Abstract:
An exhaust treatment fluid delivery system ( 16, 22, 116 ) may include a supply passageway ( 46, 146 ), a supply manifold ( 38, 138 ), injectors ( 42, 142 ), a bypass passageway ( 50, 150 ) and first and second pressure sensors ( 34, 134, 40, 140 ). The supply passageway ( 46, 146 ) receives the exhaust treatment fluid from a tank ( 26, 126 ) and provides the exhaust treatment fluid to the supply manifold ( 38, 138 ). The bypass passageway ( 50, 150 ) connects the supply passageway ( 46, 146 ) with the return passageway ( 48, 148 ) and includes a bypass valve ( 36, 136 ) controlling fluid flow therebetween. The first pressure sensor ( 34, 134 ) measures a first pressure of exhaust treatment fluid in the supply passageway ( 46, 146 ) based upon which the bypass valve ( 36, 136 ) is controlled. The second pressure sensor ( 40, 140 ) measures a second pressure of exhaust treatment fluid in the supply manifold ( 38, 138 ) based upon which the injectors ( 42, 142 ) are controlled.

Description:
FIELD 
       [0001]    The present disclosure relates to an exhaust aftertreatment system for a combustion engine. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure and is not necessarily prior art. 
         [0003]    Emission regulation requirements are mandating that engines have exhaust aftertreatment 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 fluid delivery systems that inject a fluid (e.g., a hydrocarbon fluid, urea or other reagent) 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, for example, may 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 fluid delivery systems involve the integration of injectors, pumps, filters, valves, and other necessary control devices to control the dosing of each of these fluids into the exhaust stream. In general, fluid delivery systems for light, medium, and heavy-duty trucks, for example, may include a single injection source for dosing the fluid into the exhaust stream. Fluid delivery systems for large-scale engines for locomotive, marine, and stationary applications may include multiple injection sources for injecting the fluid 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. The principles of the present disclosure provide for more precise control of fluid pressure at the injectors so that the spray droplet size of the fluid can be more precisely regulated within a tighter tolerance. 
       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]    In one form, the present disclosure provides an exhaust aftertreatment system for treating exhaust gas discharged from a combustion engine. The exhaust aftertreatment system may include a catalyst component, an exhaust treatment fluid delivery system for injecting an exhaust treatment fluid into an exhaust stream at a location upstream of the catalyst component. The exhaust treatment fluid delivery system may include a tank for holding the exhaust treatment fluid, a supply passageway, one or more injectors (e.g., 1-10 injectors or more), a bypass valve, and a control module. The supply passageway receives the exhaust treatment fluid from the tank and provides the exhaust treatment fluid to a supply manifold. The plurality of injectors receive the exhaust treatment fluid from the supply manifold and dose the exhaust treatment fluid into the exhaust stream. The bypass valve selectively allows a portion of the exhaust treatment fluid in the supply passageway to return to the tank via a bypass passageway without flowing through the injectors. The control module controls the bypass valve and the injectors based on a first fluid pressure in the supply passageway and a second fluid pressure between an inlet of the supply manifold and the injectors. 
         [0008]    In some embodiments, the control module controls the bypass valve to achieve a predetermined fluid pressure in the supply passageway that is a higher than a target fluid pressure at the injectors. 
         [0009]    In some embodiments, the control module controls the bypass valve and injectors to account for pressure head due to differences in vertical height among the injectors and one or more pumps of the fluid delivery system. 
         [0010]    In some embodiments, the aftertreatment system includes return passageway that returns un-injected exhaust treatment fluid from the injectors to the tank and allows for cooling of the injectors. 
         [0011]    In some embodiments, the exhaust treatment fluid delivery system includes a return valve disposed along the return passageway between a return manifold and the bypass passageway. 
         [0012]    In some embodiments, the control module controls the return valve based on a third fluid pressure in the return passageway. 
         [0013]    In some embodiments, the bypass valve and the return valve are pulse-width-modulated. 
