GB2592254A

GB2592254A - Fuel spray nozzle

Info

Publication number: GB2592254A
Application number: GB2002460.0A
Authority: GB
Inventors: Brown Nicholas; Rafferty Christopher; Rimmer John
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2020-02-21
Filing date: 2020-02-21
Publication date: 2021-08-25
Also published as: GB202002460D0

Abstract

A fuel spray nozzle 300 has, in order from radially inner to outer with respect to a fuel spray nozzle centreline ‘C’, a coaxial arrangement of: an inner air swirler passage 204 to produce a primary swirling air flow, an annular fuel prefilming lip 206 and at least one annular outer air swirler passage 208 to produce a secondary swirling air flow. Fuel exiting the fuel prefilming lip is atomised into a spray by the primary and secondary swirling air flows. The fuel spray nozzle further includes an annular wall 220 surrounding at least one annular outer air swirler passage 208. A radial distance between the nozzle centreline ‘C’ and a radially inner extremum of the annular wall is defined as a conic exit radius (CER). A radial distance between the nozzle centreline ‘C’ and the prefilming lip is defined as a fuel exit radius (FER), and the conic exit radius and the fuel exit radius have a defined ratio. The annular wall can radially surround the at least one annular outer air swirler passage, and the ratio of the conic exit radius to the fuel exit radius is within the range of 1.5 and 3.0. The fuel nozzle can be modified so that the annular wall dimension increases the ratio of the conic exit radius to the fuel exit radius.

Description

Fuel spray nozzle

Field of the Invention

The present disclosure relates to a fuel spray nozzle for a combustor in a gas turbine engine, to a method of modifying a fuel spray nozzle, and to a method of retrofitting a gas turbine engine with a fuel spray nozzle.

Backqround of the Invention Fuel spray nozzles are a type of injector used in gas turbine engines to provide fuel to combustors for combustion. A key requirement for fuel spray nozzles is to atomise liquid fuel passing therethrough. In some fuel spray nozzles, atomisation of the liquid is achieved by applying high velocity air to both sides of a thin film of liquid fuel dispensed from an annular fuel prefilmer.

The high velocity air is typically provided as swirling air streams, either co-rotating or counter-rotating depending on the required combustor functional performance. When swirl is applied to a high velocity air stream a portion of the flow having maximum axial velocity within the swirled flow tends to move radially outboard from the centre of the nozzle. In order to counteract this effect, the air stream radially outboard of the fuel prefilmer is typically ducted inboard towards the fuel prefilmer using an annular wall having a conic portion to ensure that the air having the maximum axial velocity comes into close proximity with the liquid fuel sheet.

Summary of the Invention

According to a first aspect, there is provided a fuel spray nozzle for a combustor, the fuel spray nozzle comprising, in order from radially inner to outer with respect to a fuel spray nozzle centreline, a coaxial arrangement of: an inner air swirler passage configured to produce a primary swirling air flow; an annular fuel prefilming lip; and at least one annular outer air swirler passage configured to produce a secondary swirling air flow, whereby fuel exiting the fuel prefilming lip is atomised into a spray by the primary and secondary swirling air flows, wherein the fuel spray nozzle further comprises: an annular wall radially surrounding at least one annular outer air swirler passage, wherein a conic exit radius is defined as a radial distance between the fuel spray nozzle centreline and a radially inner extremum of the annular wall, wherein a fuel exit radius is defined as a radial distance between the fuel spray nozzle centreline and the prefilming lip, and wherein a ratio of the conic exit radius to the fuel exit radius is within the range of 1.5 to 3.0.

The ratio of the conic exit radius (CER) to the fuel exit radius (FER) may be greater than 1.6, may be greater than 1.7 or may be greater than 1.8.

The ratio of the conic exit radius (CER) to the fuel exit radius (FER) may be in the range of 1.6 to 2.4, in the range of 1.7 to 2.3 or in the range of 1.8 to 2.2.

Optionally, the annular wall comprises a radially convergent portion.

Optionally, the radially convergent portion is angled between 0° and 85° with respect to the fuel spray nozzle centreline within a plane intersecting the fuel spray nozzle 20 centreline.

