Patent Description:
Afterburners are a known means of providing a large and rapid increase in the amount of thrust produced by a gas turbine engine. Due to their relative fuel inefficiency compared to normal operation of the gas turbine engine, they are usually used in circumstances where a short-term increase in thrust is required to achieve a particular objective (e.g. launch of an aircraft from a short runway, catapult-assisted launch of an aircraft from the deck of an aircraft carrier, evasive manoeuvring of an aircraft during combat, etc.).

<CIT> discloses a reheat device for a turbo-jet engine comprising a fuel manifold to be supplied with fuel through an altitude-responsive control, a flame stabilizer downstream of the manifold, and means for supplying a predetermined additional rate of flow of fuel and oxygen to the interior of the stabilizer at and above a predetermined altitude. The altitude-responsive control being operative to reduce to zero the flow of fuel to the fuel manifold at the predetermined maximum operating altitude. The flame stabilizer comprises an annular casing supported by struts of aerofoil cross-section. The casing is flared at its open down-stream end, and fuel and oxygen are supplied to its interior at its closed upstream end by nozzles fed through passages within the struts. The axial spacing of the fuel manifold is such that fuel from the manifold is at least partly vaporized by the time it reaches the stable flame zone at the downstream end of the stabilizer casing. The fuel supply to manifold is controlled by the altitude responsiye control to decrease progressively with increase in altitude until at maximum altitude all the reheating is effected by the fuel and oxygen supplied to the stabilizer; at low altitudes.

<CIT> discloses a thrust augmentor heat shield for enclosing radially extending fuel pipes which can be attached to and removed from the outer duct wall from within the augmentor. The heat shield includes a hollow, elongate housing extending substantially entirely along the length of the fuel pipe, a nose projecting forwardly from the housing and received within a slot formed in the duct wall and a bolt for clamping the housing to the duct wall and urging the nose of the housing into the slot. The housing includes an opening between the outer duct wall and the diffuser wall for conveying cooling air radially inwardly along the housing, and openings along lateral sides of the housing in registry with the fuel discharge ports of the fuel tube. The housing includes a diffuser flow path segment such that, when the housings are arranged in a spoke pattern, the segments form a continuous annular wall joined by splined connections.

<CIT> discloses a bypass augmentation burner and strut arrangement for a gas turbine engine of the bypass type wherein the struts are located downstream of the bypass burner and receive impingement of a cooling airflow directly from a plurality of cold chutes interleaved between a plurality of hot chutes about the convoluted trailing edge of the bypass burner.

In accordance with a first aspect of the disclosure there is provided an afterburner arrangement comprising:.

characterised in that a fuel pathway of the plurality of fuel pathways extends through the internal casing to a respective fuel nozzle attached to the internal casing and configured to discharge fuel radially inward of the internal casing, and a fuel nozzle of the plurality of fuel nozzles is fixedly attached to the mounting strut at a location radially between the internal and external casings.

The mounting strut provides a mechanical connection between the internal and external casings, restricting movement of the internal casing relative to the external casing in upstream and downstream directions of the bypass pathway, while performing the additional function of partly housing a fuel pathway for the fuel nozzle. In previously considered arrangements the fuel supply to the nozzle was carried out by a separate feed line affixed to the internal or external casing. The present disclosure therefore enables the construction of an afterburner arrangement with fewer components than was previously achievable.

In some examples, each and every mounting strut between the internal casing and the external casing is associated with at least one fuel nozzle and at least partly houses a fuel pathway to provide fuel to the fuel nozzle.

Previously, nozzles projecting through an opening in the fuel casing were supplied with fuel via a manifold located within the bypass pathway. Locating a manifold in this position obstructs airflow through the bypass path, which can cause undesirable pressure variations within the bypass pathway. The present disclosure removes the need for a manifold within the bypass pathway by supplying fuel through the mounting strut.

In some examples, a fuel nozzle of the plurality is fixedly attached to the mounting strut. In previously considered afterburner arrangements nozzles are either attached to the internal or external casing, or are attached to a fuel feed line which is attached to the internal or external casing. The present disclosure allows the mounting strut to provide a further function of directly supporting a fuel nozzle configured to spray fuel into the bypass pathway.

