Patent Publication Number: US-8528530-B2

Title: Diesel engine system and control method for a diesel engine system

Description:
BACKGROUND OF THE INVENTION 
     The subject matter described herein relates generally to internal combustion engines, such as diesel engines. 
     Diesel engines include cylinders having combustion chambers with pistons disposed in the combustion chambers. The pistons move in the combustion chambers to rotate a shaft. The shaft may be coupled with an alternator or generator to create electric current. The electric current may be used to power one or more devices, such as traction motors of a powered rail vehicle that propel the rail vehicle. 
     In some known diesel engines, the pistons move within the combustion chambers based on a four-stroke cycle. During the four-stroke cycle, intake air is directed into the combustion chambers and is compressed and thereby heated to ignite diesel fuel sprayed into the combustion chamber towards the end of the compression stroke. The combustion of the diesel fuel creates a gaseous exhaust in the combustion chamber. The gaseous exhaust of the cylinders may include pollutants, such as nitrogen oxide (NOx) and soot. In order to reduce pollution emitted by the diesel engines, some known diesel engines attempt to change the composition of the intake air by recirculating parts of the exhaust gas back into the intake. These diesel engines may be referred to as exhaust gas recirculation (EGR) diesel engines. 
     In a certain configuration, an EGR diesel engine recirculates the gaseous exhaust from one or more dedicated cylinders to the other cylinders. For example, the gaseous exhaust from a first cylinder, such as an EGR donating cylinder, may be recirculated back to a set of different, second cylinders and form at least a part of the intake air that is received by the second cylinders and used to ignite the diesel fuel in the second cylinders. 
     In such an EGR donor engine, typically a fixed number of exhaust gas donating cylinders are provided. The amount of exhaust that is recirculated by the fixed number of donating cylinders may be unable to adapt to changing load demands of the engine or changing emissions limits. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a diesel engine system is provided. The system includes a cylinder, an exhaust manifold, an exhaust gas recirculation (EGR) manifold, and a valve. The cylinder has a piston disposed within a combustion chamber with the combustion chamber receiving intake air and fuel to combust the fuel and move the piston within the combustion chamber. The exhaust manifold is fluidly coupled with the cylinder and directs exhaust generated in the combustion chamber to an exhaust outlet that delivers the exhaust to an external atmosphere. The EGR manifold is fluidly coupled with the cylinder and recirculates the exhaust generated in the combustion chamber back to the combustion chamber as at least part of the intake air that is received by the combustion chamber. The valve is disposed between the combustion chamber of the cylinder and the exhaust manifold and between the combustion chamber and the EGR manifold. The valve has a donating mode and a non-donating mode. The valve fluidly couples the combustion chamber with the EGR manifold when the valve is in the donating mode and fluidly couples the combustion chamber with the exhaust manifold when the valve is in the non-donating mode. 
     In another embodiment, a control method for a diesel engine system is provided. The method includes directing exhaust generated in a combustion chamber of a cylinder in the diesel engine system to a valve disposed between and fluidly coupled with the combustion chamber and each of an exhaust manifold and an exhaust gas recirculation (EGR) manifold. The valve is switchable between a donating mode and a non-donating mode. The method includes directing the exhaust from the cylinder through the exhaust manifold to an external atmosphere when the valve is in the non-donating mode. The method includes recirculating the exhaust back to the combustion chamber through the EGR manifold as at least part of intake air that is injected into the combustion chamber when the valve is in the donating mode. 
     In another embodiment, a tangible and non-transitory computer readable storage medium comprising instructions for a control module of a diesel engine system is provided. The instructions direct the control module to monitor at least one of an efficiency parameter, an emissions parameter, or an operating condition of a cylinder of the diesel engine system that has a piston disposed in a combustion chamber and that receives intake air and diesel fuel to combust the diesel fuel and move the piston. The instructions further direct the control module to switch a valve between a non-donating mode and a donating mode based on the at least one of the efficiency parameter, the emissions parameter, or the operating condition. The valve is disposed between the combustion chamber of the cylinder and is fluidly coupled with the combustion chamber and each of an exhaust manifold and an exhaust gas recirculation (EGR) manifold. The valve is switchable between a donating mode and a non-donating mode. When the valve is in the non-donating mode, exhaust generated in the combustion chamber is directed through the exhaust manifold to an external atmosphere. When the valve is in the donating mode, the exhaust is recirculated back to the combustion chamber through the EGR manifold as at least part of the intake air that is injected into the combustion chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a powered rail vehicle in accordance with one embodiment. 
         FIG. 2  is an illustration of a cylinder of a diesel engine shown in  FIG. 1  in accordance with one embodiment. 
         FIG. 3  is a diagram of a diesel engine system shown in  FIG. 1  in accordance with one embodiment. 
         FIG. 4  is a cross-sectional view of a throttle valve in accordance with one embodiment. 
         FIG. 5  is a flowchart of a control method for the diesel engine system shown in  FIG. 1  in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The foregoing summary, as well as the following detailed description of certain embodiments of the presently described subject matter, will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (for example, processors or memories) may be implemented in a single piece or multiple pieces of hardware (for example, a general purpose signal processor, microcontroller, random access memory, hard disk, and the like). Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. The various embodiments are not limited to the arrangements and instrumentality shown in the drawings. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the presently described subject matter are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. 
     It should be noted that although one or more embodiments may be described in connection with powered rail vehicle systems having locomotives with trailing passenger or cargo cars, the embodiments described herein are not limited to trains. In particular, one or more embodiments may be implemented in connection with different types of vehicles. For example, one or more embodiments may be implemented with a vehicle that travels on one or more rails, such as single locomotives and railcars, powered ore carts and other mining vehicles, light rail transit vehicles, and other vehicles, such as automobiles, ships, and the like. 
     Example embodiments of systems and methods for controlling an exhaust gas recirculation (EGR) diesel engine are provided. As described below, one or more of these embodiments provides for a system and method that changes the number of cylinders in the EGR diesel engine that donate, or recirculate, the exhaust generated by the cylinders to other non-donating cylinders. The non-donating cylinders use the exhaust from the donating cylinders as at least part of the intake air that is received by the non-donating cylinders and used to ignite diesel fuel in the non-donating cylinders. The number of cylinders that are donating cylinders and that recirculate the exhaust generated by the donating cylinders to the non-donating cylinders may be based on a number of factors, including an efficiency parameter, an emissions parameter, and/or other operating conditions of the donating and/or non-donating cylinders. At least one technical effect described herein includes a system and method that reduces the emissions of pollutants without significant loss of efficiency of the diesel engine in order to meet efficiency and/or emissions limits under varying load, speed, pressure, and/or temperature conditions of the diesel engine. 
