Claims:1. A centrifugal compressor having enhanced choke limit and/or surge limit comprises of, a housing (101), said housing (101) having an annular inlet (102) and an outlet (103); a shaft (104), said shaft (104) is positioned axially in the centre of the housing (101); a compressor wheel (105), said compressor wheel (105) is coupled with the shaft (104), wherein a plurality of blades (106) circumferentially spaced apart having a first edge is joined to the surface of the compressor wheel and a second edge extending radially outwards, said second edge of the plurality of blades (106) comprising a leading edge (107) and a trailing edge (108); a shroud wheel (109), said shroud wheel (109) is positioned radially adjacent to the second end of the plurality of blades (106); and a bleed port (110), wherein the bleed port (110) is formed between the annular inlet (102) of the housing (101) and the shroud wheel (109), said bleed port (110) having a first opening (111) and a second opening (112), wherein the first opening (111) and the second opening (112) having an appropriate geometry,

characterized in that the geometry of the first opening (111) and the geometry of the second opening (112) is a diverging geometry.

2. A centrifugal compressor having enhanced choke limit and/or surge limit as claimed in claim 1, said diverging geometry of the first opening (111) and the second opening (112) is with respect to the direction of fluid flow through the bleed port (110).

3. A centrifugal compressor having enhanced choke limit and/or surge limit as claimed in claim 1, wherein said fluid is selected from gas, liquid, aerosol mixture and/or combinations thereof.
, Description:A CENTRIFUGAL COMPRESSOR FOR TURBOCHARGER
FIELD OF THE INVENTION
The present invention is related to a centrifugal compressor. In particular, the present invention is related to a centrifugal compressor for turbochargers having enhanced surge and/or choke limit.
BACKGROUND OF THE INVENTION
Turbochargers are generally used to increase the performance of an internal combustion engine. A turbocharger extracts energy from engine exhaust via a turbine to drive a compressor that compresses the intake air and direct it to the engine. Turbochargers typically rely on compressor wheels consisting of fins or blades that rotate inside a casing. A rotating compressor wheel within a compressor housing sucks air through an intake port, compresses it in an impeller passage, and diffuses it into a volute. The compressed air is then supplied to an intake manifold of an internal combustion engine. It is known that the clearance existing between the compressor wheel end and the casing forming the internal wall of the airflow duct degrades the efficiency of the engine.
A compressor flow map (plot of pressure ratio versus mass fluid flow) helps to characterize the performance of a compressor. It is important for any compressor to have a wide operating envelope, as measured between the "choke line" at which the mass flow rate is maximum and the "surge line" which is a minimum mass air flow that is maintainable at a given rotational speed of a compressor wheel. Surging airflow occurs when a compressor operates at a relatively low flow rate with respect to the compressor pressure ratio, and the resulting fluid flow throughout the compressor becomes unstable, for example fluctuations in pressure and flow reversal may occur. Surge is usually initiated by aerodynamic stall or flow separation in one or more of the compressor components. Surge causes a significant loss in performance and thus is highly undesirable. In some cases, compressor surge can also result in damage to the engine or its intake pipe system.
It is a challenging task to develop a compressor having an adequately wide flow range from surge on the low end to the choke on the high end. Many researches in this field have developed a host of designs and methods for extending the usable flow range.
Probably the most widely used and effective design for compressor flow range enhancement is to provide bypass ports in the compressor housing at suitable locations radially adjacent to the impeller at blade passage path known as ported shroud. These cavities/shroud is placed opposite to the blade for the purpose of reinjecting the fluid flowing into the clearance region. In a compressor, low momentum flow along the outer shroud of the compressor is known to be detrimental to the aerodynamic performance and triggers premature engine stall. Accordingly, bleeding such low momentum air flow at the shroud is performed to improve engine performance and operability. The shroud is provided with one or more ports that extend through a bypass passage defined in the housing, and the other end of the bypass passage opens into an inlet duct at the clearance region of the compressor. At low-flow operating conditions near the surge line, part of the fluid is by-passed through the port in the shroud and recirculated back to the compressor inlet via the bypass passage. This recirculation and reintroduction of air which bled off back into the compressor flow has been found advantageous to improve the stall margin of the compressor. The ported shroud typically improves the surge characteristics of a compressor by rerouting some air passing through the impeller passage back to the intake port during low-airflow operation, thereby extending the range over which the compressor can operate without experiencing a surge condition.
At high-flow operating conditions near choke, some of the fluid entering the inlet duct can flow from the inlet duct into the bypass passage and out through the port. The prevention of compressor surge and choke can expand the useful operating range of the compressor. Thus controlling the flow of air at the blade end constitutes an essential aim for obtaining both good aerodynamic efficiency of the compressor and a sufficient margin against the surge phenomenon. However, stall margin improvement by such known recirculation systems typically comes at the expense of performance loss. Therefore there exists a need in the art for an improved compressor with optimized positioning of the ported shroud to improve the surge margin thereby increasing its aerodynamic efficiency.