At least part of the radially convergent portion may be angled between 0° and 85° with respect to the fuel spray nozzle centreline within a plane intersecting the fuel spray nozzle centreline. Within the plane intersecting the fuel spray nozzle centreline, a tangent of the radially convergent portion may be angled between 0° and 85°. The annular wall may have a variable angle with respect to the fuel spray nozzle centreline along its axial extent.

The angle of the radially convergent portion with respect to the fuel spray nozzle centreline, within a plane intersecting the fuel spray nozzle centreline, may be determined by reference to a radially inner wall surface of the radially convergent portion.

Optionally, within a plane intersecting the fuel spray nozzle centreline, the annular wall has a curved profile.

Optionally, the annular wall has a curved profile such that there is a variable angle between tangents to the annular wall and the fuel spray nozzle centreline, along an axial extent of the annular wall with respect to the fuel spray nozzle centreline, and wherein the annular wall is curved so that, along at least a portion of the annular wall, the angle reduces in magnitude towards a tip of the annular wall.

Optionally, the fuel spray nozzle comprises two annular outer air swirler passages radially separated by the annular wall.

According to a second aspect, there is provided a method of retrofitting a gas turbine engine, the gas turbine engine comprising a combustor and a plurality of fuel spray nozzles, the method comprising: removing one of the fuel spray nozzles from the gas turbine engine; and replacing the removed fuel spray nozzle with a fuel spray nozzle according to the first aspect According to a third aspect, there is provided a method of modifying a fuel spray nozzle for a combustor, the fuel spray nozzle comprising, in order from radially inner to outer with respect to a fuel spray nozzle centreline, a coaxial arrangement of: an inner air swirler passage configured to produce a primary swirling air flow; an annular fuel prefilming lip; and at least one annular outer air swirler passage configured to produce a secondary swirling air flow, whereby fuel exiting the fuel prefilming lip is atomised into a spray by the primary and secondary swirling air flows, wherein the fuel spray nozzle further comprises: an annular wall surrounding at least one annular outer air swirler passage, the annular wall having a radially convergent portion, wherein a conic exit radius is defined as a radial distance between the fuel spray nozzle centreline and a radially inner extremum of the annular wall, and wherein a fuel exit radius is defined as a radial distance between the fuel spray nozzle centreline and the prefilming lip, the method comprising: modifying a dimension of the annular wall to increase a ratio of the conic exit radius to the fuel exit radius.

Optionally, the step of modifying a dimension of the annular wall comprises reducing a length of the convergent portion of the annular wall to increase the ratio of the conic exit radius to the fuel exit radius.

Optionally, the step of modifying a dimension of the annular wall comprises adjusting an angle of the convergent portion of the annular wall to increase the ratio of the conic exit radius to the fuel exit radius.

Optionally, the dimension is modified to increase the ratio of the conic exit radius (CER) to the fuel exit radius (FER) to within the range of 1.5-3.0. The ratio of the conic exit radius (CER) to the fuel exit radius (FER) may be increased to greater than 1.6, may be increased to greater than 1.7 or may be increased to greater than 1.8. The increased ratio of the conic exit radius (CER) to the fuel exit radius (FER) may be in the range of 1.6 to 2.4, in the range of 1.7 to 2.3 or in the range of 1.8 to 2.2.

Optionally, the fuel spray nozzle comprises two annular outer air swirler passages separated by the annular wall.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutafis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Brief description of the drawings

Figure 1 shows a longitudinal cross-section through a ducted fan gas turbine engine; Figure 2 shows a longitudinal cross-section through the combustor of the gas turbine engine of Fig. 1; Figure 3 shows a partial cross-sectional view of an illustrative fuel spray nozzle; Figure 4 shows a graph of measured particulate matter exiting a combustor on the y-axis against conic exit radius on the x-axis; Figure 5 shows a graph of weak extinction performance on the y-axis against conic exit radius on the x-axis; Figure 6 schematically shows a partial cross -sectional view of a fuel spray nozzle according to an embodiment of the invention; Figure 7 schematically shows a partial cross -sectional view of a fuel spray nozzle according to an embodiment of the invention; Figure 8 schematically shows a partial cross -sectional view of a fuel spray nozzle according to an embodiment of the invention; and Figure 9 schematically shows a partial cross -sectional view of a fuel spray nozzle according to an embodiment of the invention.

Detailed description

Figure 1 schematically shows a ducted fan gas turbine engine 10 suitable for use with the present invention. The gas turbine engine 10 has a principal and rotational axis X-X. The gas turbine engine 10 comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustor 15, a high-pressure turbine 16, an intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.

