GB2541934A

GB2541934A - Turbocharger

Info

Publication number: GB2541934A
Application number: GB1515757.1A
Authority: GB
Inventors: John Monaghan Christopher; Eifion Roach Paul; Joseph Geoffrey Heyes Francis; Anthony Mullen James
Original assignee: Napier Turbochargers Ltd
Current assignee: Napier Turbochargers Ltd
Priority date: 2015-09-07
Filing date: 2015-09-07
Publication date: 2017-03-08
Anticipated expiration: 2035-09-07
Also published as: GB201515757D0; GB2541934B

Abstract

A turbocharger with a radial inflow turbine wheel 24, an inlet casing 16 with inlet portion 18 and outlet portion 22 for delivering exhaust gas circumferentially around the inflow turbine rotor 24. A row of stator vanes or fins 28 direct the flow to the turbine wheel and the inlet casing is configured so that the flow upstream of the vanes is parallel to the axis of the turbine wheel and the flow has a component directed radially inwards. The outlet casing 30 may be fitted to the turbine at an axially centred cavity formed by the outlet portion of the inlet casing. The inlet casing may be constructed so that the exhaust stream in the inlet portion is also parallel to the axis of the rotor. The inlet casing may have a bend (32, figure 5) producing a right or acute angle between the axis of the turbine and the gas flow direction. An engine with internal combustion cylinders may be fitted with the turbocharger and may have an exhaust pipe (6, figure 1) connected to the inlet portion. The cylinders may be in two parallel rows with respective exhaust pipes and turbochargers.

Description

TURBOCHARGER

Field of the Invention

The present invention relates to a turbocharger.

Background

Turbochargers for industrial diesel and gas engines are typically of two types: those with axial inflow turbines and those with radial inflow turbines. As used herein, by a “radial inflow turbine” or “radial turbine” we mean a turbine which, ignoring any tangential or swirl component of flow, receives a purely radial inflow of engine exhaust gas, or receives an inflow of exhaust gas which has both radial and axial inflow components (sometimes referred to as a “mixed inflow turbine” or “mixed-flow turbine”). Radial inflow turbine wheels are usually formed as one-piece castings from materials such as a nickel based superalloy; axial inflow turbine wheels can be cast in the same way from similar materials, or made from individual forged blades slotted into a separate disc. In general, for the same turbine flow capacity, an axial wheel has a lower rotational inertia than a radial wheel, and the radial wheel would generally be a larger and heavier casting than a corresponding cast axial wheel.

Generally, smaller turbochargers have radial turbines. In contrast, very large turbochargers have axial flow turbines since the size and weight of a radial turbine casting would be impractical. However, for a range of industrial diesel and gas engines, typically known as medium speed engines, the turbocharger may be either radial or axial type.

The assembly of a radial wheel on the turbocharger rotor is usually arranged so that the thrust load from the compressor is offset by the thrust load from the turbine: this means that the overall thrust load is low and consequent mechanical losses reduced. The engine exhaust flow enters the radial turbine turbocharger in a direction tangential to the axis of the turbocharger, in the middle of the turbocharger, and the gas exhausts from the turbocharger in a generally axial direction along the axis of the turbocharger.

For the axial turbine turbocharger, the flow enters the turbine blading in an axial direction and exhausts from the turbocharger in a radial direction from a location near the middle of the turbocharger. This means that the axial loading from the turbine adds to that from the compressor and the thrust load is high. The consequently increased mechanical losses mean that an axial turbine turbocharger can have a lower efficiency than a similarly sized radial turbine turbocharger.

Arrangements of turbochargers on industrial diesel and gas internal combustion engines are constrained by the engine exhaust pipe, which runs the length of the engine axis, and by the locations of the air inlet to the turbocharger compressor and the exhaust from the turbocharger turbine. Preferably, to avoid poor performance and an increased length of arrangement, the engine exhaust pipe should not be kinked or twisted before it reaches the turbocharger.

For a radial turbine turbocharger, because of the turbine inlet flow location, the turbocharger axis tends to lie generally perpendicular to the axis of the engine, whereas for an axial turbine turbocharger, the turbocharger can be arranged with its axis generally more parallel to that of the engine.