       FIG. 1  is a diagram of a powered rail vehicle  100  in accordance with one embodiment. While one embodiment of the presently described subject matter is set forth in terms of a powered rail vehicle, alternatively the subject matter may be used with another type of vehicle, such as an automobile, a truck, a ship, and the like. The rail vehicle  100  includes a lead powered unit  102  coupled with several trailing cars  104  that travel along one or more rails  106 . In one embodiment, the lead powered unit  102  is a locomotive disposed at the front end of the rail vehicle  100  and the trailing cars  104  are cargo cars for carrying passengers and/or other cargo. The lead powered unit  102  includes a diesel engine system  116 . The diesel engine system  116  provides tractive effort to propel the rail vehicle  100 . The diesel engine system  116  includes a diesel engine  108  that powers traction motors  110  coupled with wheels  112  of the rail vehicle  100 . For example, the diesel engine  108  may rotate a shaft  318  (shown in  FIG. 2 ) that is coupled with an alternator or generator (not shown). The alternator or generator creates electric current based on rotation of the shaft  318 . The electric current is supplied to the traction motors  110 , which turn the wheels  112  and propel the rail vehicle  100 . 
     The rail vehicle  100  includes a control module  114  that is communicatively coupled with the diesel engine  108 . For example, the control module  114  may be coupled with the diesel engine  108  by one or more wired and/or wireless connections. The control module  114  communicates with switching valve sets  224  (shown in  FIG. 3 ) to direct the exhaust generated by one or more donating cylinders  202  (shown in  FIG. 3 ) of the diesel engine  108 . The control module  114  manages the switching valve sets  224  to control which of the donating cylinders  202  are generating exhaust that is recirculated back to other non-donating cylinders  200  (shown in  FIG. 3 ) of the diesel engine  108  and which of the donating cylinders  202  are generating exhaust that is directed away from the non-donating cylinders  200  and out of the diesel engine  108  in one embodiment. 
     The control module  114  may include a processor, such as a computer processor, controller, microcontroller, or other type of logic device, that operates based on sets of instructions stored on a tangible and non-transitory computer readable storage medium  118 . The computer readable storage medium  118  may be an electrically erasable programmable read only memory (EEPROM), simple read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), FLASH memory, a hard drive, or other type of computer memory. 
       FIG. 2  is an illustration of a cylinder  300  of the diesel engine  108  in accordance with one embodiment. The diesel engine  108  includes two or more cylinders  300  that operate to rotate the shaft  318 . Rotation of the shaft  318  may be used to generate tractive power for the rail vehicle  100  (shown in  FIG. 1 ). For example, rotation of the shaft  318  may create electric current, which powers the traction motors  110  (shown in  FIG. 1 ). The cylinder  300  includes a combustion chamber  302  with a piston  304  disposed within the combustion chamber  302 . In the view shown in  FIG. 2 , the piston  304  moves up and down within the combustion chamber  302 . The piston  304  is coupled to the shaft  318  by a crankshaft  306 . The crankshaft  306  converts the movement of the piston  304  in the combustion chamber  302  into rotation of the shaft  318 . In one embodiment, the shaft  318  is a common shaft that several pistons  304  of the diesel engine  108  are joined. 
     The cylinder  300  includes an intake valve  308  that opens to permit intake air to enter into the combustion chamber  302  and closes to prevent additional intake air from entering the combustion chamber  302 . For example, the cylinder  300  may include an inlet conduit  310  that directs intake air to the combustion chamber  302 . The intake valve  308  is disposed between the combustion chamber  302  and the inlet  310 . The intake valve  308  opens to allow intake air into the combustion chamber  302  and closes to prevent intake air from leaving the combustion chamber  302 . 
     The cylinder  300  includes an exhaust valve  312  that opens to direct gaseous exhaust out of the combustion chamber  302  and closes to prevent the gaseous exhaust and/or intake air from exiting the combustion chamber  302 . The cylinder  300  may include an outlet conduit  314  that directs the exhaust out of the combustion chamber  302 . The exhaust valve  312  opens to allow gaseous exhaust in the combustion chamber  302  to exit the combustion chamber  302  into the outlet conduit  314 . 
     The cylinder  300  includes a fuel injector  316  that directs fuel, such as diesel fuel, into the combustion chamber  302 . The fuel injector  316  is disposed between a source or supply of fuel (not shown), such as a fuel tank and fuel pump, and the combustion chamber  302 . The fuel injector  314  injects or sprays the fuel into the combustion chamber  302 . 
     The cylinder  300  may operate based on a multi-stroke cycle in one embodiment. The piston  304  moves within the combustion chamber  302  during the multi-stroke cycle to rotate the shaft  318 . In one embodiment, the multi-stroke cycle is a four-stroke cycle that includes an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. Alternatively, the cylinder  300  may operate based on a different cycle. During the intake stroke, the inlet valve  308  opens to direct intake air into the combustion chamber  302 . The influx of intake air into the combustion chamber  302  drives the piston  304  away from the inlet valve  308  and toward the shaft  318 . In the illustrated embodiment, the intake air moves the piston  304  downward. 
     Following the intake stroke is the compression stroke. During the compression stroke, the piston  304  moves in an opposite direction toward the fuel injector  316 . For example, in the illustrated embodiment, the piston  304  moves upward toward the top of the combustion chamber  302 . The intake and exhaust valves  308 ,  312  remain closed during the compression stroke. As the piston  304  moves upward, the volume in the combustion chamber  302  decreases while the intake air in the combustion chamber  302  remains the same. As a result, the intake air in the combustion chamber  302  is compressed by the piston  304 . The compression of the intake air heats the intake air inside the combustion chamber  302 . 
     Following the compression stroke is the combustion stroke. During the combustion stroke, diesel fuel is injected into the combustion chamber  302  by the fuel injector  316 . For example, as the piston  304  reaches or approaches the top of the combustion chamber  302 , the fuel injector  316  may spray diesel fuel into the combustion chamber  302  in the illustrated embodiment. The compressed and heated intake air in the combustion chamber  302  ignites the diesel fuel in the combustion chamber  302 . The ignition of the diesel fuel creates increased pressure within the combustion chamber  302  and forces the piston  304  away from the fuel injector  316 . For example, the combustion of the diesel fuel may force the piston  304  downward in the view shown in  FIG. 2 . 
     Following the combustion stroke is the exhaust stroke. The combustion of the diesel fuel within the combustion chamber  302  generates gaseous exhaust in the combustion chamber  302 . The gaseous exhaust may include pollutants such as nitrogen oxide (NOx). During the exhaust stroke, the piston  304  moves back up toward the fuel injector  316  and the exhaust valve  312  opens to direct the gaseous exhaust out of the combustion chamber  302 . For example, the exhaust valve  312  may open to permit the gaseous exhaust to flow from the combustion chamber  302  into the outlet conduit  314 . 
       FIG. 3  is a diagram of the diesel engine system  116  in accordance with one embodiment. The diesel engine system  116  includes the diesel engine  108  coupled with the control module  114 . In the illustrated embodiment, the diesel engine  108  is communicatively coupled with the diesel engine  108  by one or more wired and/or wireless connections. The dashed lines extending between the switching valve sets  224  of the diesel engine  108  and the control module  114  illustrate at least one communication path between the control module  114  and the diesel engine  108 . 
