Abstract:
A method and a system for determining if fuel containing more than the desired concentration of sulfur is being combusted in an engine. The engine includes a selected catalytic reduction (SCR) module or a lean NOx trap (LNT) and the system includes various sensors and a controller for calculating NOx conversion ratio and ammonia slip. Timers are utilized for purposes of positively identifying when sulfur in the fuel is causing a substandard performance of the exhaust system. If the timers or time periods are not satisfied, a conversion ratio failure or an ammonia slip failure is attributable to equipment failure, and not sulfur in the fuel. However, if the timers are satisfied, then sulfur in the fuel is positively identified as the problem thereby enabling the operator to eliminate equipment failure as a possible source of the conversion ratio or ammonia slip failure.

Description:
TECHNICAL FIELD 
       [0001]    This document discloses various methods and systems for detecting contaminant concentrations in a fuel. For example, this document discloses methods and systems for detecting sulfur concentrations in a fuel, such as diesel fuel. Still more specifically, this document discloses methods and systems for detecting if a low sulfur diesel (LSD) has been introduced into an engine intended to run on ultra-low sulfur diesel (ULSD). 
       BACKGROUND 
       [0002]    Power systems for engines, factories, and power plants produce emissions that contain a variety of pollutants. These pollutants may include, for example, particulate matter (e.g., soot), nitrogen oxides (NOx), and sulfur compounds. Due to heightened environmental concerns, engine exhaust emission standards have become increasingly stringent. In order to comply with emission standards, engine manufactures have developed and implemented a variety of exhaust after-treatment components to reduce pollutants in exhaust gas prior to the release of exhaust gas into the atmosphere. 
         [0003]    The exhaust after-treatment components may include, for example, a diesel particulate filter (DPF), one or more selective catalytic reduction (SCR) devices, a lean NOx trap (LNT), a diesel oxidation catalyst (DOC), an ammonia oxidation catalyst (AMOX), a heat source for regeneration of the DPF, an exhaust gas recirculation (EGR) system, a muffler, and other similar devices. This document is directed to power systems equipped with NOx aftertreatment components, with or without additional components. 
         [0004]    A NOx abatement catalyst module converts nitrogen NOx, with the aid of a catalyst, into diatomic nitrogen, N 2 , and water, H 2 O. A reductant, typically anhydrous ammonia, aqueous ammonia or urea, is injected upstream of the NOx abatement catalyst module so the reductant is adsorbed onto a catalyst of the SCR. Gaseous or liquid reductant may be injected into the exhaust stream. Liquid reductants are often referred to as diesel emission fluids (DEFs). DEF has become popular because of its liquid form, which is easy to store and handle. Further, DEF reduces the need to rely upon EGR to meet modern emission requirements. 
         [0005]    Both SCR and LNT components may utilize platinum group metal (PGM) catalysts. As a result, exhaust after-treatment systems are sensitive to sulfur content in fuel because sulfur adsorbs onto and fouls PGM catalysts. Desulfation of a PGM catalyst requires permitting the exhaust gas to reach high temperatures (e.g., a catalyst bed temperature of about 650° C.) at a rich air/fuel ratio for an extended period, typically requiring at least several minutes of high-idle operation and an inconvenience to the operator. Desulfation occurs periodically, typically every 50 to 150 hours of engine operation, depending on the level of sulfur in the fuel, fuel consumption of the engine, and the NOx storage capacity of the PGM catalyst. Further, the use of PGM catalysts typically requires the use of ultra-low sulfur diesel (ULSD) fuel having a sulfur concentration of 15 ppm or less as opposed to low sulfur diesel (LSD) fuel having a sulfur concentration of 500 ppm or less in order to extend the time period between desulfation events. The inadvertent use of LSD fuel will quickly reduce the NOx reducing ability of a PGM catalyst. 
         [0006]    Thus, when the sulfur content in the fuel is higher than expected, such as when LSD is erroneously added to the fuel tank instead of ULSD, time-based regenerations are inadequate and the NOx reducing performance of the exhaust after-treatment system is quickly reduced. While systems and methods for monitoring the performance of exhaust after-treatment systems may be useful for maintaining the performance of the exhaust after-treatment system, such monitoring systems do not identify why the after-treatment system is performing in a substandard fashion. Further, if an operator mistakenly uses LSD fuel, more frequent desulfations of the PGM catalyst must be carried out, which leads to frustration over increased fuel consumption and reduced available utilization time corresponding to the time it takes to regenerate the PGM catalyst. 
         [0007]    US Patent Publication No. 2011/0271569 discloses a sensor for detecting sulfur in an exhaust stream that is positioned upstream of an exhaust after-treatment system. However, US Patent Publication No. 2011/0271569 does not disclose a means for a real-time detection of whether the sulfur content of the fuel is fouling an SCR catalyst. 
