Patent Publication Number: US-2018045095-A1

Title: Emission control with switchability between emission standards

Description:
TECHNICAL FIELD 
     The present disclosure is directed to emission control and, more particularly, to an emission control system that provides switchability between emission standards. 
     BACKGROUND 
     Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine in order to generate a mechanical power output. Such combustion engines exhaust a complex mixture of air pollutants as byproducts of the combustion process, and due to increased attention on the environment, exhaust emission regulations continue to become more stringent. The amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine. For example, the International Maritime Organization (IMO) has designated various emission zones off of the coasts of North America and Europe. Effective in 2014, the IMO&#39;s emissions regulations (IMO II and IMO III) will be most stringent in a first zone extending approximately 200 miles from the coast of these continents (IMO III), and will be less stringent in a second zone extending beyond approximately 200 miles from such coastal areas (IMO II). 
     Various methods have been implemented by engine manufacturers to comply with the regulation of exhaust emissions. EGR systems operate by recirculating a portion of the exhaust produced by the engine back to the intake of the engine to mix with fresh combustion air. The resulting mixture has a lower combustion temperature and, subsequently, produces a reduced amount of regulated pollutants. Although such EGR systems may be useful in reducing the amount of regulated pollutants produced during combustion, utilizing EGR can adversely affect, for example, the air compressing capabilities of the engine&#39;s air induction system. For example, diverting a portion of the combustion exhaust to the EGR system may cause one or more turbochargers associated with the engine to operate below its peak efficiency range. Thus, the reduced air compressing capability caused by activation of the EGR system may reduce the engine&#39;s fuel economy and, possibly, the amount of power generated by the engine. 
     Regulated air pollutants are composed of gaseous compounds including, among other things, the oxides of nitrogen (NO x ). In order to reduce NO x  emissions into the atmosphere, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR). SCR is an exhaust treatment process where a reductant, most commonly urea ((NH 2 ) 2 CO) or a water/urea solution, is selectively injected from an onboard supply into the exhaust gas stream of an engine. In the case of diesel engines, the reductant may be referred to as diesel exhaust fluid (DEF). The injected urea solution decomposes to form ammonia (NH 3 ), HCO, and H 2 O, and the NH 3  is adsorbed onto a downstream substrate, often referred to as an SCR catalyst. NH 3  that is adsorbed by the SCR catalyst reacts with NO x  in the exhaust gas to form water (H 2 O) and diatomic nitrogen (N 2 ). 
     One attempt to reduce emissions in accordance with location specific fuel emissions compliance for a mobile vehicle is disclosed in U.S. Pat. No. 7,062,371 issued to Gault et al. on Jun. 13, 2006 (“the &#39;371 patent”). Specifically, the &#39;371 patent discloses a system for providing location specific fuel emissions compliance for a mobile vehicle. The system includes means for determining a mobile vehicle location, means for determining a current emissions zone based on the vehicle location, means for determining at least one location specific emissions parameter based on the current emissions zone, and means for modifying a vehicle function based on the location specific emissions parameter. 
     Although the system of the &#39;371 patent may allow certain locales to meet specific air quality standards, there is still a need for a system that will enable an operator of a mobile vehicle to readily switch between emission standards depending on factors such as the geographic location of the vehicle at any particular time, and how long the vehicle will be operated in a particular emission standards zone. 
     The emissions control system of the present disclosure addresses one or more of the needs set forth above and/or other problems of the prior art. 
     SUMMARY 
     In one aspect of the present disclosure, an emissions control system for an engine includes a user interface configured to include an emission standards switchability button. The switchability button may be configured to initiate a plurality of control operations to effect a switch between two different emission standards applicable to operation of the engine. A controller may be communicatively coupled with the user interface and may comprise a memory encoding one or more processor-executable routines and a processor configured to access and execute the one or more routines encoded in the memory. The routines, when executed upon activation of the emission standards switchability button on the user interface, may cause the processor to turn off reductant dosing under a first set of engine operational parameters in a selective catalytic reduction (SCR) system fluidly coupled to receive exhaust from the engine, turn on reductant dosing in the SCR system under a second set of engine operational parameters, turn power off under the first set of engine operational parameters to one or more SCR sensors configured to generate signals indicative of operational characteristics of the SCR system, and turn power on to the one or more SCR sensors under the second set of engine operational parameters. 