     The diesel engine  108  includes several cylinders  200 ,  202 , referred to herein as non-donating cylinders  200  (“normal non-donating cylinders”) and donating cylinders  202 . The non-donating cylinders  200  may be referred to as exhaust gas recirculation (EGR) cylinders. In the illustrated embodiment, the diesel engine  108  includes three non-donating cylinders  200  and three donating cylinders  202 . Alternatively, the diesel engine  108  may include a different number of the non-donating and/or donating cylinders  200 ,  202 . The non-donating cylinders  200  and donating cylinders  202  may be similar to the cylinder  300  described in connection with  FIG. 2 . For example, each of the non-donating and donating cylinders  200 ,  202  may include pistons  304  (shown in  FIG. 2 ) that move within combustion chambers  302  (shown in  FIG. 3 ) based on a multi-stroke cycle to rotate the shaft  318 . 
     In the illustrated embodiment, the non-donating cylinders  200  are fluidly coupled with an exhaust manifold  206 . For example, the outlet conduits  314  (shown in  FIG. 2 ) of the non-donating cylinders  200  may be coupled with the exhaust manifold  206  such that gaseous and/or liquid matter, such as gaseous exhaust, flows from the outlet conduits  314  to the exhaust manifold  206 . The exhaust manifold  206  includes one or more conduits that direct gaseous exhaust from the non-donating cylinders  200  away from the diesel engine  108 . The exhaust manifold  206  includes an exhaust outlet  208 . The exhaust outlet  208  may be an opening at an end of the exhaust manifold  206  that directs exhaust from the diesel engine  108  to an external atmosphere. For example, the exhaust outlet  208  may be disposed at a terminal end of the exhaust manifold  206  that directs the exhaust to a turbocharger  210 . 
     The turbocharger  210  may use the exhaust to draw in and pump ambient air  214  from the external atmosphere into an input manifold  212 . After the exhaust is used by the turbocharger  210 , the exhaust may be emitted into the environment outside of the diesel engine  108  and/or turbocharger  210 . Alternatively, the exhaust outlet  208  may direct the exhaust to the external atmosphere without directing the exhaust to the turbocharger  210 . For example, the exhaust outlet  208  may direct the exhaust to an area or volume that is not disposed within the diesel engine  108 . By directing the exhaust to the external atmosphere, the exhaust outlet  208  prevents the exhaust from being recirculated back to the donating and/or non-donating cylinders  202 ,  202  within the diesel engine  108  in one embodiment. 
     The input manifold  212  is fluidly coupled with an intake manifold  216  of the diesel engine system  116  by an EGR intake junction  218 . The input manifold  212  receives the ambient air  214  from the turbocharger  210  and directs the ambient air  214  to the EGR intake junction  218 . 
     The donating cylinders  202  are fluidly coupled with an EGR manifold  220 . For example, the outlet conduits  314  (shown in  FIG. 2 ) of the donating cylinders  202  may be coupled with the EGR manifold  220  such that gaseous and/or liquid matter, such as gaseous exhaust, flows from the outlet conduits  314  to the EGR manifold  220 . The EGR manifold  220  includes one or more conduits that direct exhaust from the donating cylinders  202  to an EGR cooler  222 . The EGR cooler  222  is a device that reduces the temperature or thermal energy of the gaseous exhaust from the donating cylinders  202 . For example, the EGR cooler  222  may include one or more heat exchangers, compressors, or fans that cool the exhaust from the donating cylinders  202 . The EGR cooler  222  is fluidly coupled with the EGR intake junction  218 . The EGR intake junction  218  fluidly couples the input manifold  212  with the EGR cooler  222  such that the exhaust of the donating cylinders  202  that is cooled by the EGR cooler  222  can be mixed with the ambient air  214  from the input manifold  212 . 
     The mixture of ambient air and the cooled exhaust may be referred to as “intake air,” or the air that is received by the non-donating and/or donating cylinders  200 ,  202  and used by the non-donating and/or donating cylinders  200 ,  202  to combust diesel fuel. The intake air is directed by the EGR intake junction  218  into the intake manifold  216 . The intake manifold  216  is fluidly coupled with the non-donating and donating cylinders  200 ,  202  and directs the intake air to the non-donating and donating cylinders  200 ,  202  in the illustrated embodiment. For example, the intake manifold  216  may be coupled with the inlet conduits  310  (shown in  FIG. 2 ) of the non-donating and donating cylinders  200 ,  202  such that the intake air flows through and is directed by the intake manifold  216  and inlet conduits  310  into the combustion chambers  302  (shown in  FIG. 2 ) of the non-donating and donating cylinders  200 ,  202 . 
     The switching valve sets  224  include one or more valves that are fluidly coupled with the donating cylinders  202 , the EGR manifold  220 , and the exhaust manifold  206 . For example, the switching valve sets  224  are fluidly coupled with the donating cylinders  202 , the EGR manifold  220 , and the exhaust manifold  206  such that a gas or liquid may flow from the donating cylinders  202  to the EGR manifold  220  and/or the exhaust manifold  206  through the switching valve sets  224 . The switching valve sets  224  may include a three-way valve, two or more two-way valves, or other valves or groups of valves. In one embodiment, the switching valve sets  224  each include a plurality of two-way valves that restrict the flow of exhaust through each two-way valve in a complementary manner. For example, a first two-way valve may permit only 40% of the exhaust to pass through the two-way valve while a second two-way valve permits 60% of the exhaust to pass through. 
     In the illustrated embodiment, the switching valve sets  224  are disposed between the donating cylinders  202  and each of the exhaust manifold  206  and the EGR manifold  220 . For example, the switching valve sets  224  are disposed downstream of the donating cylinders  202  and upstream of the exhaust manifold  206  and the EGR manifold  220  along a path that the exhaust of the donating cylinders  202  flows. 
     The switching valve sets  224  alternate between different modes to direct the exhaust from the donating cylinders  202  along different paths. For example, the switching valve sets  224  may have a donating mode and a non-donating mode. In the donating mode, the switching valve sets  224  fluidly couple the donating cylinders  202  with the EGR manifold  220 . By fluidly coupling the donating cylinders  202  with the EGR manifold  220 , the exhaust generated by the donating cylinders  202  is directed to the EGR manifold  220 . As a result, the exhaust is recirculated back to the non-donating and donating cylinders  200 ,  202  as at least part of the intake air of the non-donating and donating cylinders  200 ,  202 . For example, the switching valve sets  224  direct the exhaust from the donating cylinders  202  to the EGR manifold  220 , which directs the exhaust to the EGR cooler  222  and the intake manifold  216  by way of the EGR intake junction  218 . 
     The switching valve sets  224  may prevent flow of exhaust to the exhaust manifold  206  when the switching valve sets  224  are in the donating mode. For example, the switching valve sets  224  may block flow of the exhaust from the donating cylinders  202  from passing into the exhaust manifold  206 . Alternatively, the switching valve sets  224  may controllably restrict the flow of exhaust into the exhaust manifold  206 . The switching valve sets  224  may be controlled by the control module  114  to direct some, but not all, of the exhaust into the exhaust manifold  206 . The remaining portion of the exhaust may be directed into the EGR manifold  220  by the switching valve sets  224 . For example, the switching valve sets  224  may direct 5%, 10%, 20%, 30%, 40%, 50%, and the like, of the exhaust flowing out of one or more donating cylinders  202  into the exhaust manifold  206  while the corresponding remaining 95%, 90%, 80%, 70%, 60%, 50%, and the like, of the exhaust is recirculated into the EGR manifold  220 . The switching valve sets  224  may change between the donating and non-donating modes by adjusting the percentage of exhaust that is directed by the switching valve sets  224  to the EGR manifold  220  or the exhaust manifold  206 . 
