Low smoke and emissions fuel nozzle

A fuel nozzle having a fuel conveying member surrounded by a sheath. An air passage is defined between the fuel conveying member and the sheath for directing air to an air swirler provided at one end of the fuel conveying member. At one flow director is provided in the air passage for promoting air and fuel uniformity and distribution at a spray tip of the fuel nozzle.

TECHNICAL FIELD

The invention relates generally to a fuel nozzle for gas turbine engines and, more particularly, to a fuel nozzle promoting air and fuel uniformity and distribution.

BACKGROUND OF THE ART

It is desirable for a fuel nozzle to demonstrate uniformity in the air and fuel droplets distribution. The uniformity of air is essential to assist in fuel atomization and help promote fuel spray uniformity. A lower size droplet distribution promotes better mixing and heat release per nozzle thereby resulting in a lower smoke number and low emissions.

Accordingly, there is a need to provide a fuel nozzle that provides uniformity of air and fuel to impose better mixing and promote low emissions.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a fuel nozzle proving uniformity of air and fuel to impose better mixing and promote low emissions.

In one aspect, the present invention provides a gas turbine engine fuel nozzle comprising: a fuel conveying member defining at least one fuel passage, a spray tip connected in fluid flow communication with said at least one fuel passage, the spray tip having an air swirler, a sheath provided about the fuel conveying member, an air passage defined between the fuel conveying member and the sheath, the air passage leading to air openings defined through the air swirler, an air inlet defined in the sheath for connecting the air passage in fluid flow communication with a source of air, and at least one flow director provided in the air passage between the sheath and the fuel conveying member.

In another aspect, the present invention provides a fuel nozzle comprising a stem having at least one fuel passage extending therethrough, a spray tip connected in fluid flow communication with the stem, the spray tip having an air swirler, a tubular sheath having a sidewall surrounding the stem defining an air passage therebetween, the air passage being connected in fluid flow communication with said spray tip, the sidewall of the tubular sheath defining an aperture in fluid flow communication with the air passage, and at least one wing-like projection extending from said stem into said air passage for directing air entering the air passage from the aperture to the air swirler of the spray tip.

In still another aspect, the present invention provides a method of promoting fuel spray uniformity at a spray tip of a gas turbine engine fuel nozzle: comprising the steps of: a) capturing the dynamic head imposed by a flow of incoming air, and b) directing the air into an air swirler of the spray-tip for atomizing the fuel flowing through said spray tip.

Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates a gas turbine engine10of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan12through which ambient air is propelled, a multistage compressor14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases. The resulting high temperature combustion gases are used to turn the turbine section18and produce thrust when passed through a nozzle.

Reference is now made toFIG. 2of the drawings which illustrates one exemplary embodiment of the combustor16. The combustor16shown is a reverse flow combustor16, however it should be understood that other types of combustor, such as an axial flow combustor, may have also been exemplified. The combustor16is fixedly mounted by suitable means in an air flow path, designated generally by arrows20, and receiving air from the compressor14or any other source of air. More particularly, the combustor16is mounted within the engine casing22which defines an annular or cylindrical flow path. The combustor16comprises an annular or cylindrical housing24which defines a primary combustion zone26and a dilution zone28. Mounted to the engine casing walls22and to the combustor housing24is a plurality of fuel nozzles30, one of which is shown inFIG. 2. The fuel nozzle30extends through the engine casing22and the combustor housing24such that it is in fluid flow communication with the primary combustion zone26.

The fuel nozzle30exemplified inFIGS. 3 to 5comprises a fluid conveying member which might, for instance, include a stem32. The stem32is adapted to be coupled at the inlet end34thereof to a fuel manifold adapter36and at the outlet end38thereof to a spray tip assembly40. Accordingly, the spray tip assembly40is coupled through the stem32to the fuel manifold adapter36which is connected to a fuel injector (not shown). The configuration of the stem32allows for the source of fuel supplied by the fuel injector to be directed from the inlet end34to the outlet end38. The fuel is then atomized by the spray tip assembly40for ignition in the primary combustion zone26, as is well known in the art.

More particularly, the stem32may include primary and secondary fuel conduit flow passages (not shown) directing a primary and a secondary fuel flow from the inlet end34to the outlet end38. A portion of the inlet end34of the stem32is adapted to be inserted into a receiving opening (not shown) defined in the bottom portion of the fuel manifold adapter36. The fuel manifold adapter36is provided with primary and secondary fuel outlets (not shown) configured for connection with the primary and secondary conduit inlets (not shown) of the stem32thereby defining a flow relationship. The stem32may be secured to the fuel manifold adapter36by way of welding, brazing or the like.

As seen inFIGS. 2 to 5, the fuel manifold adapter36is provided with a flange42for mounting the fuel nozzle30to the engine casing22of the gas turbine engine10.

