Area-controlled progressive vane type diffuser

Abstract

A controlled area progressive vane diffuser (CAPVD) for a compressor may be defined by a bearing diffuser wall of a bearing housing and a compressor diffuser wall of a compressor housing, the bearing diffuser wall and the compressor diffuser wall being spaced apart in an axial direction, wherein a plurality of vanes extend between the diffuser walls and are spaced circumferentially about the axis of rotation of the compressor wheel. Airflow from the compressor wheel enters the CAPVD through the diffuser inlet, flows between the diffuser walls and past the vanes, and flows out from the diffuser outlet to the volute. The diffuser walls may be shaped such that the width of the narrow point between the diffuser inlet and the blade is less than the width at the blade, and the width of the diffuser outlet is less than the width at the blade.

Description

Technical Field

[0001] This disclosure generally relates to turbocharger systems for internal combustion engines, and more particularly to compressors having controlled-area progressive blade diffusers configured for efficient operation. Background Technology

[0002] Turbochargers are used in many applications, such as automotive, marine, and aerospace. A turbocharger operates by forcing more intake air into the combustion chamber of an internal combustion engine to improve engine efficiency and power output. A turbocharger typically includes a compressor connected to a turbine via an interconnecting shaft. The turbine extracts energy from the exhaust stream to drive the compressor via the interconnecting shaft, and the compressor increases the intake air pressure for delivery to the combustion chamber. The compressor may include: a radial impeller that accelerates the intake air and discharges it radially; and a diffuser that slows down the discharged air to increase its pressure.

[0003] The design of turbocharger compressors is a highly sophisticated technology. The shape, curvature, and surface finish of the compressor rotor, compressor housing, and diffuser are designed to generate maximum pressure boost within the desired operating conditions. When very high pressure ratios are required, such as in large commercial diesel engines, vaned diffusers may be superior to bladeless diffusers because they offer a higher maximum pressure ratio and increased efficiency, although often at the cost of a reduced graph width (as depicted on compressor graphs well known in the art, illustrating the relationship between pressure ratio and volumetric or mass flow rate). The vanes of a vaned diffuser define channels through which high-speed gas from the compressor is received and slowed to convert its kinetic energy into static pressure. Circumferentially spaced guide vanes provide pathways whose area expands radially to diffuse the flow.

[0004] While effective, the operating range of a turbocharger compressor may be limited to certain mass flow rates and pressure ratios outside which the compressor may exhibit undesirable blocking or surge behavior. Specifically, the compressor's operating range can be characterized by a compressor profile of operable mass flow rates and pressure ratios, where the right and left boundaries define the compressor's blocking and surge lines, respectively. The blocking line defines the compressor's maximum mass flow rate, and the surge line defines its minimum mass flow rate. Compressor surge occurs under conditions of low mass flow rates and high pressure ratios when the flow direction through the compressor is reversed to release pressure at the compressor outlet. That is, at certain low mass flow rates and high pressure ratios, the flow can no longer adhere to the suction side of the blades, thus interrupting the discharge process and causing pressure buildup at the compressor outlet. The direction of airflow through the compressor can be reversed until a stable pressure ratio is reached, at which point the airflow resumes its forward direction. This flow instability persists within the surge range of the compressor profile and generates noise known as "surge." Prolonged operation of a turbocharger in surge is undesirable and can negatively impact turbocharger performance. Summary of the Invention