U. S Patent No. 7775759 discloses a centrifugal compressor comprises a compressor wheel having a hub and a plurality of circumferentially spaced blades joined to the hub and extending generally radially outwardly there from. Each blade has a root attached to the hub and an opposite tip. The compressor wheel is connected to a shaft that is rotatable about a rotational axis A and is driven by a device such as a turbine or electric motor. The compressor wheel is mounted within a compressor housing. The compressor housing includes an inlet duct formed by a duct wall that encircles the axis. The compressor housing further includes a wheel shroud that is radially adjacent the tips of the compressor blades and, together with the hub of the compressor wheel, defines a flowpath for fluid to flow through the blade passages of the compressor wheel. The inlet duct is configured such that the fluid flow approaches the leading edges of the compressor blades in a direction substantially parallel to the rotational axis A. The flowpath defined by the hub and wheel shroud is configured to turn the fluid flow radially outwardly as the fluid flows through the blade passages. The fluid exits the blade passages at the blade trailing edges in a generally radially outward direction (and passes through a diffuser passage into a discharge volute that comprises a generally toroidal or annular chamber surrounding the compressor wheel. Furthermore, the compressor includes a bleed flow recirculation system for controlling surge of the compressor. The recirculation system includes a bleed port defined in the wheel shroud at a location intermediate the leading edges and trailing edges of the compressor blades. The bleed port is connected to a connecting passage defined in the duct wall. The connecting passage extends in a generally axial direction opposite to the direction of the main fluid flow in the inlet duct, to a point spaced upstream of the compressor blade leading edges. The connecting passage at that point connects with a converging injection nozzle that opens into the main fluid flowpath in the inlet duct. This invention does not teach about enhancement of choke limit.
U.S Application No. 14405205 discloses a compressor housing for a turbocharger with a recirculation cavity formed between a volute base portion, an inducer and an inlet section to bleed airflow from a compressor impeller back into the inlet section. Bleed airflow can enter an angled recirculation slot adjacent to the compressor impeller and then flow through a recirculation cavity formed in the compressor housing to an inlet re-entry slot in the inlet section. Such recirculated airflow can improve surge margin. However the said prior-art document fails to teach about the enhancement of the choke margin.
US patent document 8272832 provides a centrifugal compressor with surge control comprising of a compressor wheel, and a compressor housing having an inlet duct through which the fluid enters in an axial direction and is led by the inlet duct into the compressor wheel, and an inner surface located radially adjacent the tips of the blades. A bleed port is defined in the inner surface of the compressor housing at a location intermediate the leading and trailing edges of the blades, for bleeding off a bleed portion of the fluid, the bleed port leading to a recirculation flow channel that feeds the bleed portion back into the inlet duct. Highly cambered vanes are disposed in the recirculation flow channel for turning the bleed portion to take out and in some cases reverse the swirl in the bleed portion. However, said prior-art document provides a channelled fluid flow with swirl elements making the construction of compressor housing a more complex task.
US patent application 12630530 provides a compressor stabilizer having an annular circulation chamber arranged in the interior of a compressor housing, this circulation chamber radially surrounds a main flow duct and extends from an intake region to an encircling circulation opening in a region of rotor blades of the compressor wheel. Between the circulation openings, the circulation chamber is delimited from the main flow duct by an annular contoured wall. The contoured wall is connected to the inner compressor housing by plural struts which are spaced apart from one another to different extents in the circumferential direction. As a result of the irregular distribution of the struts in the circumferential direction, generation of undesired vibration excitations can be reduced and/or eliminated. This prior-art document provides a more complex construction of compressor housing for stabilizing the compressor fluid flow and does not teach anything about the operation range of the compressor.
US patent document 4930978 provides a turbocharger with a compressor stage having an inducer shroud with two or more vents. A first vent is provided with a second vent upstream thereof, allowing for outflow during surge conditions and inflow during choking conditions. Surge line characteristics may be varied by selectively locating the position of the first and of the second vents, and by selectively determining the effective width of the vents. The vents may be circumferential slots, and may be slanted. An outer shroud is provided forming a venting chamber for recirculation of gas into the gas intake. A third vent may be provided to vent the diffuser. However the said prior-art document is provided with multiple vented shroud making the fluid flow more uncertain than as desired.
Therefore for above reasons there is a need in the art for a compressor having enhanced choke limit and surge limit. Such compressor system is particularly useful for engine turbocharger which are intended to operate over a wide range of rotational speeds under various conditions of engine speed, load and ambient pressure.
OBJECTIVE OF THE INVENTION
Main objective of the present invention is to provide a centrifugal compressor with ported shroud having enhanced choke and/or surge limit.
Another objective of the present invention is to provide a centrifugal compressor with optimised port geometry for enabling wide operating range of the compressor system.