         [0008]    Thus, there is a need for an exhaust aftertreatment control system that can quickly identify if a reduced NOx abatement performance of an exhaust aftertreatment system is being caused by the sulfur content of the fuel or if the reduced NOx abatement performance has an alternative cause, such as an equipment malfunction. 
       SUMMARY 
       [0009]    In one aspect, this document discloses a method for detecting if a fuel containing more than a sulfur concentration threshold value is being combusted in an engine. The engine may include a selective catalytic reduction (SCR) module. The disclosed method may include desulfating the NOx abatement catalyst module and detecting a proper functioning of the NOx abatement catalyst module. The detecting of the proper functioning of the NOx abatement catalyst module may be carried out by at least one of the following: detecting a NOx conversion ratio that is above a NOx conversion ratio threshold value; and detecting an ammonia slip value downstream of the NOx abatement catalyst module that is below an ammonia slip threshold value. The method may further include detecting a malfunction of the NOx abatement catalyst module by at least one of the following: detecting that the NOx conversion ratio is below the NOx conversion ratio threshold value; and detecting that the ammonia slip value downstream of the NOx abatement catalyst module is above the ammonia slip threshold value. The method may further include determining a first operating time of the engine between the desulfating and the detecting of the malfunction. If the first operating time is less than a predetermined maximum time and greater than a predetermined minimum time, the method may include increasing a frequent desulfation counter by 1. Further, the method may include sending a fault signal indicating that the sulfur concentration of the fuel exceeds the sulfur concentration threshold value concentration when the frequent desulfation counter exceeds a FDC threshold value. 
         [0010]    In another aspect, this document discloses a system for detecting when an engine is combusting fuel containing more than a sulfur concentration threshold value. The system may include a selective catalytic reduction (SCR) module that includes an SCR catalyst. The system may further include at least one sensor for detecting at least one of the following: a NOx concentration downstream of the NOx abatement catalyst module; and a NH 3  concentration downstream of the NOx abatement catalyst module. The at least one sensor may be linked to a controller. The controller may be configured to calculate at least one of a conversion ratio of NOx by the NOx abatement catalyst module and a degree of ammonia slip. The controller may further be configured to initiate desulfation of the SCR catalyst if at least one of the conversion ratio or the degree of ammonia slip fails to meet at least one predetermined criteria. The controller may further be configured to record when a desulfation is complete and the controller may further be configured to determine a desulfation request time (DRT) between completion of a desulfation and initiation of a new desulfation. The controller may further be configured to increment a frequent desulfation counter (FDC) each time the DRT is greater than a predetermined minimum time and less than a predetermined maximum time. The controller may further be configured to initiate a sulfur alarm signal when the FDC reaches a NOx conversion ratio threshold value. 
         [0011]    This document also discloses a power system. The disclosed power system may include an engine that includes a manifold exhaust passage in communication with a selective catalytic reduction (SCR) module that includes an SCR catalyst. The NOx abatement catalyst module may be in communication with an exhaust outlet. The power system may further include at least one sensor for detecting at least one of the following: a NOx concentration downstream of the NOx abatement catalyst module; and a NH 3  concentration downstream of the NOx abatement catalyst module. The at least one sensor may be linked to a controller. The controller may be configured to calculate at least one of a conversion ratio of NOx by the NOx abatement catalyst module and a degree of ammonia slip. The controller may be further configured to initiate desulfation of the SCR catalyst if at least one of the conversion ratio or the degree of ammonia slip fails to meet at least one of a predetermined criteria. The controller may further be configured to record when a desulfation is complete. The controller may further be configured to determine a desulfation request time (DRT) between completion of a desulfation and initiation of a new desulfation. The controller may further be configured to increment a frequent desulfation counter (FDC) each time the DRT is greater than a predetermined minimum time period and less than a predetermined maximum time period. The controller may further be configured to initiate a sulfur alarm signal when the FDC reaches a NOx conversion ratio threshold value. 
         [0012]    The features, functions, and advantages discussed above may be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail on the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a schematic and diagrammatic illustration of an exemplary disclosed power system. 
           [0015]      FIG. 2  is a time line that schematically illustrates the desulfation request timer (DRT), the frequent slip timer (FST) and the frequent desulfation timer (FDT). 
           [0016]      FIG. 3  is a flow chart illustrating the action of a controller when the desulfation request timer (DRT) exceeds a predetermined maximum time period. 
           [0017]      FIG. 4  is a flow chart illustrating the indexing of the frequent desulfation counter (FDC) and the infrequent desulfation counter (IDC). 
           [0018]      FIG. 5  is a flow chart illustrating the disclosed system and method for determining whether the sulfur concentration in the fuel being combusted is causing the decreased conversion ratio or ammonia slip failure or whether a component malfunction is causing the failure. 