During operation, air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 13 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted.

The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

Figure 2 shows a longitudinal cross-section through the combustion equipment 15 of the gas turbine engine 10 of Fig. 1. A row of fuel spray nozzles 100 spray the fuel into an annular combustor 110. One or more of the fuel spray nozzles 100 may be provided by a fuel spray nozzle according to the present invention, for example as described herein with respect to Figures 6-9.

Figure 3 schematically shows a partial cross-sectional view of an illustrative fuel spray nozzle 200. The fuel spray nozzle 200 comprises a central post 202 (also known as a "bullet") aligned with a fuel spray nozzle axis C. The fuel spray nozzle further comprises, in order from radially inner to outer (relative to the fuel spray nozzle axis C), a coaxial arrangement of an inner air swirler passage 204, an annular fuel prefilming lip 206, an annular outer air swirler passage 208, and an annular shroud air swirler passage 210. An annular shroud 218 surrounds the shroud air swirler passage 210. The fuel prefilming lip 206 receives fuel from a fuel supply line (not shown).

In operation, an air flow (e.g. from the high pressure compressor 14 shown in Figures 1 and 2) enters the respective upstream ends of the inner air swirler passage 204, the outer air swirler passage 208 and the shroud air swirler passage 210 to form respective air streams therein. The three air streams are discharged from their respective passages at a downstream end of the fuel spray nozzle 200. As depicted in Figure 3, the upstream end of the fuel spray nozzle 200 is at the left side of the page and the downstream end of the fuel spray nozzle 200 is at the right side of the page.

The air stream discharged from the inner air swirler passage 204 constitutes a primary air flow through the fuel spray nozzle 200. The air stream discharged from the outer air swirler passage 208 combines with the air stream discharged from the shroud air swirler passage 210 to form a secondary air flow through the fuel spray nozzle.

An inner air swirler 212 is disposed in the inner air swirler passage 204. The inner air swirler 212 swirls the air stream flowing through the inner air swirler passage 204 (i.e. imparts a circumferential/tangential component to the air stream). Similarly, an outer air swirler 214 is disposed in the outer air swirler passage 208 and a shroud air swirler 216 is disposed in the shroud air swirler passage 210 to swirl the air streams flowing through those passages. The inner air swirler 212, outer air swirler 214 and shroud air swirler 216 each comprise axial and/or radial vanes to impart a circumferential/tangential component to the air stream flowing through each swirler.

An annular wall 220 separates the outer air swirler 214 from the shroud air swirler 216. In this example, the wall 220 is an annular wall since it is supported at one end (in this example, between the vanes of the outer air swirler 214 and the shroud air swirler 216, and projects downstream from the swirlers such that it is configured to project into a chamber in which the fuel spray nozzle is installed). The annular wall 220 has a conic portion that separates the outer air swirler passage 208 from the shroud air swirler passage 210. The conic portion converges towards the fuel spray nozzle centreline C in the downstream direction (i.e. in the direction of air flow through the fuel spray nozzle) at an angle 0 with respect to the fuel spray nozzle centreline C. The angle B is 550 in the fuel spray nozzle 200 shown in Figure 3. In other nozzles, the angle 8 may be between 52° and 57°.

A fuel exit radius is defined by a radial distance between the fuel spray nozzle centreline C and the fuel prefilming lip 206. In Figure 3 the fuel exit radius is labelled FER.

A conic exit radius is defined by a radial distance between the fuel spray nozzle centreline C and a radially inner extremum of the annular wall 220 (i.e. a point on the annular wall 220 -in this case a point on the conic portion of the annular wall 220 -which is most radially inward). In Figure 3 the conic exit radius is labelled CER.

Using these two measurements, a conic radius ratio (CRR) is calculated using the following formula: CRR = CER / FER In the illustrative fuel spray nozzle shown in Figure 3, the conic radius ratio is 1.475.

Figure 4 shows a graph of measured particulate matter exiting a combustor (mg/m3) on the y-axis against conic exit radius (mm) on the x-axis. The origin of the x-axis corresponds to the conic exit radius of the nozzle of Figure 3.

