Patent Application
20110067403
1. Field of the Invention
The present invention relates to fuel injectors and nozzles, and more particularly to injectors and nozzles for gas turbine engines.
2. Description of Related Art
A variety of devices and methods are known in the art for injecting fuel into gas turbine engines. Of such devices, many are directed to injecting fuel into combustors of gas turbine engines while reducing undesirable emissions. With the increased regulation of emissions from gas turbine engines have come a number of concepts for reducing pollutant emissions while improving the efficiency and operability of the engines.
Modern gas turbine engine designs include providing high temperature combustion temperatures for thermal efficiency throughout a range of engine operating conditions. High temperature combustion minimizes emissions of some undesired gaseous combustion products, such as carbon monoxide (CO) and unburned hydrocarbons (UHC), and particulates, among other things. However, high temperature combustion also tends to increase the production of nitrogen oxides (NOX). Thus measures must be taken to provide thermally efficient operation within a temperature range that minimizes NOX, CO, and UHC.
One method often used to reduce unwanted emissions is staged fuel injection, wherein the combustion process is divided into two (or more) zones or stages, which are generally separated from each other by a physical distance, but still allowed some measure of interaction. Each stage is designed to provide a certain range of operability, while maintaining control over the levels of pollutant formation. For low power operation, only the pilot stage is active. For higher power conditions, both the pilot and the main stages may be active. In this way, proper fuel-to-air ratios can be controlled for efficient combustion, reduced emissions, and good stability. The staging can be accomplished by axial or radial separation. Staged fuel injectors for gas turbine engines are well known in the art.
It is difficult to provide thermally efficient, low emissions operation over the widening range of conditions in gas turbine engine designs. Additionally, during low power operating conditions, conventional staged fuel injectors only have fuel flowing through one of the staged fuel circuits. Measures must be taken to control temperatures in the stagnant fuel circuit to prevent coking within the injector. In the past, attempts were made to extend injector life by passively insulating, actively cooling, or otherwise protecting the fuel circuitry of fuel injectors from carbon formation during low power engine operation.
Along with staged combustion, pollutant emissions can be reduced by providing a more thoroughly mixed fuel-air mixture prior to combustion wherein the fuel-to-air ratio is below the stoichiometric level so that the combustion occurs at lean conditions. Lean burning results in lower flame temperatures than would occur with stoichiometric burning. Since the production of NOX is a strong function of temperature, a reduced flame temperature results in lower levels of NOX. The technology of directly injecting liquid fuel into the combustion chamber and enabling rapid mixing with air at lean fuel-to-air ratios is called lean direct injection (LDI).
U.S. Pat. No. 6,389,815 to Hura et al. describes a lean direct injection system, which utilizes radially-staged combustion within a single injector. The pilot fuel delivery is of the “swirl-cup” type shown in U.S. Pat. No. 3,899,884 to Ekstedt, wherein a pressure swirl atomizer sprays liquid fuel onto a filming surface where the liquid film is stripped off into droplets by the action of compressor discharge air. The main fuel delivery system utilizes a series of discrete atomizers that spray radially outward into a swirling cross-flow of air. The main fuel delivery is staged radially outboard of the pilot, and operates in the fuel-lean mode. Separation of the pilot combustion zone from the main combustion zone is achieved by radial separation as well as an air jet located radially between the two combustion zones.
U.S. Pat. No. 6,272,840 to Crocker et al. discloses a lean direct injection system, which also utilizes radially-staged combustion within a single injector. The pilot fuel delivery is of either a simplex air-blast type, or a prefilming air-blast type, and the main fuel delivery system is of a prefilming air-blast type. The radial staging of the pilot and main combustion zones is achieved by ensuring that the pilot combustion zone remains on-axis with no central recirculation zone.
U.K. Patent Application No. GB 2 451 517 to Shui-Chi et al. describes a pilot circuit divided into a primary and secondary fuel split. The primary circuit includes a pressure atomizer (simplex) on the centerline that is used for low power operation. The secondary pilot circuit is radially outboard of the primary circuit and is in the form of circumferentially spaced ports aimed towards the centerline. These circumferentially spaced ports are prone to external and internal carbon concerns.
Such conventional methods and systems have been generally considered satisfactory for their intended purposes. However, there still remains a continued need in the art to provide for staged operation in a pilot only mode for a substantial portion of the operating thrust while having lower requirements of fuel delivery pressure and reducing the chance of carbon formation. There also remains a need in the art for such methods and devices that are easy to make and use. The subject invention provides a solution for these problems.
The subject invention is directed to a new and useful fuel injector for a gas turbine engine. The fuel injector includes a nozzle body defining a central axis and having a main fuel circuit. An air circuit is formed within the nozzle body inboard of the main fuel circuit. A primary pilot fuel circuit is formed within the nozzle body inboard of the air circuit. A secondary pilot fuel circuit is formed within the nozzle body inboard of the air circuit and outboard of the primary pilot fuel circuit.
In accordance with certain embodiments, the fuel injector further includes a pilot air circuit inboard of the secondary pilot fuel circuit. The primary pilot fuel circuit is inboard of the pilot air circuit. At least one of the main fuel circuit and secondary pilot fuel circuit can include a prefilming air-blast atomizer, which can be a diverging prefilming air-blast atomizer. It is also contemplated that the primary pilot fuel circuit can include a pressure swirl atomizer, which can be defined in an inner air swirler along the axis of the nozzle body.
