Abstract:
An exhaust system including a selective catalytic reduction (SCR) component and an oxidation catalyst component. The exhaust system also includes an exhaust treatment fluid injection system for dispersing an exhaust treatment fluid into an exhaust stream at a location adjacent either the SCR component or the oxidation catalyst component, wherein the exhaust treatment fluid injection device includes a common rail that provides the exhaust treatment fluid under pressure to a plurality of injectors that dose the exhaust treatment fluid into the exhaust stream. The exhaust treatment fluid injection device also includes a return rail for returning unused exhaust treatment fluid to the fluid source.

Description:
FIELD 
       [0001]    The present disclosure relates to a reductant injection system for an exhaust system. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    Emission regulation requirements are mandating that engines have exhaust after-treatment systems to eliminate, or at least substantially minimize, the emission of, for example, particulate matter and NO x . To eliminate or reduce the emission of particulate matter and NO x , exhaust after-treatment systems can include components such as a particulate filter (e.g., a diesel particulate filter (DPF)), a selective catalyst reduction (SCR) component, and a diesel oxidation catalyst (DOC) component. 
         [0004]    SCR and DOC components generally work in conjunction with reductant injection systems that inject a reductant into the exhaust stream to treat the exhaust before the exhaust enters the SCR or DOC components. In the case of SCR, a reductant solution including urea is injected into the exhaust stream before entry into the SCR component. In the case of DOC, a hydrocarbon reductant such as diesel fuel is injected into the exhaust stream before entry into the DOC component. 
         [0005]    The injection systems for each of SCR and DOC exhaust after-treatments involve the integration of injectors, pumps, filters, regulators, and other necessary control mechanisms to control the dosing of each of these reductants into the exhaust stream. In general, fluid injection delivery systems for, for example, light, medium, and heavy-duty trucks require only a single injection source for dosing the reductant into the exhaust stream. Large-scale engines for locomotive, marine, and stationary applications, however, can require multiple injector sources for injecting the reductant into the exhaust stream. These large-scale applications, therefore, can be difficult to design to overcome various issues such as maintaining proper injector pressure, system durability, sufficient reductions of harmful emission (e.g., particulate matter and NO x ), cost, and maintenance. 
       SUMMARY 
       [0006]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0007]    The present disclosure provides an exhaust system including a selective catalytic reduction (SCR) component and an oxidation catalyst component. The exhaust system also includes an exhaust treatment fluid injection system for dispersing an exhaust treatment fluid into an exhaust stream at a location adjacent either the SCR component or the oxidation catalyst component, wherein the exhaust treatment fluid injection device includes a common rail that provides the exhaust treatment fluid under pressure to a plurality of injectors that dose the exhaust treatment fluid into the exhaust stream. The exhaust treatment fluid injection device also includes a return rail for returning unused exhaust treatment fluid to the fluid source. 
         [0008]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0009]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0010]      FIG. 1  schematically illustrates an exhaust treatment system according to a principle of the present disclosure; 
           [0011]      FIG. 2  schematically illustrates a common rail injection system for hydrocarbon injections according to a principle of the present disclosure; 
           [0012]      FIG. 3  schematically illustrates a common rail injection system for urea injections according to a principle of the present disclosure; and 
           [0013]      FIG. 4  illustrates a large scale exhaust treatment system including the common rail injection systems according to principles of the present disclosure. 
       
    
    
       [0014]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0015]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0016]      FIG. 1  schematically illustrates an exhaust system  10  according to the present disclosure. Exhaust system  10  includes at least an engine  12  in communication with a fuel source  14  that, once consumed, will produce exhaust gases that are discharged into an exhaust passage  16  having an exhaust after-treatment system  18 . Downstream from engine  12  can be disposed a DOC component  20 , a DPF component  22 , and a SCR component  24 . Although not required by the present disclosure, exhaust after-treatment system  18  can further include components such as a burner  26  to increase a temperature of the exhaust gases passing through exhaust passage  16 . Increasing the temperature of the exhaust gas is favorable to achieve light-off of the catalyst in DOC and SCR components  20  and  24  in cold-weather conditions and upon start-up of engine  12 , as well as initiate regeneration of DPF  22  when required. To provide fuel to burner  26 , the burner can include an inlet line  27  in communication with fuel source  14 . 