         [0014]    In some embodiments, the exhaust treatment fluid delivery system includes a valve-bypass line allowing fluid to bypass the return valve. 
         [0015]    In some embodiments, the valve-bypass line includes a check valve that allows fluid flow through the valve-bypass line in a first direction from a first location between the return valve and the tank and a second location between the return valve and the return manifold and prevents fluid flow through the valve-bypass line in a second direction opposite the first direction. 
         [0016]    In some embodiments, the exhaust treatment fluid delivery system includes a pump for pressurizing the supply manifold and inlet lines of the injectors. 
         [0017]    In some embodiments, the exhaust treatment fluid is a hydrocarbon exhaust treatment fluid. The hydrocarbon exhaust treatment fluid may be dispersed at a location adjacent the catalyst component. 
         [0018]    In some embodiments, the catalyst component is an oxidation catalyst component. 
         [0019]    In some embodiments, the exhaust treatment fluid is a urea exhaust treatment fluid. The urea exhaust treatment fluid may be dispersed at a location adjacent the catalyst component. 
         [0020]    In some embodiments, the catalyst component is a selective-catalytic-reduction catalyst. 
         [0021]    In some embodiments, the exhaust aftertreatment system includes a urea quality sensor disposed upstream of at least one of the injectors. 
         [0022]    In some embodiments, the plurality of injectors inject the exhaust treatment fluid into a common exhaust stream. 
         [0023]    In some embodiments, the plurality of injectors inject the exhaust treatment fluid into separate exhaust streams corresponding to multiple combustion engines. 
         [0024]    In another form, the present disclosure provides a fluid delivery system for injecting exhaust treatment fluid into a stream of exhaust gas discharged by a combustion engine. The fluid delivery system may include a tank for containing the exhaust treatment fluid, a supply passageway, a supply manifold, a one or more injectors, a return passageway, a bypass passageway, and first and second pressure sensors. The supply passageway receives the exhaust treatment fluid from the tank. The supply manifold receives the exhaust treatment fluid from the supply passageway. The plurality of injectors receive the exhaust treatment fluid from the supply manifold. The exhaust treatment fluid is returned from the injectors to the tank through the return passageway. The bypass passageway connects the supply passageway with the return passageway and may include a bypass valve controlling fluid flow therebetween. The first pressure sensor may measure a first pressure of exhaust treatment fluid in the supply passageway. The bypass valve is controlled based on the first pressure. The second pressure sensor may measure a second pressure of exhaust treatment fluid in the supply manifold. The injectors may be controlled based on the second pressure. 
         [0025]    In some embodiments, the bypass valve is controlled to achieve a predetermined fluid pressure in the supply passageway that is a higher than a target fluid pressure at the injectors. 
         [0026]    In some embodiments, the fluid delivery system includes a return valve disposed along the return passageway between a return manifold and the bypass passageway. 
         [0027]    In some embodiments, the return valve is controlled based on a third pressure in the return passageway. 
         [0028]    In some embodiments, the bypass valve and the return valve are pulse-width-modulated. 
         [0029]    In some embodiments, the fluid delivery system includes a valve-bypass line allowing fluid to bypass the return valve. 
         [0030]    In some embodiments, the valve-bypass line includes a check valve that allows fluid flow through the valve-bypass line in a first direction from a first location between the return valve and the tank and a second location between the return valve and the return manifold. The check valve prevents fluid flow through the valve-bypass line in a second direction opposite the first direction. 
         [0031]    In some embodiments, the fluid delivery system includes a pump for pressurizing the supply manifold and inlet lines of the injectors. 
         [0032]    In some embodiments, the exhaust treatment fluid is a hydrocarbon exhaust treatment fluid. The hydrocarbon exhaust treatment fluid may be injected into an exhaust stream at a location adjacent a catalyst component. 
         [0033]    In some embodiments, the catalyst component is an oxidation catalyst component. 
         [0034]    In some embodiments, the exhaust treatment fluid is a urea exhaust treatment fluid. The urea exhaust treatment fluid may be injected at a location adjacent a catalyst component. 
