Patent Description:
Fuel nozzles are used for injecting fuel and air mixtures into the combustors of gas turbine engines. Compressed fuel is typically fed under pressure into a fuel nozzle and a surrounding array of pressurized air flow channels is provided to form an atomized air/fuel mixture.

The fuel nozzles may comprises a fuel swirler assembled from a swirler housing with an interior chamber and a swirler core that is press fit into the interior chamber of the swirler housing. The combined configuration of control surfaces between the swirler housing and swirler core define fuel flow channels and shaped surfaces. These channels and surfaces may control the direction, pressure and kinetic energy of the pressurized fuel flow to achieve a desired set of parameters for the fuel spray exiting the fuel outlet orifice.

In such fuel swirlers, the fuel typically travels through channels or grooves between the swirler core and the swirler housing. The proximity of the fuel to the outer surface of the fuel swirler may lead to undesirably high fuel temperatures, which may lead to issues such as fuel choking and a potential reduction of the fuel nozzle's life expectancy.

In addition, such typical swirler cores are often asymmetrically shaped to account for the outer fuel channels, for instance having features such as one or more flat portions on their exterior surface. This may lead to undesirable consequences such as bending and/or plastic deformation of the swirler core when inserted into the swirler housing, potentially blocking or restricting the flow of fuel through the channels or grooves.

A method of assembling a fuel swirler for a gas turbine engine, according to the prior art is known from <CIT>.

According to the invention, there is provided a method of assembling a fuel swirler for a gas turbine engine, the fuel swirler including a swirler housing and a swirler core, the method comprising: inserting an end of the swirler core into an interior chamber of the swirler housing, an annular air gap forming between the swirler core and the swirler housing; abutting the inserted end of the swirler core against a transition portion of the interior chamber adjacent a fuel outlet in the swirler housing, the fuel outlet in fluid communication with an axial fuel path extending through an internal bore of the swirler core and through one or more exit holes fluidly connecting the internal bore to one or more fuel channels disposed in the inserted end of the swirler core; modulating the depth of the inserted end of the swirler core based on a desired engagement level between the transition portion and the one or more fuel channels; and fixing the swirler core to the swirler housing, wherein modulating the depth of the inserted end of the swirler core further includes directing fuel through the axial fuel path, monitoring the rate of fuel flow exiting through the fuel outlet, and selecting the desired level of engagement based on a desired rate of exiting fuel flow.

Optionally, and in accordance with any of the above, fixing the swirler core to the swirler housing includes applying a heat-based adhesive to a shoulder portion of the swirler core prior to inserting the end of the swirler core into the interior chamber, and applying heat to the fuel swirler to activate the adhesive subsequent to modulating the depth of the inserted end of the swirler core.

Optionally, and in accordance with any of the above, applying the heat-based adhesive to the shoulder portion of the swirler core includes applying a gold-based brazing compound.

Optionally, and in accordance with any of the above, applying heat to the fuel swirler includes placing the fuel swirler in a furnace to activate the adhesive.

<FIG> shows an axial cross-section through an example gas turbine engine. While <FIG> illustratively shows a turbo-fan type gas turbine engine, it is understood that the present disclosure is applicable to other types of gas turbine aircraft engines as well. In the illustrated case, air intake into the engine passes over fan blades <NUM> in a fan case <NUM> and is then split into an outer annular flow through the bypass duct <NUM> and an inner flow through the low-pressure axial compressor <NUM> and high-pressure centrifugal compressor <NUM>. Compressed air exits the compressor <NUM> through a diffuser <NUM> and is contained within a plenum <NUM> that surrounds the combustor <NUM>. Fuel is supplied to the combustor <NUM> through fuel tubes <NUM> and fuel is mixed with air from the plenum <NUM> when sprayed through nozzles into the combustor <NUM> as a fuel air mixture that is ignited. A portion of the compressed air within the plenum <NUM> is admitted into the combustor <NUM> through orifices in the side walls to create a cooling air curtain along the combustor walls or is used for cooling to eventually mix with the hot gases from the combustor <NUM> and pass over the nozzle guide vane <NUM> and turbines <NUM> before exiting the tail of the engine as exhaust.

