Abstract:
A connecting duct for providing a fluid pathway between an outlet of a low pressure compressor and an inlet of a high pressure compressor is provided. The connecting duct includes a main body that defines a fluid pathway adapted to direct a flow of fluid between a main body inlet and a main body outlet. The main body also includes a diffusing section that decreases a velocity of the flow of fluid. A flow de-swirling section is disposed between the diffusing section and the outlet of the main body. The flow de-swirling section straightens the flow of fluid.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a fluid compression system and, more particularly, to a connecting duct for a fluid compression system having a series of compression stages.  
       BACKGROUND  
       [0002]     Many applications require a supply of a pressurized fluid, such as, for example, pressurized air. These applications may include a compression system that increases the pressure of a fluid from a first pressure to a second pressure for use in the particular application. The compression system may include a series of compression stages that apply work to the fluid to achieve the desired pressure increase. For example, the compression system may include a first compressor that increases the pressure of the fluid from a first pressure to an intermediate pressure and a second compressor that increases the pressure of the fluid from the intermediate pressure to the second pressure.  
         [0003]     A vehicle such as, for example, an on highway truck, is one example of an application that may require a flow of pressurized air. A compression system on a vehicle may include one or more superchargers and/or turbochargers that increase the pressure of a flow of intake air for an internal combustion engine. The pressurized intake air may be used to increase the air mass within the combustion chambers of the engine, which may lead to an increase in the mass of fuel that may be injected and, thus, an increase in the power output of the engine. A compression system with a greater efficiency may provide a greater power increase than a compression system with a lower efficiency.  
         [0004]     The efficiency of a compression system may be increased by reducing the amount of energy required to increase the pressure of the fluid from the first pressure to the second pressure. A compressor may most efficiently increase the pressure of a flow of fluid when the fluid enters the compressor with a uniform flow profile, such as, for example, in a laminar flow. However, the fluid flowing out of a compressor typically includes a rotational component or vortex. This rotational component contains dynamic pressure that may be lost when the fluid flow enters a second compressor. Thus, additional energy may be required to drive the second compressor to achieve the desired pressure increase. In other words, the presence of the swirl, or other irregularity in the fluid flow between compression stages, may result in a reduction of the overall efficiency of the compression system.  
         [0005]     The present disclosure is directed to overcoming one or more of the problems as set forth above.  
       SUMMARY OF THE INVENTION  
       [0006]     According to one aspect, the present disclosure is directed to a connecting duct for providing a fluid pathway between an outlet of a low pressure compressor and an inlet of a high pressure compressor. The connecting duct includes a main body that defines a fluid pathway adapted to direct a flow of fluid between a main body inlet and a main body outlet. The main body also includes a diffusing section that decreases a velocity of the flow of fluid. A flow de-swirling section is disposed between the diffusing section and the outlet of the main body to straighten the flow of fluid.  
         [0007]     According to another aspect, the present disclosure is directed to a method of compressing a flow of fluid. A flow of fluid is compressed from a first pressure to an intermediate pressure with a first compressor. A velocity of the flow of fluid from the first compressor is reduced. The flow of fluid is straightened. The flow of fluid is compressed to a second pressure with a second compressor.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a diagrammatic and schematic illustration of a compression system in accordance with an exemplary embodiment of the present invention;  
         [0009]      FIG. 2  is a top plan view of a connecting duct for a compression system in accordance with an exemplary embodiment of the present invention; and  
         [0010]      FIG. 3  is a diagrammatic and schematic illustration of an exemplary engine system having a compression system in accordance with an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]      FIG. 1  illustrates an exemplary embodiment of a compression system  10 . Compression system  10  includes a first compressor  12  and a second compressor  14 . First and second compressors  12  and  14  may be radial compressors, such as, for example, impeller type compressors. First and second compressors  12  and  14  may also be any other type of compressor that is typically used in a turbocharging or supercharging system that may be associated with an internal combustion engine.  
         [0012]     Compression system  10  also includes an inlet passage  11 . Inlet passage  11  directs a flow of fluid to an inlet of first compressor  12 . The fluid may be, for example, air, such as intake air for an internal combustion engine.  
         [0013]     Compression system  10  may also include a power source to drive first compressor  12 . The power source may be a first motor  16  that is connected to first compressor  12  through a shaft  17 . It is contemplated that compression system  10  may include other types of power sources to drive first compressor  12 . For example, the power source may be a turbine, such as when first compressor  12  is included within a turbocharger.  