     In another aspect of the present disclosure, a vessel may include an engine and a clean emissions module (CEM) configured to receive exhaust generated by the engine. The CEM may include a selective catalytic reduction (SCR) system, a diesel particulate filter (DPF), and a diesel oxidation catalyst (DOC). The SCR system may include a SCR catalyst, and an ammonia oxidation catalyst (AMOX). The vessel may also include a pump electronics tank unit (PETU) configured to control, store, and supply reductant to the SCR system, and an emission control system for the engine. The emission control system may include a user interface configured to include an emission standards switchability button. The switchability button may be configured to initiate a plurality of control operations to effect a switch between two different emission standards applicable to operation of the engine. A controller may be communicatively coupled with the user interface and may comprise a memory encoding one or more processor-executable routines and a processor configured to access and execute the one or more routines encoded in the memory. The routines, when executed upon activation of the emission standards switchability button on the user interface, may cause the processor to turn off reductant dosing under a first set of engine operational parameters in the selective catalytic reduction (SCR) system fluidly coupled to receive exhaust from the engine, turn on reductant dosing in the SCR system under a second set of engine operational parameters, turn power off under the first set of engine operational parameters to one or more SCR sensors configured to generate signals indicative of operational characteristics of the SCR system, and turn power on to the one or more SCR sensors under the second set of engine operational parameters. 
     In a further aspect of the present disclosure, a method of controlling emissions from an engine may include initiating a plurality of control operations using an emission standards switchability button on a user interface to cause a controller to toggle between two different emission standards applicable to operation of the engine. The method may include implementing, under a first set of engine operational parameters and upon a first activation of the switchability button, using at least one processor of the controller, actions to turn off reductant dosing in a selective catalytic reduction (SCR) system fluidly coupled to receive exhaust from the engine. The method may further include implementing, under a second set of engine operational parameters and upon a second activation of the switchability button, using the at least one processor, actions to turn on reductant dosing in the SCR system. The method may still further include implementing, under the first set of engine operational parameters and upon the first activation of the switchability button, using the at least one processor, actions to turn power off to one or more SCR sensors configured to generate signals indicative of operational characteristics of the SCR system, and implementing, under the second set of engine operational parameters and upon the second activation of the switchability button, using the at least one processor, actions to turn power on to the one or more SCR sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic illustration of an exemplary emission control system according to this disclosure; 
         FIG. 2  is a flow chart illustrating an algorithm that may be implemented by a controller and one or more processors of the exemplary emission control system of  FIG. 1 ; and 
         FIG. 3  a schematic illustration of an exemplary exchange of commands between components of the emission control system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic illustration of an emission control system  100  in accordance with an exemplary embodiment of this disclosure. The various illustrated components and interconnections may be associated with a diesel-fueled, internal combustion engine. In alternative embodiments the engine may embody any other type of combustion engine such as, for example, a gasoline or a gaseous fuel-powered engine burning compressed or liquefied natural gas, propane, methane, or any other suitable fuel. 
     Multiple separate sub-systems may be associated within an engine or external to the engine and cooperate to facilitate the production of power and to simultaneously control the emission of pollutants to the atmosphere. For example, an internal combustion engine may include or be associated with an air induction system, an exhaust system, and an aftertreatment system. The air induction system may be configured to direct air or an air and fuel mixture into the engine for subsequent combustion. The exhaust system may exhaust byproducts of combustion to the atmosphere. The aftertreatment system may function to reduce the discharge of regulated constituents by the engine to the atmosphere. 
     The air induction system may include multiple components configured to condition and introduce compressed air into cylinders of the engine. For example, the air induction system may include an air cooler located downstream of one or more compressors. The compressors may be connected to pressurize inlet air directed through the air cooler. The air induction system may include different or additional components such as, for example, a throttle valve, variable valve actuators associated with each cylinder, filtering components, compressor bypass components, and other known components that may be selectively controlled to affect an air-to-fuel ratio of the engine, if desired. The compressor and/or air cooler may be omitted, if a naturally aspirated engine is desired. 