[0005] In one aspect of this disclosure, a controlled-area progressive blade diffuser for a compressor is disclosed. The compressor may include: a bearing housing, in which a shaft is supported by bearings for rotation about an axis of rotation; a compressor impeller disposed on the shaft and having a compressor radius; and a compressor housing connected to the bearing housing, defining a chamber and a volute, in which the compressor impeller rotates, and the volute for receiving airflow generated by the compressor impeller. The controlled-area progressive blade diffuser may include: a bearing diffuser wall of the bearing housing having an annular shape and extending from the chamber to the volute; and a compressor diffuser wall of the compressor housing having an annular shape and extending from the chamber to the volute, wherein the bearing diffuser wall and the compressor diffuser wall are spaced apart in the axial direction. The controlled area progressive blade diffuser may further include: a plurality of blades extending from the bearing diffuser wall and the compressor diffuser wall and circumferentially spaced around an axis of rotation, each blade having a leading edge and a trailing edge; a diffuser inlet adjacent to the chamber; and a diffuser outlet adjacent to the volute, wherein airflow from the compressor impeller enters the controlled area progressive blade diffuser through the diffuser inlet, passes between the bearing diffuser wall and the compressor diffuser wall and through the plurality of blades, and exits from the diffuser outlet to the volute. The bearing diffuser wall and the compressor diffuser wall may be spaced apart at the blade leading edge by a blade leading edge width, the bearing diffuser wall and the compressor diffuser wall may define a narrow point between the diffuser inlet and the blade leading edge, wherein the narrow point has a narrow point width smaller than the blade leading edge width, and the diffuser outlet may have a diffuser outlet width smaller than the blade leading edge width.

[0006] Additional aspects are defined by the claims of this patent. Attached Figure Description Figure 1 This is a schematic diagram of an engine airflow system, which includes a turbocharger for an internal combustion engine, in which a controlled area progressive blade diffuser according to this disclosure can be implemented. Figure 2 yes Figure 1 A partial cross-sectional view of a prior art compressor for a turbocharger in an engine airflow system; Figure 3 yes Figure 2 A graph showing the relationship between the diffuser annular area and the diffuser radius of the compressor diffuser; Figure 4 It is a compressor having an embodiment of a controlled-area progressive blade diffuser according to this disclosure. Figure 2 Partial cross-sectional view; and Figure 5 It is Figure 2The vane diffuser of the compressor and Figure 4 Comparison of compressor pressure ratio and compressor mass flow rate with controlled area progressive blade diffusers of compressors. Compressor graphs. Detailed Implementation

[0007] The following descriptions of the various embodiments are illustrative in nature and are not intended to limit the scope, application, or use of the invention in any way.

[0008] like Figure 1 As shown, the engine airflow system 12 may include an internal combustion engine 14, which may have multiple cylinders to control the combustion of fuel to generate power. Exhaust gas produced during combustion may exit the engine 14 at an exhaust manifold 16, which may connect to an exhaust passage 18. The exhaust passage 18 may lead to a turbine 20 of a turbocharger. The exhaust gas may expand within the turbine 20, releasing energy to rotate the turbine impeller 22. The exhaust gas may continue from the turbine 20 through an exhaust passage 24, an exhaust aftertreatment device 54, and an exhaust throttle valve 56 to an exhaust outlet 26.

[0009] The turbine impeller 22 can be directly or indirectly connected to the compressor impeller 28 via the shaft 30. The compressor impeller 28 can be housed within the compressor 32. By guiding the exhaust gas to rotate the turbine impeller 22, the compressor impeller 28 can be correspondingly rotated via the shaft 30. The rotating compressor impeller 28 draws in and compresses air through the intake passage 34. The compression of the intake air can pressurize the intake system 36 of the engine 14 through the passage 38, the boost air cooler 40, the passage 42, and the intake manifold 44. An intake throttle valve 45 can be provided to selectively throttle the passage 42 when needed, but in embodiments of the engine airflow system 12, the intake throttle valve 45 can be omitted.

[0010] Although the controlled area progressive blade diffuser (CAPVD) according to this disclosure is shown and described herein as being implemented in a turbocharger of an internal combustion engine, those skilled in the art will understand that CAPVD can be implemented in any centrifugal compressor used to improve the performance of a power source. For example, CAPVD can be implemented in an electric-driven turbocharger driven by an electric motor (rather than a turbine driven by combustion exhaust). Alternatively, CAPVD can be implemented in the fuel cell air supply of an electric vehicle, which may or may not include a turbine. The inventors have envisioned further alternative implementations of CAPVD according to this disclosure in a centrifugal compressor. Furthermore, although compressor 32 is described herein as drawing in air, compressing air, and discharging air, the compressor according to this disclosure can be implemented to compress any gas flowing through the process, such as exhaust gas.