         [0017]    To assist in reduction of the emissions produced by engine  12 , exhaust after-treatment system  18  can include injectors  28  and  30  for periodically injecting exhaust treatment fluids into the exhaust stream. As illustrated in  FIG. 1 , injector  28  can be located upstream of DOC  20  and is operable to inject a hydrocarbon exhaust treatment fluid that assists in at least reducing NO x  in the exhaust stream, as well as raising exhaust temperatures for regeneration of DPF  22 . In this regard, injector  28  is in fluid communication with fuel source  14  by way of inlet line  32  to inject a hydrocarbon such as diesel fuel into the exhaust passage  16  upstream of DOC  20 . Injector  28  can also be in communication with fuel source  14  via return line  33 . Return line  33  allows for any hydrocarbon not injected into the exhaust stream to be returned to fuel source  14 . Flow of hydrocarbon through inlet line  32 , injector  28 , and return line  33  also assists in cooling injector  28  so that injector  28  does not overheat. Although not illustrated in the drawings, injectors  28  can be configured to include a cooling jacket that passes a coolant around injectors  28  to cool them. 
         [0018]    Injector  30  can be used to inject an exhaust treatment fluid such as urea into exhaust passage  16  at a location upstream of SCR  24 . Injector  30  is in communication with a reductant tank  34  via inlet line  36 . Injector  30  also is in communication with tank  34  via return line  38 . Return line  38  allows for any urea not injected into the exhaust stream to be returned to tank  34 . Similar to injector  28 , flow of urea through inlet line  36 , injector  30 , and return line  38  also assists in cooling injector  30  so that injector  30  does not overheat. 
         [0019]    Large-scale diesel engines used in locomotives, marine applications, and stationary applications can have exhaust flow rates that exceed the capacity of a single injector. Accordingly, although only a single injector  28  is illustrated for hydrocarbon injector and only a single injector  30  is illustrated for urea injection, it should be understood that multiple injectors for both hydrocarbon and urea injection are contemplated by the present disclosure. When multiple injectors are used, however, the exhaust system  10  can experience pressure fluctuations at each injector that can affect the spray quality and amount of treatment fluid that is injected into the exhaust stream due to activation/deactivation of the injectors. 
         [0020]    To effectively supply exhaust treatment fluid to the exhaust stream using multiple injectors without sacrificing spray quality and quantity, the present disclosure utilizes a plurality of injectors in fluid communication with a common rail that serves as a distributor of fluid and avoids pressure fluctuations arising from individual injector activations and deactivations.  FIG. 2  schematically illustrates a common rail injection system  40  that can be used for supplying a hydrocarbon exhaust treatment fluid to the exhaust stream. 
         [0021]    Common rail injection system  40  generally includes fuel source  14 , from which a hydrocarbon treatment fluid such as diesel fuel is pumped through a filter  44  by pump  46 . Although filter  44  is illustrated as being upstream from pump  46 , it should be understood that filter  44  can be located downstream from pump  46  as well without departing from the scope of the present disclosure. Pump  46 , in addition to being operable to draw treatment fluid from fuel source  14 , is also operable to pressurize common rail  48  and injector inlet lines  50 . In the illustrated exemplary embodiment, common rail injection system  40  includes eight injectors  28 , with each of the injectors  28  corresponding to a respective exhaust passage  16  of exhaust system  10  for, for example, a diesel powered locomotive. Although eight injectors  28  are illustrated in  FIG. 2 , it should be understood that more or fewer injectors  28  are contemplated, dependent on the application in which common rail injection system  40  is to be utilized. 
         [0022]    Between pump  46  and common rail  48  may be disposed a reducing pressure regulator  52 . In general, pump  46  is operable to pump the hydrocarbon treatment fluid at a pressure of about 120 psi, which is greater than a pressure (e.g., approximately 85 psi to 90 psi) in common rail  48  necessary to satisfactorily affect spray quality and quantity. To reduce the pressure in common rail  48 , the reducing pressure regulator  52  reduces pressures in common rail  48  to the desired pressure. It should be understood that although the above-noted pressures are desirable, the present disclosure should not be limited thereto. That is, depending on the application size and scope, different pressures can be used and are contemplated, as one skilled in the art will readily acknowledge and appreciate. Regardless, between reducing pressure regulator  52  and pump  46  can be disposed a backpressure regulator  54 . Backpressure regulator  54  located upstream from reducing pressure regulator  52  can be used to divert excess flow from pump  46  back to fuel source  14  through overflow line  55 . Such a configuration allows pump  46  to run at full capacity without stalling or resonating. 