In some examples, a fuel nozzle of the plurality is attached to the internal casing at a location spaced apart from a structural attachment point between the mounting strut and the internal casing, and the afterburner arrangement further comprises a fuel feed line at least partly defining the fuel pathway and extending between the mounting strut and the respective fuel nozzle (i.e. the fuel nozzle associated with the respective fuel pathway). Previously, nozzles attached to the internal casing were supplied with fuel by a fuel line extending through the external casing. The present disclosure provides an afterburner arrangement with fewer holes cut in the external casing, as the fuel feed line utilises a hole which is already present to house the mounting strut.

In some examples, the fuel feed line is fixedly attached to the mounting strut.

In some examples, the mounting strut is fixedly attached to the internal casing. This can be through the use of removable fasteners, or it can be a permanent attachment (e.g. a welded connection).

In some examples, the external casing comprises an inner surface exposed to the bypass pathway and an outer surface opposed to the inner surface, and the mounting strut passes through a hole in the external casing from the inner surface to the outer surface. The present disclosure enables a novel build order for the afterburner components. Previously, the mounting strut and feed lines for the fuel nozzles were all attached from the external surface of the outer casing.

In some examples, the mounting strut and the hole in the external casing are configured so that the mounting strut can only be received in the hole from an inner side of the external casing. In other words, a radially inner portion of the mounting strut is configured so that it cannot pass through the hole in the external casing. This enables the strut to move up and down within the hole, which in turn enables the absorption of vibrations of the internal and external casings which are experienced during operation of the afterburner arrangement due to rapid airflow through the bypass pathway. The sliding up / down movement also allows the arrangement to accommodate relative movement between the internal casing and the external casing due to thermal expansion. In operation, the external casing remains relatively cold while the internal casing becomes relatively hot.

In some examples, the bypass pathway has a first, upstream end and a second, downstream end opposite the upstream end, and a portion of the mounting strut which at least partly houses the fuel pathway extends upstream or downstream of the hole in the external casing such that the portion of the mounting strut has a cross-section larger than a cross-section of the hole in the external casing. This is enabled by the novel build method in which the mounting strut is inserted into a hole in the external casing from within the bypass pathway. Previously, the upstream and downstream extent of the mounting strut was limited by the size of the hole.

In some examples, a fuel pathway of the plurality is configured to convey fuel from an external side of the external casing, through a portion of the mounting strut and out of the mounting strut within the bypass pathway. This allows fuel to be provided from a fuel source on an outer surface of the external casing to a fuel nozzle within the bypass pathway or attached to the internal casing, without creating an additional hole in the external casing to house a fuel feed line.

The respective pluralities of fuel pathways and fuel nozzles may comprise at least:.

In some examples, the mounting strut comprises a distribution block, wherein there are at least two fuel pathways each comprising a borehole in the distribution block. The provision of a distribution block as the mounting strut enables the fuel pathways to be simply drilled into the block, which is a quick and cost-effective method of fabrication.

In some examples, the mounting strut is one of a plurality of mounting struts circumferentially distributed around the afterburner arrangement, each having one or more associated fuel nozzles and fuel pathways at least partly housed in the respective strut.

In some examples, the afterburner arrangement further comprises a manifold configured to provide fuel to at least some of the fuel pathways associated with different mounting struts, wherein the manifold is disposed radially outside of the bypass pathway and each one of the respective fuel pathways is configured to convey the fuel through a wall of the external casing defining the bypass pathway. In some previously considered arrangements, manifolds were placed within the bypass pathway (e.g. to supply nozzles projecting through an opening in the internal casing). The present disclosure enables all manifolds to be located on an external side of the external casing, which reduces the number of obstructions within the bypass pathway.

In accordance with a second aspect of the disclosure there is provided a gas turbine engine comprising an afterburner arrangement according to the first aspect.

In accordance with a third aspect of the disclosure there is provided a method of assembling an afterburner arrangement, the method comprising:.