As can be seen, as the conic exit radius increases, the particulate matter reduces in a non-linear relationship. Specifically, for small changes in conic exit radius there is a relatively substantial reduction in particulate matter. Less substantial reductions are obtained once the conic exit radius exceeds a threshold.

The mass of particulate matter per unit volume decreases as the conic exit radius increases because the air streams that contribute to the secondary air flow (i.e. the swirled air streams passing through the outer air swirler passage 208 and the shroud air swirler passage 210) are permitted to comingle further upstream than they otherwise would with a conic portion having the conic exit radius of the nozzle of Figure 3. By comingling further upstream, better mixing is achieved both within the secondary air flow, and between the primary and secondary air flow.

The better mixing promotes atomisation of fuel exiting the fuel prefilming lip 206 and mixing of air flows, resulting in an air-fuel mixture which is more thoroughly mixed, therefore reducing fuel rich regions which are responsible for the production of particulate matter.

Figure 5 shows a graph of weak extinction performance (expressed in terms of the air to fuel ratio required to prevent flame-out) on the y-axis against conic exit radius (mm) on the x-axis. Again, the origin of the x-axis corresponds to the conic exit radius of the nozzle of Figure 3.

As can be seen, as the conic exit radius increases the weak extinction performance (i.e. a measure of how well a combustor resists flame-out) decreases in a substantially linear relationship.

Combining these two relationships, the applicant has found that, through a relatively small increase in the conic exit radius, a substantial drop in particulate matter emissions can be obtained in return for a relatively small reduction in weak extinction performance. Using the fuel exit radius as a datum, the applicant has found that a modification of the conic exit radius of the annular wall to obtain a conic radius ratio of between 1.5 and 3.0 results in a fuel spray nozzle having relatively low particulate matter discharge from the combustor while having a minimal impact on the weak extinction performance.

In other examples, a modification of the conic portion to obtain a conic radius ratio of between 1.5 and 2.0 has been found to produce a fuel spray nozzle exhibiting a substantial reduction in particulate matter, with only a moderate reduction in weak extinction performance.

As can be seen from the graphs of Figs. 4 and 5, reduced particulate matter may be achieved in return for reduced weak extinction performance. Specifically, as the air-fuel mixture becomes more evenly mixed (corresponding to reduced particulate matter), more fuel is required in the air-to-fuel ratio in the gas turbine engine to prevent flame-out. However, it is thought that particulate matter reduction can be prioritised over weak extinction performance, as it is possible to make modifications elsewhere in the gas turbine engine to mitigate against weak extinction, whereas a reduction in particulate matter cannot be so easily achieved through other means.

Figure 6 schematically shows a partial cross-sectional view of a fuel spray nozzle according to an embodiment of the invention. The fuel spray nozzle has the same configuration as that described above with respect to Figure 3, and that description applies equally to Figure 6 except as described below, such that like reference numerals from Figure 3 have been retained to indicate the same parts. In the following description, the configuration of the annular wall may be described by comparison with the fuel spray nozzle of Figure 3 (for example by describing a feature as modified relative to that fuel spray nozzle). However it will be appreciated that example fuel spray nozzles can be originally manufactured with the configurations described below, and need not be physically modified from one having a different configuration. The same applies equally to the following descriptions of the example fuel spray nozzles of Figures 7 and 8.

In the fuel nozzle of Figure 6, the annular wall 220 has been modified such that the conic radius ratio is between 1.5 and 3.0. The value of the fuel exit ratio (FER) (i.e. the radial distance between the fuel spray nozzle centreline C and the fuel prefilming lip 206) is the same as for e.g. the fuel spray nozzle 200 shown in Figure 3. Therefore, in order to achieve a conic radius ratio (CRR) of between 1.5 and 3.0, the annular wall 220 has been modified compared to e.g. the fuel spray nozzle of Figure 3 in order to increase the conic exit radius (CER).

Specifically, in the fuel spray nozzle 300 shown in Figure 6, the length L of the conic portion of the annular wall 220 has been reduced compared to the length of a conic portion of an annular wall of e.g. the fuel spray nozzle of Figure 3. Additionally, the angle 0 that the conic portion forms with the fuel spray nozzle centreline C has been increased compared to the angle that the conic portion of an annular wall of e.g. the fuel spray nozzle of Figure 3 forms with respect to the fuel spray nozzle centreline C. In the embodiment shown in Figure 6, the conic portion forms an angle of 85° with respect to the fuel spray nozzle centreline C, and the length L has been reduced such that the conic radius ratio (CRR) is 2.1.