         [0035]    In some embodiments, the catalyst component is a selective-catalytic-reduction catalyst. 
         [0036]    In some embodiments, the injectors inject the exhaust treatment fluid into a common exhaust stream. 
         [0037]    In some embodiments, the injectors inject the exhaust treatment fluid into separate exhaust streams corresponding to multiple combustion engines. 
         [0038]    In another form, the present disclosure provides a method that may include supplying exhaust treatment fluid from a tank to a supply manifold; controlling an injector that receives the exhaust treatment fluid from the supply manifold based on a first fluid pressure in the supply manifold; selectively allowing a portion of the exhaust treatment fluid to bypass the injector; and controlling an amount of the exhaust treatment fluid that is allowed to bypass the injector based on a second fluid pressure upstream of the supply manifold. 
         [0039]    In some embodiments, the method includes measuring the second fluid pressure with a pressure sensor disposed along a supply passageway providing the exhaust treatment fluid from the tank to the supply manifold. 
         [0040]    In some embodiments, controlling the injector includes adjusting a pulse-width-modulation duty cycle of the injector. 
         [0041]    In some embodiments, controlling the amount of the exhaust treatment fluid that is allowed to bypass the injector includes adjusting a pulse-width-modulation duty cycle of a bypass valve. 
         [0042]    In some embodiments, the method includes controlling a backpressure of fluid at the injector with a return valve disposed in a return passageway through which exhaust treatment fluid is returned from the injector to the tank. 
         [0043]    In some embodiments, controlling the backpressure of fluid at the injector with the return valve includes controlling the return valve based on a third fluid pressure in the return passageway. 
         [0044]    In some embodiments, the method includes selectively allowing exhaust treatment fluid to bypass the return valve. 
         [0045]    In some embodiments, the method includes detecting fluid leaks by pumping fluid through the return passageway toward a return manifold. 
         [0046]    In some embodiments, controlling the return valve includes adjusting a pulse-width-modulation duty cycle of the return valve. 
         [0047]    In some embodiments, supplying exhaust treatment fluid includes supplying a hydrocarbon exhaust treatment fluid. 
         [0048]    In some embodiments, the method includes injecting the hydrocarbon exhaust treatment fluid into an exhaust stream adjacent an oxidation catalyst. 
         [0049]    In some embodiments, supplying exhaust treatment fluid includes supplying a urea exhaust treatment fluid. 
         [0050]    In some embodiments, the method includes injecting the urea exhaust treatment fluid into an exhaust stream adjacent a selective-catalytic-reduction catalyst. 
         [0051]    In some embodiments, the method includes controlling a plurality of injectors that receive the exhaust treatment fluid from the supply manifold based on the first fluid pressure in the supply manifold. 
         [0052]    In some embodiments, the method includes injecting the exhaust treatment fluid into a single exhaust stream with the plurality of injectors. 
         [0053]    In some embodiments, the method includes injecting the exhaust treatment fluid into a plurality of exhaust streams with the plurality of injectors. Each of the exhaust streams may correspond to one of a plurality of combustion engines. 
         [0054]    In some embodiments, the method includes returning un-injected exhaust treatment fluid from the injector to the tank. 
         [0055]    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 
         [0056]    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. 
           [0057]      FIG. 1  is a schematic representation of an exhaust aftertreatment system according to the principles of the present disclosure; 
           [0058]      FIG. 2  is a schematic representation of a fluid delivery system of the exhaust aftertreatment system of  FIG. 1 ; 
           [0059]      FIG. 3  is a schematic representation of a control module controlling a valve and injectors of the fluid delivery system of  FIG. 2 ; 
           [0060]      FIG. 4  is a schematic representation of another fluid delivery system according to the principles of the present disclosure; and 
           [0061]      FIG. 5  is a schematic representation of a control module controlling valves and injectors of the fluid delivery system of  FIG. 4 . 