[0011] Figure 2 An embodiment of a compressor 32 for a turbocharger is shown. The description of compressor 32 may include a reference to an axial direction, indicated by reference numeral 61 and signifying a direction along or parallel to the axis of rotation A of shaft 30. The description may further include a reference to a radial direction, indicated by reference numeral 63 and signifying a direction toward or away from the axis of rotation A of shaft 30 at any angle of 360 degrees. Shaft 30 may be supported by bearings (not shown) in bearing housing 60, which may be disposed between compressor 32 and turbine 20. Compressor impeller 28 may be disposed in chamber 62, which may be defined by bearing housing 60 and compressor housing 64. Compressor impeller 28 may include: a central hub 66 having an annular outer edge 68 and connected to shaft 30; and a plurality of circumferentially spaced blades 70 having tips 72 at their radial ends. A compressor inlet 74 leading to chamber 62 may be defined by compressor housing 64, through which compressor impeller 28 draws air. Air can be delivered from the compressor impeller 28 through the diffuser 80 and collected in the volute 82 for communication with passage 38 via the compressor outlet (not shown). The diffuser 80 can be defined between the bearing diffuser wall 84 of the bearing housing 60 and the compressor diffuser wall 86 of the compressor housing 64. A plurality of circumferentially spaced blades 88, known in the art, can extend between the diffuser walls 84, 86 to define passages through which high-speed gas flows and is decelerated. The diffuser 80 can form an annular passage that extends radially outward from the chamber 62 to the volute 82 near the blade tip 70. Air drawn in through the compressor inlet 74 can be acted upon by the blades 68 of the compressor impeller 28 in the chamber 62 and delivered to the volute 82 via the diffuser 80.

[0012] The airflow exiting the compressor impeller end 72 enters the adjacent section of the diffuser 80 (this section can be referred to as diffuser inlet 90) and exits the diffuser 80 at diffuser outlet 92 to reach the volute 82. Diffuser inlet 90 is the section of the diffuser 80 closest to the compressor impeller 28, and this section also has the highest gas flow velocity due to the annular area A of the diffuser 80. D The radial inward movement is smaller, while the radial outward movement becomes larger. The diffuser 80 is located at a given radial distance r from the axis A of the compressor impeller 28. D The annular area A at the location D It can be determined by the following formula: A D =2πr D *w D (1) Among them, w DThe diffuser 80 is at a given radial distance r D The width at that location. Figure 2 In compressor 32, diffuser 80 has a conventional design, wherein diffuser walls 84 and 86 are parallel, and as diffuser 80 extends radially from diffuser inlet 90 to outlet reaching volute 82, diffuser width w D It is constant. Each blade 88 can begin at the leading edge (VLE) 94 near the diffuser inlet 90 and extend through the diffuser 80 to the trailing edge (VTE) 96 near the diffuser outlet 92 and the volute 82.

[0013] Figure 3 The graph 100 is presented, which represents the diffuser annular area A. D The diffuser radius r of the blade diffuser D The relationship. Line 102 represents the vane diffuser 80 of the conventional compressor 32, which varies with the diffuser radius r. D The area increases gradually. Initially, as the compressor housing 64 converges toward the compressor blade tip 72 and bearing housing 60 until reaching the diffuser inlet 90, the diffuser width w... D and the corresponding diffuser annular area A D It can be reduced from the outer edge 68 of the compressor impeller hub 66. After the diffuser inlet 90, the diffuser width w D Keep constant, and the diffuser walls 84 and 86 change with the diffuser radius r D Increase while maintaining parallelism, and the diffuser annular area A D The diffuser increases linearly until the diffuser 80 intersects the volute 82 at the diffuser outlet 92. Although the compressor 32 is shown and described as having a diffuser inlet 90 extending radially outward from the outer edge 68 of the hub 66 and near the blade tip 72, the diffuser inlet 90 can be defined at any location near the compressor impeller 28, relevant to a particular embodiment of the diffuser 80. Regardless of the defined location of the diffuser inlet 90, in a conventional compressor 32, the diffuser walls 84, 86 are parallel, with a fixed diffuser width w from the diffuser inlet 90 to the diffuser outlet 92. D .