         [0023]    Common rail  48  receives flow from reducing pressure regulator  52  and is designed to maintain constant pressure across all injectors  28 . In this regard, a volume of common rail  48  has an effect on pressure fluctuations that occur within common rail  48  as injectors  28  are activated and deactivated, where increasing the volume of common rail  48  decreases pressure fluctuations. Accordingly, a volume of common rail  48  can be tailored according to the specific application in which common rail injection system  40  will be used. When common rail injection system  40  is used in, for example, a locomotive application, common rail  48  can be formed from a stainless steel pipe having an outer diameter ranging between 1.5 to 3 inches, a wall thickness ranging between 0.05 to 0.1 inches, and a length ranging between 96 to 120 inches. Other dimensions for common rail  48 , however, are contemplated and would be apparent to one skilled in the art. For example, when common rail  48  is used in a marine or stationary application, the dimensions of common rail  48  can be dimensioned appropriately. To monitor pressures within common rail injection system  40 , various pressure sensors  41  can be located at common rail  48  and injectors  28 . 
         [0024]    The exhaust treatment fluid is fed from common rail  48  into injector inlet lines  50  and then into injectors  28 , from which the treatment fluid is then injected into the respective exhaust passages  16 . Injectors  28  can also be provided with return lines  51  that each feed into a return rail  56 . Return rail  56  can have dimensions similar to or less than common rail  48 . Similar to common rail  56 , return rail  56  can be dimensioned according to the application for which the injection system is being used. 
         [0025]    Although variable, each injector  28  may have a nozzle orifice (not shown) ranging between about 0.01 and 0.05 inches, and an internal return restriction orifice (not shown) ranging between about 0.01 and 0.05 inches. The internal return restriction orifice controls the rate of fluid flowing through injector  28 , and provides backpressure for injector  28  to maintain spray quality. The size of nozzle orifice, however, has the greatest effect on droplet size and spray angle during injector dosing. Exhaust treatment fluid present in return rail  56  returns any unused treatment fluid to fuel source  14 . 
         [0026]    During use of common rail injection system  40 , injectors  28  may be activated simultaneously or in a staggered manner. To activate and deactivate injectors  28  either simultaneously or in a staggered manner, common rail injection system  40  can include a controller  58  ( FIG. 4 ) that is operable to control the timing of each injector  28 , control pump  46 , and monitor pressure sensors  41 . Controller  58  may, in turn, be in communication with an engine control unit (not shown) used to control operation of engine  12 . Controller  58  is operable to activate injectors  28  in any manner desired. For example, all injectors  28  may be activated simultaneously, or groups of injectors  28  (e.g., groups of two or four) may be activated while the remaining injectors  28  are deactivated. 
         [0027]    Although common rail  48  is designed to reduce pressure fluctuations in injectors  28 , the activation of all injectors  28  simultaneously can result in various pressure fluctuations at each injector  28 . The activation of groups of injectors  28  intermittently, however, negates pressure fluctuations in common rail  48  and, therefore, each injector  28  does not experience pressure fluctuations during staggered activations. Regardless, if simultaneous activation of each injector  28  is desired, common rail  48  can include an accumulator  60 . Use of accumulator  60  on common rail  48  assists in reducing pressure fluctuations during simultaneous activation of each injector  28 . 
         [0028]    Now referring to  FIG. 3 , a common rail injection system  40 ′ is illustrated that is operable to inject a urea exhaust treatment fluid into the exhaust stream. Common rail injection system  40 ′ is similar to common rail injection system  40 , with the largest differences being that twelve injectors  30  are used rather than eight, and that a pump  46 ′ used to pump urea treatment fluid and pressurize a common rail  48 ′ and injector inlet lines  50 ′ is reversible. Pump  46 ′ is reversible because the urea treatment fluid can freeze. As the urea treatment fluid can freeze, any non-injected urea treatment fluid needs to be purged from common rail injection system  40 ′ back into tank  34  when common rail injection system  40 ′ is not in use. An additional difference lies in the manner in how pressure in a common rail  48 ′ of common rail injection system  40 ′ is regulated. 