       
    
    
       [0019]    The drawings are not necessarily to scale and illustrate the disclosed embodiments diagrammatically and in partial views. In certain instances, this disclosure may omit details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive. Further, this disclosure is not limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates an exemplary power system  10 . For the purposes of this disclosure, the power system  10  is depicted and described as a diesel-fueled, internal combustion engine. However, it is contemplated that the power system  10  may embody any other type of combustion engine, such as, for example, a gasoline or a gaseous fuel-powered engine burning compressed or liquefied nature gas, propane, etc. The power system  10  may include an engine block  12  that may at least partially define a plurality of cylinders  13 , and a plurality of piston assemblies (not shown) disposed within the cylinders  13 . It is contemplated that power system  10  may include any number of cylinders  13  and that the cylinders  13  may be disposed in an “in-line” configuration, a “V” configuration, or any other conventional configuration. 
         [0021]    Multiple separate sub-systems may be included within the power system  10 . For example, the power system  10  may include an air induction system  14  and an exhaust system  15 . The air induction system  14  may direct air or an air and fuel mixture into the power system  10  for subsequent combustion. The exhaust system  15  may exhaust the byproducts of combustion to the atmosphere. The operation of air induction and exhaust systems  14 ,  15  may be controlled to reduce the production of regulated constituents and their discharge to the atmosphere. 
         [0022]    The air induction system  14  may include multiple components that cooperate to condition and introduce compressed air into the cylinders  13 . For example, the air induction system  14  may include an air cooler  17  located downstream of a compressor  18 , although a plurality of compressors may be employed. The compressor  18  may connect to pressurize inlet air directed through the air cooler  17 . A throttle valve (not shown) may be located upstream of the compressor  18  to selectively regulate (i.e., restrict) the flow of inlet air into power system  10 . A restriction may result in less air entering the power system  10  and, thus, affect an air-to-fuel ratio of power system  10 . It is contemplated that the air induction system  14  may include different or additional components than described above such as, for example, variable valve actuators associated with each cylinder  13 , filtering components, compressor bypass components, and other known components that may be controlled to affect the air-to-fuel ratio of power system  10 . It is further contemplated that the compressor  18  and/or the air cooler  17  may be omitted, if the power system  10  is naturally aspirated. 
         [0023]    The exhaust system  15  may include multiple components that condition and direct exhaust from the cylinders  13  to the atmosphere. For example, the exhaust system  15  may include an exhaust manifold conduit  19 , an exhaust outlet  21  and a turbine  22 . Although a single turbine  22  is shown in  FIG. 1  for purposes of clarity, a plurality of turbines may be employed. The turbine  22  is driven by the exhaust flowing through exhaust manifold conduit  19 . The exhaust system  15  may further include a NOx abatement catalyst module  23  fluidly connected downstream of the turbine  22 . The NOx abatement catalyst module  23  may be a SCR module or another catalyst module capable of reducing NOx in the exhaust, as will be apparent to those skilled in the art. The exhaust system  15  may further include different or additional components than described above such as bypass components, an exhaust compression or restriction brake, a sound attenuation device, additional exhaust treatment devices, and other known components. 
         [0024]    The turbine  22  may be located to receive exhaust leaving the engine block  12 , and may connect to the compressor  18  of the air induction system  14  by way of a common shaft  24  to form a turbocharger. As the hot exhaust gases exit the power system  10  and move through the turbine  22  and expand against the vanes (not shown) thereof, the turbine  22  may rotate and drive the connected compressor  18  to pressurize the inlet air. In one embodiment, the turbine  22  may be a variable geometry turbine (VGT) or include a combination of variable and fixed geometry turbines. 
         [0025]    The NOx abatement catalyst module  23  may receive exhaust from the turbine  22  and reduce constituents of the exhaust to innocuous gases. In one example, the NOx abatement catalyst module  23  may include a catalyst substrate (not shown) located downstream from a reductant injector  25 . A gaseous or liquid reductant, most commonly urea ((NH 2 ) 2 CO), a water/urea mixture, a hydrocarbon for example diesel fuel, or ammonia gas (NH 3 ), may be sprayed or otherwise advanced into the exhaust upstream of the NOx abatement catalyst module  23  by the reductant injector  25 . For this purpose, an onboard reductant supply  26  and a pressurizing device or a pump  27  may be associated with the reductant injector  25 . As the reductant is adsorbed onto the surface of catalyst substrate (not shown) of the NOx abatement catalyst module  23 , the reductant may react with NOx (NO, NO 2 , and NO 3 ) in the exhaust stream to form water (H 2 O) and elemental nitrogen (N 2 ). The reduction process performed in the NOx abatement catalyst module  23  may be most effective when a ratio of NO to NO 2  supplied to the NOx abatement catalyst module  23  is adjusted to optimize the NOx reduction at the catalyst. 