[0014] In this embodiment, as the diffuser extends from the diffuser inlet 90 to the volute 82, the diffuser width w is changed. D To control the gradual increase in area. Figure 4 An embodiment of compressor 32 is shown, wherein CAPVD 110 has a varying diffuser width caused by compressor diffuser wall 112, which is profiled relative to bearing diffuser wall 84. The outer edge 68 of compressor hub 66 defines a compressor radius r from the axis of rotation A. CFurthermore, the diffuser inlet 116 can be limited to a diffuser inlet radius r. DI At this location, the diffuser inlet radius is approximately equal to the radial distance to the blade tip 70. The diffuser inlet 116 may have a diffuser inlet width w between corresponding portions of the diffuser walls 84 and 112. DI As CAPVD 110 extends radially outward from diffuser inlet 116, the first compressor diffuser wall portion 118 can be angled toward bearing diffuser wall 84, causing the width of CAPVD 110 to decrease until the compressor diffuser wall 112 reaches the first transition point or narrow point 120, with a radius of r. PP And the width of the narrow point is w PP The radial direction extends beyond the narrow point 120, and the second compressor diffuser wall portion 122 forms an angle away from the bearing diffuser wall 84, causing the width of CAPVD 110 to increase until the compressor diffuser wall 112 reaches the second transition point 124, the radius of which is r. 2TP The diffuser width is w D The VLE of blade 88 can be located at VLE radius r. VLE At this point, the VLE radius can be equal to the radius r of the second transition point, as shown in the figure. 2TP Alternatively, in an alternative implementation, it can be greater than the radius r of the second transition point. 2TP .

[0015] Radially extending beyond the second transition point 124, the third compressor diffuser wall portion 126 can be parallel to the bearing diffuser wall 84 to increase the diffuser width w D Maintain at least along the radial length of blade 88 up to the VTE radius r VTE In some embodiments, the compressor diffuser wall 112 may continue to extend parallel to the bearing diffuser wall 84 beyond VTE 96 to the diffuser outlet 92. However, in the illustrated embodiment, it extends radially beyond the third transition point 128 (the radius of the third transition point is r). 3TP The fourth compressor diffuser wall portion 130 can be angled toward the bearing diffuser wall 84, causing the width of CAPVD 110 to decrease until the compressor diffuser wall 112 reaches the diffuser outlet 132, with a diffuser outlet radius of r. DO The diffuser outlet width is w DO The radius r of the third transition point 3TP As shown in the figure, it can be equal to the VTE radius r VTE or greater than the VTE radius r VTE This makes the third transition point 128 radially outside of VTE96.

[0016] Return to reference Figure 3Line 140 represents the asymptotic area of ​​the diffuser 110. Similar to line 140 of a conventional bladed diffuser 80, the annular area A increases as the compressor housing 64 converges toward the compressor blade tip 72 and bearing housing 60 until it reaches the diffuser inlet 116. D It can decrease from the outer edge 68 of the compressor impeller hub 66. From the diffuser inlet 116 to the narrow point 120, as the first compressor diffuser portion 118 extends radially, the annular area A... D The increase is at a low rate because, in formula (1), the reduced diffuser width offsets the increased radial dimension. After the narrow point 120, the annular area A increases with both the radius and the diffuser width. D It increases at a relatively high rate until it approaches the second transition point 124 near VLE 94. From the second transition point 124 to the third transition point 128, as the radius increases and the diffuser width remains constant, the annular area A... D It increases at a relatively low rate, which can be approximately linear. After the third transition point 128, as the diffuser 110 extends to the diffuser outlet 132, the annular area A increases as the decrease in diffuser width offsets the increase in radius. D It can be reduced as shown in the figure.