In accordance with a non claimed fourth aspect there is provided an afterburner arrangement which differs from afterburner arrangements in accordance with the first aspect above by having a fuel nozzle associated with the mounting strut (as opposed to a plurality of such fuel nozzles), and a corresponding fuel pathway at least partly housed in the mounting strut (as opposed to a plurality of such fuel pathways). Advantages of such an arrangement include that the fuel nozzle may be spaced apart from a structural attachment point between the mounting strut and the internal casing, without necessitating a fuel pathway entirely separate from the mounting strut that requires passage through and/or mounting in the external casing separate from the mounting strut.

A gas turbine engine <NUM> is shown in <FIG> and comprises an air intake <NUM> and a propulsive fan <NUM> that generates two airflows A and B. The gas turbine engine <NUM> comprises, in axial flow A, an intermediate pressure compressor <NUM>, a high-pressure compressor <NUM>, a combustor <NUM>, a high pressure turbine <NUM>, an intermediate pressure turbine <NUM>, a low pressure turbine <NUM> and an exhaust nozzle <NUM>. An external casing <NUM> surrounds the gas turbine engine <NUM> and defines, in axial flow B, a bypass <NUM>. The radially inner extent of the bypass <NUM> is defined by an annular internal casing <NUM>. The internal casing <NUM> defines at least two exemplary fire zones, zone z2 and zone z3, that are axially separated by a barrier wall <NUM>. Downstream of the barrier wall <NUM> there is an array of ventilation inlets <NUM> that are equi-angularly spaced around at least a portion of the circumference of the annular inner wall <NUM> to permit air to flow from the bypass <NUM> into fire zone z3 to ventilate and purge it.

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. two) 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.

<FIG> schematically shows a side cross-sectional view of a gas turbine engine <NUM> including a previously considered afterburner arrangement <NUM>. The afterburner arrangement <NUM> comprises an internal casing <NUM> radially within an external casing <NUM>, which define a bypass pathway <NUM> between them. Further components of the afterburner arrangement <NUM> are located within the bypass pathway <NUM>, and these can be seen in more detail in <FIG>.

<FIG> schematically shows a cross-sectional view of a portion of the previously considered afterburner arrangement shown in <FIG>, and like reference numerals are retained as appropriate. The cross-sectional view is in a plane normal to the engine centreline. In this view it can be seen that a mounting strut <NUM> extends from the internal casing <NUM> to the external casing <NUM>, forming a structural connection therebetween. Also visible in this view are a first fuel nozzle <NUM>, a second fuel nozzle <NUM> and a third fuel nozzle <NUM>. The first fuel nozzle <NUM> is configured to spray fuel into a volume adjacent of the internal casing. The second fuel nozzle <NUM> and the third fuel nozzle <NUM> are configured to spray fuel into a volume rearward of the internal casing <NUM>. The first, second and third nozzles receive fuel from respective fuel feed lines, as will be described in more detail with reference to <FIG>. While only a limited angular portion of the afterburner arrangement is shown in <FIG>, the same configuration of fuel nozzles is replicated at various circumferential locations around the annulus between the internal casing <NUM> and the external casing <NUM>.

The shaded area in <FIG> represents the cross-sectional area through which substantially undisturbed air flow may pass through the bypass pathway <NUM> - i.e. airflow which is relatively unobstructed by obstacles in the bypass pathway. It is desirable to maximize the cross-sectional area for undisturbed air flow. Obstructions in the bypass pathway <NUM> that obstruct air flow may cause pressure loss within the bypass pathway <NUM> that may reduce the efficiency of the operation of the gas turbine engine <NUM>, or may generate an undesirable flow behaviour. It can be seen in <FIG> that the mounting strut <NUM> represents an obstruction in the bypass pathway <NUM>. A manifold <NUM> surrounds the internal casing <NUM>. The manifold <NUM> distributes fuel to the plurality of second fuel nozzles <NUM> arranged around the internal casing <NUM>. The manifold <NUM> presents an obstruction in the bypass pathway <NUM>.