As will be discussed in further detail below, the present disclosure is directed to fuel nozzles at the terminus of the fuel tubes <NUM> which direct an atomized fuel-air mixture into the combustor <NUM>. A fuel nozzle includes a concentric array of compressed air orifices to create a swirling air flow surrounding a central fuel injecting swirler. The resultant shear forces between air and fuel cause the fuel and air mix together and form an atomized fuel-air mixture for combustion.

<FIG> shows an isometric cross-section view of an exemplary embodiment of a fuel swirler <NUM> for a fuel nozzle. For simplicity, the outer components of the fuel nozzle that serve to direct compressed air are not shown. The fuel swirler <NUM> comprises a swirler core <NUM> having an internal bore <NUM> extending longitudinally through the swirler core <NUM> along a longitudinal axis L through which fuel is transported as will be discussed in further detail below. According to the illustrated embodiment the internal bore <NUM> is a central bore coaxial to the centerline of the swirler core. The swirler core <NUM> is axially mounted inside an interior chamber <NUM> of a swirler housing <NUM>. The swirler core <NUM> is axially insertable through an opening <NUM> in the swirler housing <NUM> at an upstream end U. of the fuel swirler <NUM> relative to a fuel flow direction F. As will be discussed in further detail below, fuel from the swirler core <NUM> exits the fuel swirler <NUM> via a fuel outlet <NUM> at a downstream end D. of the fuel swirler <NUM>. The interior chamber <NUM> includes a socket portion <NUM> downstream of the opening <NUM> and a transition portion <NUM> downstream of the socket portion <NUM> and upstream of the fuel outlet <NUM>. In various cases, the outer surface of the swirler housing <NUM> is shaped to optimize the aerodynamic performance of the fuel swirler <NUM> in relation to the streams of compressed air while maintaining the required strength and structural integrity of the fuel swirler <NUM>.

The swirler core <NUM> has a generally cylindrical exterior surface and includes a shank portion <NUM> concentrically positionable within the socket portion <NUM> of the interior chamber <NUM>. An annular air channel or air gap <NUM> is formed radially between the exterior surface of the swirler core <NUM> and the bounding wall of the interior chamber <NUM> of the swirler housing <NUM>. This air gap <NUM> may extend, for instance along the axial length of the shank portion <NUM>. Such an air gap <NUM> may provide an added layer of thermal insulation for the flow of fuel F travelling internally through the swirler core <NUM>. In various cases, the swirler core <NUM> and/or swirler housing <NUM> may be dimensioned to increase or decrease the thickness of the air gap <NUM> to vary the provided level of thermal insulation. Fuel may be provided to the internal bore <NUM> via a fuel inlet <NUM>, receiving fuel from the fuel tubes <NUM>. According to the illustrated embodiment, the fuel inlet <NUM> is provided at the upstream end of the swirler core <NUM> and is axially aligned with the internal bore <NUM>.

Referring additionally to <FIG> and <FIG>, the swirler core <NUM> further includes a downstream end portion <NUM> abuttable against the wall of the transition portion <NUM> of the interior chamber <NUM>. As will be discussed in further detail below, the level of engagement between the end portion <NUM> and the transition portion <NUM> may be chosen to meter or control the rate of fuel flow F exiting the fuel swirler <NUM> through fuel outlet <NUM>. Illustratively, the end portion <NUM> includes a frustoconical portion <NUM> and a protruding tapered abutting portion <NUM> extending axially from the frustoconical portion <NUM>. In the shown embodiment, as can be seen in <FIG>, the frustoconical portion <NUM> begins to taper axially upstream of the transition portion <NUM> of the interior chamber <NUM>, creating an annular fuel gallery <NUM>. Fuel may exit the internal bore <NUM> of the swirler core <NUM> via one or more exit holes <NUM> disposed in the end portion <NUM>, illustratively on the frustoconical portion <NUM>. The exit holes <NUM> are fluidly connected to the fuel gallery <NUM> to direct the fuel passing through the internal bore <NUM> into the fuel gallery <NUM>. While the shown swirler core <NUM> includes three exit holes <NUM>, it is understood that more or less exit holes <NUM> may be provided depending on the desired fuel flow. In addition while the shown exit holes <NUM> are circular, other shaped holes may be contemplated as well. In the shown case, the exit holes <NUM> are formed into the swirler core <NUM> at an acute angle with the longitudinal axis L, for instance by being drilled or otherwise machined. The angle at which the exit hole(s) <NUM> are formed may vary, for instance, to increase or decrease the swirling effect provided to the exiting fuel.

