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 
       [0001]    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 
       [0002]    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&#39;s modern diesel engines is the Diesel Oxidation Catalyst (DOC), which uses oxygen (O 2 ) in the exhaust gas stream to convert carbon monoxide (CO) and unburned hydrocarbons to water and to carbon dioxide (CO 2 ). The DOC however, does not effectively treat the nitrous oxide (NO x ) emissions from the diesel engines. 
         [0003]    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 x  and ammonia (NH 3 ) emissions to help achieve near-zero emissions standards. However, a loss in oxidation functionality of the SCR and AMO x  catalysts often leads to a decrease in the intended catalyst functions. The loss of catalysts&#39; 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. 
         [0004]    The decrease in the catalyst&#39;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&#39;s ability to convert NO x  to NO 2  and to adsorbed nitrogen oxides and also a decrease in the catalyst&#39;s ability to convert unburned hydrocarbons to CO 2 . The AMO x  and 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 x  catalysts having copper-zeolite- or iron-zeolite based catalysts that would experience a decline in the aftertreatment system&#39;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. 
         [0005]    Accordingly, what is needed is a system and method of regenerating diesel engine aftertreatment catalysts in an internal combustion engine. 
       SUMMARY OF THE INVENTION 
       [0006]    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 
         [0007]      FIG. 1  is an illustration of a typical diesel engine aftertreatment system  10 . 
           [0008]      FIG. 2  is a graphical illustration of an SCR model-based treatment of sulphur on an SCR catalyst. 
           [0009]      FIG. 3  is a graphical illustration of the adsorption of sulphur entering the SCR. 
           [0010]      FIG. 4  illustrates nitric oxide (NO x ) oxidation to nitrogen dioxide (NO 2 ). 
           [0011]      FIG. 5  illustrates NO x  conversion of a copper-zeolite SCR catalyst in a selected temperature region. 
           [0012]      FIG. 6  illustrates the logic flow for the proposed deSO x  controller. 
           [0013]      FIG. 7  illustrates a feedforward block diagram of a proposed deSO x  controller  700  for use in a diesel engine aftertreatment system. 
           [0014]      FIG. 8  illustrates a feedforward block diagram of a proposed desorb controller for use in a diesel engine aftertreatment system. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The present invention relates generally to diesel fuel engines and more specifically to the improved robustness of aftertreatment catalysts. 
         [0016]    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. 
         [0017]    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. 
         [0018]      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 x  catalyst  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 NO 2 /NO X  ratios 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. 
         [0019]      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. 
         [0020]      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 . 
         [0021]      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. 
         [0022]      FIG. 5  illustrates NO x  conversion 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 x  conversion 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. 
         [0023]      FIG. 6  illustrates the logic flow for the proposed deSO x  controller  600 . A deSO x  is 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&#39;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. 
         [0024]      FIG. 7  illustrates a feedforward block diagram of a proposed deSO x  controller  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 x  controller  700  comprises a DOC catalyst  12 ′, an SCR catalyst  14 ′ and an AMO x  catalyst  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. 
         [0025]    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 NO 2 /NO x . The output of the threshold comparator in step  710  is then sent to the deSO x  threshold monitor  712 . In step  714 , the inlet sulphur&#39;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 x  storage 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. 
         [0026]    Next, in step  722 , the AMO x  storage 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 x  release 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 x  catalyst. 
         [0027]      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 x  catalyst  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&#39;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. 
         [0028]    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 NO 2 /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&#39;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 x  storage 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 x  storage estimator. 
         [0029]    Next, in step  822 , AMO x  storage 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 x  release 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 x  catalyst. 
         [0030]    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. 
         [0031]    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. 
         [0032]    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. 
         [0033]    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.