Figure 7 schematically shows a partial cross-sectional view of a fuel spray nozzle 400 according to an embodiment of the invention.

In the fuel nozzle of Figure 7, the annular wall 220 has been modified such that the conic radius ratio is between 1.5 and 3.0. The value of the fuel exit ratio (FER) (i.e. the radial distance between the fuel spray nozzle centreline C and the fuel prefilming lip 206) is the same as for e.g. the fuel spray nozzle 200 shown in Figure 3. Therefore, in order to achieve a conic radius ratio (CRR) of between 1.5 and 3.0, the annular wall 220 has been modified compared to e.g. the fuel spray nozzle of Figure 3 in order to increase the conic exit radius (CER).

Specifically, in the fuel spray nozzle 400 shown in Figure 7, the length L of the conic portion of the annular wall 220 has been reduced compared to the length of a conic portion of an annular wall of e.g. the fuel spray nozzle 200 of Figure 3. Additionally, the angle 0 that the conic portion forms with the fuel spray nozzle centreline C has been decreased compared to the angle that the conic portion of an annular wall of e.g. the fuel spray nozzle of Figure 3 forms with respect to the fuel spray nozzle centreline C. In the embodiment shown in Figure 7 the conic portion forms an angle of 25° with respect to the fuel spray nozzle centreline C, and the length L has been reduced such that the conic radius ratio (CRR) is 1.9.

While the conic exit radius (CER) has been reduced in Figures 6 and 7 by varying both the length L of the conic portion and the angle 0 that the conic portion forms with the fuel spray nozzle centreline C, in some examples the conic exit radius (CER) may be reduced by varying solely the length L or the angle O. Figure 8 schematically shows a partial cross-sectional view of a fuel spray nozzle 500 according to an embodiment of the invention.

In the embodiment shown in Figure 8, the conic exit radius (CER) has been modified by bending a distal portion D of the conic portion of the annular wall 220 radially outward away from the fuel spray nozzle centreline C. In this way, the conic exit radius (CER) can by increased without modifying the overall length L of the conic portion or modifying the angle 0 that the conic portion forms with the fuel spray nozzle centreline C at the point where the conic portion joins the portion of the annular wall 220 that separates the outer air swirler 214 and shroud air swirler 216. Instead, the angle 0 that the conic portion forms with the fuel spray nozzle centreline C is only modified near to the distal portion D. Figure 9 schematically shows a partial cross-sectional view of a fuel spray nozzle 600 according to an embodiment of the invention.

The fuel spray nozzle 600 comprises a central post 602 aligned with a fuel spray nozzle axis C. The fuel spray nozzle further comprises, in order from radially inner to outer (relative to the fuel spray nozzle axis C), a coaxial arrangement of an inner air swirler passage 604, an annular fuel prefilming lip 606, an annular outer air swirler passage 608, and an annular wall 620. The fuel prefilming lip 606 receives fuel from a fuel supply line (not shown).

In operation, an air flow (e.g. from the high pressure compressor 14 shown in Figures 1 and 2) enters the respective upstream ends of the inner air swirler passage 604 and the outer air swirler passage 608 to form respective air streams therein. The two air streams are discharged from their respective passages at a downstream end of the fuel spray nozzle 600. As depicted in Figure 9, the upstream end of the fuel spray nozzle 600 is at the left side of the page and the downstream end of the fuel spray nozzle 600 is at the right side of the page.

The air stream discharged from the inner air swirler passage 604 constitutes a primary air flow through the fuel spray nozzle 600. The air stream discharged from the outer air swirler passage 608 forms a secondary air flow through the fuel spray nozzle.

An inner air swirler 612 is disposed in the inner air swirler passage 604. The inner air swirler 612 swirls the air stream flowing through the inner air swirler passage 604 (i.e. imparts a circumferential/tangential component to the air stream). Similarly, an outer air swirler 614 is disposed in the outer air swirler passage 608 to swirl the air stream flowing through the outer air swirler passage 608. The inner air swirler 612 and outer air swirler 614 each comprise axial and/or radial vanes to impart a circumferential/tangential component to the air stream flowing through each swirler.