           [0062]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       
    
    
     DETAILED DESCRIPTION 
       [0063]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0064]    Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. 
         [0065]    Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
         [0066]    The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0067]    When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0068]    Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
         [0069]      FIG. 1  depicts an exhaust gas aftertreatment system  10  for treating the exhaust output from a combustion engine  12  in an exhaust passageway  14 . The exhaust aftertreatment system  10  may include a first fluid delivery system  16 , a diesel oxidation catalyst (DOC)  18 , a diesel particulate filter (DPF)  20 , a second fluid delivery system  22 , and a selective-catalytic-reduction (SCR) catalyst  24 . While  FIG. 1  depicts a single engine  12  discharging exhaust gas into the exhaust passageway  14 , in some embodiments, a plurality of combustion engines may discharge exhaust gas into the exhaust passageway  14  so that the exhaust aftertreatment system  10  may treat exhaust gas from all of those combustion engines. The plurality of combustion engines may operate concurrently and/or independently of each other. 
         [0070]    The first fluid delivery system  16  may spray a hydrocarbon (e.g., diesel fuel) into the exhaust stream at or upstream of the DOC  18 . The second fluid delivery system  22  may spray urea (or another reagent) into the exhaust stream at or upstream of the SCR catalyst  24 . It will be appreciated that the specific components of the aftertreatment system  10  and the positioning of those components relative to the fluid delivery systems  16 ,  22  may vary from the configuration described above and shown in  FIG. 1 . It will be appreciated that the principles of the present disclosure are applicable to such variations. 
         [0071]      FIG. 2  depicts an exemplary fluid delivery system. Either or both of the first fluid delivery systems  16 ,  22  may be configured as shown in  FIG. 2 . Therefore, the following description of the fluid delivery system shown in  FIG. 2  may apply equally to the first and second fluid delivery systems  16 ,  22 . 
         [0072]    As shown in  FIG. 2 , the fluid delivery system  16 ,  22  may include a tank  26 , a filter  28 , a temperature sensor  30 , a pump  32 , a first pressure sensor  34 , a bypass valve  36 , one or more supply manifolds  38 , a second pressure sensor  40 , one or more injectors  42  and one or more return manifolds  44 . The tank  26  may provide fluid to a supply passageway  46  and receive fluid from a return passageway  48 . A bypass passageway  50  may directly fluidly connect the supply passageway  46  with the return passageway  48 . While the fluid delivery system  16 ,  22  depicted in  FIG. 2  includes two injectors  42 , it will be appreciated that the fluid delivery system  16 ,  22  could include any number of injectors  42 . Additionally or alternatively, the fluid delivery system  16 ,  22  could include one or more injectors  42  that inject fluid into separate exhaust gas passageways  14  that correspond to different ones of a plurality of engines. At any given time, some of such engines may be running while others may be shutdown, or all of the engines may be running concurrently or shutdown concurrently. Therefore, one or more of the injectors  42  may be shut down while one or more other injectors  42  may be injecting fluid into an exhaust stream. 
         [0073]    The pump  32  may draw fluid stored in the tank  26  through the filter  28  and the temperature sensor  30 . The temperature sensor  30  may detect a temperature of the fluid flowing therethrough and communicate the temperature data to a control module  52  ( FIG. 3 ) continuously, intermittently or on demand. From the pump  32 , the fluid may flow through the first pressure sensor  34  and into the supply passageway  46 . The first pressure sensor  34  may detect a pressure of the fluid flowing therethrough and communicate the pressure data to the control module  52  continuously, intermittently or on demand. From the first pressure sensor  34 , some or all of the fluid in the supply passageway  46  may flow into the supply manifold  38 . The second pressure sensor  40  may detect a pressure of the fluid in the supply manifold  38  and communicate the pressure data to the control module  52  continuously, intermittently or on demand. 