     In the emission control system  100  illustrated in  FIG. 1 , a clean emissions module (CEM)  120  may be configured to receive exhaust generated by the engine. A selective catalytic reduction (SCR) system may be provided as part of the CEM  120 , and the SCR system may include a SCR catalyst, and an ammonia oxidation catalyst (AMOX). A pump electronics tank unit (PETU)  124  may be interconnected with the CEM and provided with AC power connections. The PETU may be responsible for storing, controlling, and supplying an appropriate quantity of a reductant to be used by the SCR system. In the case of a diesel engine, the reductant may be diesel exhaust fluid (DEF) used by the SCR system to reduce NOx emissions in the exhaust. The DEF is typically a solution of urea dissolved in deionized water to produce a concentration that is about ⅓ urea and ⅔ water. The CEM  120  may also include a diesel particulate filter (DPF) that traps particulate matter that may be carried in the exhaust stream, preventing it from being released into the atmosphere. Inside the DPF, particulate matter, sometimes referred to as soot, is trapped until it is oxidized during regeneration of the DPF. A diesel oxidation catalyst (DOC) may also be provided as part of the CEM, and may use a chemical process to reduce hydrocarbons and carbon monoxide in the exhaust stream. 
     As further shown in  FIG. 1 , the CEM  120  may be interconnected with the PETU  124 , with engine AC and DC power connections, with one or more engine electronic control modules (ECMs), with one or more exhaust aftertreatment ECMs, with an engine controller  130  and associated control module panel display (CMPD), and with a remote control panel  140 . The emission control system  100  according to various embodiments of this disclosure may include a user interface on one or more of the CMPD and the remote control panel  140 . The user interface may be configured to include an emission standards switchability button, and the switchability button may be configured to initiate a plurality of control operations to effect a switch between two different emission standards applicable to operation of the engine. 
     One or more controllers may be communicatively coupled with the user interface and may be included as part of the engine controller  130 , one or more engine or aftertreatment ECMs, or at a remote location such as with the remote control panel  140 . The one or more controllers may include one or more memories encoding one or more processor-executable routines and at least one processor configured to access and execute the one or more routines encoded in memory. The routines, when executed upon activation of the emission standards switchability button on the user interface may cause the processor to turn off reductant dosing in the selective catalytic reduction (SCR) system fluidly coupled to receive exhaust from the engine. The processor may be configured to turn off the reductant dosing under a first set of engine operational parameters, and turn on the reductant dosing in the SCR system under a second set of engine operational parameters. The processor may also be configured to turn power off under the first set of engine operational parameters to one or more SCR sensors configured to generate signals indicative of operational characteristics of the SCR system, and turn power on to the one or more SCR sensors under the second set of engine operational parameters. 
     The user interface may be provided on the remote control panel  140 , and/or on the control module panel display (CMPD) of the engine controller  130 . The remote panel  140  may be connected over ethernet, or via a wireless connection to the CMPD of the engine controller  130 . The user interface may be configured to include one or more emission standards switchability button(s) according to various embodiments of this disclosure. The switchability button may be configured to initiate a plurality of control operations to effect a switch between two different emission standards applicable to operation of the engine. 
     A controller may be communicatively coupled with the user interface and comprise a memory encoding one or more processor-executable routines and a processor configured to access and execute the one or more routines encoded in the memory. The routines, when executed upon a first activation of the emission standards switchability button on the user interface, may cause the processor to turn off reductant dosing under a first set of engine operational parameters in a selective catalytic reduction (SCR) system fluidly coupled to receive exhaust from the engine. The routines, when executed upon a second activation of the emission standards switchability button on the user interface, may cause the processor to turn the reductant dosing in the SCR system back on under a second set of engine operational parameters. The first activation of the switchability button may also cause the processor to turn power off under the first set of engine operational parameters to one or more SCR sensors configured to generate signals indicative of operational characteristics of the SCR system. Additionally, the second activation of the switchability button may cause the processor to turn power back on to the one or more SCR sensors under the second set of engine operational parameters. 
     The one or more routines encoded in the memory of the controller may further enable the processor to initiate actions included in the purging of reductant from lines and components included in the SCR system subsequent to turning off reductant dosing in the SCR system and turning off power to the one or more SCR sensors. The purging of reductant from the lines and components in the SCR system may be performed when a current set of engine operational parameters indicates that the engine will be geographically located in an emissions zone where the SCR system will not be needed to meet regulated levels of emissions for an extended period of time. The one or more SCR sensors may include at least one NOx sensor, and the processor may be further configured to receive a first signal from the at least one NOx sensor. The first signal from the at least one NOx sensor may be indicative of the concentration of NOx in exhaust gas generated by the engine. The one or more SCR sensors may include sensors configured to generate signals indicative of one or more of total reductant used in the SCR system, SCR catalyst intake gas temperature, SCR catalyst intake gas pressure, SCR catalyst outlet gas temperature, SCR catalyst outlet gas pressure, reductant temperature, and reductant pressure. 