         [0014]     First motor  16  may be operated to drive first compressor  12 . The operation of first compressor  12  may increase the pressure of the fluid received through inlet passage  11 . The pressurized fluid may be discharged through the outlet of first compressor  12 .  
         [0015]     Compression system  10  may include a connecting duct  20  that has a main body  21 , a duct inlet  24 , and a duct outlet  30 . Main body  21  defines a fluid passageway  22  between duct inlet  24  and duct outlet  30 . Fluid passageway  22  of connecting duct  20  may have, for example, a substantially circular cross-sectional shape. Duct inlet  24  may be connected to the outlet of first compressor  12  and duct outlet  30  may be connected to an inlet of second compressor  14  to provide fluid communication between first and second compressors  12  and  14 .  
         [0016]     As shown in  FIG. 2 , duct inlet  24  may include a flexible section  48 . Flexible section  48  may include, for example, a series of bellows that provide for easy connection with the outlet of first compressor  12 . One skilled in the art will recognize that connecting duct  20  may be connected to first and second compressors  12  and  14  in any readily apparent manner.  
         [0017]     Connecting duct  20  may also include an arcuate section  23 . Arcuate section  23  may redirect the flow of fluid between first compressor  12  and second compressor  4 . For example, arcuate section  23  may redirect the flow of fluid through an angle of between about 90° and 180°. Arcuate section  23  may allow first and second compressor  12  and  14  to be arranged relative to the other in a manner that reduces the total amount of space required for compression system  10 .  
         [0018]     Compression system  10  may also include a power source to drive second compressor  14 . The power source used to drive second compressor  14  may be similar to the power source used to drive first compressor  12 . For example, compression system  10  may include a second motor  18  that is connected to second compressor  14  through a shaft  19 . Alternatively, compression system  10  may drive second compressor  14  with a power source that is different than the power source used to drive first compressor  12 . For example, first compressor  12  may be driven by a motor, whereas second compressor  14  is driven by a turbine.  
         [0019]     Second motor  18  may be operated to drive second compressor  14 . The operation of second compressor  14  may further increase the pressure of the fluid received through connecting duct  20 . The pressurized fluid may be discharged from second compressor  18  through a fluid outlet  32 .  
         [0020]     Compression system  10  may be adapted to increase the pressure of the flow of fluid from a first pressure, which may be, for example, ambient pressure, to a second pressure. First compressor  12  may be adapted to increase the pressure of the flow of fluid from the first pressure to an intermediate pressure. Second compressor  14  may be adapted to further increase the pressure of the flow of fluid from the intermediate pressure to the second pressure. Since second compressor  14  compresses the fluid to a higher pressure than first compressor  12 , second compressor  14  may be referred to as a high pressure compressor and first compressor  12  may be referred to as a low pressure compressor.  
         [0021]     First and second compressors  12  and  14  may be sized to provide substantially similar compression ratios. For example, first and second compressors  12  and  14  may both provide compression ratios of between 1.5 to 1 and 3 to 1. Alternatively, first and second compressors  12  and  14  may have different compression ratios. For example, first compressor  12  may have a compression ratio of 1.5 to 1 and second compressor  14  may have a compression ratio of 3 to 1.  
         [0022]     It should be noted that compression system  10  may include additional compression stages. Some applications may require a greater increase in fluid pressure that may be best achieved by adding additional compression stages. It is contemplated connecting duct  20  may be used to provide fluid communication with the additional compression stages.  
         [0023]     As will be recognized by one skilled in the art, the flow of fluid leaving first compressor  12  will typically include a steady swirl, such as, for example, a rotational component or vortex. This swirl is caused by the exit characteristics of the compressor. The swirl may include a relatively high magnitude of dynamic energy. Connecting duct  20  may be adapted to recover the dynamic energy from the swirl.  
         [0024]     As shown in  FIG. 2 , connecting duct  20  may include a diffuser  26  and a flow de-swirling section  27 . Diffuser  26  is adapted to reduce the velocity of the flow of fluid. Flow de-swirling section  27  is adapted to straighten the flow of fluid. For the purposes of the present disclosure, the phrase “straighten the flow” includes reducing the swirl induced by first compressor  12  or altering the profile of the fluid flow to achieve a substantially uniform flow profile.  