<FIG> schematically shows a detailed side cross-sectional view of the previously considered afterburner arrangement <NUM> shown in <FIG>, and like reference numerals are retained as appropriate.

The afterburner arrangement <NUM> comprises a first fuel feed line <NUM>. The first fuel feed line <NUM> extends from a first end on an outer surface of the external casing <NUM> (i.e. on the side of the external casing <NUM> opposite to the bypass pathway <NUM>), through a flanged connector in the external casing <NUM>, to a second end comprising a flanged connection with the internal casing <NUM>. The first fuel feed line <NUM> is configured to receive fuel at its first end from a first manifold <NUM> that extends circumferentially about an outer surface of the external casing <NUM>. The second end of the first fuel feed line <NUM> is aligned with a hole in the internal casing <NUM>, and the first fuel feed line <NUM> is configured to supply fuel to a first fuel nozzle through this hole. The first fuel feed line <NUM> does not form a structural connection between the internal casing and the external casing.

As shown in <FIG>, the mounting strut <NUM> comprises a mount <NUM> on the internal casing <NUM>, and a strut <NUM> fixedly attached to and extending from the external casing <NUM> towards the mount <NUM>. The mount <NUM> is received in an opening of the strut <NUM>. The strut <NUM> is fixed to the external casing <NUM> through a flanged connector. The mount <NUM> and the strut <NUM> interact at a sliding interface <NUM>. The interface <NUM> prevents movement of the mount <NUM> with respect to the strut <NUM> in the upstream and downstream directions of the bypass pathway <NUM>, which in turn prevents relative movement of the internal casing <NUM> with respect to the external casing <NUM> in the upstream and downstream directions of the bypass pathway <NUM>. However, the interface <NUM> permits relative movement of the mount <NUM> towards and away from the strut <NUM> (i.e. radially, in this example), which in turns permits relative movement of the internal casing <NUM> towards and away from the external casing <NUM>. During operation of the afterburner arrangement <NUM>, pressure variations in the bypass pathway and differential thermal expansion of components may cause the internal casing <NUM> to move towards and away from the external casing <NUM>. If these movements are not absorbed by the mounting strut <NUM> they can cause premature wear or structural damage to components of the afterburner arrangement <NUM>.

The afterburner arrangement <NUM> further comprises a second fuel feed line <NUM>. The second fuel feed line <NUM> extends from a first end outside the external casing <NUM> through a flanged connector in the external casing <NUM>, to a second end comprising a flanged connection with the internal casing <NUM>. The second fuel feed line <NUM> is configured to receive fuel at its first end and to supply fuel at its second end to a second manifold <NUM> that extends circumferentially about a radially-outer surface of the internal casing <NUM> (i.e. the surface of the internal casing <NUM> that is exposed to the bypass pathway <NUM>, or the "gas-washed" surface). The second end of the second fuel feed line <NUM> is also configured to supply fuel to the second fuel nozzle <NUM>. The second fuel feed line <NUM> does not form a structural connection between the internal casing and the external casing.

The afterburner arrangement further comprises a third fuel feed line <NUM>. The third fuel feed line <NUM> extends from a first end outside the external casing <NUM>, through a flanged connector in the external casing <NUM>, to a second end comprising the third fuel nozzle <NUM>. The third fuel feed line <NUM> is configured to receive fuel at its first end from a third manifold <NUM> that extends circumferentially about an outer surface of the external casing <NUM>. Fuel is discharged from the third fuel nozzle <NUM> into the bypass pathway <NUM>.

While the mounting strut <NUM> is configured to absorb relative movement of the internal casing <NUM> with respect to the external casing <NUM> as may occur in use in a gas turbine engine, the first and second fuel feed lines <NUM>, <NUM> are not configured to absorb such relative movement. In particular, the internal casing <NUM> heats up during use, and expands both radially outward and axially outward (upstream and downstream) from the mounting strut <NUM>, while the relatively cold external casing <NUM> does not expand to the same extent. This may cause the feed lines <NUM>, <NUM> to bend, leading to potential failure of the feed lines.

The present disclosure aims to provide an improved afterburner arrangement.