[0017] Those skilled in the art will understand that the shape of line 140 can be varied for a specific design of diffuser 110, as the radial positions and various widths of diffuser inlet 116, VLE 94, VTE 96, points 120, 124, 128, and diffuser outlet 132 are adjusted to achieve desired performance characteristics for that design and for a turbocharger or other device (where a compressor 32 with diffuser 110 according to this disclosure is implemented). Table 1 below provides an overview of the parameters related to the design of diffuser 110 discussed above: Table 1 parameter Value range Example scaling value <![CDATA[Compressor radius (r C )]]> not applicable <![CDATA[1.0r C ]]> <![CDATA[Diffuser inlet width (w DI )]]> <![CDATA[0.08-0.14*r C ]]> <![CDATA[0.11r C ]]> <![CDATA[Diffuser width (w D )]]> <![CDATA[0.7-1.2*w DI ]]> <![CDATA[1.16w DI ]]> <![CDATA[Diffuser outlet radius (r DO )]]> <![CDATA[1.65-2.00*r C ]]> <![CDATA[1.94r C ]]> <![CDATA[Diffuser outlet width (w DO )]]> <![CDATA[0.7-1.2*w DI ]]> <![CDATA[0.84w DI ]]> <![CDATA[Narrow point radius (r PP )]]> <![CDATA[1.05-1.3*r C ]]> <![CDATA[1.125r C ]]> <![CDATA[Narrow point width (w PP )]]> <![CDATA[0.6-1.0*w DI ]]> <![CDATA[0.86w DI ]]> <![CDATA[VLE radius (r VLE )]]> <![CDATA[1.1-1.4*r C ]]> <![CDATA[1.29r C ]]> <![CDATA[VLE width (w VLE )]]> <![CDATA[1.0*w D ]]> <![CDATA[1.0w D ]]> <![CDATA[VTE radius (r VTE )]]> <![CDATA[1.3-1.7*r C ]]> <![CDATA[1.56r C ]]> <![CDATA[VTE width (w VTE )]]> <![CDATA[1.0*w D ]]> <![CDATA[1.0w D ]]>

[0018] The first column of Table 1 lists Figure 3 The parameters shown in the table and discussed in the accompanying text are listed below, and the second column provides an approximate range for each parameter, which can provide guidance when designing the diffuser 110 for a specific application. The range of parameter values ​​can be derived from the compressor 32 that implements the diffuser 110. For example, the diffuser inlet width w DI The value can be obtained from the compressor radius r of the compressor impeller 28. C It is derived that, and in the compressor radius r C Within the range of 0.08-0.14 times. Then it can be determined from the compressor radius r. C Or diffuser inlet width w DIOther values ​​are derived. An exemplary design of diffuser 110 may have scaling values ​​shown in the third column, which indicate that the parameter values ​​in the exemplary design fall within the value range of the respective parameters.

[0019] The parameter value ranges in the example design in Table 1 are also exemplary for CAPVD 110 according to this disclosure. For example, the value ranges and scaling values ​​in Table 1 show the VLE width w VLE and VTE width w VTE The diffuser width wD is equal to and therefore equal to each other, such that the diffuser walls 84, 112 are parallel from VLE 94 to VTE 96. In an alternative embodiment, the VLE width wD is equal to and therefore equal to the diffuser width wD. VLE It can be greater than or less than the VTE width w VTE This makes the portion of CAPVD 110 from VLE 94 to VTE 96 tapered. Alternative geometries for CAPVD 110 according to this disclosure are envisioned. Industrial applicability

[0020] The CAPVD 110 can provide improved efficiency compared to conventional bladed diffusers (such as diffuser 80). Figure 5 Compressor graph 140 shows the relationship between compressor pressure ratio (outlet pressure relative to inlet pressure) and compressor mass flow rate. Compressor graph 140 represents a compressor with... Figure 2 Baseline blade diffuser 80 and Figure 4 A comparison of simulation data of the operation of compressor 32 with controlled area progressive blade diffuser 110 having the exemplary parameter values ​​described in Table 1. In compressor plot 140, blockage line 142 defines the maximum compressor mass flow rate of compressor 32 with diffuser 80. Above this maximum compressor mass flow rate, high flow rate and low compressor pressure ratio may cause compressor 32 to block. Surge line 144 of diffuser 80 may define the minimum compressor mass flow rate. Below this minimum compressor mass flow rate, the discharge process may be interrupted. Line 146 may represent a combination of compressor pressure ratio and corresponding compressor mass flow rate for various speeds of compressor impeller 28.