     In the non-donating mode, the switching valve sets  224  fluidly couple the donating cylinders  202  with the exhaust manifold  206 . By fluidly coupling the donating cylinders  202  with the exhaust manifold  206 , the exhaust generated by the donating cylinders  202  is directed to the exhaust manifold  206 . As a result, the exhaust is directed out of the diesel engine  108  and into the turbocharger  210 . The exhaust may pass through the turbocharger  210  and be expelled out of the turbocharger  210  and into the external atmosphere. 
     The switching valve sets  224  may prevent flow of exhaust to the EGR manifold  220  when the switching valve sets  224  are in the non-donating mode. For example, the switching valve sets  224  may block flow of the exhaust from the donating cylinders  202  from passing into the EGR manifold  220  and being recirculated to the donating and/or non-donating cylinders  202 ,  200 . Alternatively, the switching valve sets  224  may controllably restrict the flow of exhaust into the EGR manifold  220 . For example, the switching valve sets  224  may recirculate 5%, 10%, 20%, 30%, 40%, 50%, and the like, of the exhaust flowing out of one or more donating cylinders  202  into the EGR manifold  220  while the remaining 95%, 90%, 80%, 70%, and the like, of the exhaust is emitted into the external atmosphere through into the exhaust manifold  206  and the turbocharger  210 . 
     The switching valve sets  224  may include one or more stop valves and/or check valves. For example, the switching valve sets  224  may include one or more two-way valves, three-way valves, globe valves, gate valves, butterfly valves, ball valves, and the like. In one embodiment, the switching valve sets  224  include a throttle valve that decreases pressure losses in the exhaust flowing from the donating cylinders  202  to the EGR manifold  220 . 
       FIG. 4  is a cross-sectional view of a throttle valve  400  in accordance with one embodiment. The throttle valve  400  may be used for one or more of the switching valve sets  224  (shown in  FIG. 3 ) or in combination with one or more other valves to collectively form one or more of the switching valve sets  224 . For example, the throttle valve  400  may be combined with a two-way valve to control the flow of exhaust from the donating cylinder  202  (shown in  FIG. 3 ) to the exhaust manifold  206  (shown in  FIG. 3 ) and/or EGR manifold  220  (shown in  FIG. 3 ). Alternatively, a valve other than the throttle valve  400  may be used for one or more of the switching valve sets  224 . 
     The throttle valve  400  may be fluidly coupled with the exhaust manifold  206 , the outlet conduit  314  of the donating cylinder  202  (shown in  FIG. 3 ), and the EGR manifold  220 . For example, when the throttle valve  400  is in the non-donating mode, the throttle valve  400  is disposed downstream of the outlet conduit  314  and upstream of the exhaust manifold  206  along the path that the exhaust flows from the donating cylinder  202  to the exhaust manifold  206 . 
     The throttle valve  400  includes a conduit  402  with a plug  414  disposed inside the conduit  402 . In one embodiment, the exhaust from the donating cylinder  202  (shown in  FIG. 3 ) flows through the conduit  402  to the exhaust manifold  206  when the throttle valve  400  is in the non-donating mode. Alternatively, the exhaust may flow through the conduit  402  to the EGR manifold  220  when the throttle valve  400  is in the donating mode. The conduit  402  is elongated over a longitudinal axis  404  and has a cross-sectional shape that changes at different locations  406 ,  408 ,  410 ,  412  along the longitudinal axis  404  in the illustrated embodiment. For example, the conduit  402  shown in  FIG. 4  has approximately the same cross-sectional shape or area at upper and lower locations  406 ,  408 . The upper location  406  is disposed between the plug  414  and the exhaust manifold  206  and the lower location  412  is disposed between the plug  414  and the outlet conduit  314  of the donating cylinder  202 . 
     The cross-sectional shape of the conduit  402  extends outward to a bulb  416  disposed between the upper and lower locations  406 ,  412 . In the illustrated embodiment, the cross-sectional area of the conduit  402  is larger within the bulb  416  than in the remainder of the conduit  402 . For example, the conduit  402  may have a larger cross-sectional area at a distended location  410  that is located within the bulb  416  of the conduit  402  than at the upper and lower locations  406 ,  412 . The conduit  402  may have a smaller cross-sectional area at a reduced location  408 . For example, the cross-sectional area of the conduit  402  at the reduced location  408  between the bulb  416  and the upper location  406  may be smaller than the cross-sectional area of the conduit  402  at the other locations  406 ,  410 ,  412 . 
     The plug  414  has a conical body in the illustrated embodiment. For example, the plug  414  may have an approximate shape of a tear drop with the plug  414  having an elongated conical body extending along the longitudinal axis  404  from a tip end  418  to an opposite end  420 . As shown in  FIG. 4 , the cross-sectional area of the plug  414  may increase along the length of the plug  414  from the cross-sectional area at the tip end  418  to a cross-sectional area at a blocking location  422  of the plug  414 . The cross-sectional area may decrease along the length of the plug  414  from the blocking location  422  to the opposite end  420 , with the cross-sectional area at the opposite end  420  being larger than the cross-sectional area at the tip end  418 . 
     The plug  414  is shown in two locations in  FIG. 4 . The plug  414  is labeled as plug  414 A in a closed position and as plug  414 B in an open position. The plug  414  is moved between the open and closed positions to switch between the non-donating and donating modes in the illustrated embodiment. For example, the plug  414 A is in a closed position when the throttle valve  400  is in the donating mode. When the plug  414 A is in the closed position, the plug  414 A engages the conduit  402  to shut off flow of the exhaust from the outlet conduit  314  of the donating cylinder  202  (shown in  FIG. 3 ) to the exhaust manifold  206 . As a result, the exhaust from the outlet conduit  314  is directed to the EGR manifold  220 . 
     The plug  414 B is in an open position when the throttle valve  400  is in the non-donating mode in one embodiment. When the plug  414 B is in the open position, the plug  414 B does not engage the conduit  402  to block flow of the exhaust to the exhaust manifold  206 . As a result, the exhaust can flow from the outlet conduit  314  to the exhaust manifold  206 . 
     In order to reduce pressure losses caused by the switching valve sets  224  (shown in  FIG. 3 ) being disposed between the exhaust manifold  206  and the EGR manifold  220 , the throttle valve  400  may be used. For example, the switching valve sets  224  may be subjected to backpressure due to the flow of exhaust along the exhaust manifold  206  from the non-donating cylinders  200  (shown in  FIG. 3 ) and/or other donating cylinders  202  (shown in  FIG. 3 ). The pressure of the exhaust in the EGR manifold  220  may be greater than the pressure of the exhaust in the exhaust manifold  206 . As a result, the greater backpressure in the EGR manifold  220  may cause the exhaust to be split between flowing to the exhaust manifold  206  and the EGR manifold  220  when a valve located between the exhaust manifold  206  and the EGR manifold  220  is opened. Consequently, a pressure loss of the exhaust flowing to the exhaust manifold  206  may occur and the flow rate of exhaust that passes into the exhaust manifold  206  can be decreased. 