The annular wall 620 surrounding the outer air swirler 614 has a conic portion surrounding the outer air swirler passage 608, wherein the annular wall converges towards the fuel spray nozzle centreline C in the downstream direction (i.e. in the direction of air flow through the fuel spray nozzle).

A fuel exit radius is defined by a radial distance between the fuel spray nozzle centreline C and the fuel prefilming lip 606. In Figure 9 the fuel exit radius is labelled FER.

A conic exit radius is defined by a radial distance between the fuel spray nozzle centreline C and a radially inner extremum of the annular wall 620 (i.e. a point on the annular wall 620 -in this case a point on the conic portion of the annular wall 620 -which is most radially inward). In Figure 9 the conic exit radius is labelled CER.

Using these two measurements, a conic radius ratio (CRR) is calculated using the following formula: CRR = CER / FER In the fuel nozzle of Figure 9, the annular wall 620 is dimensioned such that the conic radius ratio is between 1.5 and 3.0. The value of the fuel exit ratio (FER) (i.e. the radial distance between the fuel spray nozzle centreline C and the fuel prefilming lip 606) is the same as for e.g. the fuel spray nozzle 200 shown in Figure 3. Therefore, in order to achieve a conic radius ratio (CRR) of between 1.5 and 3.0, the annular wall 620 has been modified compared to e.g. the fuel spray nozzle of Figure 3 in order to increase the conic exit radius (CER).

Specifically, in the fuel spray nozzle 600 shown in Figure 9, the length L of the conic portion of the annular wall 620 has been reduced compared to the length of a conic portion of an annular wall of e.g. the fuel spray nozzle of Figure 3.

In any of the examples described above with respect to Figures 6-9, a reduction in the conic exit radius may result in the secondary air flow (from the outer air swirler passage, and shroud air swirler passage, where present) being less effectively ducted toward the fuel prefilming lip 206, 606 than in e.g. the fuel spray nozzle of Figure 3.

This effect may be mitigated by providing vanes at a downstream end of the outer air swirler 214, 614 and/or the shroud air swirler 216 that direct the air stream passing through the respective air swirler radially inwardly towards the fuel spray nozzle centreline C. Said vanes may be angled with respect to the fuel spray nozzle centreline C, for example at an angle of between zero and 75° with respect to the fuel spray nozzle centreline C. Further, in any of the examples described above with respect to Figures 6-9 an axial offset may be defined as a distance by which a conic axial exit (i.e. an axially downstream extremum of the annular wall) projects beyond a prefilmer axial exit (i.e. an axially downstream extremum of the annular fuel prefilming lip) in an axially downstream direction with respect to the fuel spray nozzle centreline C. In all embodiments of the invention described herein it is envisaged that where the conic axial exit projects beyond the prefilmer axial exit in an axially downstream direction (for example, as shown in Figs. 7-9), the axial offset is no larger than 6mm. In other examples, the axial offset can have negative values, i.e. where the conic axial exit does not project beyond the prefilmer axial exit (for example, as shown in Fig. 6).

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

While the example described above is suitable for a combustor in a gas turbine engine of an aircraft, the present invention is not restricted to aerospace applications, and could be applied to any engine incorporating a combustor (e.g. a stationary gas turbine engine).

