Patent Application
20180195727
This application is based upon and claims the benefit of priority from British Patent Application No. 1700465.6 filed 11 Jan. 2017, the entire contents of which are incorporated herein.
The present disclosure concerns fuel injectors used for providing fuel to the combustion chamber of a gas turbine engine. More particularly, the fuel injector is of a jet-in-crossflow type.
In a gas turbine engine, fuel is mixed with air prior to delivery into a combustion chamber where the mixture is ignited. Arrangements for mixing the fuel and air vary. In prefilming arrangements, fuel is formed in a film along a prefilmer surface adjacent to a nozzle. Pressurised, turbulent air streams are directed against the prefilmer surface and serve to shear fuel from the surface and mix the sheared fuel into the turbulent air streams. In vaporiser designs fuel is forced through a small orifice into a more cavernous air filled chamber. The sudden pressure drop and acceleration of the fuel flow upon entering the chamber disperses the fuel into a spray. High temperatures subsequently vaporise the fuel. Turbulent air flows in the chamber again encourage mixing.
Both methods have associated advantages and disadvantages. Prefilming fuel injectors have highly complex and intricate designs that are expensive to manufacture. Design iterations are slow, due to complexity of the manufacturing process. Whilst relatively simple in design and generally cheaper in manufacture, vaporiser fuel injectors provide inferior fuel preparation when compared to prefilming fuel injectors thereby resulting in inferior engine performance.
Jet in crossflow is an air blast technique wherein the energy for atomisation is primarily provided by an airstream encountered by a fuel jet. The fuel is rapidly distributed over a range of radii, giving an opportunity for improved fuel/air mixing; and the mechanical design of the injector is simpler, permitting a reduction in manufacturing cost. A fuel passage is arranged centrally of an annular air swirler. Air flows generally from upstream to downstream in a direction substantially parallel with the fuel passage. The swirler imparts a spin on the air such that it spirals through the air swirler. One or more outlets of the fuel passage are arranged inclined to the flow direction of swirled air passing the outlet. The outlet is configured to deliver the fuel as a jet which crosses the swirled air flow. Walls of the swirler passages in the air swirler may be radially convergent in a manner which directs the exiting air flow towards the fuel passage outlet to encourage mixing of the fuel and air in the outlet chamber and minimise filming of fuel on walls of the air swirler. The radially convergent passages accelerate the air flow providing more kinetic energy to act upon the fuel and improve atomisation. The configuration ensures maximal atomisation of the fuel as it joins the relatively high velocity air stream.
In accordance with the present disclosure there is provided a fuel injector comprising;
at least one elongate fuel passage having an elongate axis extending from an upstream inlet end to a downstream outlet end;
one or more outlets at the outlet end, the outlet extending obliquely with respect to the elongate axis;
the elongate fuel passage defined by an inner skin of a double skinned pipe, the double skinned pipe defining a first annular cavity between the inner skin and an outer skin;
the inner skin and the outer skin meeting adjacent the one or more outlets to close an end of the first annular cavity;
a second annular cavity defined by an annular outer wall extending from downstream of the outlet end to a position upstream of the one or more outlets, the annular outer wall being convergent at a downstream end whereby to define an orifice centred nominally coincident with the elongate axis, the second annular cavity having a second annular cavity inlet at an upstream end and wherein the fuel passage outlets emerge at a radially outer surface of the annular outer wall.
The inner and outer skin may meet adjacently upstream of the one or more outlets.
In use, a stream of non-swirling air enters the second annular cavity inlet, passes over the fuel passage and exits at the orifice. The convergent end of the annular outer wall turns the annular air flow into a single jet of air.
Preferably the fuel passage has a plurality of outlets. The outlets are arranged obliquely with respect to the elongate axis and are directed radially outwards and in a downstream direction. The outlets may be inclined in a circumferential and/or axial direction. The plurality of outlets may be arranged in an annular array nominally centred on the elongate axis. The plurality of outlets may be equally spaced from each other. For example, the plurality of outlets may comprise 7 to 9 equally spaced outlets arranged in an annular array.
The annular outer wall may comprise an array of slots arranged to receive an array of fuel passage outlets. For example, the slots may extend in-line with the elongate axis. Alternatively, the annular outer wall may comprise an array of holes through which the outlets may be arranged to protrude. The annular outer wall may form part of an annular air swirler which surrounds the fuel passage.
Multiple fuel passages may be arranged, in use, to provide staged fuel staging within the injector.
A fuel passage may incorporate a nose section terminating adjacent the orifice of the annular outer wall. The nose section may extend downstream of the fuel passage outlets. The nose section may be convergent towards the downstream end. For example the nose portion is cone shaped. The end of the nose portion may be arranged slightly upstream of the orifice. The nose portion may have ribs arranged circumferentially between the outlets. These ribs may be configured to provide mechanical strength, or to allow manufacture via additive methods such as direct laser deposition.