     The shape of the conduit  402  and/or plug  414  of the throttle valve  400  may reduce these pressure losses when the throttle valve  400  is switched from the donating mode (shown as plug  414 B) to the non-donating mode (shown as plug  414 A). When the plug  414 B is in the closed position, the plug  414 B engages the conduit  402  and blocks exhaust from flowing to the exhaust manifold  206 . As exhaust flows from the outlet conduit  314  to the EGR manifold  220 , the pressure of the exhaust in the conduit  402  of the throttle valve  400  may build up. For example, the pressure of the exhaust in the bulb  416  of the conduit  402  may increase. The plug  414 B may be moved to the position represented by the plug  414 A to switch the throttle valve  400  from the donating mode to the non-donating mode. As the plug  414 B is moved to the position of the plug  414 A, the built-up pressure in the bulb  416  flows into the upper portion of the conduit  402 , or the portion of the conduit  402  between the bulb  416  and the exhaust manifold  206 . The exhaust flowing from the outlet conduit  314  may then flow into the exhaust manifold  206  instead of being split between the exhaust manifold  206  and the EGR manifold  220 . 
     The control module  114  (shown in  FIG. 1 ) controls the position of the plug  414  inside the conduit  402  in one embodiment. For example, the plug  414  may be coupled with a motor or other device (not shown) that moves the plug  414  along the longitudinal axis  404  in response to commands received from the control module  114 . The control module  114  may move the plug  414  to positions located between the positions represented by plug  414 A and plug  414 B. For example, the control module  114  may move the plug  414  to a position between the positions of plug  414 A and plug  414 B. Depending on the position of the plug  414  between the positions of plug  414 A and plug  414 B, the rate of flow of the exhaust into the exhaust manifold  206  and/or the EGR manifold  220  may be controlled by the control module  114 . For example, as the plug  414  moves from the position of plug  414 A toward the position of plug  414 B, the gap between the plug  414  and the conduit  402  increases. As the gap between the plug  414  and the conduit  402  increases, the rate at which the exhaust flows into the exhaust manifold  206  increases while the rate that the exhaust flows into the EGR manifold  220  decreases in one embodiment. 
     Returning to the discussion of the diesel engine system  116  shown in  FIG. 3 , the control module  114  manages which mode the switching valve sets  224  operate within the donating mode or non-donating mode in one embodiment. For example, the control module  114  may alternate the switching valve sets  224  between the donating mode and the non-donating mode during a trip along a route by the rail vehicle  100  (shown in  FIG. 1 ). The control module  114  may communicate with and controls which of the switching valve sets  224  are in the donating mode and which of the switching valve sets  224  are in the non-donating mode to manage the efficiency and/or emissions of the diesel engine  108 . The control module  114  may base the number of switching valve sets  224  that are in each of the donating and non-donating modes based on at least one of an efficiency parameter, an emissions parameter, and/or an operating condition of the diesel engine  108 . 
     In one embodiment, the control module  114  manages the fraction or percentage of exhaust that is recirculated by the switching valve sets  224 . For example, instead of blocking all flow of exhaust from being recirculated when the switching valve sets  224  are in the non-donating mode, the control module  114  may cause one or more of the switching valve sets  224  to direct some of the exhaust out of the diesel engine  108  (shown in  FIG. 1 ) through the turbocharger  210  (shown in  FIG. 2 ) while recirculating the rest of the exhaust back to the donating and non-donating cylinders  202 ,  200 . For example, the switching valve sets  224  may be controlled by the control module  114  to direct some, but not all, of the exhaust into the exhaust manifold  206 . The remaining portion of the exhaust may be directed into the EGR manifold  220  by the switching valve sets  224 . For example, the switching valve sets  224  may direct 5%, 10%, 20%, 30%, 40%, 50%, and the like, of the exhaust flowing out of one or more donating cylinders  202  into the exhaust manifold  206  while the corresponding remaining 95%, 90%, 80%, 70%, 60%, 50%, and the like, of the exhaust is recirculated into the EGR manifold  220 . The control module  114  may base the percentage or fraction of exhaust that is recirculated by the switching valve sets  224  back into the EGR manifold  220  based on at least one of an efficiency parameter, an emissions parameter, and/or an operating condition of the diesel engine  108 . 
     The efficiency parameter represents a measurement or quantifiable characterization of the operation of the diesel engine  108  in one embodiment. The efficiency parameter may a measurement of an efficiency of one or more of the donating and/or non-donating cylinders  202 ,  200 . For example, the efficiency parameter may include a measurement of the efficiency of the donating cylinders  202  in converting diesel fuel into power. The efficiency parameter may include other measurements of the performance or operation of the engine  108 . In one embodiment, the efficiency parameter includes multiple measurements of the performance of the engine  108 , such as measurements of the power generated by the donating cylinders  202  and/or the efficiency of the donating cylinders  202 . The efficiency parameter may be measured by the control module  114 . 
     The emissions parameter represents a measurement or quantifiable characterization of the exhaust generated by the diesel engine  108  in one embodiment. In one example, the emissions parameter includes a measurement of an exhaust volume flow rate of the gaseous exhaust flowing from one or more of the donating and/or non-donating cylinders  202 ,  200 . The emissions parameter may be a measurement of the mass flow rate of the gaseous exhaust that flows from the donating and/or non-donating cylinders  202 ,  200 . The exhaust volume flow rate may be measured by a sensor (not shown), such as a mass flow sensor coupled with the control module  114 . The exhaust volume flow rate may be expressed as the mass of the gaseous exhaust from the donating and/or non-donating cylinders  202 ,  200  that passes through a surface area per unit of time. 
     In one example, an emissions parameter may include a measurement of a composition of one or more constituents of the gaseous exhaust generated by the diesel engine  108 . For example, the emissions parameter may be a concentration of one or more pollutants in the gaseous exhaust generated by the donating and/or non-donating cylinders  202 ,  200 , such as the concentration of nitrogen oxide (NOx). 
     The emissions parameter may include multiple measurements of the exhaust of the diesel engine  108 . For example, the emissions parameter may include or be based on measurements of the exhaust volume flow rate of the gaseous exhaust from the donating and/or non-donating cylinders  202 ,  200  and the concentration of one or more constituents in the gaseous exhaust from the donating and/or non-donating cylinders  202 ,  200 . 
     The operating conditions represent one or more measurements or quantifiable characterizations of the conditions under which the diesel engine  108  operates in one embodiment. In one example, the operating conditions may include a pressure and/or temperature of the exhaust generated by the donating cylinders  202  in another example. 