         [0026]    To help provide a more optimal concentration of NO to NO 2  at the NOx abatement catalyst module  23 , an oxidation catalyst, such as a diesel oxidation catalyst (DOC) may be located upstream of the NOx abatement catalyst module  23 , and in some embodiments, in the form of an optional combined diesel oxidation catalyst/diesel particulate filter (DOC/DPF) module  28 . The oxidation catalyst may include a porous ceramic honeycomb structure or a metal mesh substrate coated with a material, such as a precious metal that catalyzes a chemical reaction to alter the composition of the exhaust. For example, the oxidation catalyst may include palladium, platinum, vanadium, or a mixture thereof that facilitates the conversion of NO to NO 2 . 
         [0027]    During operation of the power system  10 , it may be possible for too much urea or too much ammonia to be injected into the exhaust (i.e., urea or ammonia in excess of that required for appropriate NOx reduction). In this situation, known as “ammonia slip,” some amount of ammonia may pass through the NOx abatement catalyst module  23  to the atmosphere, if not otherwise accounted for. To minimize the magnitude of ammonia slip, an ammonia oxidation (AMOx) module  29  may optionally be located downstream of the NOx abatement catalyst module  23 . The AMOx module  29  may include a substrate coated with a catalyst that oxidizes residual NH 3  in the exhaust to form water and elemental nitrogen (N 2 ). 
         [0028]    The power system  10  may include components configured to regulate the treatment of the exhaust prior to its discharge to the atmosphere. Specifically, the power system  10  may include a controller  31  in communication with a plurality of sensors  32 - 39  (the communication lines are not shown in  FIG. 1  for purposes of clarity). The controller  31  may also be in communication with the pump  27 . Based on inputs from the sensors  32 - 39 , the controller  31  may determine an amount of NOx being produced by power system  10 , an operational parameter of the NOx abatement catalyst module  23  and an optimal amount of urea to be sprayed by the reductant injector  25  into the exhaust passageway  41  based on the NOx production amount and the operational parameter. Using the sensors  32 - 39 , the controller  31  may also determine a performance parameter of the NOx abatement catalyst module  23  and an adjustment of the urea injection based on the performance parameter. The controller  31  may then regulate operation of the reductant injector  25  and the pump  27  such that the adjusted amount of urea is sprayed into the exhaust flow upstream of the NOx abatement catalyst module  23 . 
         [0029]    The controller  31  may embody a single or multiple microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), etc. that include a means for controlling an operation of power system  10  in response to signals received from the various sensors. Numerous commercially available microprocessors may perform the functions of the controller  31 . The controller  31  may embody a microprocessor separate from that controlling other non-exhaust related power system functions, or the controller  31  may be integral with a general power system microprocessor and be capable of controlling numerous power system functions and modes of operation. If separate from the general power system microprocessor, the controller  31  may communicate with the general power system microprocessor via datalinks or other methods. Various other known circuits may be associated with the controller  31 , including power supply circuitry, signal-conditioning circuitry, actuator driver circuitry (i.e., circuitry powering solenoids, motors, or piezo actuators), communication circuitry, and other appropriate circuitry. 
         [0030]    A first sensor  32  of the power system  10  may be a constituent sensor configured to generate a signal indicative of the presence of a particular constituent within the exhaust flow. For example, the sensor  32  may be an engine-out NOx sensor configured to determine an amount (i.e., quantity, relative percent, ratio, etc.) of NO and/or NO 2  present within the exhaust of the power system  10 . If embodied as a physical sensor, the engine-out NOx sensor  32  may be located upstream or downstream of the optional DOC/DPF module  28 . Whether located upstream or downstream of the oxidation catalyst of the optional DOC/DPF module  28 , the engine-out NOx sensor  32  may be situated to sense a production of NOx by the power system  10 . The engine-out NOx sensor  32  may generate a signal indicative of these measurements and send the signal to the controller  31 . 
         [0031]    The engine-out NOx sensor  32  may alternatively embody a virtual sensor. A virtual sensor may produce a model-driven estimate based on one or more known or sensed operational parameters of the power system  10  and/or the optional DOC/DPF module  28 . For example, based on a known operating speed, load, temperature, boost pressure, ambient conditions (humidity, pressure, temperature), and/or other parameters of the power system  10 , a model may be referenced to determine an amount of NO and/or NO 2  produced by power system  10 . Similarly, based on a known or estimated NOx production of the power system  10 , a flow rate of exhaust exiting the power system  10 , and/or a temperature of the exhaust, the model may be referenced to determine an amount of NO and/or NO 2  leaving the optional DOC/DPF module  28  and entering the NOx abatement catalyst module  23 . As a result, the signal directed from engine-out NOx sensor  32  to the controller  31  may be based on calculated and/or estimated values rather than direct measurements. Rather than employing a separate element, virtual sensing functions may be accomplished by the controller  31 . 