     A processor of the controller in the emission control system  100  may be configured to determine the first and second sets of engine operational parameters based on a geographic location of the engine. The processor may be further configured to determine whether the first set of engine operational parameters is expected to last for a time period greater than a threshold period of time, e.g., greater than one month. The user interface and switchability button may be communicatively coupled with an engine electronic control module (ECM)  122 , and the engine ECM may be communicatively coupled with an exhaust aftertreatment ECM  122  over a controller area network (CAN) bus  126 . The user interface may be configured to toggle between an enable mode and a disable mode for each of the two different emission standards upon touch activation of the switchability button. The enable mode may include at least one of turning on the reductant dosing in the SCR system and turning power on to the one or more SCR sensors. The disable mode may include at least one of turning off the reductant dosing in the SCR system and turning power off to the one or more SCR sensors. The user interface may be a display on at least one of an engine controller  130  connected over a controller area network (CAN) bus  126  to the engine, and a remote panel  140  configured to communicate with the engine controller  130  over an ethernet connection. The engine controller  130  may be configured to receive input data from the engine over the CAN bus  126  and provide engine control logic to the engine based on the input data. 
     As shown in the exemplary implementation of  FIG. 3 , a technician  300  may activate the switchability button on a user interface in order to cause a controller and processor to send an exhaust aftertreatment enable status message to an engine ECM  320 . In some implementations the technician may be required to first enter a personal identification code before the controller and processor will send the status message to the ECM. In the exemplary implementation shown in  FIG. 3 , the status message may pertain to the SCR system of a diesel engine, and toggling of the switchability button may enable any of a short term disable message, wherein dosing of reductant in the SCR system is temporarily discontinued, a long term disable message, wherein dosing of reductant is discontinued for a period of time in excess of a predetermined threshold, and an enable message, wherein dosing of reductant is initiated. The engine ECM  320  may relay the status message over the CAN bus to an exhaust aftertreatment ECM  328 , and in the case of a marine vessel, may relay the current status of the engine ECM to a user interface (marine panel)  324 , which may be a control module panel display (CMPD) of an engine controller, or a remote panel display connected via an ethernet connection or a wireless connection to the engine controller. In the exemplary implementation of  FIG. 3 , the processor of the controller for the emission control system may require the status at both the engine ECM and the user interface of the marine panel  324 , or at all of the engine ECM  320 , the exhaust aftertreatment ECM  328 , and the user interface of the marine panel  324  to be the same before allowing a change in status between enable and disable of reductant dosing in the SCR system of the exhaust aftertreatment system. 
     An exemplary marine vessel including an emission control system according to various embodiments of this disclosure may include an engine, and a clean emissions module (CEM) configured to receive exhaust generated by the engine. The CEM of the vessel may include a diesel particulate filter (DPF), a diesel oxidation catalyst (DOC), and a selective catalytic reduction (SCR) system. The SCR system may include a SCR catalyst and an ammonia oxidation catalyst (AMOX). The vessel may also include a pump electronics tank unit (PETU) configured to store, control, and supply an appropriate quantity of a reductant to be used by the SCR system. An emission control system as described above may be provided on the vessel in order to enable toggling between two different emission standards applicable to operation of the engine by touch activation of an emission standards switchability button on a user interface. 
     An exhaust system for the engine provided with the emission control system according to this disclosure may include multiple components that condition and direct exhaust from cylinders of the engine to the atmosphere. For example, the exhaust system may include an exhaust passage configured to receive an exhaust flow from engine, and one or more turbines may be fluidly connected to the exhaust passage and driven by the exhaust flow. An exhaust system for the engine may include different or additional components such as, for example, bypass components, an exhaust compression or restriction brake, an attenuation device, and other known components, if desired. The one or more turbines may be located to receive exhaust leaving the engine, and may be connected to one or more compressors of an air induction system by way of a common shaft to form a turbocharger. As the hot exhaust gases exit the engine and move through the one or more turbines and expand against vanes thereof, the turbine may rotate and drive the connected compressor to pressurize inlet air. 