     In another example, the operating conditions may include a load demand of the diesel engine  108 , or one or more of the donating and/or non-donating cylinders  202 ,  200 . The load demand represents the power demanded or required from the diesel engine  108  or one or more of the donating and/or non-donating cylinders  202 ,  200 . For example, the load demand may represent the horsepower required to propel the rail vehicle  100  (shown in  FIG. 1 ) and associated cargo and/or passengers along a predetermined route. The load demand may change along the route due to variances in grades, speed limits, and the like of the route. 
     In another example, the operating conditions may include a speed demand of the diesel engine  108 , or of one or more of the donating and/or non-donating cylinders  202 ,  200 . The speed demand represents the speed at which the shaft  318  is demanded or required to be rotated by the diesel engine  108  or one or more of the donating and/or non-donating cylinders  202 ,  200 . For example, the speed demand may represent the speed at which the diesel engine  108  is demanded to rotate the shaft in order to generate sufficient electric current to power the traction motors  110  (shown in  FIG. 1 ). The speed demand may change along the route due to variances in grades, speed limits, and the like of the route. 
     The control module  114  may base how many of the switching valve sets  224  operate within the donating mode or non-donating mode based on one or more of an upper exhaust volume flow rate limit or a lower exhaust volume flow rate limit. The control module  114  may base the percentage or fraction of the exhaust that is recirculated to the EGR manifold  220  by the switching valve sets  224  based on one or more of an upper exhaust volume flow rate limit or a lower exhaust volume flow rate limit. The upper and/or lower exhaust volume flow rate limits may establish a range of exhaust volume flow rates that are emitted by the diesel engine system  116  through the external outlet  208 . For example, the upper exhaust volume flow rate limit may be an upper limit on the rate of exhaust emissions directed into the external atmosphere by the diesel engine system  116 . The lower exhaust volume flow rate limit may be a lower limit on the rate of exhaust emissions directed into the external atmosphere by the diesel engine system  116 . In one embodiment, the upper and/or lower exhaust volume flow rate limits are predetermined thresholds. Alternatively, the upper and/or lower exhaust volume flow rate limits may vary based on one or more of a position of the rail vehicle  100  (shown in  FIG. 1 ), the efficiency parameter, the emissions parameter, and/or an operating condition of the diesel engine  108 . With respect to the position of the rail vehicle  100 , different areas through which the rail vehicle  100  travels may have different emission limits. The upper and/or lower exhaust volume flow rate limits may be based on these different emission limits as the rail vehicle  100  travels through different areas. 
       FIG. 5  is a flowchart of a control method  500  for the diesel engine system  116  (shown in  FIG. 1 ) in accordance with one embodiment. The operations described in connection with the control method  500  may be performed by the control module  114  (shown in  FIG. 1 ) to manage which of the switching valve sets  224  (shown in  FIG. 3 ) are operating in the donating or non-donating mode and/or the percentage or fraction of exhaust that is directed by the switching valve sets  224  (shown in  FIG. 3 ) to the EGR manifold  220  (shown in  FIG. 3 ) and/or the external atmosphere. At  502 , one or more donating cylinders  202  (shown in  FIG. 3 ) and one or more non-donating cylinders  200  (shown in  FIG. 2 ) are operated to rotate the shaft  318  (shown in  FIG. 2 ) of the diesel engine system  116 . As the donating and non-donating cylinders  202 ,  200  operate, gaseous exhaust is generated. 
     At  504 , the exhaust generated in the donating cylinders  202  (shown in  FIG. 3 ) is directed to the switching valve sets  224  (shown in  FIG. 3 ). The exhaust from the non-donating cylinders  200  (shown in  FIG. 3 ) may be directed to the external atmosphere by way of the exhaust manifold  206  (shown in  FIG. 3 ). 
     At  508  and  506 , the exhaust from the donating cylinders  202  (shown in  FIG. 3 ) is directed to the external atmosphere by way of the exhaust manifold  206  (shown in  FIG. 3 ) and/or is recirculated back to the donating and/or non-donating cylinders  202 ,  200  (shown in  FIG. 3 ). For example, the switching valve sets  224  (shown in  FIG. 3 ) that are in the non-donating mode direct the exhaust to the exhaust manifold  206  while the switching valve sets  224  that are in the donating mode recirculate the exhaust. The exhaust may be recirculated back to the donating and/or non-donating cylinders  202 ,  200  and used as at least part of the intake air that is received by the donating and/or non-donating cylinders  202 ,  200  and used to ignite diesel fuel in the donating and/or non-donating cylinders  202 ,  200 . 
     At  510 , one or more parameters and/or operating conditions of the diesel engine  108  (shown in  FIG. 1 ) are determined. For example, an efficiency parameter, an emissions parameter, and/or an operating condition such as a load demand, speed demand, exhaust pressure, and/or exhaust temperature may be determined by the control module  114  (shown in  FIG. 1 ). Alternatively, one or more of the parameters and/or operating conditions may be measured by a sensor (not shown) and communicated to the control module  114 . 
     At  512 , the parameters and/or operating conditions are compared to flow control criteria. The flow control criteria include one or more rules or thresholds to which the parameters and/or operating conditions are compared in order to determine if the number of switching valve sets  224  (shown in  FIG. 3 ) that are in the non-donating mode needs to change. For example, the efficiency parameter may include a measurement of the efficiency of the diesel engine  108  (shown in  FIG. 1 ) that is compared to a threshold efficiency of the flow control criteria. In another example, the emissions parameter may include an exhaust volume flow rate that represents the flow rate of the exhaust flowing from the donating and/or non-donating cylinders  202 ,  200  (shown in  FIG. 3 ). The exhaust volume flow rate may be compared to an upper and/or lower exhaust volume flow rate limit. The load demand may be compared to a load threshold. The speed demand may be compared to a speed threshold. In another example, the temperature of the exhaust generated by the donating cylinders  202  may be compared to a temperature threshold. In another example, the pressure of the exhaust generated by the donating cylinders  202  may be compared to a pressure threshold. 
     At  514 , a determination is made whether to change the number of switching valve sets  224  (shown in  FIG. 3 ) that are in the non-donating mode to the donating mode. For example, based on the comparison of the parameters and/or conditions to the flow control criteria, the set of switching valve sets  224  that are in the non-donating mode may need to be changed. In one embodiment, if the efficiency parameter includes an efficiency measurement of the diesel engine  108  (shown in  FIG. 1 ) that exceeds an efficiency threshold, then the efficiency measurement may indicate that the diesel engine  108  is operating at a sufficiently high efficiency. As a result, one or more of the switching valve sets  224  that are in the non-donating mode may be changed to the donating mode. Alternatively, the percentage or fraction of the exhaust that is directed by the switching valve sets  224  to the exhaust manifold  206  (shown in  FIG. 3 ) may be reduced, or the percentage or fraction of exhaust that is directed to the EGR manifold  220  (shown in  FIG. 3 ) may be increased. Increasing the number of switching valve sets  224  in the donating mode, reducing the percentage of exhaust that is directed to the exhaust manifold  206 , and/or increasing the percentage of exhaust that is directed to the EGR manifold  220  may reduce the efficiency of the diesel engine  108 , but also may reduce the emissions of pollutants from the diesel engine  108 . 