[0021] The data for diffuser 110 includes blockage line 152, surge line 154, and constant compressor speed line 156, which are located to the left of blockage line 142 in this comparison. As the data shows, the surge line 154 of diffuser 110 is offset to the left from the surge line 144 of diffuser 80, indicating that diffuser 110 will allow compressor 32 to operate at lower compressor mass flow rates without encountering surge. The region between surge lines 144 and 154 represents the operating conditions under which the geometry of diffuser 110 has a significant effect on suppressing surge mechanisms.

[0022] The data further demonstrates that efficiency improvements can be achieved using the controlled-area progressive blade diffuser according to this disclosure. As shown in compressor diagram 140, diffuser 110 can achieve efficiency improvements in both blocking and surge conditions. The maximum efficiency gain can be achieved near the blocking lines 142 and 152 and the surge lines 144 and 154 in compressor diagram 140.

[0023] The controlled-area progressive blade diffuser disclosed herein allows the turbocharger compressor to operate more efficiently at low compressor mass flow rates and reduces surge during low mass flow conditions. This is achieved by shaping the compressor diffuser wall 112 to vary the diffuser width w. D By controlling the asymptotic area of ​​the diffuser 110, air separation from the diffuser walls 84 and 112 can be suppressed at low mass flow rates, and the amount of separation can be reduced to decrease resistance within the diffuser 110 and maintain the efficiency of the compressor 32 under these conditions. The controlled area asymptotic design allows for controlled pressure within the diffuser 110, which suppresses separation and instability within the diffuser 110, thereby improving efficiency.

[0024] The previously known diffuser 80 provides two variables for controlling the performance of the diffuser within the compressor 32: diffuser width w D The radial length of the diffuser 80. The controlled-area progressive blade diffuser 110 according to this disclosure provides greater flexibility in adjusting the diffuser to improve the efficiency of the compressor 32 by contouring the shape of the compressor diffuser wall 112. Contour shaping of the compressor diffuser wall 112 helps reduce the annular area A in regions of diffuser flow instability and tendency to separate. D Conversely, at locations where the diffuser flow is stabilized by the blades, the annular area A can be increased. D This reduces flow velocity and frictional losses. A more stable flow through diffuser 110 can produce higher efficiency and can achieve improved efficiency while maintaining or expanding the width of compressor pattern 140.

[0025] In previously known bladed diffusers (such as bladed diffuser 80), VLE 94 is typically located at approximately 1.1–1.2 r. C This is because it is believed that positioning blade 88 near the compressor impeller 28 achieves optimal efficiency. In contrast, VLE 94 in the vane diffuser 110 of this design can be positioned at 1.3-1.4r. C Within this range, this is because the narrow point 120 stabilizes the fluid flow near the diffuser inlet 90. By positioning the blades 88 away from the compressor impeller 28, efficiency can be maintained while potentially reducing vibration and high-cycle fatigue (HCF) on the compressor blades 70. Although the foregoing text provides detailed descriptions of many different embodiments, it should be understood that the scope of legal protection is defined by the wording of the claims listed at the end of this patent. This detailed description is to be interpreted as illustrative only and does not describe all possible embodiments, as it is impractical to describe all possible embodiments, though not impossible. Many alternative embodiments can be implemented using present technology or technology developed after the date of this patent application, and these embodiments will still fall within the scope of these limiting claims.

[0026] It should also be understood that unless a term is explicitly defined herein, there is no intention to explicitly or implicitly limit the meaning of that term beyond its original or ordinary meaning, and such term should not be construed as limiting the scope of any statement made in any part of this patent (other than the language of the claims). Any term referenced in the claims at the end of this patent is expressed in a manner consistent with a single meaning, done only for clarity so as not to confuse the reader, and is not intended to limit such claim terms to that single meaning by implication or otherwise.