     The aftertreatment system may receive exhaust from the one or more turbines and reduce particular constituents of the exhaust. The aftertreatment system may include components configured to trap, catalyze, reduce, or otherwise remove regulated constituents from the exhaust flow of the engine prior to discharge to the atmosphere. As discussed above, the aftertreatment system may include the CEM with a SCR system. The SCR system may include one or more serially-arranged catalyst substrates located downstream from a reductant injector lance disposed in an exhaust passage. A gaseous or liquid reductant, or DEF, most commonly urea ((NH 2 ) 2 CO), a water/urea mixture, a water/urea/ammonium formate mixture, a hydrocarbon such as diesel fuel, or ammonia gas (NH 3 ), may be sprayed or otherwise advanced into the exhaust flow within the exhaust passage at a location upstream of the catalyst substrate(s) by the reductant injector lance. The reductant may include NH 3  or may decompose to form NH 3  (along with other byproducts), and the NH 3  may be adsorbed onto the surface of catalyst substrate(s). Adsorbed NH 3  may react with NO x  (NO and NO 2 ) in the exhaust gas to form water (H 2 O) and elemental nitrogen (N 2 ). To prevent extra NH 3  that did not react with NO x  from being released into the atmosphere (known as NH 3  slip), a cleanup catalyst (AMOX) may be positioned downstream of SCR catalyst substrate(s) that oxidize residual NH 3  in the exhaust to form water and elemental nitrogen. 
     The reduction process performed by the SCR system may be most effective when a concentration of NO to NO 2  supplied to the SCR system is about 1:1. To help provide the correct concentration of NO to NO 2 , the CEM  120  of the exhaust aftertreatment system may further include an oxidation catalyst upstream of the SCR system. The oxidation catalyst may be, for example, a diesel oxidation catalyst (DOC). As a DOC, oxidation catalyst may include a porous ceramic honeycomb structure or a metal mesh substrate coated with a material, for example a precious metal, which catalyzes a chemical reaction to alter the composition of the exhaust. In some implementations the oxidation catalyst may include a washcoat of palladium, platinum, vanadium, or a mixture thereof that facilitates the conversion of NO to NO 2 . 
     In some embodiments, the oxidation catalyst may also perform particulate trapping functions. That is, the oxidation catalyst may be a catalyzed particulate trap such as a continuously regenerating particulate trap or a catalyzed continuously regenerating particulate trap. A particulate trap is a filter designed to trap or collect particulate matter. 
     The process of injecting reductant upstream of the catalyst substrate(s) is known as “dosing” the catalyst substrate(s). To facilitate the dosing of the catalyst substrate(s) by an injector, an onboard supply of reductant (DEF) and a pressurizing device may be associated with the injector. The reductant sprayed into the exhaust passage may flow downstream with the exhaust flow from the engine. A mixer may be disposed within the exhaust passage at the location of the reductant injector and configured to evenly spread the reductant throughout the exhaust passing through exhaust passage. 
     Using a dosing injector to dose a catalyst substrate may be undesirable under some operating conditions. For example, when exhaust temperatures are low, such as after a cold start, the reductant, particularly solutions containing urea, may not decompose at a high enough rate to form a sufficient quantity of NH 3  to achieve desired NO x  levels before reaching the catalyst substrate(s). Urea that has not fully decomposed may form deposits on the catalyst substrate(s) (and other components of aftertreatment system) and reduce its ability to react with NO N . Thus, the aftertreatment system may include a reductant storage system configured to store a portion of the reductant in the exhaust flow that has already decomposed to form NH 3 . The stored NH 3  may then be selectively released from reductant storage system using the PETU and returned to the exhaust flow under cold start conditions to react with NO x  inside the SCR system of the CEM. 