         [0029]    Common rail injection system  40 ′ generally includes urea tank  34  from which a urea treatment fluid is drawn by pump  46 ′ through filter  44 ′. Although filter  44 ′ is illustrated as being downstream from pump  46 ′, it should be understood that filter  44 ′ can be located upstream from pump  46 ′ without departing from the scope of the present disclosure. Pump  46 ′, in addition to being operable to draw urea treatment fluid from tank  34 , is also operable to pressurize common rail  48 ′ and injector inlet lines  50 ′. In the illustrated exemplary embodiment, common rail injection system  40 ′ includes twelve injectors  30 . Although twelve injectors  30  are illustrated in  FIG. 3 , it should be understood that more or fewer injectors  30  are contemplated, dependent on the application in which common rail injection system  40 ′ is to be utilized. 
         [0030]    As noted above, a difference between common rail injection system  40  and common rail injection system  40 ′ lies in the manner in which the pressure within common rails  48  and  48 ′ is regulated. In common rail injection system  40 ′, no reducing pressure regulator is needed to maintain a lower pressure in common rail  48 ′ in comparison to that which is generated by pump  46 ′. The reasons that a reducing pressure regulator is not required are that the nozzle orifice (not shown) of injectors  30  is smaller in comparison to that of injectors  28 , and that a smaller volume of urea treatment fluid is required to be injected into exhaust system  10  in comparison to the volume of hydrocarbon treatment fluid that may be required. The nozzle orifice (not shown) of injectors  30  is about 0.008 inches and an internal return restriction orifice (not shown) of about 0.024 inches. The nozzle orifice (not shown) of injector  30  is smaller in comparison to the nozzle orifice (now shown) of injector  28  because of the increased atomization required during urea dosing. 
         [0031]    Although a reducing pressure regulator is not required for common rail injection system  40 ′, a backpressure regulator  54 ′ can still be utilized that is located downstream from pump  46 ′ to divert excess flow from pump  46 ′ back to tank  34  through overflow line  55 ′. Such a configuration allows pump  46 ′ to run at full capacity without stalling or resonating. 
         [0032]    The urea exhaust treatment fluid is fed from common rail  48 ′ into injector inlet lines  50 ′ and then into injectors  30 , from which the urea treatment fluid is then injected into the respective exhaust passages  16 . Injectors  30  can also be provided with return lines  51 ′ that each feed into a return rail  56 ′. Similar to injectors  28  for hydrocarbon injection, injectors  30  may require a constant supply of fluid flowing through them to stay cool and function properly. Exhaust treatment fluid present in return rail  56 ′ returns any unused urea treatment fluid to tank  34 . 
         [0033]    Like injectors  28 , injectors  30  may be activated simultaneously or in a staggered manner. To activate and deactivate injectors  30  either simultaneously or in a staggered manner, common rail injection system  40 ′ can include a controller  58 ′ that is operable to control the timing of each injector  30 , operate pump  46 ′, and monitor pressure sensors  41 ′. Alternatively, in lieu of using a separate controller  58  to control common rail injection system  40 ′ and if exhaust system  10  is configured to include both common rail injection system  40  and common rail injection system  40 ′, controller  58  can also be used to simultaneously control common rail systems  40  and  40 ′. Regardless, controller  58 ′ (if used) may be in communication with an engine control unit (not shown) used to control operation of engine  12 , and controller  58 ′ is operable to activate injectors  30  in any manner desired. That is, all injectors  30  may be activated simultaneously, or groups of injectors  30  (e.g., groups of two, four, or six) may be activated while the remaining injectors  30  are deactivated. As noted above, activation of groups of injectors can assist in reducing pressure fluctuations in the system. Common rail injection system  40 ′ can also include an accumulator  60 ′, if desired. 
         [0034]    Because the urea treatment fluid can freeze, common rail injection system  40 ′ may require purging when not in use. As noted above, pump  46 ′ is a reversible pump that, when common rail injection system  40 ′ is not being used, can pump the urea treatment fluid from common rail  48 ′ and injector inlet lines back into tank  34 . Simply running pump  46 ′ in reverse, however, can sometimes be insufficient to completely purge injector return lines  51 ′, which leaves the return lines  51 ′ susceptible to rupture if any urea treatment fluid remains in the return lines during freezing conditions. 
         [0035]    To further assist in the purging of the urea treatment fluid from common rail injection system  40 ′ during non-use thereof, return rail  56 ′ can be located above common rail  48 ′. By placing return rail  56 ′ above common rail  48 ′ and thus at the highest point in the common rail injection system  40 ′, gravity can assist in purging the urea treatment fluid from the return lines  51 ′. More particularly, when return rail  56 ′ is located above common rail  48 , the urea treatment fluid located in return rail  56 ′ will naturally want to flow back into return lines  51 ′ when the injection system  40 ′ is not in use. Further, when pump  46 ′ is run in reverse to purge injection system  40 ′, the urea treatment fluid will be pulled from return rail  56 ′ through return lines  51 ′ and injectors  30 , through inlet lines  50 ′ and common rail  48 ′ to tank  34 . 