         [0074]    From the supply manifold  38 , fluid may be supplied to the injectors  42  via supply lines  54 . In some embodiments of the fluid delivery system  22 , one or more urea quality sensor  58  may be disposed along one or more supply lines  54 . The urea quality sensor  58  may sense the concentration of the urea (e.g., level of ammonia in the fluid) that is being supplied to the injectors  42 . The urea quality sensor  58  may be in communication with the control module  52 . The control module  52  may alter its control of the bypass valve  36 , the injectors  42  and/or the pump  32  and/or shutdown the pump  32  based on data from the urea quality sensor  58 . 
         [0075]    A first portion of the fluid flowing through the supply lines  54  is injected into the exhaust stream flowing through exhaust passageway  14 . Surplus fluid (un-injected fluid) at the injectors  42  flow to the return manifold  44  through return lines  56 . The control module  52  may control operation of the injectors  42  to control the amount of fluid that is injected into the exhaust stream based on data from one or more of the temperature sensor  30 , the first pressure sensor  34  and the second pressure sensor  40 . In some embodiments, the injectors  42  may be pulse-width-modulated. From the return manifold  44 , the fluid is returned to the tank  26  for storage therein and/or recirculation through the fluid delivery system  16 ,  22 . 
         [0076]    The control module  52  may control operation of the bypass valve  36  to selectively allow a portion of the fluid in the supply passageway  46  to flow directly to the return passageway  48  through the bypass passageway  50 . In some embodiments, the bypass valve  36  may be pulse-width-modulated. The control module  52  may control operation of the bypass valve  36  based on data from one or more of the temperature sensor  30 , the first pressure sensor  34  and the second pressure sensor  40 . 
         [0077]    As described above, the control module  52  is in communication with the first and second pressure sensors  34 ,  40 , the temperature sensor  30 , the bypass valve  36  and the injectors  42 . The control module  52  may include or be part of an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and/or memory (shared, dedicated or group) that execute one or more software or firmware programs, and/or a combinational logic circuit, for example, and/or other suitable components that provide the described functionality. The control module  52  may be a part of or include a control unit controlling one or more other vehicle systems. Alternatively, the control module  52  may be a control unit dedicated to the exhaust aftertreatment system  10  or the fluid delivery system  16 ,  22 . In some embodiments, the control module  52  may be in communication with and control operation of the pump  32 . In some embodiments, the control module  52  may control the pump  32  (e.g., vary a speed or duty cycle of the pump  32 ) to achieve desired flow rates and/or fluid pressures based on data received from one or more of the sensors  30 ,  34 ,  40 . 
         [0078]    Based on data received from the first pressure sensor  34 , the control module  52  may control the bypass valve  36  to achieve a first predetermined fluid pressure in the supply passageway  46 . The first predetermined fluid pressure may be a pressure that is above a desired target fluid pressure at one or more of the injectors  42 . The first predetermined fluid pressure and/or the target pressure at the injectors may be constant values or values that change based on operating conditions of the one or more engines  12  (e.g., engine speed, engine load, engine temperature, exhaust gas temperature, exhaust gas flow rate) and/or temperature data from the temperature sensor  30 , for example. 
         [0079]    The control module  52  may adjust the pulse-width-modulation (PWM) duty cycle to achieve the first predetermined fluid pressure in the supply passageway  46 . That is, when fluid pressure in the supply passageway  46  (i.e., at the first pressure sensor  34 ) is higher than the first predetermined fluid pressure, the control module  52  may adjust the PWM duty cycle to allow more fluid from the supply passageway  46  to flow through the bypass passageway  50  to the return passageway  48  (which leads back to the tank  26 ). When fluid pressure in the supply passageway  46  (i.e., at the first pressure sensor  34 ) is lower than the first predetermined fluid pressure, the control module  52  may adjust the PWM duty cycle to restrict fluid flow through the supply passageway  46 , thereby providing more fluid to the supply manifold  38 . 