The fuel swirler <NUM> further includes one or more spaced apart recessed fuel channels or slots <NUM> disposed in the end portion <NUM>, illustratively on the abutting portion <NUM>. In the shown embodiment, the abutting portion <NUM> includes a frustoconical sidewall <NUM> and a flat end face <NUM>. Illustratively, the fuel channel(s) <NUM> begin at an annular recessed portion <NUM> of the end portion <NUM>, extend the axial length of the sidewall <NUM> and open at the end face <NUM>. The fuel channels <NUM> cooperate with the wall of the swirler housing <NUM> circumscribing the transition portion <NUM> to define metering passages for metering the flow of fuel from the fuel gallery <NUM>. Other configurations for the end portion <NUM> may be contemplated as well.

Fuel exiting the internal bore <NUM> of the swirler core <NUM> through the exit hole(s) <NUM> is directed through the fuel channel(s) <NUM> towards the fuel outlet <NUM>. The fuel travels through the one or more fuel channels <NUM> in a smaller, i.e. less voluminous, stream than in the internal bore <NUM>, and as such is enabled to atomize into small droplets as it exits through the fuel outlet <NUM>. The fuel exiting through the fuel outlet <NUM> in this atomized state, i.e. in small droplets, is combined with compressed air (not shown) and directed towards the combustor <NUM>. In the shown case, three fuel channels <NUM> with square cross-sectional shapes are helically disposed about the abutting portion <NUM>, although in other cases the number, cross-sectional shape and/or positioning about the abutting portion <NUM> may vary. For instance, while the illustrated fuel channels <NUM> are helically disposed about the abutting portion <NUM>, in other cases the fuel channel(s) <NUM> may be axially disposed about the abutting portion <NUM>, i.e. parallel to the longitudinal axis L. In addition, while the illustrated fuel channels <NUM> include square cross-sectional shapes, in other cases the cross-sectional shape of the fuel channel(s) <NUM> may be semi-circular or triangular. Other cross-sectional shapes may be contemplated as well.

The flow of fuel is best shown in <FIG> together with additional reference to <FIG> and <FIG>. Fuel under pressure enters via the fuel inlet <NUM> into the internal bore <NUM> of the swirler core <NUM>. The fuel exits the internal bore <NUM> via the exit hole(s) <NUM> and is directed via the fuel gallery <NUM> through the fuel channel(s) <NUM> disposed in the end portion <NUM> towards the fuel outlet <NUM> and out of the fuel swirler <NUM>. An axial fuel path is thus defined between the fuel inlet <NUM> and the fuel outlet <NUM>.

In various embodiments, the number of exit holes <NUM> corresponds to the number of fuel channels <NUM>. In some cases, the number of fuel channels <NUM> is a multiple of the number of exit holes <NUM>. Illustratively, the end portion <NUM> includes three exit holes <NUM> and three fuel channels <NUM>, although other numbers of exit holes <NUM> and/or fuel channels <NUM> may be considered. In an alternate embodiment, for instance, the end portion <NUM> may include two exit holes <NUM> and four fuel channels <NUM>. Other numbers of exit holes <NUM> and fuel channels <NUM> may be contemplated as well. The exit of the holes <NUM> can be placed such that the fuel directly feeds into the fuel channels <NUM>, or feeds in between the channels <NUM>. In the exemplary embodiment shown in <FIG>, the exit of the holes <NUM> are circumferentially in-between the channels <NUM>. That is the "clocking" of the exit holes <NUM> is different from that of the channels <NUM>.

In the shown case, the internal bore <NUM> is a central cylindrical bore along the longitudinal axis L through which fuel is transported, although other bore shapes and configurations may be contemplated as well. For instance, in some cases the internal bore <NUM> may be slightly offset from and parallel to the longitudinal axis L. In other cases, the swirler core <NUM> may alternatively include two or more internal bores <NUM> to transport the fuel. In various cases, the dimensions of the internal bore <NUM> and the exit hole(s) <NUM> are selected so that the flow of fuel through the swirler is metered by the fuel channel(s) <NUM>. Stated differently, the swirler core <NUM> may be dimensioned so that the rate of fuel flow F through the internal bore <NUM> and the hole(s) <NUM> is greater than the allowable rate of fuel flow through the combined one or more fuel channel <NUM>. For instance, the swirler core <NUM> may be dimensioned so that the cross-sectional area of the internal bore <NUM> is three times greater than the combined cross-sectional areas of the fuel channel(s) <NUM>. In the illustrated case where the end portion <NUM> includes three fuel channels <NUM>, each fuel channel <NUM> may allow a rate of fuel flow that is nine times less than the rate of fuel flow F through the internal bore <NUM>. Other relative fuel flow rates may be contemplated as well. In various cases, when the cross-sectional area of the internal bore <NUM> is greater than the combined cross-sectional areas of the fuel channel(s) <NUM>, the fuel channels <NUM> will be metering the flow of fuel F. In various cases, fuel exiting the internal bore <NUM> via exit holes <NUM> may accumulate in the fuel gallery <NUM> before passing through the fuel channel(s) <NUM>.