     Conversely, if the efficiency measurement does not exceed an efficiency threshold, then the efficiency measurement may indicate that the diesel engine  108  (shown in  FIG. 1 ) is operating at an insufficient efficiency, or an efficiency that needs to be increased. As a result, one or more of the switching valve sets  224  (shown in  FIG. 3 ) that are in the donating mode may be changed to the non-donating mode. Alternatively, the percentage or fraction of exhaust that is directed by the switching valve sets  224  to the EGR manifold  220  (shown in  FIG. 3 ) may be decreased such that a larger percentage of the exhaust is directed to the exhaust manifold  206  (shown in  FIG. 3 ). Increasing the number of switching valve sets  224  that are in the non-donating mode, increasing the percentage of exhaust that is directed to the exhaust manifold  206 , and/or reducing the percentage of exhaust that is directed to the EGR manifold  220  may increase the efficiency of the diesel engine  108 , but also may increase the emission of pollutants from the diesel engine  108 . 
     In another example, if the emissions parameter includes an exhaust volume flow rate of the diesel engine  108  (shown in  FIG. 1 ) that exceeds an upper exhaust volume flow rate limit, then the emissions parameter may indicate that the diesel engine  108  is emitting too much exhaust into the external atmosphere. As a result, one or more of the switching valve sets  224  (shown in  FIG. 3 ) that are in the non-donating mode may be changed to the donating mode, the percentage of exhaust that is directed to the EGR manifold  220  (shown in  FIG. 3 ) by the switching valve sets  224  may be increased, and/or the percentage of exhaust that is directed to the exhaust manifold  206  (shown in  FIG. 3 ) may be reduced. Increasing the number of switching valve sets  224  in the donating mode, increasing the flow of exhaust to the EGR manifold  220 , and/or reducing the flow of exhaust to the exhaust manifold  206  may reduce the emissions of pollutants from the diesel engine  108 . 
     In another example, if the emissions parameter does not exceed a lower exhaust volume flow rate limit, then the emissions parameter may indicate that the diesel engine  108  (shown in  FIG. 1 ) can increase the exhaust volume flow rate, or the flow rate of exhaust generated by the engine  108 . As a result, one or more of the switching valve sets  224  that are in the donating mode may be changed to the non-donating mode, the percentage of exhaust that is directed to the EGR manifold  220  (shown in  FIG. 3 ) by the switching valve sets  224  may be decreased, and/or the percentage of exhaust that is directed to the exhaust manifold  206  (shown in  FIG. 3 ) may be increased. Increasing the number of switching valve sets  224  that are in the non-donating mode, decreasing the exhaust directed to the EGR manifold  220 , and/or increasing the exhaust directed to the exhaust manifold  206  may increase the emission of pollutants from the diesel engine  108 . 
     Alternatively, the number of switching valve sets  224  (shown in  FIG. 3 ) that are in the donating mode and/or the percentage of exhaust that is directed into the EGR manifold  220  (shown in  FIG. 3 ) by the switching valve sets  224  may be based on a difference between the upper and lower exhaust volume flow rate limits. As the difference increases, the number of switching valve sets  224  that are in the non-donating mode increases while the number of switching valve sets  224  that are in the donating mode decreases in one embodiment. Alternatively, as the difference in exhaust volume flow limits increases, the percentage of exhaust that is directed to the exhaust manifold  206  (shown in  FIG. 3 ) may increase while the percentage of exhaust directed to the EGR manifold  220  decreases. Conversely, as the difference in exhaust volume flow limits decreases, the number of switching valve sets  224  that are in the non-donating mode may decrease while the number of switching valve sets  224  that are in the donating mode may increase. Alternatively, as the difference in exhaust volume flow limits decreases, the percentage of exhaust that is directed to the exhaust manifold  206  may decrease while the percentage of exhaust directed to the EGR manifold  220  increases. 
     In another example, if the load demand and/or speed demand does not exceed an associated threshold, then the relatively low load and/or speed demand may indicate that the power output of the diesel engine  108  (shown in  FIG. 1 ) needs to be increased. As a result, one or more of the switching valve sets  224  (shown in  FIG. 3 ) that are in the donating mode may be changed to the non-donating mode. Increasing the number of switching valve sets  224  that are in the non-donating mode may increase the power output of the diesel engine  108 . Alternatively, the percentage of exhaust that is directed to the EGR manifold  220  (shown in  FIG. 3 ) instead of the exhaust manifold  206  (shown in  FIG. 3 ) by the switching valve sets  224  may be increased. 
     In another example, if the temperature of the exhaust exceeds a temperature threshold, then the relatively high temperature of the exhaust may indicate that the exhaust of too many donating cylinders  202  (shown in  FIG. 3 ) is being recirculated back to the donating and non-donating cylinders  202 ,  200  (shown in  FIG. 3 ). As a result, one or more of the switching valve sets  224  (shown in  FIG. 3 ) that are in the non-donating mode may be changed to the donating mode and/or the percentage of exhaust that is directed to the exhaust manifold  206  (shown in  FIG. 3 ) instead of the EGR manifold  220  (shown in  FIG. 3 ) may be increased by the switching valve sets  224 . Increasing the number of switching valve sets  224  that are in the donating mode and/or decreasing the percentage of exhaust that is directed to the EGR manifold  220  may reduce the temperature of the exhaust as less exhaust is being recirculated. 
     In another example, if the pressure of the exhaust exceeds a pressure threshold, then the relatively high pressure of the exhaust may indicate that too much exhaust of too many donating cylinders  202  (shown in  FIG. 3 ) is being recirculated back to the donating and non-donating cylinders  202 ,  200  (shown in  FIG. 3 ). As a result, one or more of the switching valve sets  224  (shown in  FIG. 3 ) that are in the donating mode may be changed to the non-donating mode and/or the percentage of exhaust that is directed to the EGR manifold  220  (shown in  FIG. 3 ) by the switching valve sets  224  may be decreased. Increasing the number of switching valve sets  224  that are in the non-donating mode and/or reducing the exhaust that is directed to the EGR manifold  220  may reduce the amount and pressure of the exhaust that is being recirculated. 
     If one or more of the switching valve sets  224  (shown in  FIG. 3 ) in the non-donating mode need to be changed to the donating mode and/or the percentage of exhaust being directed to the EGR manifold  220  (shown in  FIG. 3 ) by the switching valve sets  224  needs to change based on the comparison of the parameters and/or operating conditions with the flow control criteria, then flow of the method  500  proceeds to  516 . Alternatively, if one or more of the switching valve sets  224  in the donating mode need to be changed to the non-donating mode and/or the percentage of exhaust being directed to the EGR manifold  220  by the switching valve sets  224  needs to change based on the comparison of the parameters and/or operating conditions with the flow control criteria, then flow of the method  500  also proceeds to  516 . Conversely, if the mode of one or more of the switching valve sets  224  does not need to be changed and/or the percentage of exhaust being directed by the switching valve sets  224  does not need to change, then flow of the method  500  proceeds to  518 . 