         [0080]    Based on data received from the second pressure sensor  40 , the control module  52  may control the PWM duty cycle of the injectors  42  to achieve a desired target pressure in the supply lines  54  proximate the injectors  42 . That is, when fluid pressure at the second pressure sensor  40  is lower than a second predetermined fluid pressure, the control module  52  may adjust the PWM duty cycle of the injectors  42  to reduce the amount of fluid injected into the exhaust stream  14 . When fluid pressure at the second pressure sensor  40  is higher than the second predetermined fluid pressure, the control module  52  may adjust the PWM duty cycle of the injectors  42  to increase the amount of fluid injected into the exhaust stream  14 . The second predetermined fluid pressure may be a constant value or a value that changes based on operating conditions of the one or more engines  12  (e.g., engine speed, engine load, engine temperature, exhaust gas temperature, exhaust gas flow rate) and/or temperature data from the temperature sensor  30 , for example. 
         [0081]    It will be appreciated that at any given time, it may be desirable for one or more of the injectors  42  to be injecting fluid into the exhaust stream  14 , while another or more of the injectors  42  are shutdown (i.e., injecting no fluid into the exhaust stream  14 ). In controlling the PWM duty cycle of the bypass valve  36  and/or one or more of the injectors  42 , the control module  52  may account for whether or not one or more of the injectors  42  are shutdown at any given time and adjust the duty cycles of the operating injectors  42  accordingly. In some embodiments, one or more injectors  42  may operate under a different PWM duty cycle than one or more other injectors  42 . In some embodiments, one or more of the injectors  42  may have a different orifice size than one or more other injectors  42  for injecting different amounts of fluid at the same or different pressures. 
         [0082]    With reference to  FIGS. 4 and 5 , another fluid delivery system  116  is provided. The fluid delivery system  116  may be incorporated into the exhaust aftertreatment system  10  instead of either of the fluid delivery systems  16 ,  22 . The structure and function of the fluid delivery system  116  may be similar or identical to that of the fluid delivery system  16 ,  22  described above, apart from any exceptions described below and/or shown in the figures. Therefore, similar features will not be described again in detail. 
         [0083]    The fluid delivery system  116  may include a tank  126 , a filter  128 , a temperature sensor  130 , a pump  132 , a first pressure sensor  134  (disposed in a supply passageway  146 ), a bypass valve  136  (disposed in a bypass passageway  150 ), one or more supply manifolds  138 , a second pressure sensor  140 , one or more supply lines  154 , one or more injectors  142 , one or more return lines  156 , one or more return manifolds  144 , a third pressure sensor  145 , a return valve  147  (disposed in a return passageway  148 ), and a check valve  149  (disposed in a valve-bypass line  151 ). A control module  152  may be in communication with the first, second and third pressure sensors  134 ,  140 ,  145  the temperature sensor  130 , the bypass valve  136 , the injectors  142  and the return valve  147 . The control module  152  may control operation of the bypass valve  136 , the injectors  142  and the return valve  147  based on data received from one or more of the sensors  130 ,  134 ,  140 ,  145 . The structure and function of the control module  152 , sensors  130 ,  134 ,  140 , bypass valve  136  and injectors  142  may be similar or identical to that of the control module  52 , sensors  30 ,  34 ,  40 , bypass valve  36  and injectors  42  described above, apart from any exceptions described below. Therefore, similar features will not be described again in detail. 
         [0084]    In some embodiments, one or more of the supply lines  154  may include a urea quality sensor  158 . The structure and function of the urea quality sensor  158  may be similar or identical to that of the urea quality sensor  58  described above. 
         [0085]    The third pressure sensor  145  may detect a pressure of fluid in the return passageway  148  and communicate that data to the control module  152  continuously, intermittently or on demand. Based on data from the third pressure sensor  145 , the control module  152  may adjust the PWM duty cycle of the return valve  147  to achieve a third predetermined fluid pressure in the return passageway  148 . That is, when fluid pressure in the return passageway  148  (i.e., at the third pressure sensor  145 ) is higher than the third predetermined fluid pressure, the control module  152  may adjust the PWM duty cycle to allow more fluid through the return passageway  148 . When fluid pressure in the return passageway  148  (i.e., at the third pressure sensor  145 ) is lower than the third predetermined fluid pressure, the control module  152  may adjust the PWM duty cycle of the return valve  147  to restrict fluid flow therethrough. Controlling the return valve  147  in this manner acts to tune backpressure at the injectors  142  and tune an amount of heat transfer from the injectors  142  to the un-injected fluid. The third predetermined fluid pressure may be a constant value or a value that changes based on operating conditions of the one or more engines  12  (e.g., engine speed, engine load, engine temperature, exhaust gas temperature, exhaust gas flow rate) and/or temperature data from the temperature sensor  130 , for example. 