SUMMARY OF THE INVENTION
A centrifugal compressor of turbocharger having enhanced choke limit and/or surge limit comprises of: a housing (101), said housing (101) having an annular inlet (102) and an outlet (103); a shaft (104); a compressor wheel (105), said compressor wheel (105) is coupled with the shaft (104); a shroud wheel (109), said shroud wheel (109) is positioned radially adjacent to the second end of the plurality of blades (106); a bleed port (110), wherein the bleed port (110) is formed between the annular inlet (102) of the housing (101) and the shroud wheel (109), said bleed port (110) having a first opening (111) and a second opening (112), wherein the first opening (111) and the second opening (112) having an appropriate geometry, characterized in that the geometry of the first opening (111) and the geometry of the second opening (112) is a diverging geometry, said diverging geometry is with respect to the direction of fluid flow through the bleed port (110).
BREIF DESCRIPTION OF THE DIAGRAM
Figure 1 represents the general state of art of the centrifugal compressor of turbocharger having a shroud wheel which forms a bleed port.
Figure 2 depicts the centrifugal compressor of turbocharger having inlet and outlet of the bleed port, wherein geometry of the said port is converging with respect to the main flow.
Figure 3 shows the centrifugal compressor of turbocharger having inlet and outlet of the bleed port, wherein geometry of the said port is diverging with respect to the main flow.
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention as embodied by a centrifugal compressor for turbocharger, succinctly fulfils the above-mentioned need(s) in the art. The present invention has objective(s) arising as a result of the above-mentioned need(s), said objective(s) being enumerated below. In as much as the objective(s) of the present invention are enumerated, it will be obvious to a person skilled in the art that, the enumerated objective(s) are not exhaustive of the present invention in its entirety, and are enclosed solely for the purpose of illustration. Further, the present invention encloses within its scope and purview, any structural alternative(s) and/or any functional equivalent(s) even though, such structural alternative(s) and/or any functional equivalent(s) are not mentioned explicitly herein or elsewhere, in the present disclosure. The present invention therefore encompasses also, any improvisation(s)/modification(s) applied to the structural alternative(s)/functional alternative(s) within its scope and purview. The present invention may be embodied in other specific form(s) without departing from the spirit or essential attributes thereof.
Throughout this specification, the use of the word "comprise" and variations such as "comprises" and "comprising" may imply the inclusion of an element or elements not specifically recited.
The present invention provides a centrifugal compressor for turbochargers having enhanced choke limit and/or surge limit, comprising of: a housing (101), said housing (101) having an annular inlet (102) and an outlet (103); a shaft (104), said shaft (104) is positioned axially in the centre of the housing (101); a compressor wheel (105), said compressor wheel (105) is coupled with the shaft (104), wherein a plurality of blades (106) circumferentially spaced apart having its first edge attached to the surface of the compressor wheel and its second edge extending radially outwards, said second edge of the plurality of blades (106) comprising a leading edge (107) and a trailing edge (108); a shroud wheel (109), said shroud wheel (109) is positioned radially adjacent to the second end of the plurality of blades (106); a bleed port (110), wherein the bleed port (110) is formed between the annular inlet (102) of the housing (101) and the shroud wheel (109), said bleed port (110) having a first opening (111) and a second opening (112), wherein the first opening (111) and the second opening (112) having an appropriate geometry, characterized in that the said geometry of the first opening (111) and the said geometry of the second opening (112) is diverging, wherein said diverging geometry is with respect to the direction of fluid flow through the bleed port (110).
In the preferred embodiment of the present invention, wherein said fluid is selected from gas, liquid, aerosol mixture and/or combinations thereof.
In an embodiment of the present invention as shown in the figure 2, when the fluid flow is conveyed at minimum flow rate (nearing the surge limit) to the centrifugal compressor through the annular inlet (102) of the housing (101) and thereby forming the main flow of the fluid. Said fluid is re-circulated by entering the second opening (112) of the bleed port (110) and exits the bleed port (110) through the first port (111) and merge with the main flow. The geometry of the first opening (111) and the second opening (112) is diverging with respect to the direction of fluid flow through the bleed port (110). Wherein the geometry of the first opening (111) and the second opening (112) is converging with respect to the direction of the main flow through the bleed port (110). Thus the centrifugal compressor is operated with enhanced surge limit.
In another embodiment of the present invention as shown in figure 3, fluid is conveyed at maximum flow rate (nearing the choke limit) to the centrifugal compressor through the annular inlet (102) of the housing (101) and thereby forming the main flow of the fluid. Said fluid enters the bleed port (110) through the first opening (111) and exits the bleed port (110) through the second opening (112). Wherein the geometry of the first opening (111) and the second opening (112) is diverging with respect to the direction of fluid flow through the bleed port (110) and also with respect to the direction of the main flow. Thus the centrifugal compressor is operated with enhanced choke limit.
It will be apparent to a person skilled in the art that the above description is for illustrative purposes only and should not be considered as limiting. Various modifications, additions, alterations, and improvements without deviating from the spirit and the scope of the invention may be made by a person skilled in the art.