Claims

1. A controlled area progressive vane diffuser (CAPVD) for a compressor, wherein, The compressor includes: a bearing housing, a shaft supported by bearings in the bearing housing for rotation about a rotation axis; a compressor impeller disposed on the shaft and having a compressor radius; and a compressor housing connected to the bearing housing, a chamber defining a chamber in which the compressor impeller rotates, and a volute for receiving airflow generated by the compressor impeller, the CAPVD including: The bearing housing has a bearing diffuser wall that has an annular shape and extends from the chamber to the volute. The compressor housing has a compressor diffuser wall that has an annular shape and extends from the chamber to the volute, wherein the bearing diffuser wall and the compressor diffuser wall are spaced apart in the axial direction; Multiple blades, the multiple blades extending from the bearing diffuser wall and the compressor diffuser wall and circumferentially spaced around the axis of rotation, each blade having a leading edge and a trailing edge; A diffuser inlet, the diffuser inlet being adjacent to the chamber; and A diffuser outlet, located near the volute, wherein airflow from the compressor impeller enters the CAPVD through the diffuser inlet, passes between the bearing diffuser wall and the compressor diffuser wall, through the plurality of blades, and exits from the diffuser outlet to the volute. The bearing diffuser wall and the compressor diffuser wall are spaced apart by the blade leading edge width at the blade leading edge. Wherein, the bearing diffuser wall and the compressor diffuser wall define a narrow point between the diffuser inlet and the leading edge of the blade, wherein the narrow point has a width smaller than the width of the leading edge of the blade, and The diffuser outlet has a diffuser outlet width that is smaller than the leading edge width of the blade.

2. The CAPVD as described in claim 1, wherein, The diffuser inlet width at the diffuser inlet is greater than the narrow point width.

3. The CAPVD as described in claim 2, wherein, The diffuser inlet width ranges from 0.04 to 0.07 times the compressor radius.

4. The CAPVD as described in claim 2, wherein, The diffuser inlet width is smaller than the blade leading edge width.

5. The CAPVD as described in claim 2, wherein, The blade leading edge width is in the range of 0.7 to 1.2 times the diffuser inlet width.

6. The CAPVD as described in claim 2, wherein, The diffuser outlet width is in the range of 0.7 to 1.2 times the diffuser inlet width.

7. The CAPVD as described in claim 2, wherein, The width of the narrow spot is in the range of 0.6 to 1.0 times the width of the diffuser inlet.

8. The CAPVD as claimed in claim 1, wherein, The diffuser outlet radius from the rotation axis to the diffuser outlet is in the range of 1.45 to 2.0 times the radius of the compressor.

9. The CAPVD as claimed in claim 1, wherein, The radius of the narrow point from the axis of rotation to the narrow point is in the range of 1.05 to 1.3 times the radius of the compressor.

10. The CAPVD as claimed in claim 1, wherein, The blade leading edge radius from the rotation axis to the blade leading edge is in the range of 1.1 to 1.4 times the compressor radius.

11. The CAPVD as claimed in claim 1, wherein, The leading edge radius of the blade is in the range of 1.3 to 1.4 times the radius of the compressor.

12. The CAPVD as claimed in claim 1, wherein, The radius of the blade trailing edge from the axis of rotation to the trailing edge of the blade is in the range of 1.3 to 1.7 times the radius of the compressor.

13. The CAPVD as claimed in claim 1, wherein, The bearing diffuser wall and the compressor diffuser wall are spaced apart at the trailing edge of the blade by the width of the blade trailing edge, wherein the width of the blade trailing edge is equal to the width of the blade leading edge.

14. The CAPVD as claimed in claim 1, wherein, The axial distance between the bearing diffuser wall and the compressor diffuser wall decreases at a constant rate from the diffuser inlet to the narrow point.

15. The CAPVD as claimed in claim 1, wherein, The axial distance between the bearing diffuser wall and the compressor diffuser wall increases at a constant rate from the narrow point to the leading edge of the blade.

16. The CAPVD as claimed in claim 1, wherein, The axial distance between the bearing diffuser wall and the compressor diffuser wall decreases at a constant rate from the trailing edge of the blade to the diffuser outlet.

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