing sensor set currently available within the existing architecture of a diesel engine.
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one or ordinary skill in the art without departing from the spirit and scope of the appended claims.

Claims

What is claimed is:

1. A method of treating a catalyst in an internal combustion engine comprising:

detecting efficiency of a catalyst;

sending the catalyst efficiency to a threshold monitor; and

heating the catalyst when the detected catalyst efficiency is below a predetermined percentage.

2. The method of claim 1 comprising detecting the efficiency of the catalyst based on the threshold monitor.

3. The method of claim 1 wherein the catalyst comprises a copper-zeolite based catalyst.

4. The method of claim 2 wherein the threshold monitor comprises a sulphur estimator.

5. The method of claim 2 wherein the threshold monitor comprises a catalyst efficiency monitor.

6. The method of claim 2 wherein the threshold monitor comprises a timing device.

7. The method of claim 2 wherein the threshold monitor comprises a humidity monitor.

8. The method of claim 1 wherein heating the catalyst in response to the predetermined percentage further comprises regenerating the catalyst by applying a high temperature treatment.

9. The method of claim 7 wherein regenerating the catalyst by a high temperature treatment further comprises temperatures of at least 650° C.

10. The method of claim 8 wherein the high temperature treatment increases the oxidation functionality of the catalyst.

11. The method of claim 1 wherein heating the catalyst in response to the predetermined percentage comprises a thermal event.

12. The method of claim 6 wherein the thermal event comprises a system deSO_xwhich removes sulphur from the internal combustion engine.

13. The method of claim 6 wherein the thermal event comprises a system desorb which removes unburned hydrocarbons from the internal combustion engine.

14. A system for treating a catalyst in an internal combustion engine comprising:

a diesel exhaust fluid valve; and

a plurality of threshold monitors for initiating a catalyst regeneration.

15. The system of claim 14 further comprising a diesel particulate filter (DPF).

16. The system of claim 14 wherein the catalyst comprises a DOC, SCR, or AMO_xcatalyst.

17. The system of claim 14 wherein the threshold monitors comprise a timing device, a sulphur estimator, a catalyst efficiency monitor, or a humidity monitor.

18. The system of claim 14 wherein the catalyst regeneration comprises heating the system to a temperature of at least 200° C.

19. An engine system comprising:

an engine; and

a catalyst system coupled to the engine; wherein the catalyst system comprises a catalyst; a diesel exhaust fluid valve; and a plurality of threshold monitors for initiating a catalyst regeneration.

20. The engine system of claim 19 further comprising a diesel particulate filter (DPF).