     The exhaust aftertreatment system controlled by the emission control system according to various implementations of this disclosure may also include additional components configured to help regulate the treatment of exhaust prior to discharge to the atmosphere. Specifically, the aftertreatment system may include sensors positioned throughout the aftertreatment system and configured to generate signals indicative of an exhaust and/or component parameter such as, for example, a temperature (e.g., intake and outlet temperatures of the SCR system), a pressure (e.g., intake and outlet pressures of the SCR system), a mass flow rate (e.g., exhaust mass flow rate through an exhaust passage), an exhaust constituent level (e.g., NO N , CO 2 , NO, NO 2 , etc.), and a reductant concentration (e.g., urea, NH 3 , hydrocarbon). Based on the signals, one or more processors of a controller of the emission control system  100  may determine, among other things, an amount of NO X  being produced by the engine, a reductant flow rate through portions of the aftertreatment system, a performance parameter of the SCR system (e.g., a reduction efficiency), a history of the performance parameter (e.g., the reduction efficiency tracked over a period of time), an amount of reductant passing through the catalyst substrate(s), an amount of reductant stored in the catalyst substrate(s), and/or an amount of reductant (i.e. to yield an amount of NH 3 ) that should be sprayed by a reductant injector lance into the exhaust flow of an exhaust passage to sufficiently reduce the NO X  present within the exhaust to meet IMO standards for the particular geographical location of the engine at any particular point in time. 
     Any one or more of sensors 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 engine and/or the aftertreatment system. For example, based on a known operating speed, load, temperature, boost pressure, ambient conditions (humidity, pressure, temperature, etc.), and/or other parameters of the engine, a model may be referenced to determine an amount of NO x  produced by the engine. Similarly, based on a known or estimated NO X  production of the engine, a flow rate of reductant leaving a reductant supply or a reductant injector, a reductant injection history, and temperatures within the aftertreatment system, a model of reductant storage within the SCR system and a reductant storage device may be generated. As a result, any signal directed from the various sensors to the one or more processors and controllers of the emission control system  100  may be based on calculated and/or estimated values rather than direct measurements, if desired. 
     It should be appreciated that the engine ECM and exhaust aftertreatment ECM may include a memory, a secondary storage device, a processor, and any other components for running an application. Various other circuits may be associated with one or more controllers, such as power supply circuitry, signal conditioning circuitry, actuator driver circuitry, and other types of circuitry. The one or more controllers may embody a single or multiple microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), etc. that may include means for controlling an operation of the emission control system in response to signals received from the various sensors described above. Numerous commercially available microprocessors can be configured to perform the functions of the controllers. It should be appreciated that one or more controllers of the emission control system  100  could readily embody a microprocessor separate from that controlling other non-exhaust related power system functions, or could 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(s), various controllers may communicate with the general power system microprocessor via datalinks such as the CAN bus datalink or other methods. Various other known circuits may be associated with the controllers, 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. 
     INDUSTRIAL APPLICABILITY 
     The disclosed emission control system may be employed in any power system application where aftertreatment of exhaust includes utilization of a SCR system. Various air induction and exhaust gas recirculation (EGR) systems may be used in conjunction with the SCR system in applications that may include any of a number of construction, mining, power generation, on-highway transportation, off-highway transportation, and/or marine applications. Accordingly, the disclosed emission control system  100  may be configured for use on, in, or with any vehicle or machine commonly used in such applications. Such machines may include, for example, marine vessels, wheel loaders, motor graders, excavators, on-highway vehicles, off-highway vehicles, and/or other known machines associated with such applications. 
     During operation of an engine provided with an emission control system  100  in accordance with various implementations of this disclosure, one or more sensors may determine one or more characteristics of exhaust generated by the engine and/or of fuel provided to the engine. For example, one or more sensors may sense and/or otherwise determine a volume, flow rate, NOx concentration, temperature, pressure, and/or other characteristic of the exhaust. Such exhaust characteristics may be determined anywhere within the emission control system  100 . Alternatively, such characteristics may be associated with exhaust within specific combustion chambers of an engine, exhaust exiting the engine via one or more exhaust manifolds, or exhaust passing to one or more turbochargers. One or more of the sensors may be disposed at any of the above locations for determining such characteristics, and such sensors may be configured to send one or more signals to the processors of one or more controllers included in the emission control system. The controllers may then control operation of one or more valves or other devices based on or in response to such characteristics or signals. 
     A method of controlling emissions from an engine in accordance with various implementations of this disclosure may include initiating a plurality of control operations using a controller to effect a switch between two different emission standards applicable to operation of the engine. As illustrated in the flow chart of  FIG. 2 , at Step  200  an operator may activate an emissions standards switchability button on a display panel (user interface) of a vehicle in order to commence the control operations applicable for either a transient vessel moving between IMO III and IMO II emission standards zones (Step  220 ) or for an “extended stay” vessel that will be operating outside of an IMO III zone for more than one month (Step  222 ). The period of time outside of an IMO III zone that qualifies as “extended stay” may vary from one month, and may include periods of time that are less than or more than one month. 