         [0032]    The operational parameters of the NOx abatement catalyst module  23  may be monitored by way of the temperature sensor  34  and/or the flow meter sensor  35 . The temperature sensor  34  may be located anywhere within exhaust system  15  to generate a signal indicative of an operating temperature of the NOx abatement catalyst module  23 . In one example, the temperature sensor  34  may be located upstream of the NOx abatement catalyst module  23 . In another example, the temperature sensor  34  may be located in contact with or downstream of the NOx abatement catalyst module  23 . The flow meter sensor  35  may embody any type of sensor utilized to generate a signal indicative of an exhaust flow rate through the NOx abatement catalyst module  23 . The temperature and/or flow rate signals may be utilized by the controller  31  to determine a NOx reducing capacity of the NOx abatement catalyst module  23 . That is, based on known dimensions and the age of the catalyst of the NOx abatement catalyst module  23 , and based on the measured operational parameters, a NOx reducing performance of the NOx abatement catalyst module  23  may be predicted. It is contemplated that the flow meter sensor  35  may alternatively embody a virtual sensor, similar to the engine-out NOx sensor  32 . 
         [0033]    Similar to the NOx abatement catalyst module  23 , the operation of the optional DOC/DPF module  28  may be monitored by way of the temperature sensor  34  or another dedicated temperature sensor (not shown). The temperature signal may be utilized by the controller  31  to determine a model driven estimate of the ratio or split of NO:NO 2  exiting the optional DOC/DPF module  28 . 
         [0034]    Thus, a NOx production signal, a temperature signal, and a flow rate signal from sensors  32 ,  34 ,  35 , may be utilized by the controller  31  to determine an optimal amount of reductant to be injected via the reductant injector  25  to reduce the produced NOx to a regulated level or less. The controller  31  may also subsequently adjust the injection amount based on actual performance parameters measured downstream of the NOx abatement catalyst module  23 . That is, after an initial reductant injection of the quantity determined above, controller  31  may sense the actual performance of the NOx abatement catalyst module  23  and adjust future reductant injections accordingly. For this purpose, the power system  10  may include a post-aftertreatment NOx sensor  36  located downstream of the NOx abatement catalyst module  23 . This process of adjusting the injection amount based on a measured performance parameter is known as feedback control. 
         [0035]    Similar to the engine-out NOx sensor  32 , the post-aftertreatment NOx sensor  36  may also generate a signal indicative of the presence of NOx within the exhaust flow. For instance, the post-aftertreatment NOx sensor  36  may determine an amount (i.e., quantity, relative percent, ratio, etc.) of NO and/or NO 2  present within the exhaust flow downstream of the NOx abatement catalyst module  23 . The post-aftertreatment NOx sensor  36  may generate a signal indicative of these measurements and send it to the controller  31 . If the amount of NOx monitored by the post-aftertreatment NOx sensor  36  exceeds a threshold level, the controller  31  may provide feedback to the reductant injector  25  to increase the amount of urea (or ammonia) injected into the exhaust passageway  41  to reduce NOx within the NOx abatement catalyst module  23 . In contrast, if the amount of NOx monitored by the post-aftertreatment NOx sensor  36  is below a threshold level, less urea (or ammonia) may be injected in an attempt to conserve urea (or ammonia) and/or extend the useful life of oxidation catalyst within the AMO x  module  29 . Alternatively, the post-aftertreatment NOx sensor  36  may embody a sensor useful in determining the amount of NH 3  entering the AMO x  module  29 . 
         [0036]    If the oxidation catalyst of the optional DOC/DPF module  28  is overloaded with particulate matter, the relative amount of NO 2  received by the NOx abatement catalyst module  23  could be negatively affected, even though the optional DOC/DPF module  28  may be properly converting NO to NO 2 . To accommodate this situation, the soot loading of the oxidation catalyst of the optional DOC/DPF module  28  may be monitored, and the operation of the NOx abatement catalyst module  23  adjusted accordingly. For this purpose, an additional sensor  33  may be associated with oxidation catalyst of the optional DOC/DPF module  28 . The sensor  33  may embody any type of sensor utilized to determine an amount of particulate buildup within an oxidation catalyst. For example, the sensor  33  may embody a pressure sensor or pair of pressure sensors, a temperature sensor, a model driven virtual sensor, an RF sensor, or any other type of sensor known in the art. The sensor  33  may generate a signal directed to the  31  indicative of a particulate buildup, and the controller  31  may adjust the injection of reductant through the reductant injector  25  accordingly. 
         [0037]    The controller  31  may also adjust reductant injections based on an amount of urea available for injection. Thus, the power system  10  may include a sensor  37  associated with the reductant supply  26 . The sensor  37  may be a temperature sensor, a viscosity sensor, a fluid level sensor, a pressure sensor, or any other type of sensor configured to generate a signal indicative of an amount of urea (or ammonia or reductant) available for injection. This signal may be directed from sensor  37  to the controller  31 . 