Particularly for a V-engine, where there are two banks of engine cylinders and usually a pair of exhaust pipes and a corresponding pair of turbochargers, there can be a distinct advantage to use of axial turbine turbochargers: because the turbocharger axes can lie parallel to the axis of the engine, the two axial turbine turbochargers can sit in close proximity to each other and within the footprint of the engine. The location and orientation of the axial turbine turbocharger exhausts also allows close proximity of the turbochargers.

For a pair of radial turbine turbochargers on a V-engine, the naturally transverse orientation of the turbocharger axis means that the turbocharger exhaust casings come into close proximity: this means that the turbochargers have to be mounted further apart and this can cause the turbochargers to lie outside the footprint of the engine. To reduce the footprint, it is possible for the exhaust streams from the two turbochargers to be fed into a single turbine outlet casing, but in general this is not a preferred solution due to increased risks of thermal stress cracking. Another option is for the radial turbine turbochargers to be mounted at an angle to each other, introducing a bend into the engine exhaust pipe, and thus lengthening the engine.

Summary

It would be desirable to be able to combine the relatively high efficiency of a radial turbine turbocharger with the ease of mountability to an engine of an axial turbine turbocharger.

Accordingly, in a first aspect, the present invention provides a turbocharger having a turbine for extracting energy from exhaust gas flowing from an engine, the turbine including: a radial inflow turbine wheel; an inlet casing having an inlet portion for receiving the exhaust gas, and an annular outlet portion which delivers the exhaust gas as a flow which is circumferentially distributed around the radial inflow turbine wheel; and a circumferential row of stator vanes which direct the circumferentially distributed flow to the turbine wheel; wherein the inlet casing is configured such that the circumferentially distributed flow upstream of the stator vanes is substantially parallel to the axis of the turbine wheel, and the stator vanes are configured to condition the circumferentially distributed flow so that it has a component which is directed radially inwardly and so that it swirls in the direction of rotation of the turbine wheel.

Advantageously, the inlet casing and the stator vanes allow the turbocharger to be mounted on an engine with its axis generally parallel to that of the engine, in a manner similar to that of conventional axial turbine turbochargers. Particularly on a V-engine, a compact arrangement of twin turbochargers can thus be achieved. Moreover, since the turbocharger is of radial turbine type with a relatively low thrust load, the turbocharger’s efficiency can be kept to a high level similar to that of conventional radial turbine turbochargers.

In a further aspect, the present invention provides an engine having one or more internal combustion cylinders which produce exhaust gas, and being fitted with the turbocharger of the first aspect such that the inlet portion of the turbocharger receives the produced exhaust gas. For example, the engine may have a row of the internal combustion cylinders and an exhaust pipe extending along the cylinder row to collect the exhaust gas from the cylinders, the inlet portion of the turbocharger being connected to the exhaust pipe. More particularly, the engine (e.g. a V-engine) may have two parallel such rows of internal combustion cylinders with respective exhaust pipes and respective turbochargers.

Optional features of the invention will now be set out. These are applicable singly or in any combination with any aspect of the invention.

The stator vanes may be further configured to condition the circumferentially distributed flow so that, on a longitudinal section through the turbine, the flow is at an angle of at least 45° to the axis of the turbine wheel. Indeed, the flow may be conditioned so that, on such a section, it is perpendicular to the axis (i.e. it has substantially no axial component). The turbine wheel may be configured to receive a flow which is directed radially inwardly and swirls in the direction of rotation of the turbine wheel, or preferably which (on a longitudinal section through the turbine) is at an angle of at least 45° to the axis of the wheel or is perpendicular to the axis.

The inlet portion of the inlet casing is typically configured for connection to an exhaust pipe of the engine. However, if the turbocharger is a low pressure turbocharger of a two stage turbocharger arrangement, the inlet portion can be configured for connection to the turbine outlet of the high pressure stage.

The inlet portion is typically offset from the axis of the turbine wheel (i.e. the turbocharger axis) and guides the flow approaching the turbine wheel in a largely axial direction. The annular outlet portion can then distribute the flow around the circumference of the turbine wheel.

The flow can exit the inlet casing in a substantially axial direction. Conveniently, the stator vanes can then be positioned at the exit to the casing to condition the flow.

