FUEL INJECTOR

Abstract

A fuel injection system for a gas turbine engine comprises; a pilot fuel injector section and a main airblast fuel injector section, the main airblast fuel injector section having an aft end facing a combustion chamber. A surface of the injection system exposed to air flow through an injection system is non-axisymmetric or non-planar in a reference circumferential plane and/or is configured to generate controlled and varying acoustic impedance at or adjacent the aft end where, in use, the air flow collides with an oncoming acoustic wave.

Claims

1. A fuel injection system for a gas turbine engine comprising; a main airblast fuel injector section, the main airblast fuel injector section having an aft end facing a combustion chamber and wherein a surface exposed to air flow through the injection system is non-axisymmetric, or, non-planar in a reference circumferential plane, the exposed surface is an annular wall of an air swirler and comprises an annular array of swirl vanes that are not symmetrical positioned around a circumference of the annular wall, and configured to generate acoustic impedance at or adjacent the aft end where, in use, the air flow collides with an oncoming acoustic wave.

2. The fuel injection system as claimed in claim 1 wherein the annular wall is extended axially along part of its circumference.

3. The fuel injection system as claimed in claim 1 wherein the annular array of swirl vanes are not symmetrical positioned around the circumference of the annular wall because the annular array of swirl vanes includes an axial step.

4. The fuel injection system as claimed in claim 1 wherein the annular array of swirl vanes are not symmetrical positioned around the circumference of the annular wall because the annular array of swirl vanes include a first plurality of vanes with a first length, pitch and thickness and a second plurality of vanes having a second length, pitch and thickness, the first length being shorter than the second length, the first pitch being smaller than the second pitch and the first thickness being greater than the second thickness.

5. The fuel injection system as claimed in claim 4 wherein the first plurality and second plurality are divided into groups, groups of the first plurality being interspersed between groups of the second plurality around a common circumference.

6. The fuel injection system as claimed in claim 1 wherein the annular array of swirl vanes are not symmetrical positioned around the circumference of the annular wall because the annular array of swirl vanes include groups of similarly configured vanes arranged with varying pitches around a common circumference.

7. The fuel injection system as claimed in claim 6 wherein the vanes have an elongated chord configured to conserve swirl.

8. The fuel injection system as claimed in claim 1 wherein the exposed surface includes an annular array of pre-swirl vanes on the annular wall that includes a plurality of grouped vanes of similar configuration arranged along a circumferential reference plane, each group arranged at an angle to the reference plane.

9. The fuel injection system as claimed in claim 8 wherein each pre-swirl vane is extended to meet the circumferential reference plane.

10. The fuel injection system as claimed in claim 1 wherein the annular wall is provided with a radial step.

11. The fuel injection system as claimed in claim 1 comprising an annular array of main airblast fuel injector sections wherein at least a proportion of the main airblast fuel injector sections are adapted such that a surface exposed to air flow through the injection system is non-axisymmetric, or, non-planar in a reference circumferential plane, and configured to generate acoustic impedance at or adjacent the aft end where, in use, the air flow collides with an oncoming acoustic wave.

12. A gas turbine engine incorporating the fuel injection system configured according to claim 11.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0024] FIG. 1 is a sectional side view of a gas turbine engine;

[0025] FIG. 2 is a section through a fuel injection system as is known in the prior art;

[0026] FIG. 3 is a schematic plan view of a wall of an air swirler in the fuel injection system of FIG. 2.

[0027] FIG. 3 is a schematic plan view of a wall of an air swirler adapted in accordance with an embodiment of the invention;

[0028] FIG. 4 is a schematic plan view of a wall of an air swirler adapted in accordance with another embodiment of the invention;

[0029] FIG. 5 is a schematic plan view of a wall of an air swirler adapted in accordance with another embodiment of the invention;

[0030] FIG. 6 is a schematic plan view of a wall of an air swirler adapted in accordance with an embodiment of the invention;

[0031] FIG. 7 is a schematic plan view of a wall of an air swirler adapted in accordance with another embodiment of the invention;

[0032] FIG. 8 is a schematic plan view of a wall of an air swirler in the fuel injection system of FIG. 2 showing the pre-swirler vane geometry;

[0033] FIG. 9 is a schematic plan view of a wall of an air swirler adapted in accordance with another embodiment of the invention;

[0034] FIG. 10 is a schematic plan view of a wall of an air swirler adapted in accordance with another embodiment of the invention;

[0035] FIG. 11 is schematic end view of a section of an axial tip of the prefilmer adapted in accordance with another embodiment of the invention;

[0036] FIG. 12 is schematic end view of a section of an axial tip of the prefilmer adapted in accordance with another embodiment of the invention;

[0037] FIG. 13 is schematic end view of a section of an axial tip of the prefilmer adapted in accordance with another embodiment of the invention;

[0038] FIG. 14 is a schematic view showing examples of profiling of a prefilming surface in an axial direction in accordance with embodiments of the invention; and

[0039] FIG. 15 is a schematic end view showing an annular array of main airblast fuel injectors arranged in a combustor of a gas turbine engine.

DETAILED DESCRIPTION OF DRAWINGS AND EMBODIMENTS

[0040] With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, a low-pressure turbine 17 and an exhaust nozzle 18. A nacelle 20 generally surrounds the engine 10 and defines the intake 12.