Now referring concurrently toFIGS. 3 and 4, the spray tip assembly40may include a primary swirler44, a secondary swirler46and an air swirler48, for imparting a swirling motion to the air and fuel passing therethrough as will be further described lateron. The swirling action of the air and fuel enhances mixing thereof. Specifically, the primary swirler44is connected to the primary fuel conduit outlet (not shown) for receiving the primary fuel flow. Similarly, the secondary air swirler46is connected to the secondary fuel conduit outlet for receiving the secondary fuel flow.

The air swirler48of the spray tip assembly40is provided with a plurality of circumferentially spaced air passages50that are adapted to convey a swirling air flow for blending with the primary and secondary fuel sprays emanating from the primary and secondary spray orifices (not shown) of the spray tip assembly40. Preferably, the spray tip assembly40is brazed into the receiving opening defined at the outlet end38of the stem32. Also, the primary, secondary and air swirlers44,46and48respectively are preferably inter-brazed so as to form an integral spray tip assembly40.

The fuel nozzle30also comprises a tubular sheath52having a sidewall54that surrounds the stem32defining an annular flow passage56therebetween. A single air inlet or aperture58is defined in the sidewall54of the sheath52at a first open end portion60thereof. As shown inFIG. 2, the aperture58is disposed in the air flow path20in facing relationship with the incoming discharged compressor air. The aperture58connects the air flow passage56in fluid flow communication with the air flow path20. The aperture58has an elongated shape and extends about haft of the circumference of the sheath52, as best illustrated inFIG. 4. The first end portion60of the sheath52is adapted for attachment to the flange42of the fuel manifold adapter36. The sheath52has a second end portion62adapted for attachment to the spray tip assembly40such that the flow passage56leads to the air passages50defined in the air swirler48. A slanted opening61is defined in the second end62of the sheath52to receive the air swirler48, as best shown inFIGS. 2 and 3.

More specifically, the first end portion60is preferably sealingly coupled, for example by a weld or a braze, to a surface64projecting from the flange42adjacent the inlet end34of the stem32. The second open end portion62is sealingly coupled to the air swirler48of spray tip assembly40in a similar fashion such that the flow passage56is in fluid flow communication with the air passages50of the air swirler48.

The sheath52is preferably cylindrical in shape. The surface64extending from the flange42is also circular to mate with the first end portion60and the air swirler48of the spray tip assembly40has a generally circular periphery66to mate with the outline of the opening61provided at the second end portion60of the tubular sheath52. It should be understood however that various alternatives are also contemplated.

Furthermore, the fuel nozzle30comprises at least one flow directing member68preferably disposed on the stem32and extending in the flow passage56for directing a fluid flow passing therethrough. In accordance with the preferred embodiment illustrated, inFIGS. 3 to 5, a pair of directing members68extends outwardly from opposite sides of the stem32. The directing members68extend axially from the inlet end34to approximately ¾ of the stem32length (FIG. 4). Moreover, the pair of directing members68is preferably wing shaped. Those wing shaped projections are positioned in facing relationship with the inlet aperture58(seeFIG. 5) and are spaced from the inner surface of the sheath52.

Thus, optimally operating the fuel nozzle30entails positioning the aperture58in the tubular sheath52to face the air flow path20so as to intake oncoming compressor discharged air. The sheath52with its single air inlet captures the dynamic head that is imposed by the incoming compressor air. The main functionality of the pair of directing members68is to direct the air towards the air swirler48of the spray tip assembly40coupled to the second end portion62of the tubular sheath52. The pair of directing members68imposes a flow condition to redistribute the air on the full surface of the air swirler48due to pressure recovery inside the annular flow passage56between the stem32and the tubular sheath52.

Advantageously, the uniformity of the air entering the air passages50of the air swirler48assists the fuel atomization and helps promote fuel spray uniformity. Uniformity in the air and fuel leads to better fuel droplet size. The fuel nozzle30embodied herein yields small fuel droplets that are preferably below 30 microns in size. Therefore, the winged stem32in operation with the tubular sheath52advantageously yields excellent air and fuel uniformity and distribution which allows for better mixing and heat release per fuel nozzle30and promotes low emissions and low invisible smoke number. Furthermore, the fuel nozzle30described herein helps prolong the life of the combustor16and hot end components such as the carrier ring and turbine blades of the gas turbine engine10. The fuel nozzle30also helps promote a low noise emitting combustor16.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. For example, the directing member may be provided in many forms and can be mounted otherwise so long as its functionality remains the same: directing a fluid flow entering the aperture towards the air swirler in a uniform distribution. It should also be understood that the tubular sheath may be attached to the fuel adapter and spray tip assembly in many different ways. The tubular sheath may even be joined to the stem directly. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.