<FIG> schematically shows a side cross-sectional view of a gas turbine engine <NUM> incorporating an afterburner arrangement <NUM> according to an embodiment of the disclosure. As in the above described afterburner arrangement of <FIG>, the afterburner arrangement <NUM> comprises an inner casing <NUM> and an outer casing <NUM> defining a bypass pathway <NUM> therebetween.

<FIG> schematically shows a view of a cross-sectional view of the afterburner arrangement <NUM> shown in <FIG>. The example afterburner arrangement <NUM> comprises a mounting strut <NUM> that (at least partly) houses fuel pathways for a first fuel nozzle <NUM>, a second fuel nozzle <NUM> and a third fuel nozzle <NUM>, although in other examples there may be fewer (for example one) or more nozzles and fuel pathways.

A comparison of <FIG> with <FIG> shows that the mounting strut <NUM> presents less of an obstacle to the airflow in the bypass pathway <NUM> compared to the mounting strut <NUM> and flow lines <NUM>, <NUM> in the above described afterburner arrangement <NUM>. This is partly because the mounting strut <NUM> is circumferentially aligned with the second fuel nozzle <NUM> and the third fuel nozzle <NUM>. This is enabled by the mounting strut <NUM> partly housing fuel pathways for the at least the first, and also the second and third fuel nozzles. The obstruction is also at least partly reduced by virtue of there being no manifold within the bypass flow. The obstruction is also at least partly reduced because the fuel pathway extending from the strut to the first fuel nozzle <NUM> at the internal casing departs from the strut at a location proximal to the internal casing (whereas a comparable flow line in the example described above would extend fully from the external casing to the internal casing).

In previously considered afterburner arrangements, the crowding of the flanges of the flanged connectors for each of the first, second and third fuel feed lines, and the flange of the mounting strut itself, on the exterior surface of the external casing would not permit circumferential alignment of the mounting strut with the second and third fuel nozzles. By incorporating the fuel feed lines into the mounting strut, fewer flanged connectors are necessary, which gives a larger degree of design freedom in the circumferential placement of the mounting strut. It also means that there is a lower axial space claim on the external casing to provide for the structural connection to the internal casing, and the provision of fuel flow pathways to the various nozzles.

<FIG> schematically shows a detailed view of the example afterburner arrangement <NUM> shown in <FIG>, and like reference numerals are retained as appropriate. The afterburner arrangement <NUM> comprises an internal casing <NUM> and an external casing <NUM> forming a bypass pathway <NUM> therebetween as described above. The bypass pathway <NUM> has a first, upstream end (the left side in <FIG>) and a second, downstream end opposing the first end (the right side in <FIG>). A mounting strut <NUM> is fixedly attached to the internal casing <NUM> at a structural attachment point <NUM> and has an outer end which is received in a hole in the external casing <NUM>. In this example, the outer end is configured to slide with respect to the hole.

The mounting strut <NUM> partly houses a first fuel pathway <NUM>. The first fuel pathway <NUM> runs from a first end on an outer surface of the external casing <NUM>, through the mounting strut <NUM>, to a second end comprising a flanged connection with the internal casing <NUM> which is spaced apart from the structural attachment point <NUM>. The first end of the first fuel pathway <NUM> is configured to receive fuel from a first manifold <NUM>, which extends circumferentially around the outer surface of the external casing <NUM>. Part of the first fuel pathway <NUM> is defined by a fuel feed line that extends from a side of the mounting strut <NUM> (in this example, a side facing the upstream end of the bypass pathway) to the second end of the first fuel pathway <NUM> where it interfaces with the internal casing. The fuel feed line departs from a portion of the strut which is proximal to the internal casing, for example in the inner half of the strut, the inner third or the inner quarter of the strut. This may minimise obstruction of the bypass flow. Whilst the fuel feed line attached to the internal casing at a position spaced apart from the structural attachment point, stress on the fuel line in response to relative movement between the internal and external casing may be reduced as compared to an arrangement as described above with respect to <FIG> in which there is a separate strut and feed line, since there is a single attachment point at the external casing, and the spaced-apart attachment points at the internal casing would be at similar temperature to each other and close together, such that there would be minimal relative movement between them owing to thermal expansion.