         [0038]    As noted above, in some situations, too much urea or reductant may be injected resulting in “ammonia slip.” Although the AMO x  module  29 , if present, may oxidize the slipping ammonia such that little, if any, ammonia is exhausted to the atmosphere, the extra ammonia may still unnecessarily increase the operational costs of the power system  10 . For this reason, the controller  31  may adjust reductant injections based on a measured amount of ammonia downstream of the NOx abatement catalyst module  23  or upstream or downstream of the AMO x  module  29 . Ammonia slip may be monitored by a sensor  38 , which may be a virtual sensor that generates an ammonia slip signal based on post processing of a signal generated by a true NOx sensor. Thus, the sensor  38  may be an NOx sensor that may be used to virtually detect ammonia slip. 
         [0039]    The interaction of the controller  31  with the sensors  32 - 38  is further illustrated in  FIGS. 2-5 .  FIG. 2  is a timeline that illustrates certain times between events that are recorded and used by the controller  31  to determine whether fuel with a sulfur concentration above a threshold concentration (e.g., 15 ppm) is being combusted in the cylinders  13 . At  51 , the controller  31  has determined a failure in either: (1) a conversion ratio of the NOx (i.e., the concentration of NOx detected by the sensor  32  minus the concentration of NOx detected by the post-aftertreatment NOx sensor  36  divided by the concentration of NOx detected by the engine-out NOx sensor  32 ); or (2) a degree of ammonia slip detected by the sensor  38 . If either the NOx conversion ratio falls below an NOx conversion ratio threshold value or the ammonia slip falls above an ammonia slip threshold value, the controller  31  registers a failure and initiates a request for desulfation of the catalyst of the NOx abatement catalyst module  23 . Desulfation may be carried out in a variety of ways most of which include permitting the catalyst bed of the NOx abatement catalyst module  23  to reach an elevated temperature of about 550° C. When the desulfation is complete at  52 , a desulfation request time or timer (DRT) is initiated as shown in  FIG. 2 . The DRT is the time between completion of a desulfation at  52  and a subsequent conversion ratio or slip failure and a request for a new desulfation at  53 . Typically, if a fuel containing too much sulfur, such as LSD, is combusted in the power system  10 , the time between a completed desulfation at  52  and a subsequent conversion ratio or ammonia slip failure at  53  will fall within a time range that is greater than about 3 hours and less than about 10 hours. Specifically, if the DRT, or the time between a completed desulfation at  52  and a subsequent conversion ratio or ammonia slip failure at  53 , is less than 3 hours, it is evident that a component of the power system  10  is malfunctioning and the subsequent conversion ratio or ammonia slip failure at  53  is not caused by a sulfur buildup on the catalyst because it takes a minimum of about 3 hours for LSD to foul a properly desulfated catalyst. Thus, if DRT is less than 3 hours, a malfunction in the exhaust system  15  cannot be caused exclusively by LSD or a fuel with an excessive amount of sulfur. Similarly, if DRT exceeds 10 hours, excess sulfur in the fuel may be ruled out as the cause of the subsequent conversion ratio or slip failure at  53  because, if the power system  10  was burning LSD fuel, the conversion ratio or slip failure would occur before the duration of 10 hours, not after 10 hours has elapsed. Thus, for a conversion ratio or ammonia slip failure to be attributable to sulfur in the fuel, the DRT should fall within the 3 to 10 hour time range in this example. Of course, the lower and upper limits for the DRT may vary, as will be apparent to those skilled in the art. 
         [0040]    Still referring to  FIG. 2 , if an ammonia slip sensor  38  ( FIG. 1 ) is employed, the controller  31  may send a signal to activate or deactivate the ammonia slip sensor  38  as needed. As shown in  FIG. 2 , the time between an activation of the ammonia slip sensor  38  at  54  and the subsequent conversion ratio or slip failure at  53  is referred to as the frequent slip time or timer (FST). The FST must be greater than about 3 hours for sulfur in the fuel to cause the subsequent conversion ratio or ammonia slip failure at  53 . If the FST is less than 3 hours, the problem is attributed to a component malfunction or a problem other than fouling of the catalyst of the NOx abatement catalyst module  23 . Further, after a conversion ratio or slip failure at  51  and a subsequent desulfation at  52 , the controller  31  continuously monitors data from the sensors  32 ,  36 ,  38 . When a conversion ratio or ammonia slip measurement passes at  55  (i.e., the conversion ratio of NOx exceeds a threshold value and an ammonia slip value falls below a threshold value), the frequent desulfation timer (FDT) is initiated at  55 . As shown in  FIG. 2 , FDT represents the time between a conversion ratio and ammonia slip pass at  55  and a subsequent conversion ratio or ammonia slip failure at  53 . To register a conversion ratio and ammonia slip pass at  55 , for the power system  10  shown in  FIG. 1 , both the data from the NOx sensors  32 ,  36  as well as the data from the ammonia slip sensor  38  must satisfy the threshold criteria. In other words, both NOx and ammonia slip (if both types of sensors are utilized) must pass at  55  while either the NOx conversion ratio or ammonia slip value can fail at  53  to register a failure. 