As discussed above, the fuel swirler <NUM> may be assembled by inserting the swirler core <NUM> through the opening of the <NUM> of the swirler housing <NUM>. In various embodiments, the rate of fuel flow F may be controlled based on the depth of insertion of the swirler core <NUM> into the interior chamber <NUM> of the swirler housing <NUM>. By selectively pressing the abutting portion <NUM> against the transition portion <NUM> of the interior chamber <NUM>, the fuel channel(s) <NUM> become increasingly covered or closed off due to the tapered profiles of the transition portion <NUM> and the frustoconical sidewall <NUM> of the abutting portion <NUM>. As such, the rate of fuel flow F may be controlled. In various cases, the transition portion <NUM> and the frustoconical sidewall <NUM> may taper at different rates to alter the effect that the continued insertion of the swirler core <NUM> into the interior chamber <NUM> has on the rate of fuel flow F.

For instance, in an exemplary assembly process, the swirler core <NUM> is inserted into the interior chamber with the abutting portion <NUM> engaging the transition portion <NUM>. Then, fuel is directed through the internal bore <NUM> via the fuel inlet <NUM>, with the rate of fuel flow F exiting the fuel swirler <NUM> via the fuel outlet <NUM> is monitored, for instance via a flow meter (not shown). Then, the depth of the swirler core <NUM> within the interior chamber <NUM> is adjusted in either direction to modulate the exposed portion of the fuel channel(s) <NUM>, i.e. the surface area through which fuel may exit from the fuel channel(s) <NUM>, thus increasing or decreasing the rate of fuel flow F until a desired flow rate has been achieved. At such a point, the flow of fuel F may be stopped. As such, a desired level of engagement between the transition portion <NUM> and the abutting portion <NUM> may be selected to modulate the desired fuel flow rate. Other methods of achieving a desired fuel flow rate may be contemplated as well.

By assembling the fuel swirler <NUM> via the above-described method, the fuel channel(s) <NUM> may be manufactured into the end portion <NUM> with larger dimensions than required since their cross-sectional area is reduced as the swirler core <NUM> is inserted into the interior chamber <NUM>. Such allowance may facilitate the overall manufacturing process of the fuel swirler, for instance by appeasing various manufacturing tolerances.

Once a desired flow rate has been achieved, the swirler core <NUM> is fixed to the swirler housing <NUM>. In some cases, the swirler core <NUM> and swirler housing <NUM> may be fixed together through a brazing process. For instance, a thin layer of gold paste (not shown) is applied to a shoulder <NUM> of the swirler core <NUM> before its insertion into the swirler housing <NUM>. Once a desired flow rate has been achieved, the fuel swirler <NUM> may be heated, for instance in a furnace, to solidify the gold paste into an adhesive. Such an adhesive may maintain the swirler core <NUM> at the previously-selected depth for a desired flow rate and affix the swirler core <NUM> and swirler housing <NUM> together, readying the fuel swirler <NUM> for use. Other methods of fixing the swirler core <NUM> to the swirler housing <NUM> may be contemplated as well, for instance through various welding processes.

In the shown case, the interior chamber <NUM> of the swirler housing <NUM> includes a radially thicker portion <NUM>, illustratively at the downstream end of the socket portion <NUM>. This thicker portion <NUM> decreases the diameter of the interior chamber <NUM>, adding a level of resistance when inserting the swirler core <NUM> into the interior chamber <NUM>. This added resistance may facilitate the above-described method of metering the flow of fuel, for instance by offering more control of the depth of the swirler core <NUM> to the user. The thickness of the thicker portion <NUM> may be selected based on the desired level of resistance against the inserted swirler core <NUM>, among other considerations. In addition, in various cases the thicker portion <NUM> may provide a barrier between the air gap <NUM> and the annular fuel gallery <NUM> when the swirler core <NUM> is inserted in the interior chamber <NUM>, preventing the fuel in the fuel gallery <NUM> and the air in the air gap <NUM> from undesirably mixing.