Claims

CLAIMS: 1. A fuel spray nozzle (300, 400, 500, 600) for a combustor (110), the fuel spray nozzle (300, 400, 500, 600) comprising, in order from radially inner to outer with respect to a fuel spray nozzle centreline (C), a coaxial arrangement of: an inner air swirler passage (204, 604) configured to produce a primary swirling air flow; an annular fuel prefilming lip (206, 606); and at least one annular outer air swirler passage (208, 608) configured to produce a secondary swirling air flow, whereby fuel exiting the fuel prefilming lip (206, 606) is atomised into a spray by the primary and secondary swirling air flows, wherein the fuel spray nozzle (300, 400, 500, 600) further comprises: an annular wall (220, 620) radially surrounding at least one annular outer air swirler passage (208, 608), wherein a conic exit radius (CER) is defined as a radial distance between the fuel spray nozzle centreline (C) and a radially inner extremum of the annular wall (220, 620), wherein a fuel exit radius (FER) is defined as a radial distance between the fuel spray nozzle centreline (C) and the prefilming lip (206, 606), and wherein a ratio of the conic exit radius (CER) to the fuel exit radius (FER) is within the range of 1.5 and 3.0.
2. The fuel spray nozzle (300, 400, 500, 600) according to claim 1, wherein the ratio of the conic exit radius (CER) to the fuel exit radius (FER) is greater than 1.6, greater than 1.7 or greater than 1.8.
3. The fuel spray nozzle (300, 400, 500, 600) according to claim 1 or claim 2, wherein the ratio of the conic exit radius (CER) to the fuel exit radius (FER) is in the range of 1.6 to 2.4, in the range of 1.7 to 2.3 or in the range of 1.8 to 2.2.
4 The fuel spray nozzle (300, 400, 500, 600) according to any preceding claim, wherein the annular wall (220, 620) comprises a radially convergent portion.
5. The fuel spray nozzle (300, 400, 500, 600) according to claim 4, wherein the radially convergent portion is angled between 0° and 85° with respect to the fuel spray nozzle centreline (C) within a plane intersecting the fuel spray nozzle centreline.
6. The fuel spray nozzle (300, 400, 500, 600) according to any preceding claim, wherein within a plane intersecting the fuel spray nozzle centreline (C), the annular wall (220, 620) has a curved profile.
7. The fuel spray nozzle (300, 400, 500, 600) according to claim 6, wherein the annular wall (220, 620) has a curved profile such that there is a variable angle between tangents to the annular wall (220, 620) and the fuel spray nozzle centreline (C), along an axial extent of the annular wall (220, 620) with respect to the fuel spray nozzle centreline (C), and wherein the annular wall (220, 620) is curved so that, along at least a portion of the annular wall (220, 620), the angle reduces in magnitude towards a tip of the annular wall (220, 620).
8. The fuel spray nozzle (300, 400, 500) according to any preceding claim, wherein the fuel spray nozzle (300, 400, 500) comprises two annular outer air swirler passages (208, 210) radially separated by the annular wall (220).
9. A method of retrofitting a gas turbine engine (10), the gas turbine engine (10) comprising a combustor (110) and a plurality of fuel spray nozzles, the method 20 comprising: removing one of the fuel spray nozzles from the gas turbine engine (10); and replacing the removed fuel spray nozzle with a fuel spray nozzle (300, 400, 500, 600) according to any preceding claim.
10. A method of modifying a fuel spray nozzle (300, 400, 500, 600) for a combustor (110), the fuel spray nozzle (300, 400, 500, 600) comprising, in order from radially inner to outer with respect to a fuel spray nozzle centreline (C), a coaxial arrangement of: an inner air swirler passage (204, 604) configured to produce a primary swirling air flow; an annular fuel prefilming lip (206, 606); and at least one annular outer air swirler passage (208, 608) configured to produce a secondary swirling air flow, whereby fuel exiting the fuel prefilming lip (206, 606) is atomised into a spray by the primary and secondary swirling air flows, wherein the fuel spray nozzle (300, 400, 500, 600) further comprises: an annular wall (220, 620) surrounding at least one annular outer air swirler passage (208, 608), the annular wall (220, 620) having a radially convergent portion, wherein a conic exit radius (CER) is defined as a radial distance between the fuel spray nozzle centreline (C) and a radially inner extremum of the annular wall (220, 620), and wherein a fuel exit radius (FER) is defined as a radial distance between the fuel spray nozzle centreline (C) and the prefilming lip (206, 606), the method comprising: modifying a dimension of the annular wall (220, 620) to increase a ratio of the conic exit radius (CER) to the fuel exit radius (FER).
11. The method according to claim 10, wherein the step of modifying a dimension of the annular wall (220, 620) comprises reducing a length of the convergent portion of the annular wall (220, 620) to increase the ratio of the conic exit radius (CER) to the fuel exit radius (FER).
12. The method according to claim 10 or claim 11, wherein the step of modifying a dimension of the annular wall (220, 620) comprises adjusting an angle of the convergent portion of the annular wall (220, 620) to increase the ratio of the conic exit radius (CER) to the fuel exit radius (FER).
13. The method according to any of claims 10-12, wherein the dimension is modified to increase the ratio of the conic exit radius (CER) to the fuel exit radius (FER) to within the range of 1.5-3.0.
14. The method according to any of claims 10 to 13, wherein the fuel spray nozzle (300, 400, 500) comprises two annular outer air swirler passages (208, 210) separated by the annular wall (220).