In use, the fuel injector may be arranged nominally centrally of an annular air swirler to form a fuel spray nozzle. The annular air swirler may optionally be attached to the fuel injector, alternatively the air swirler is supported by a separate component such that it floats around the fuel injector. In such a configuration a spherical section may be incorporated into the outer surface of the injector where it interfaces with the air swirler or seal in order to accommodate axial and angular movement of the injector relative to the air swirler or seal.
Such a fuel spray nozzle may comprise a component of a gas turbine engine. Optionally the fuel spray nozzle is one of a plurality of fuel injectors in the gas turbine engine. A plurality of fuel spray nozzles may be arranged in an annular array around an engine axis of a gas turbine engine.
Some embodiments of the present disclosure will now be further described with reference to the accompanying Figures in which;
An annular air swirler 34 (shown in outline only) typically mounted to the combustor (not shown) sits around the injector 26. The injector 36 is joined to a double skinned fuel feed tube 35, 35a by welds W1 and W2.
In use fuel is delivered through fuel passage 38 and exits through outlets 38a. The outlets 38a are directed so as to project fuel across an air flow path which passes over the outer wall 40a and through air swirler 34. Annular heatshield cavity 39 is closed at the injector outlet end and contains air to insulate the fuel passage 38. In contrast, annular cavity 40 is open at the injector outlet end and a continuous stream of air is channelled through this annular cavity 40 and out through the air outlet 40b which sits just downstream of the cone shaped nose 31. The converging outer wall 40a of cavity 40 and the cone shaped nose 31 together create a single jet of air at the outlet 40b. The outer wall 40a includes an array of holes 40c which encircle protruding fuel outlets 38a. Some air from the annular cavity 40 thus exits through these holes 40c insulating the outlets 38a and providing an air film that may prevent the build-up of fuel in this region reducing the incidence of local coke formation.
The gas turbine engine 610 works in the conventional manner so that air entering the intake 612 is accelerated by the fan 613 to produce two air flows: a first air flow into the high-pressure compressor 614 and a second air flow which passes through a bypass duct 621 to provide propulsive thrust. The high-pressure compressor 614 compresses the air flow directed into it before delivering that air to the combustion equipment 615.
In the combustion equipment 615 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 616, 617 before being exhausted through the nozzle 18 to provide additional propulsive thrust. The high 616 and low 617 pressure turbines drive respectively the high pressure compressor 614 and the fan 613, each by suitable interconnecting shaft. An array of fuel injectors in accordance with the present diclosure may conveniently be provided at an inlet end of the combustion equipment 615.
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.
The second swirler portion 66 comprises a plurality of vanes 84 and a third member 86. The third member 86 is arranged coaxially around the second member 74. The vanes 84 of the second swirler 66 extend radially between the second and third members 74 and 86. The vanes 84 of the second swirler portion 66 have leading edges 88 and the third member 86 has an upstream end 90. The leading edges 88 of the vanes 84 of the second swirler portion 66 extend with radial and axial components from the upstream end 78 of the second member 74 to the upstream end 90 of the third member 86 and the radially outer ends 92 of the leading edges 88 of the vanes 84 of the second swirler portion 66 form arches 94 with the upstream end 90 of the third member 86. In particular the leading edges 88 of the vanes 84 extend with axial downstream components from the upstream end 78 of the second member 74 to the upstream end 90 of the third member 86.
The first member 72, the second member 74 and the third member 86 are generally annular members with a common axis Y. Thus, the upstream end of the first member 72 is upstream of the upstream end 78 of the second member 74 and the upstream end 78 of the second member 74 is upstream of the upstream end 90 of the third member 86.
The outer surface of the downstream end of the first member 72 tapers/converges towards the axis Y of the fuel injector head 60. The first member 72 The downstream end of the second member 74 tapers/converges towards the axis Y of the fuel injector head 60 and the inner surface of the downstream end of the third member 86 initially tapers/converges towards the axis Y of the fuel injector head 60 and then diverges away from the axis Y of the fuel injector head 60. An annular passage 104 is defined between the first member 72 and the second member 74 and an annular passage 106 is defined between the second member 74 and the third member 86. A central passage 108 is defined within the first member 74 in which a fuel passage can be received in accordance with the present diclosure.
It is seen that the fuel injector head 60 is arranged such that the leading edges 76 and 88 of the vanes 70 and 84 respectively are arranged to extend with axial downstream components from the first member 72 to the upstream end 78 of the second member 74 and from the second member 74 to the upstream end 90 of the third member 86 respectively. In addition it is seen that the fuel injector head 60 is arranged such that the radially outer ends 80 and 92 of the leading edges 76 and 88 of the vanes 70 and 84 respectively form arches 82 and 94 with the upstream ends 78 and 90 of the second and third member 74 and 86 respectively. These features enable the fuel injector head 60 and in particular the first and second swirler sections 64 and 66 of the fuel injector head 60 to be manufactured by direct laser deposition. These features enable the vanes 70 of the first swirler 64 to provide support between the first member 72 and the second member 74 and the vanes 84 of the second swirler 66 to provide support between the second member 74 and the third member 86 during the direct laser deposition process.
The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the present diclosure may be applied mutatis mutandis to any other aspect of the present diclosure.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1700465.6 | Jan 2017 | GB | national |
