Patent Application
20160108791
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).
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.
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.
A NOx abatement catalyst module converts nitrogen NOx, with the aid of a catalyst, into diatomic nitrogen, N2, and water, H2O. 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.
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.
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.
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.
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.
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.
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 NH3 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.
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 NH3 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.
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.
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:
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.
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.
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.
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
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.
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 ((NH2)2CO), a water/urea mixture, a hydrocarbon for example diesel fuel, or ammonia gas (NH3), 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, NO2, and NO3) in the exhaust stream to form water (H2O) and elemental nitrogen (N2). The reduction process performed in the NOx abatement catalyst module 23 may be most effective when a ratio of NO to NO2 supplied to the NOx abatement catalyst module 23 is adjusted to optimize the NOx reduction at the catalyst.
To help provide a more optimal concentration of NO to NO2 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 NO2.
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 NH3 in the exhaust to form water and elemental nitrogen (N2).
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
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.
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 NO2 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.
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 NO2 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 NO2 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.
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.
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:NO2 exiting the optional DOC/DPF module 28.
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.
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 NO2 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 AMOx module 29. Alternatively, the post-aftertreatment NOx sensor 36 may embody a sensor useful in determining the amount of NH3 entering the AMOx module 29.
If the oxidation catalyst of the optional DOC/DPF module 28 is overloaded with particulate matter, the relative amount of NO2 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 NO2. 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.
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.
As noted above, in some situations, too much urea or reductant may be injected resulting in “ammonia slip.” Although the AMOx 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 AMOx 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.
The interaction of the controller 31 with the sensors 32-38 is further illustrated in
Still referring to
Turning to
It will be noted that the time periods discussed above in connection with
Again, while
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
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 AMOx module 29 to the atmosphere. Within the AMOx module 29, any additional ammonia may be reduced to innocuous substances, unless the catalyst of the NOx abatement catalyst module 23 is fouled.
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
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.