         [0025]     Diffuser  26  includes a diffuser inlet  40  and a diffuser outlet  42 . Diffuser inlet  40  has a cross-sectional area that is less than the cross-sectional of diffuser outlet  42 . The increase in the cross-sectional area of flow passageway  22  between diffuser inlet  40  and diffuser outlet  42  will cause a reduction in the velocity of the fluid flowing through diffuser  26 . Thus, diffuser  26  will decrease the velocity of the pressurized fluid flowing from the outlet of first compressor  12 .  
         [0026]     Flow de-swirling section  27  is connected with diffuser outlet  42 . Flow de-swirling section  27  includes a turning vane  28 , which divides flow passageway  22  into a first flow path  44  and a second flow path  46 . Turning vane  28  will, therefore, split the flow of fluid into a first flow through first flow path  44  and a second flow through second flow path  46 . Turning vane  28  may be disposed in actuate section  23  to divide the flow of fluid after the fluid has passed through a predetermined portion of arcuate section  23 . For example, a leading edge  29  of turning vane  28  may be positioned to split the flow of fluid after direction of flow of fluid has been changed by approximately 30°.  
         [0027]     Turning vane  28  and the walls of connecting duct  20  surrounding turning vane  28  will act to straighten the flow of fluid. The curvature of arcuate section  23  may be adapted to oppose the swirl induced at the exit of first compressor  12 . In addition, the relative positioning of turning vane  28  within arcuate section  23  may further reduce the amount of swirl in the flow of fluid. In other words, the swirl may act to turn the flow of fluid into turning vane  28  and the walls of main body  21 . The impingement of the flow of fluid into turning vane  28  and the walls of main body  21  may act to straighten the flow. In this manner, the profile of the flow of fluid through connecting duct  20  may be altered to reduce the amount of swirl and/or approach a uniform flow profile.  
         [0028]     It is contemplated that the above described compression system may be used in a variety of applications. For example, as shown in  FIG. 3 , a compression system  100  may be included in a vehicle  90  to provide pressurized air to an intake manifold of an internal combustion engine  110 . The engine  110  includes an engine block  111  defining a plurality of combustion chambers  112 . In the illustrated embodiment, engine  110  includes six combustion chambers. It is contemplated that engine  110  may include a greater or lesser number of combustion chambers, depending upon the particular application.  
         [0029]     Internal combustion engine  110  may also include an intake manifold  114  and an exhaust manifold  116 . Intake manifold  114  provides fluid, such as, for example, air or a fuel/air mixture, to the combustion chambers  112 . The exhaust manifold  116  receives exhaust gas from combustion chambers  112 .  
         [0030]     Compression system  100  may include a first turbocharger  120  and a second turbocharger  140  that are arranged in series. First turbocharger  120  may have a first turbine  122  that includes a turbine wheel  128  and a first compressor  124  that includes a compressor wheel  134 . First turbocharger  120  may further include a first shaft  130  that is rotatably mounted within a housing  132  and carries both turbine wheel  128  and compressor wheel  134 . A rotation of turbine wheel  128  will, therefore, result in a corresponding rotation of compressor wheel  134 .  
         [0031]     Second turbocharger  140  may have a second turbine  142  that includes a turbine wheel  146  and a second compressor  144  that includes a compressor wheel  150 . Second turbocharger  140  may further include a second shaft  148  that is rotatably mounted within housing  132  and carries both turbine wheel  146  and compressor wheel  150 . A rotation of turbine wheel  146  will, therefore, result in a corresponding rotation of compressor wheel  150 .  
         [0032]     An air inlet  136  may provide fluid communication between the atmosphere and first compressor  124 . Connecting duct  20  may provide fluid communication between first compressor  124  and second compressor  144 . An intake duct  152  may provide fluid communication between second compressor  144  and intake manifold  114 .  
         [0033]     One or more air coolers  156  may be disposed in intake duct  152 . Air coolers  156  are structured and arranged to extract heat from the air to lower the intake manifold temperature and to increase the air density. It is contemplated that an additional air cooler (not shown), for example, an intercooler, may be disposed between first compressor  124  and second compressor  144 .  
         [0034]     It should be noted that an inter-stage air cooler, such as a heat exchanger, may be combined with connecting duct  20  and/or turning vane  28 . For example, turning vane  28  may include an internal passage (not shown) through which a coolant may be directed. The coolant may absorb heat from the flow of fluid passing through connecting duct  20 . In this manner, the temperature of the flow of fluid may be reduced as the fluid flows from first compressor  12  to second compressor  14 .  