In the embodiment shown the fuel feed line is a separate component from the strut that is welded to the side of the mounting strut <NUM>. However, in other embodiments the fuel feed line may be integrally formed with the mounting strut <NUM>, or with a portion of a feed line extending within the strut, or it may be detachably attached to the strut or a fuel pathway within the strut. The second end of the first fuel pathway <NUM> is aligned with a hole in the internal casing <NUM>, and the first fuel pathway <NUM> is configured to supply fuel to the first fuel nozzle <NUM> through this hole.

The mounting strut <NUM> partly houses a second fuel pathway <NUM>. The second fuel pathway <NUM> runs from a first end on an outer surface of the external casing <NUM>, through the mounting strut <NUM>, out of a side of the mounting strut <NUM> facing the downstream end of the bypass pathway <NUM> to a second end comprising the second fuel nozzle <NUM>. The first end of the second fuel pathway <NUM> is configured to receive fuel from a second manifold <NUM>, which extends circumferentially around the outer surface of the external casing <NUM>. The second fuel nozzle projects through a hole in the internal casing <NUM>, and in this example, there is no coupling between the second fuel pathway <NUM> and the internal casing in the vicinity of the hole. In the embodiment shown, the second fuel nozzle <NUM> is a separate component that is welded to the side of the mounting strut <NUM>. However, in other embodiments the second fuel nozzle <NUM> may be integrally formed with the mounting strut <NUM>, or with a portion of a feed line extending within the strut.

The mounting strut <NUM> partly houses a third fuel pathway <NUM>. The third fuel pathway <NUM> runs from a first end on an outer surface of the external casing <NUM>, through the mounting strut <NUM>, to a second end comprising the third fuel nozzle <NUM>. The first end of the third fuel pathway <NUM> is configured to receive fuel from a third manifold <NUM>, which extends circumferentially around the outer surface of the external casing <NUM>. In the embodiment shown the third fuel nozzle <NUM> is a separate component that is welded to the side of the mounting strut <NUM>. However, in other embodiments the third fuel nozzle <NUM> may be integrally formed with the mounting strut <NUM>.

As shown, each of the fuel pathways <NUM>, <NUM>, <NUM> extend through the outer end of the mounting strut <NUM> which is configured to form a structural connection with the external casing, such that there are no fuel line connections in the external casing which are not associated with the mounting strut <NUM>. This both reduces the space claim for the structural and fuel connections at the external casing, and reduces the number of independent connections between the internal and external casing (i.e. locally reducing the number of such connections to one) so as to avoid imparting stress into such connections and the casings when the internal casing thermally expands relative to the external casing.

<FIG> schematically shows a view of a mounting strut <NUM> for use in the present disclosure. It can be seen that mounting strut <NUM> comprises a distribution block <NUM>, i.e. a block of material at least partly forming the strut, with boreholes drilled into the block to provide first, second and third fuel pathways through the block. In this example, the distribution block <NUM> shown in <FIG> has had three vertical boreholes drilled into it from above to form the respective first ends of the first, second and third fuel pathways <NUM>, <NUM>, <NUM>.

A substantially horizontal borehole (i.e. parallel with the engine centreline) has been drilled into a first side of the distribution block <NUM> (i.e. the side of the distribution block <NUM> facing the upstream end of the bypass pathway in use) to provide an exit for the first fuel pathway <NUM> from the first side of the distribution block <NUM>.

A further horizontal borehole has been drilled into a second side of the distribution block <NUM> (i.e. the side of the distribution block <NUM> facing the downstream end of the bypass pathway in use) to provide an exit for the third fuel pathway <NUM> from the second side of the distribution block <NUM>.

A borehole angled at approximately <NUM>° has been drilled into the second side of the distribution block <NUM> to provide an exit for the second fuel pathway <NUM>.