         [0036]    Now referring to  FIG. 4 , an exhaust system  100  for, for example, a locomotive is illustrated including common rail injection systems  40  and  40 ′. For simplicity, only common rails  48  and  48 ′ are illustrated in  FIG. 4 . It should be understood, however, that common rail injection systems  40  and  40 ′ will also include return rails  56  and  56 ′ for returning unused hydrocarbon and urea back to fuel source  14  and urea tank  34 . Exhaust system  100  includes a diesel-powered engine  12  in communication with a diesel fuel source  14 . Engine  12  can feed exhaust into an exhaust turbo manifold  102 . At exhaust manifold  102  is disposed common rail injection system  40 , which injects hydrocarbon treatment fluid from diesel fuel source  14  into exhaust turbo manifold  102 , which is located upstream of DOCs  20 . Control of injectors  28  and pump  46  is controlled by controller  58 . 
         [0037]    Downstream from turbo manifold  102 , the exhaust stream is split into a plurality of exhaust passages  104 . Each exhaust passage  104  is in communication with an array of a plurality of DOCs  20  and DPFs  22 . In the illustrated embodiment, each exhaust passage  104  communicates with an array of three DOCs  20  and three DPFs  22 . After exiting the DOCs  20  and DPFs  22 , the exhaust stream is passed into exhaust passages  106 . At exhaust passages  106 , common rail injection system  40 ′ is disposed where urea treatment fluid is injected into the exhaust stream at a location upstream of SCRs  24  such that after the urea treatment fluid is injected into the exhaust stream at exhaust passages  106 , the exhaust stream travels through SCRs  24 . After passing through SCRs  24 , the treated exhaust exits exhaust system  100  through outlets  108 . 
         [0038]    As illustrated in  FIG. 4 , the common rails  48  and  48 ′ are not embodied by a simple linear pipe. This is because packaging restrictions within the locomotive may prevent the use of such a pipe as the common rails  48  and  48 ′. Rather, the common rails  48  and  48 ′ may be modular or curved to account for any packaging restrictions present during design of exhaust system  100 . In this regard, common rails  48  and  48 ′ may include various legs connected together in various orientations to account for the packaging restrictions. The modular design of common rails  48  and  48 ′ does not significantly affect performance of common rails, including the abatement of pressure fluctuations. 
         [0039]    Lastly, as illustrated in  FIGS. 2 and 4 , exhaust system  100  can include burner  26  for raising temperatures of the exhaust gases, which can raise the catalysts of the DOC  20  and SCR  24  to a light-off temperature. Further, burner  26  is sufficient for raising the exhaust gas temperature to a level sufficient to regenerate DPF  22 . To provide fuel to burner  26 , burner  26  can be in communication with common rail  48  via a feed line  110  to receive hydrocarbons from injection system  40 . Specifically, feed line  110  provides fuel to burner directly from common rail  48 . Such a configuration negates the need for a separate inlet line for burner  26  that communicates with fuel source  14 , which reduces parts necessary to manufacture exhaust system  100  and also reduces packaging constraints. 
         [0040]    As illustrated in  FIGS. 2 and 4 , burner  26  is located downstream from injectors  28 , as indicated by line  112  in  FIG. 2  which merely illustrates that burner  26  is directly coupled to exhaust passage  16 . It should be understood, however, that burner  26  can be in communication with exhaust passage  16  at a position upstream from injectors  28  so long as burner  26  is located at a position relative to DPFs  22  where burner  26  can raise exhaust temperatures to a point where regeneration of DPF  22  can be achieved. 
         [0041]    According to the above, the injection of exhaust treatment fluids for large-scale diesel applications can be effectively administered to the exhaust stream using multiple injectors without sacrificing spray quality and quantity. By using a plurality of injectors in fluid communication with a common rail that serves as a distributor of the fluid, pressure fluctuations arising from individual injector activations and deactivations are avoided. This results in the proper amount and quality of reductant consistently being provided to the exhaust stream to reduce NO x  from the exhaust stream. 
         [0042]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.