     At  516 , the mode of and/or flow of exhaust being directed by one or more of the switching valve sets  224  (shown in  FIG. 3 ) is changed. For example, based on the comparison of the parameters and/or operating conditions with the flow control criteria, the number of switching valve sets  224  that are in the donating mode may be changed so that a different number of the switching valve sets  224  are in the donating mode. Alternatively, the percentage of exhaust directed by the switching valve sets  224  to the EGR manifold  220  (shown in  FIG. 3 ) may be changed. In one embodiment, if the mode of two or more switching valve sets  224  is changed from the donating mode to the non-donating mode, then the switching valve sets  224  are sequentially changed from the donating mode to the non-donating mode. For example, the mode of one switching valve set  224  is changed before the mode of the other switching valve(s)  224  is changed. Serially or sequentially changing the mode of the switching valve sets  224  may prevent significant pressure losses in the switching valve sets  224 . 
     At  518 , a determination is made whether to change the exhaust volume flow rate of the exhaust that passes through the switching valve sets  224  (shown in  FIG. 3 ) to the external atmosphere by way of the exhaust manifold  206  (shown in  FIG. 3 ). For example, based on the comparison of the parameters and/or conditions to the flow control criteria, the rate at which the exhaust flows through the switching valve sets  224  to the exhaust manifold  206  may need to be changed. In one embodiment, if the efficiency parameter includes an efficiency measurement of the diesel engine  108  (shown in  FIG. 1 ) that exceeds an efficiency threshold, then the efficiency measurement may indicate that the diesel engine  108  is operating at a sufficiently high efficiency. As a result, the volume flow rate of the exhaust passing through one or more of the switching valve sets  224  to the exhaust manifold  206  may be increased. Increasing the flow rate of exhaust through the switching valve sets  224  to the exhaust manifold  206  may increase the efficiency of the diesel engine  108 . Conversely, if the efficiency measurement does not exceed an efficiency threshold, then the efficiency measurement may indicate that the diesel engine  108  is operating at an insufficient efficiency, or an efficiency that needs to be increased. As a result, the volume flow rate of exhaust passing through one or more of the switching valve sets  224  to the exhaust manifold  206  may be increased. Increasing the volume flow rate of exhaust passing through the exhaust manifold  206  may increase the efficiency of the diesel engine  108 . 
     In another example, if the emissions parameter includes an exhaust volume flow rate of the diesel engine  108  (shown in  FIG. 1 ) that exceeds an upper exhaust volume flow rate limit, then the emissions parameter may indicate that the volume flow rate of the exhaust that is flowing into the exhaust manifold  206  (shown in  FIG. 3 ) is too large. As a result, the volume flow rate of the exhaust passing through one or more of the switching valve sets  224  (shown in  FIG. 3 ) to the exhaust manifold  206  may be decreased. Decreasing the flow rate of exhaust that passes through the switching valve sets  224  to the exhaust manifold  206  may reduce the emissions of pollutants from the diesel engine  108 . In another example, if the emissions parameter does not exceed a lower exhaust volume flow rate limit, then the emissions parameter may indicate that the volume flow rate of the exhaust that is passing through the switching valve sets  224  to the exhaust manifold  206  can be increased. 
     Alternatively, the flow rate of exhaust that passes through the switching valve sets  224  (shown in  FIG. 3 ) to the exhaust manifold  206  (shown in  FIG. 3 ) may be based on a difference between the upper and lower exhaust volume flow rate limits. As the difference increases, the exhaust volume flow rate through the switching valve sets  224  and to the exhaust manifold  206  increases in one embodiment. As the difference decreases, the exhaust volume flow rate through the switching valve sets  224  and to the exhaust manifold  206  may decrease. 
     In another example, if the load demand and/or speed demand does not exceed an associated threshold, then the relatively low load and/or speed demand may indicate that the power output of the diesel engine  108  (shown in  FIG. 1 ) needs to be increased. As a result, the volume flow rate of the exhaust that passes through one or more of the switching valve sets  224  (shown in  FIG. 3 ) to the exhaust manifold  206  (shown in  FIG. 3 ) may be increased. Increasing the exhaust volume flow rate to the exhaust manifold  206  through the switching valve sets  224  may increase the power output of the diesel engine  108 . 
     In another example, if the temperature of the exhaust exceeds a temperature threshold, then the relatively high temperature of the exhaust may indicate that too much exhaust is being recirculated back to the donating and non-donating cylinders  202 ,  200  (shown in  FIG. 3 ). As a result, the flow rate of exhaust to the exhaust manifold  206  (shown in  FIG. 3 ) through one or more of the switching valve sets  224  (shown in  FIG. 3 ) may be increases. Increasing the exhaust volume flow rate that passes to the exhaust manifold  206  can reduce the recirculated exhaust and the temperature of the exhaust. 
     In another example, if the pressure of the exhaust exceeds a pressure threshold, then the relatively high pressure of the exhaust may indicate that the exhaust volume flow rate that passes to the exhaust manifold  206  (shown in  FIG. 3 ) through the switching valve sets  224  (shown in  FIG. 3 ) is too small. As a result, the exhaust volume flow rate passing through the switching valve sets  224  to the exhaust manifold  206  may be increased. Increasing the exhaust volume flow rate that passes through the switching valve sets  224  to the exhaust manifold  224  may reduce the amount and pressure of the exhaust that is being recirculated. 
     If the volume flow rate of the exhaust passing to the exhaust manifold  206  (shown in  FIG. 3 ) through one or more of the switching valve sets  224  (shown in  FIG. 3 ) needs to be changed based on the comparison of the parameters and/or operating conditions with the flow control criteria, then flow of the method  500  proceeds to  520 . Alternatively, if the volume flow rate of the exhaust passing to the exhaust manifold  206  through one or more of the switching valve sets  224  does not need to change, based on the comparison of the parameters and/or operating conditions with the flow control criteria, then flow of the method  500  returns to  502 . 
     At  520 , the exhaust volume flow rate through one or more of the switching valve sets  224  (shown in  FIG. 3 ) is changed. For example, based on the comparison of the parameters and/or operating conditions with the flow control criteria, the flow rate of exhaust passing through one or more of the switching valve sets  224  to the exhaust manifold  206  (shown in  FIG. 3 ) may be changed. In one embodiment, the flow rate of exhaust through one or more of the switching valve sets  224  may be varied by moving the plug  414  (shown in  FIG. 4 ) in the conduit  402  (shown in  FIG. 4 ) of the throttle valve  400  (shown in  FIG. 4 ). 
     The method  500  may proceed in a loop-wise manner back to  502 , where the donating and non-donating cylinders continue to be operated. The method  500  may proceed to change the number of switching valve sets  224  (shown in  FIG. 3 ) and/or the exhaust volume flow rate that passes through the switching valve sets  224  to the exhaust manifold  206  (shown in  FIG. 3 ) in order to reduce the emission of pollutants while avoiding significant reductions in the efficiency of the diesel engine  108  (shown in  FIG. 1 ). 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the subject matter set forth herein without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the disclosed subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the subject matter described herein should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     This written description uses examples to disclose several embodiments of the subject matter set forth herein, including the best mode, and also to enable any person skilled in the art to practice the embodiments of disclosed subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter described herein is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.