         [0035]     An exhaust duct  126  may connect exhaust manifold  116  with second turbine  142 . The fluid flow path from the exhaust manifold  116  to the second turbine  142  may include a variable nozzle (not shown) or other variable geometry arrangement adapted to control the velocity of exhaust fluid impinging on turbine wheel  146 . A conduit  137  may provide fluid communication between second turbine  142  and first turbine  122 . An exhaust outlet  154  may provide fluid communication between first turbine  122  and the atmosphere.  
       INDUSTRIAL APPLICABILITY  
       [0036]     For the purposes of explaining its operation, the compression system of the present disclosure will be described in connection with the vehicle application described above and illustrated in  FIG. 3 . During standard vehicle use, internal combustion engine  110  may operate in a known manner using, for example, the diesel principle of operation. Internal combustion engine  110  will draw intake air through intake manifold  114  and will expel exhaust gases to exhaust manifold  116 .  
         [0037]     With reference to  FIG. 3 , exhaust gas from the internal combustion engine  110  is directed from exhaust manifold  116  to exhaust duct  126 . Exhaust duct  126  directs the exhaust gas to second turbocharger  140 , where the exhaust gas impinges on and causes rotation of turbine wheel  146 . The rotation of turbine wheel  146  causes a corresponding rotation of compressor wheel  150 . The rotational speed of compressor wheel  150  will therefore correspond to the rotational speed of turbine wheel  146 .  
         [0038]     The exhaust gas exits second turbocharger  140  through conduit  137 , which directs the exhaust gas to first turbocharger  120 . The exhaust gas impinges on and causes rotation of turbine wheel  128 . The rotation of turbine wheel  128  causes a corresponding rotation of compressor wheel  128 . The rotational speed of compressor wheel  134  will, therefore, correspond to the rotational speed of turbine wheel  128 . Exhaust gas from the first turbocharger  120  may be directed to the atmosphere via exhaust outlet  154 .  
         [0039]     Rotation of compressor wheel  134  of first turbocharger  120  draws air from the atmosphere through air inlet  136 . Compressor wheel  134  applies work to the air to increase the pressure of the air from an ambient pressure to an intermediate pressure and directs the flow into connecting duct  20 . In this manner, a portion of the energy of the exhaust gas from engine  110  is used to increase the pressure of the intake air flow.  
         [0040]     As noted previously, the flow of air exiting first compressor  124  may include a constant swirl. This swirl represents dynamic pressure that may be recaptured. The dynamic pressure may be recaptured by reducing the velocity of the flow of fluid and then straightening the flow of fluid.  
         [0041]     The velocity at which the air is flowing will decrease as the flow of air passes through diffuser  26 . The flow area of diffuser  26  increases between diffuser inlet  40  and diffuser outlet  42 . The reduction in velocity also translates to an increase in the flow pressure of the fluid as some of the dynamic pressure of is converted to flow pressure.  
         [0042]     As the flow of air enters de-swirling section  27 , the flow of air is split into two flows by turning vane  28 . The split in flow provides a narrowed diameter flow path for each flow of fluid. The walls of the first flow path  44  and second flow path  46  (referring to  FIG. 2 ) will act to straighten, or de-swirl, the flow of fluid. The straightened flow may then be directed through duct outlet  30 .  
         [0043]     The air flows from duct outlet  30  to second compressor  144 . Compressor wheel  150  of second compressor  144  further increases the pressure of the air to a second pressure. The flow of pressurized air may then be directed to intake manifold  114  of engine  110  via air outlet line  152 . The compressed air may be cooled by one or more air coolers  156  before reaching intake manifold  114 . The pressurized air flows from intake manifold  114  into combustion chambers  112 .  
         [0044]     Accordingly, the described connecting duct may increase the efficiency of a multi-stage compression system. The efficiency increase results from the recapture of dynamic pressure present in a flow of fluid that leaves a first compressor. The flow of fluid is also straightened to approach a uniform profile flow. This allows the second compressor to increase the pressure of the fluid to the desired magnitude with a reduced energy input. It is contemplated that the concepts of the present disclosure may be applied to any multi-stage compression system, including, for example, an intake air compression system for an internal combustion engine.  
         [0045]     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed compression system without departing from the scope of the disclosure. Other embodiments of the system may be apparent to those skilled in the art from consideration of the specification and practice of the system disclosed herein. It is intended that the specification and examples be considered as exemplary only.