An outlet casing can receive the exhaust gas as an axially directed flow from the turbine wheel, the outlet casing being fitted to the turbine at an axially centred cavity formed by the annular outlet portion of the inlet casing. Typically, the outlet casing is configured to decelerate the flow. Conveniently, the outlet casing may turn the flow direction from axial to radial, e.g. for onward delivery to an exhaust stack. However, if turbocharger is a high pressure turbocharger of a two stage turbocharger arrangement, the outlet casing can be configured for connection to the turbine inlet of the low pressure stage.

The inlet casing may be configured such that the exhaust gas flow direction at the inlet portion is also substantially parallel to the axis of the turbine wheel.

Alternatively, the inlet casing may have a bend between the inlet portion and the annular outlet portion, the bend producing a right angle or an acute angle between the exhaust gas flow direction at the inlet portion and the axis of the turbine wheel. The acute angle can be greater than 5°. The acute angle can be less than 45°. The acute angle can be in the range from 30° to 40°.

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows schematically a V-engine fitted with twin turbochargers;

Figure 2 shows a cross section through a turbocharger;

Figure 3 shows an end-on view of twin turbochargers mounted to a V-engine with their turbine inlet casings close together;

Figure 4 shows an end-on view of a variant of the twin turbochargers;

Figure 5 shows a top view of a further variant of the twin turbochargers; and Figure 6 shows an end-on view of a further variant of a turbocharger.

Detailed Description and Further Optional Features

Figure 1 shows schematically a V-engine fitted with twin turbochargers. The engine has two rows 2 of cylinders, each row having a respective a respective air pipe 4 and exhaust pipe 6 extending along the row. The air pipes may typically be combined into a single air chest. A respective turbocharger 8 is mounted at the end of each cylinder row. Each turbocharger has a compressor wheel 10 which delivers a flow of compressed air to its air pipe 4, usually through a charge air cooler (not shown), and a turbine wheel 12 which receives an exhaust gas flow from its exhaust pipe 6, the wheels being connected by a shaft 14. The flows of air and exhaust gas are indicated by arrowed lines. The turbine wheels are of radial inflow type and the turbocharger axes are aligned with the directions of the cylinder rows.

Figure 2 shows a cross section through one of the turbochargers 8. A turbine inlet casing 16 has an inlet portion 18 with a flange that connects to the respective exhaust pipe 6 to take the engine exhaust flow approaching the turbocharger in the direction (arrowed A) of the turbocharger’s axis. The inlet portion is offset from the turbocharger axis (20). The inlet portion of the casing succeeds to an annular outlet portion 22 which is configured to circumferentially distribute the flow around the radial inflow turbine wheel 24 of the turbocharger. The flow exits the inlet casing through an annular gas passage 26 formed by the outlet portion still in a direction parallel to the turbocharger axis. The inlet casing has a space in its centre for turbocharger exhaust gases to escape along the axis of the turbocharger in a direction (arrowed B) generally opposite to the inflow to the turbine. A turbine stator vane row (nozzle ring) 28 positioned at exit from the annular gas passage 26 conditions the flow leaving the inlet casing 16 in an axial direction, to turn the flow into a generally radially inwards direction and to swirl the flow to have a component of velocity tangential to the turbocharger axis, in the direction of rotation of the turbine wheel 24. The exhaust flow then enters the turbine wheel in a direction similar to that of a conventional radial turbine turbocharger and exits the turbine along the axis of the turbocharger.

The flow then enters a turbine outlet casing 30, which typically has 90° bend diffuser. The outlet casing fits within the space formed by the inlet casing 16.

Although described above in relation to a V-engine fitted with twin turbochargers, a single turbocharger can be fitted to an inline engine with a single cylinder row.

Advantageously, due to its radial turbine wheel 24, the turbocharger generates a relatively low thrust load, which promotes the turbocharger efficiency. However, the turbocharger 8 can be mounted on the engine in a similar manner to an axial turbine turbocharger, helping to reduce the turbocharger footprint. Figure 3 shows an end-on view of twin turbochargers 8 mounted to a V-engine with their turbine inlet casings close together.