     At Step  224  for the transient vessel following activation of the switchability button on the display panel, the dosing of a diesel exhaust fluid (DEF) may be turned off in the selective catalytic reduction (SCR) system provided as part of an exhaust aftertreatment system. Dosing of DEF in the SCR system may be required in order to meet stringent NOx emission standards in IMO III zones. When the transient vessel leaves the IMO III zone, the dosing of DEF may no longer be needed in order to meet emission standards applicable to IMO II zones. At Step  228 , after turning off the dosing of DEF, the dosing system may be left in a “safe” mode in order to allow rapid re-initiation of dosing of DEF again when the transient vessel reenters an IMO III zone. At Step  232 , the power to NOx sensors included in the SCR system may be left on in order to allow for rapid re-initiation of sensing of levels of NOx in the exhaust gases. With the dosing in “safe” mode at Step  228 , and power left on to the NOx sensors in Step  232 , no operator actions may be required at Step  236  as the transient vessel remains in a state ready for switching back to the emission standards for IMO III zones. As shown at Step  240 , a transient vessel may continue to display a fault code as long as the dosing of DEF in the SCR system is turned off in order to maintain operator awareness of the reduced level of exhaust aftertreatment. When the vessel reenters an IMO III zone with more stringent NOx level parameters, at Step  244  dosing of DEF may be reactivated by simply activating the emission standards switchability button on the display panel again at Step  200 . 
     An alternate sequence of control operations may begin for an extended stay vessel at Step  222  following activation of the emissions standards switchability button at Step  200 . As shown at Step  226 , dosing of DEF in the SCR system for the extended stay vessel may be turned off, but as with the transient vessel, the dosing of DEF may remain in a “safe” mode at Step  230  in order to allow for rapid re-initiation of dosing again when the extended stay vessel is ready to reenter an IMO III zone. However, for an extended stay vessel, a number of control operations may be performed in order to ensure a reduction in reductant (DEF) consumption and preservation of the life of aftertreatment components while the vessel is outside of IMO III zones. At Step  234  the power may be turned off to the NOx sensors and other components associated with the SCR system. At Step  238 , a number of actions may be initiated by an operator, or if desired by an operator and/or an automatic controller. Examples of the actions that may be taken after the power to NOx sensors and other SCR components has been turned off for an extended stay vessel may include actions necessary to decommission the SCR system for the entire period of time when the vessel will be outside of IMO III zones. The DEF injection lance may be removed and the DEF lines and air lines may be capped off in order to prevent impurities from entering the lines or the components. The NOx sensors may be completely removed, the catalyst for the SCR system may be removed, and the lines and sensors may be purged of all DEF in order to avoid the corrosive effects of DEF that may remain stagnant in contact with components during an extended stay outside of IMO III zones. Any fault codes associated with the termination of dosing in the SCR system may also be cleared at this time or discontinued at Step  242 . At Step  246 , sensors and other dosing components may be reactivated upon reentry of the vessel into IMO III zones. 
     The various control actions described above and shown in  FIG. 2  may be implemented with at least one processor of a controller in order to control reductant dosing in a selective catalytic reduction (SCR) system fluidly coupled to receive exhaust from an engine of either a transient or extended stay vessel. Under a first set of engine operational parameters, which may include operational parameters associated with particular geographic zones subject to IMO II emission standards, one or more processors may turn off reductant dosing and turn off power to one or more SCR sensors. Under a second set of engine operational parameters, which may include operational parameters associated with particular geographic zones subject to the more stringent IMO III emission standards, one or more processors may turn on reductant dosing in the SCR system and turn power on to the one or more SCR sensors. The user interface on at least one of a display on an engine controller connected directly to a CAN bus of the vessel and a remote display connected via ethernet to the engine controller may be toggled between an enable mode and a disable mode for each of the two different emission standards upon touch activation of an emission standards switchability button on the user interface. The enable mode may include at least one of turning on the reductant dosing in the SCR system and turning power on to the one or more SCR sensors, and the disable mode may include at least one of turning off the reductant dosing in the SCR system and turning power off to the one or more SCR sensors. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed emission control system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed emission control system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.