In various embodiments, at least various portions of the swirler core <NUM> and/or swirler housing <NUM> are axisymmetric about the longitudinal axis L. In the shown case, for instance, the shank portion <NUM> of the swirler core <NUM> is axisymmetric about the longitudinal axis L. As such, when the swirler core <NUM> is inserted into the swirler housing <NUM> and abutted against the transition portion <NUM>, the shank portion <NUM> will resist against bending, plastically deforming or otherwise undesirably distorting. An axisymmetric swirler core <NUM> under axial force will have balanced compressive axial stresses radially across the uniform cross-sectional area of the swirler core <NUM>. There is no force imbalance to create non-elastic bending, buckling or lateral distortion since the axisymmetric cross-section provides an axisymmetric distribution of stress.

In the shown case, both the swirler core <NUM> and the swirler housing <NUM> are axisymmetric about the longitudinal axis L. As such, the air gap <NUM> may be consistently maintained about the circumference of the swirler core <NUM>. This provides a consistent layer of thermal insulation to the flow of fuel F throughout the internal bore <NUM>, ensuring the fuel temperature is maintained at a low enough temperature based on the given engine's requirements. In addition, by directing the fuel flow F through the internal bore <NUM> of the swirler core <NUM> rather than between the swirler core <NUM> and the swirler housing <NUM>, as is typically the case, the temperature of the fuel is further reduced, which in some cases may extend the life expectancy of the fuel nozzle. For instance, in various cases the fuel nozzles in a given gas turbine engine are surrounded by various sources of heat, so the placement of the axial fuel path through the internal bore <NUM> of the swirler core <NUM> provides the greatest possible separation between the fuel and such sources of heat.

In such axisymmetric cases, any number of exit holes <NUM> in excess of one and fuel channels <NUM> in excess of one can be arranged in a circumferentially spaced apart array that results in an axisymmetric cross-section. For instance, <FIG> shows three exit holes <NUM> and three fuel channels <NUM>, but two or more exit holes and/or two or more fuel channels <NUM> can be axisymmetrically distributed with reference to the longitudinal axis L in other manners as well.

Various manufacturing processes may be utilized to produce the swirler core <NUM> and swirler housing <NUM>. Traditional manufacturing and removal techniques using machines such as lathes and mills may be implemented. Other manufacturing techniques such as additive manufacturing and metal injection moulding may be contemplated as well. As discussed above, various brazing or welding procedures may be utilized to fix the swirler core <NUM> to the swirler housing <NUM>.

Claim 1:
A method of assembling a fuel swirler (<NUM>) for a gas turbine engine, the fuel swirler (<NUM>) including a swirler housing (<NUM>) and a swirler core (<NUM>), the method comprising:
inserting an end of the swirler core (<NUM>) into an interior chamber (<NUM>) of the swirler housing (<NUM>), an annular air gap (<NUM>) forming between the swirler core (<NUM>) and the swirler housing (<NUM>);
abutting the inserted end of the swirler core (<NUM>) against a transition portion (<NUM>) of the interior chamber (<NUM>) adjacent a fuel outlet (<NUM>) in the swirler housing (<NUM>), the fuel outlet (<NUM>) in fluid communication with an axial fuel path extending through an internal bore (<NUM>) of the swirler core (<NUM>) and through one or more exit holes (<NUM>) fluidly connecting the internal bore (<NUM>) to one or more fuel channels (<NUM>) disposed in the inserted end of the swirler core (<NUM>);
modulating the depth of the inserted end of the swirler core (<NUM>) based on a desired engagement level between the transition portion (<NUM>) and the one or more fuel channels (<NUM>); and
fixing the swirler core (<NUM>) to the swirler housing (<NUM>),
characterised in that:
modulating the depth of the inserted end of the swirler core (<NUM>) further includes directing fuel through the axial fuel path, monitoring the rate of fuel flow (F) exiting through the fuel outlet (<NUM>), and selecting the desired level of engagement based on a desired rate of exiting fuel flow (F).