Patent Application
20060042263
The present invention relates generally to gas turbine engine combustors and, more particularly, to a low cost combustor configuration having improved performance.
Gas turbine combustors are the subject of continual improvement, to provide better cooling, better mixing, better fuel efficiency, better performance, etc. at a lower cost. Also, a new generation of very small gas turbine engines is emerging (i.e. a fan diameter of 20 inches or less, with about 2500 lbs. thrust or less), however larger designs cannot simply be scaled-down, since many physical parameters do not scale linearly, or at all, with size (droplet size, drag coefficients, manufacturing tolerances, etc.). There is, therefore, a continuing need for improvements in gas turbine combustor design.
In accordance with the present invention there is provided a gas turbine engine combustor comprising a liner enclosing a combustion chamber, the liner including a dome portion at an upstream end thereof, the dome portion having defined therein a plurality of openings each adapted to receive a fuel nozzle and a plurality of holes defined around each opening, each opening having an axis generally aligned with an fuel injection axis of a fuel nozzle received by the opening, the holes adapted to direct air into the combustion chamber in a spiral around the axis of an associated one of said openings.
In accordance with another aspect there is also provided a gas turbine engine combustor comprising a liner enclosing a combustion chamber, the liner having defined therein a plurality of openings each adapted to receive a fuel nozzle for directing fuel into the combustion chamber generally along an axis of the opening, the liner also having means associated with each opening for directing air into the combustion chamber in a spiral pattern around an axis of the associated opening.
In accordance with another aspect there is also provided a method of combusting fuel in a gas turbine combustor, the method comprising the steps of injecting a mixture of fuel and air into the combustor along an axis, igniting the mixture to create at least one combustion zone in which the mixture is combusted, and directing air into the combustor around said axis in a spiral pattern;
Further details of these and other aspects of the present invention will be apparent from the detailed description and Figures included below.
Reference is now made to the accompanying Figures depicting aspects of the present invention, in which:
Referring to
A plurality of air-guided fuel nozzles 50, having supports 52 and supplied with fuel from internal manifold 54, communicate with the combustion chamber 32 through nozzle openings 56 to deliver a fuel-air mixture 58 to the chamber 32. As depicted in
In use, high-speed compressed air enters plenum 20 from diffuser 24. The air circulates around combustor 16, as will be discussed in more detail below, and eventually enters combustion chamber 32 through a plurality of holes 44 in liner 26, holes 46 and 46′ in dome 34, and holes 48 in transition 36. Once inside the combustor 16, the air is mixed with fuel and ignited for combustion. Combustion gases are then exhausted through exit 42 to turbine section 18.
Referring to
Referring now to
Referring to
The combustor 16 is preferably provided in sheet metal, and may be made by any suitable method. Holes 44, 46, and 48 are preferably drilled in the sheet metal, such as by laser drilling. It will be appreciated in light of the description, however, that holes 48 in transition 36 are provided quite close to body panels 38A,B, and necessarily are so to provide good film cooling of body panels 38A,B. This configuration, however, makes manufacturing difficult since the drilling of holes 48 may inadvertently compromise the body panel behind this hole, and thereby result in a scrapped part. While drilling can be controlled with great precision, such precision adds to the cost of the part. According to the present invention, however, providing combustor 16 with small radius transition portions 36A,B and a flat dome permits drilling to completed less precisely and with minimal risk of damaging the adjacent body panels. This is because manufacturing tolerances for drilled holes provided on curved or conical surfaces are much larger than the comparable tolerances for drilling on a flat, planar surface. Thereby, maximizing the flat area of the combustor dome, the present invention provides an increase area over which cooling holes may be more accurately provided. This is especially critical in heat shield-less combustor designs (i.e. in which the liner has no inner heat shield, but rather the dome is directly exposed to the combustion chamber), since the cooling of the dome therefore become critical, and the cooling pattern must be precisely provided therein. By improving the manufacturing tolerances of the combustor dome, the chance of holes not completely drilled-through, or drilling damage occurring on a liner surface downstream of the drilled hole (i.e. caused by the laser or drilling mechanism hitting the liner after completing the hole) are advantageously reduced. Thus, by making the dome end flat, holes may be drilled much closed to the “corners” (i.e. the intersection between the dome and the side walls), with reduced risk of accidentally damaging the liner side walls downstream of the hole (i.e. by over-drilling). Although a flat dome, depending on its configuration, may present dynamic or buckling issues in larger-sized configurations, the very small size of a combustor for a very small gas tribune engine will in part reduce this tendency. This aspect of the invention is thus particularly suited for use in very small gas turbine engines. In contrast, conventional annular reverse-flow combustors have curved domes to provide stability against dynamic forces and buckling. However, as mentioned, this typical combustor shape presents interference and tolerance issues, particularly when providing an heat shield-less combustor dome.
Referring to
Referring again to
To address this problem, the cooling hole pattern of the present invention improves the flow in the wake area by reducing the overall drag coefficient (Cd) in the wake area by providing holes 46′ in addition to holes 46, and thus permitting more direct entry of air into the combustor (since holes 46′ are not angled as harshly relative to the primary flow in plenum 20, and thus air may enter combustor 16 at a higher momentum though holes 46′ than through holes 46. This higher momentum air exiting from holes 46′ assists holes 46 in pushing away fuel from the liner walls to impede flame stabilization near the wall liner wall.
Perhaps more importantly, however, the spiral or helical flow also helps to constrain the lateral extent of fuel spray cone 58. Referring again to
The spiral flow inside the liner also provides better fuel/air mixing and thus also improves the re-light characteristic of the engine, because the spiral flow ‘attacks’ the outer shell of the fuel spray cone, which is consists of the lower density of fuel particles, and thus improves fuel-air mixing in the combustion chamber.
As a result of the hole pattern of the present invention, a novel combustor air flow pattern results. Conventionally, combustor internal aerodynamics provide either single torroidal or double torroidal flows inside the liner, however the present invention results in new aerodynamic pattern due to spiral flow introduced inside the liner.
The present invention is believed to be best implemented with a combustor having a flat dome panel. Although the invention may also be applied to conical, curved or other shaped dome panels, it is believed that the spiral flow which is introduced inside the liner will be inferior to that provided by the present hole pattern in a flat dome panel.
The above description is meant to be exemplary only, and one skilled in the art will recognize that further changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the invention may be provided in any suitable annular combustor configuration, and is not limited to application in turbofan engines. It will also be understood that holes 46′ need not be provided in a concentric circular configuration, but in any suitable pattern. Holes 46 and 46′ need not be provided in distinct regions of the dome 34, and may instead be interlaced in overlapping regions. Holes 46′ around adjacent nozzle openings 56 may likewise be interlaced with one another. The direction of vortex flow around each nozzle is preferably in the same direction, though not necessarily so. Each nozzle does not require a vortex, though it is preferred. Although the use of holes for directing air is preferred, other means such as slits, louvers, etc. may be used in place of or in addition to holes. Still other modifications 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.