The exhaust gas from the turbocharger 8 enters the turbine outlet casing 30 and then exhausts to an engine exhaust stack. Although Figure 3 shows the exits from the outlet casing bend diffusers pointing vertically upwards and parallel to each other, the outlet casings may be rotated about the turbocharger axis so that the exhaust streams approach each other, e.g. to be fed into a single exhaust stack. Additionally or alternatively, the turbine inlet portions 18 may be arranged to be below the axis of the turbocharger by rotating the turbine inlet casings. This allows the turbochargers to be mounted more closely together. Both these modifications are shown in the end-on view of Figure 4. A given turbocharger can be mounted with its axis in line with the axis of the engine or, via a bend upstream of the turbine inlet casing 16, at some angle to the engine axis. Indeed, a bend 32 may be formed in the inlet casing between the inlet portion 18 and the outlet portion 22 to allow the turbocharger to be mounted with its axis at an angle to the engine axis. For example, the angle may be an acute angle in the range from 30° to 40°. This allows the turbochargers to be mounted in an arrangement shown in the top view of Figure 5. At the limit, if the bend angle is increased to 90°, the turbochargers can be mounted with their axes perpendicular to the engine axis. A waste-gate (not shown) may be placed between inlet and the outlet to the, or each, turbine, which allows engine exhaust gas to bypass the turbine(s).

Turbine cleaning may be provided for the turbocharger. Cleaning liquids or solids can be introduced into the gas flow within the turbine inlet casing so that combustion deposits are removed from the casing itself or from the turbine blades.

For “pulse” turbocharging, multiple engine exhaust pipes can be attached to a single turbocharger with each exhaust pipe feeding a segment of the nozzle ring. In particular, this can be achieved by having a turbine inlet casing 16 with multiple inlet portions 18 as seen in the end-on view of Figure 6, which has two such portions. Baffle walls within the inlet casing then divide the flow into multiple flow streams. For constant pressure turbocharging, as opposed to pulse turbocharging, it is also possible to mount a single turbocharger with two inlet portions 18, e.g. each accepting one of the exhaust flows from a V-engine.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. For example, Figure 2 shows a “pure” radial inflow turbine wheel 12. However, in other embodiments, the turbine wheel may be of mixed inflow type. In such embodiments, the nozzle ring 28 may be adapted to condition the flow so that it has appropriate amounts of radial and axial components for the wheel. Thus, the nozzle ring may turn the flow back on itself to an extent. As another example, Figure 2 shows a single stage turbocharger. However, in other embodiments the turbocharger may be the high or low pressure stage of a two stage turbocharger arrangement. Indeed the invention can be applied to both stages of a two stage turbocharger arrangement. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

1. A turbocharger (8) having a turbine for extracting energy from exhaust gas flowing from an engine, the turbine including: a radial inflow turbine wheel (24); an inlet casing (16) having an inlet portion (18) for receiving the exhaust gas, and an annular outlet portion (22) which delivers the exhaust gas as a flow which is circumferentially distributed around the radial inflow turbine wheel; and a circumferential row (28) of stator vanes which direct the circumferentially distributed flow to the turbine wheel; wherein the inlet casing is configured such that the circumferentially distributed flow upstream of the stator vanes is substantially parallel to the axis of the turbine wheel, and the stator vanes are configured to condition the circumferentially distributed flow so that it has a component which is directed radially inwardly and so that it swirls in the direction of rotation of the turbine wheel.

2. A turbocharger according to claim 1, wherein an outlet casing (30) receives the exhaust gas as an axially directed flow from the turbine wheel, the outlet casing being fitted to the turbine at an axially centred cavity formed by the annular outlet portion of the inlet casing.

3. A turbocharger according to claim 1 or 2, wherein the inlet casing is configured such that the exhaust gas flow direction at the inlet portion is also substantially parallel to the axis of the turbine wheel.

4. A turbocharger according to claim 1 or 2, wherein the inlet casing has a bend (32) between the inlet portion and the annular outlet portion, the bend producing a right angle or an acute angle between the exhaust gas flow direction at the inlet portion and the axis of the turbine wheel.

5. An engine having one or more internal combustion cylinders which produce exhaust gas, and being fitted with the turbocharger of any one of the previous claims such that the inlet portion of the turbocharger receives the produced exhaust gas.

6. An engine according to claim 5 which has a row of the internal combustion cylinders and an exhaust pipe (6) extending along the cylinder row to collect the exhaust gas from the cylinders, the inlet portion of the turbocharger being connected to the exhaust pipe.

7. An engine according to claim 6 which has two parallel such rows of internal combustion cylinders with respective exhaust pipes and respective turbochargers.