         [0041]      FIG. 3  illustrates a situation where sulfur in the fuel is not causing a conversion ratio or ammonia slip failure. The controller  31  registers a conversion ratio or an ammonia slip failure at  51  (and requests desulfation) and the desulfation is complete at  52 . Then, the controller  31  registers a conversion ratio and an ammonia slip pass at  55  followed by a failure at  53 . If the DRT (desulfation request timer) and the FST (frequent slip timer) are both greater than 3 hours at  56  and the DRT is greater than 10 hours at  57 , then the fouling problem that occurred at  53  is not attributable to sulfur in the fuel and, therefore an equipment failure or alarm signal is issued at  58 . The equipment failure or alarm signal may be an audible tone or lamp in an operator cab or may be a flag readable as an error code on a diagnostic device among other potential signals. 
         [0042]    Turning to  FIG. 4 , when the controller  31  determines that desulfation is complete at  52 , a subsequent conversion ratio or slip failure occurs at  53 , and the FDT (frequent desulfation timer) is less than 5 hours at  59 , a frequent desulfation counter (FDC) is incremented by 1 at  61 . If the FDT is not less than 5 hours or is greater than 5 hours at  59 , then an infrequent desulfation counter is indexed by 1 at  62 . Further, if the IDC (infrequent desulfation counter) is equal to 2 or more at  63 , then the FDC is reset to 0 at  64 . 
         [0043]    It will be noted that the time periods discussed above in connection with  FIGS. 2-4  may be varied, depending upon the size and structure of the NOx abatement catalyst module  23  and various parameters of the power system  10 . For example, the threshold time period for the FDT (frequent desulfation timer) in order for the FDC (frequent desulfation counter) to be incremented may range from about 3 hours to about 7 hours as opposed to the 5 hours indicated in  FIG. 4 . Further, the requisite time period for the FST (frequent slip timer) in order for fouling to be attributable to fuel may vary from the 3 hours set forth in  FIGS. 2-3  and may range from about 2 to about 4 hours. Further, in order for fouling to be attributable to fuel, the indicated range for the DRT (desulfation request timer) may vary from the stated 3-10 hour change. The lower end of this range should correspond that of the FST, and may vary from about 2 to about 4 hours and the upper range for the DRT may range from about 6 to about 15 hours, again depending upon the structure of the NOx abatement catalyst module, the particular power system  10 , the particular catalyst utilized, and a host of other factors. 
         [0044]      FIG. 5  explains the disclosed method and system for detecting when an engine is combusting fuel containing more than a threshold concentration of sulfur. A conversion ratio or ammonia slip failure is detected at  51   a  by the controller  31  based on signals from the sensors  32 ,  36 ,  38  and the controller  31  initiates a desulfation at  51   b . The controller determines if the DRT (desulfation request timer) is less than 10 hours at  71  and, if the DRT is less than 10 hours at  71 , the FDC (frequent desulfation counter) is incremented at  72 . If the FDC exceeds 4 (or an alternative threshold value) at  73 , the controller initiates a sulfur contamination alarm/signal at  74 . After the desulfation is requested at  51   b  and the desulfation is complete at  52 , the DRT (desulfation request timer) is reset to 0 at  75 . If the controller  31  registers a conversion ratio or ammonia slip pass at  76 , the controller  31  determines if the FST (frequent slip timer) is less than 3 hours at  77 . If the FST is less than 3 hours at  77 , the conversion ratio or ammonia slip failure at  51   a  is not due to sulfur in the fuel because, as discussed above in connection with  FIG. 2 , sulfur in the fuel takes more than 3 hours to foul the catalyst of the NOx abatement catalyst module  23 . Thus, if the FST is less than 3 hours at  77 , an equipment failure alarm/signal is initiated at  78 , which indicates to the operator that the failure is not due to sulfur in the fuel. If the conversion ratio and ammonia slip passes at  76 , the controller considers it a successful desulfation at  79  and the frequent desulfation timer is reset to 0 at  81 . 