As shown, a fuel feed line has been welded to the distribution block <NUM> at the point at which the first fuel pathway <NUM> exits the first side of the distribution block <NUM>. The second fuel nozzle <NUM> has been welded to the distribution block <NUM> at the point at which the second fuel pathway <NUM> exits the distribution block <NUM>. The third fuel nozzle <NUM> has been welded to the distribution block <NUM> at the point at which the third fuel pathway exits the distribution block <NUM>. However, some or all of these components could be formed integrally with the distribution block <NUM>. The distribution block <NUM> could be formed by any suitable manufacturing process, e.g. casting, moulding, 3D printing, additive manufacture, etc..

<FIG> schematically show stages of a method of assembling an afterburner arrangement according to an embodiment of the disclosure.

In <FIG> a mounting strut <NUM> as described above with respect to <FIG> has been inserted through a hole in the external casing <NUM> in the direction of arrow P. The mounting strut <NUM> interacts with the external casing <NUM> via a sliding interface <NUM>. In <FIG> it can be seen that installing the mounting strut <NUM> in the external casing <NUM> from the inner surface (i.e. the surface that will face the bypass pathway when the afterburner arrangement is fully assembled) allows the mounting strut <NUM> to comprise parts that project upstream or downstream of the hole in the external casing (see dimensions labelled x in <FIG>). This was not possible in previously considered assembly techniques in which the mounting strut was installed from an outer surface of the external casing <NUM>.

In <FIG> an internal casing <NUM> has been inserted in the external casing <NUM> in the direction of arrow Q. As can be seen, the internal casing <NUM> has been inserted until a hole in the internal casing <NUM> aligns with the second end of the first fuel pathway through the mounting strut <NUM>. In this position, a mounting point in the internal casing <NUM> aligns with an attachment point of the mounting strut <NUM>. In other examples there may be no separate mounting of a fuel pathway to the internal casing, and the alignment may only be at the structural attachment point of the internal casing.

In <FIG> the mounting point of the internal casing <NUM> has been attached to the attachment point of the mounting strut <NUM> by inserting fasteners <NUM>, <NUM> through the attachment point of the internal casing <NUM> and into the mounting point of the mounting strut <NUM>. In the embodiment shown the fasteners <NUM>, <NUM> are removable so that the afterburner assembly can be disassembled if required. However, in some embodiments the internal casing <NUM> may be permanently affixed to the mounting strut <NUM>, e.g. by welding the two components together. While in the embodiment shown the mounting strut <NUM> is attached to the internal casing <NUM> on the part facing the external casing <NUM>, it could be attached to the internal casing <NUM> at any point, e.g. the axially rearward part of the internal casing <NUM> that is substantially perpendicular to the external casing <NUM>.

While specific embodiments of the disclosure have been described above for the purposes of illustration it will be appreciated that the disclosure is not so limited, and various alternatives and modifications will be apparent to a person skilled in the art without departing from the scope of the disclosure.

For example, while in <FIG> the internal casing <NUM> is inserted into the external casing <NUM> in a single direction as one piece, the internal casing <NUM> could alternatively comprise two parts inserted from opposite directions and subsequently joined together.

Claim 1:
An afterburner arrangement (<NUM>) comprising:
an internal casing (<NUM>) and an external casing (<NUM>) defining a bypass pathway (<NUM>) between them;
a mounting strut (<NUM>) forming a structural connection between the internal casing and the external casing; and
a plurality of fuel nozzles (<NUM>/<NUM>/<NUM>) associated with the mounting strut,
wherein the mounting strut at least partly houses a corresponding plurality of fuel pathways (<NUM>/<NUM>/<NUM>) to provide fuel to the respective fuel nozzles,
characterised in that a fuel pathway of the plurality of fuel pathways extends through the internal casing (<NUM>) to a respective fuel nozzle (<NUM>) attached to the internal casing (<NUM>) and configured to discharge fuel radially inward of the internal casing (<NUM>), and a fuel nozzle (<NUM>/<NUM>) of the plurality of fuel nozzles is fixedly attached to the mounting strut (<NUM>) at a location radially between the internal and external casings (<NUM>/<NUM>).