[0041] The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the high-pressure compressor 14 and a second air flow which passes through a bypass duct 21 to provide propulsive thrust. The high-pressure compressor 14 compresses the air flow directed into it before delivering that air to the combustion equipment 15.

[0042] In the combustion equipment 15 the air flow is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high and low-pressure turbines 16, 17 before being exhausted through the nozzle 18 to provide additional propulsive thrust. The high 16 and low 17 pressure turbines drive respectively the high pressure compressor 14 and the fan 13, each by suitable interconnecting shaft.

[0043] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. three) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

[0044] FIG. 2 shows in more detail a fuel injection system of a type known to be used in the combustion equipment 15 of a gas turbine engine 10. As can be seen a pilot fuel injector 22 is arranged on an axis with annular components coaxially arranged around it. Radially adjacent the pilot fuel injector 22 is a pilot air swirler 23. A separator 24 bounds the pilot air swirler and further serves as a radially inner wall to a radially outboard main fuel air swirler having radially outer wall 25 and vanes 26 which extend between walls 24 and 25. Radially outboard of the main fuel air swirler is an annular main airblast fuel injector 27. Fuel injected from the main airblast fuel injector 27 spreads along prefilmer surface 28 and is atomised at the axial tip of the prefilmer 29 through interaction with air exiting the main fuel air swirler. The atomised air/fuel mixture is delivered to the combustion chamber 30.

[0045] FIG. 3 shows a schematic view of a circumferential wall 25 of the main fuel air swirler and illustrates the arrangement of the vanes thereon.

[0046] FIG. 4 shows an air swirler passage wall in accordance with a first embodiment of the invention. In comparison to the air swirler of FIGS. 2 and 3, the wall 35 is made relatively longer in an axial dimension by a length d for part of the circumference. The vanes 36 are substantially the same and similarly arranged as the vanes of FIG. 3 to provide nominally similar levels of swirl but different local impedances.

[0047] FIG. 5 shows an air swirler wall in accordance with a second embodiment of the invention. In comparison to the air swirler of FIGS. 2 and 3, the passage wall 45 is made relatively longer in an axial dimension by a length d along the entire circumference. The vanes 46 are substantially the same configuration as those of FIG. 3 but are arranged in an axially stepped configuration to provide nominally similar levels of swirl but different local impedances.

[0048] FIG. 6 shows an air swirler passage wall in accordance with a third embodiment of the invention. In comparison to the air swirler of FIGS. 2 and 3, the wall 55 is made relatively longer in an axial dimension by a length d along the entire circumference. There are two groups of vanes 56 and 57. The vanes 56 are individually substantially the same configuration as those of FIG. 3 and are similarly arranged. Vanes 57 of the second group are longer and spaced further apart to provide nominally similar levels of swirl but different local impedances.

[0049] FIG. 7 shows an air swirler wall in accordance with a fourth embodiment of the invention. In comparison to the air swirler of FIGS. 2 and 3, the wall 65 is made relatively longer in an axial dimension along the entire circumference. The vanes 66 are consistent in length but are arranged at varying separations e, f, g around the circumference.

[0050] FIG. 8 shows an air swirler wall known to be used in a fuel injection system such as that in FIG. 1. This figure shows in more detail the shape of pre-swirl vanes 70 which would sit axially upstream of the vanes already discussed. The figure provides a comparison for a fifth embodiment of the invention also shown in FIG. 8. In the embodiment, vanes 76 individually have a similar configuration to those of the prior art arrangement but are grouped and each group is inclined at an angle X to a reference circumferential plane 77.

[0051] FIG. 9 shows a sixth embodiment of the invention which is broadly similar to the fifth embodiment of FIG. 8. However, in this embodiment the vanes 86 are extended back to the reference circumferential plane 87. It will be appreciated that greater inertia will be effected on the air flow in passage 88 than in passage 89.

[0052] FIG. 10 shows a seventh embodiment of the invention wherein the circumferential wall 95 of an air swirler with a radial dimension r is radially stepped to provide two regions 97 and 98 of different radial dimensions R.sub.1 and R.sub.2.

[0053] FIGS. 11, 12 and 13 show eighth, ninth and tenth embodiments of the invention. In each of these embodiments, the axially downstream facing end of the prefilmer (tip) 29 has been profiled. In FIG. 11, axially extending undulations 101 are provided. In FIG. 12, axially extending serrations are provided. In FIG. 13, an axially extending notch 103 is provided. FIG. 14 shows cross section views of the prefilmer surface of four pre-filmers which are suited to use in the present invention. Prefilmer surface 141 has a continuous radius along its length. Prefilmer surface 142 has a scarfed surface with a radius gradually increasing towards the downstream end. Prefilmer surface 143 has a concave surface, the radius varying across the surface. Prefilmer surface 144 has an undulating surface, the radius varying across the surface. A combination of the described features can be implemented around the annulus to reduce coherence and the associated acoustic waves.

[0054] In some embodiments of injection fuel systems in accordance with the present invention, multiple main airblast fuel injector sections are arranged in an annular array as shown in FIG. 15. Alternate main airblast fuel injector sections 150 are adapted in accordance with one or more of the previously described embodiments. Other main airblast fuel injector sections have a prior art configuration.

[0055] 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.