         [0086]    The valve-bypass line  151  is connected to the return passageway  148  and allows fluid to bypass the return valve  147  when the valves  136 ,  147  and the injectors are off (closed). The check valve  149  may allow fluid in the return passageway  148  between the tank  126  and the return valve  147  to flow through the valve-bypass line  151  to a location on the return passageway  148  between the return valve  147  and the return manifold  144 . The check valve  149  may prevent fluid flow through the valve-bypass line  151  in the opposite direction. In this manner, during normal operation of the aftertreatment system  10  (in which one or more of the injectors  142  are operating), the check valve  149  prevents fluid from bypassing the return valve  147 . The check valve  149  and valve-bypass line  151  allow the fluid delivery system  116  to be reverse-purged (e.g., by pumping fluid from the tank  126  or air with an auxiliary pump (not shown) toward the return manifold  144  through the return passageway  148 ) to clean the fluid delivery system  116 , check for leaks in the fluid delivery system  116 , and/or to purge liquid from one or more components or conduits of the fluid delivery system  116  to prevent liquid from freezing therein. 
         [0087]    While the valves  36 ,  136 ,  147  and injectors  42 ,  142  are described above as being pulse-width modulated, it will be appreciated that in some embodiments, some or all of the valves  36 ,  136 ,  147  and/or injectors  42 ,  142  may not be pulse-width modulated. Rather, some or all of the valves  36 ,  136 ,  147  and/or injectors  42 ,  142  may be controlled by varying valve positions between fully open and fully closed positions. 
         [0088]    While not shown in the figures, in some embodiments, the fluid delivery system  16 ,  22 ,  116  may include an additional bypass valve (e.g., a PWM bypass valve) selectively allowing fluid at the supply manifold  38 ,  138  or between the supply manifold  38 ,  138  and the injectors  42 ,  142  to bypass the injectors  42 ,  142  and flow directly to the return passageway  48 ,  148 . For example, such a valve may be advantageously incorporated into a system with a large number of injectors (e.g., 8 or more) being fed by the same supply manifold. 
         [0089]    While the systems  16 ,  22 ,  116  are shown in the figures as having a single bypass valve  36 ,  136  and a single bypass passageway  50 ,  150 , in some embodiments, the systems  16 ,  22 ,  116  may include multiple bypass valves  36 ,  136  and/or multiple bypass passageways  50 ,  150 . 
         [0090]    Furthermore, while the systems  16 ,  22 ,  116  are described above as having return passageways  48 ,  148  that receive un-injected fluid from the injectors  42 ,  142 , in some embodiments, the injectors  42 ,  142  may inject all of the fluid supplied to them. That is, the injectors  42 ,  142  may not be equipped to receive reagent fluid for cooling and returning to the tank  26 ,  126 . In such embodiments, the systems  16 ,  22 ,  116  may not include return lines  56 ,  156  fluidly coupling the injectors  42 ,  142  with return manifolds  44 ,  144  and the tank  26 ,  126 . In some embodiments, the injectors  42 ,  142  can include cooling jackets that receive a coolant fluid (e.g., a fluid other than urea or hydrocarbon fluid). 
         [0091]    It will be appreciated that the supply manifold  38 ,  138  and the return manifold  44 ,  144  could be formed from a common manifold block, or the supply manifold  38 ,  138  and the return manifold  44 ,  144  could be discrete and separate components. 
         [0092]    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.