         [0045]    Again, while  FIG. 5  indicates specific values for threshold values, such as that for the DRT, FDC and FST, these values may vary, as will be apparent to those skilled in the art. Referring to block  71  of  FIG. 5 , the DRT is less than 10 hours, fuel is considered to be the problem and the FDC is incremented at  72 . The 10-hour value for the DRT in block  71  may vary and may range from about 6 to about 15 hours, depending upon the specific NOx abatement catalyst module employed. Similarly, because conversion ratio and ammonia slip failures can result from noise or other problems with the power system  10 , prior to the issuance of a fuel sulfur contamination alarm/signal at  74 , the FDC must exceed 4 or, there must be at least 4 conversion ratio or ammonia slip failures prior to the issuance of a fuel sulfur contamination alarm/signal. Of course, the value of 4 for the FDC may vary and may range from as few as 2 to several or more. Similarly, as discussed above, the time required for sulfur and fuel to foul a catalyst is typically about 3 hours, but depending upon the NOx abatement catalyst module  23  utilized, the lower limit or the 3-hour limit for the FST may range from about 2 to about 4 hours. 
       INDUSTRIAL APPLICABILITY 
       [0046]    The method and system for detecting when an engine is combusting fuel containing more than a threshold concentration of sulfur may be applicable to any power system  10  having a reduction catalyst and which employs injection of a reductant into the exhaust upstream of the reduction catalyst. Referring to  FIG. 1 , the air induction system  14  may pressurize and force air or a mixture of air and fuel into the cylinders  13  for combustion. The fuel and air mixture may combust to produce mechanical work and an exhaust flow of hot gases through the exhaust manifold conduit  19 . The exhaust flow may contain a complex mixture of air pollutants composed of gassiest material, which can include oxides of nitrogen (NOx). Following the optional DOC/DPF module  28  shown in  FIG. 1 , the exhaust flow may be directed towards the reduction catalyst of the NOx abatement catalyst module  23 , where the NOx may be reduced to water and elemental nitrogen. 
         [0047]    Prior to reaching the reduction catalyst of the NOx abatement catalyst module  23 , the controller  31  may, based on input from the NOx sensors  32 ,  36 , determine an amount of reductant required for the NOx abatement catalyst module  23  to sufficiently reduce the NOx produced by the power system  10 . The amount of reductant injected by the reductant injector  25  may be adjusted, based on input from the sensors  33 ,  37 ,  38 , and/or  39 . After reduction takes place within the NOx abatement catalyst module  23 , the exhaust may pass through the AMO x  module  29  to the atmosphere. Within the AMO x  module  29 , any additional ammonia may be reduced to innocuous substances, unless the catalyst of the NOx abatement catalyst module  23  is fouled. 
         [0048]    To determine if the catalyst of the NOx abatement catalyst module is fouled, various time periods are kept track of. Specifically, if the time period between a conversion ratio and an ammonia slip pass and subsequent conversion ratio or ammonia slip failure (see the blocks  55  and  53  of  FIG. 2 ) is less than 3 hours or the FDT is less than 3 hours, the failure is deemed to be not attributable to sulfur in the fuel. This is because it typically takes more than a threshold value of time to foul the catalyst of the NOx abatement catalyst module  23 . In the example set forth above, this threshold time value is about 3 hours. However, this time value may vary and, in order for a conversion ratio or a slip failure to be attributable to sulfur in the fuel, the time between a previous pass (see the block  55  of  FIG. 2 ) and a subsequent failure (see the block  53  of  FIG. 2 ) must be more than a threshold time value. This threshold time value may be about 3 hours, but may range from about 2 to about 4 hours. Further, if an ammonia slip sensor  38  is utilized, a FST (frequent slip timer) is also utilized. In the examples set forth above, when the FST is less than 3 hours, a conversion ratio or slip failure is attributed to equipment failure, and not sulfur in the fuel as shown in  FIG. 5  (see blocks  77  and  78 ). This 3-hour threshold value may vary, of course, and may range from about 2 to about 4 hours. Still further, the time between a completed desulfation (see block  52  of  FIG. 2 ) and a subsequent conversion ratio or ammonia slip failure (see block  53  of  FIG. 2 ) is deemed the DRT (desulfation request timer). In order for a failure to be attributable to sulfur in the fuel, the DRT should exceed the time limit for the FST (e.g., 3 hours or a range from about 2 to about 4 hours) and the DRT must not exceed a certain time period as well. In the example set forth above, if the DRT exceeds 10 hours, (see block  71  of  FIG. 5 ), the FDC is not incremented and a sulfur contamination alarm/signal is not generated. This is because if fuel having too much sulfur is being combusted in the power system  10 , a conversion ratio or slip failure will be registered by the controller  31  within a certain time period, which may be about 10 hours or less. The 10-hour threshold value may be modified and may range from about 6 to about 15 hours, depending upon the NOx abatement catalyst module  23  utilized, the details of the power system  10  and other factors as well. Thus, the 10-hour example shown in  FIGS. 3 and 5  is but an example, as will be apparent to those skilled in the art. 
         [0049]    Alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of the present disclosure.