In certain embodiments, the primary pilot fuel circuit includes a primary pressure swirl atomizer on the axis of the nozzle body. The secondary pilot fuel circuit can include a secondary pressure swirl atomizer outboard of the primary pressure swirl atomizer. The primary and secondary pressure swirl atomizers can be combined as a dual orifice atomizer.
It is also contemplated that in certain embodiments each of the primary and secondary pilot fuel circuits includes a separate atomizer orifice. The fuel injector can include an outer air circuit formed in the nozzle body outboard of the main fuel circuit. The primary pilot fuel circuit can be configured and adapted to have a lower flow number than the secondary pilot fuel circuit.
The invention also provides an injector for a gas turbine engine, including a fuel feed arm configured and adapted to convey fuel from a main fuel circuit, a primary pilot fuel circuit, and a secondary pilot fuel circuit for combustion in a combustor of a gas turbine engine. A nozzle body depends from the fuel feed arm and includes a main prefilmer defining an axis. A main fuel swirler is provided inboard of the main prefilmer. The main fuel swirler and prefilmer define a portion of the main fuel circuit therebetween. At least one air swirler is provided inboard of the main fuel swirler. The main fuel swirler and the at least one air swirler define at least one air circuit therebetween. A primary pilot atomizer is provided inboard of the at least one air swirler. The primary pilot atomizer forms a portion the primary pilot fuel circuit. A secondary pilot prefilmer is provided inboard of the air swirler and outboard of the primary pilot atomizer. A secondary pilot fuel swirler is provided inboard of the secondary pilot fuel prefilmer and outboard of the primary pilot atomizer. The secondary pilot prefilmer and secondary pilot fuel swirler form a portion of the secondary pilot fuel circuit therebetween.
The invention also provides an injector for a gas turbine engine having an annular main fuel atomizer. The injector includes a fuel feed arm configured and adapted to convey fuel for combustion in a combustor of a gas turbine engine from a main fuel circuit, a primary pilot fuel circuit, and a secondary pilot fuel circuit. A nozzle body depends from the fuel feed arm and includes an annular main fuel atomizer defining an axis. The main fuel atomizer is an air-blast prefilming atomizer and defines a portion of the main fuel circuit. A primary pilot fuel atomizer is provided inboard of the annular main fuel atomizer. The primary pilot fuel atomizer is a pressure swirl atomizer and defines a portion of the primary pilot fuel circuit. A secondary pilot fuel atomizer is provided inboard of the main fuel atomizer and outboard of the primary pilot fuel atomizer. The secondary pilot fuel atomizer is an airblast prefilming atomizer and defines a portion of the secondary fuel circuit.
These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a fuel injector constructed in accordance with the invention is shown in
U.S. Patent Application Publication No. 2006/0248898, which is incorporated herein by reference in its entirety, describes lean direct injection atomizers for gas turbine engines. The present invention pertains to fuel injectors that deliver a fuel/air mixture into the combustion chamber of a gas turbine engine. In particular, the invention pertains to fuel injectors for staged, lean direct injection (LDI) combustion systems, wherein around 50% to 80% of the combustion air enters the combustion chamber through the fuel injector, for example. Such a system is designed to reduce pollutant emissions, particularly nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (UHC).
There is a strong desire to operate in a pilot only mode for a substantial portion of the operating thrust, such as up to 50%-70% power or more. However, due to the desire to have good atomization for the entire range of operation which generates a high turndown ratio, the size of the pilot metering points is dictated by exterior constraints such as pump capability, manifold pressure limits and cooling requirements. The present invention allows for staging of the pilot zone into subcomponents in order to increase the operating thrust in pilot only modes without exceeding desirable pressure limits. The pilot is separated into primary and secondary pilot fuel circuits, and these can take various forms as described below.
As shown in
Referring now to
With continued reference to
Referring to
With reference again to
Referring to
Secondary pilot fuel circuit 118 is shielded from high temperature compressor discharge air passing through pilot air circuit 140 by pilot air swirler 138 and fuel conduit 142 inboard of pilot air swirler 138. Referring to FIGS. 3 and 6-8, Fuel passing through secondary pilot fuel circuit 118 enters between inner and outer secondary pilot fuel swirler components 144 and 152, respectively, and is issued from secondary pilot fuel orifice 146. Centerline conduit 148 conducts fuel flowing in primary pilot fuel circuit 116 along axis 110 through primary pilot fuel swirler 150 and inside secondary pilot fuel swirler component 152 to be issued through primary pilot fuel orifice 154, which is located within secondary pilot fuel orifice 146. In this manner, primary plot fuel swirler 150 and inner and outer secondary pilot fuel swirler components 144, 152 form primary and secondary pilot fuel atomizers in the form of a dual orifice (duplex) pressure swirl atomizer.
Those skilled in the art will readily appreciate that each of the primary and secondary pilot fuel circuits can instead include a separate simplex type atomizer orifice. Those skilled in the art will also readily appreciate that the various air and fuel circuits defined in nozzle body 106 can be configured to impart co-rotational swirl or counter-rotational swirl on the respective fuel or air flow with respect to the other circuits in any suitable configuration without departing from the spirit and scope of the invention.
Injector 100 has a dual orifice (duplex) atomizer on centerline. This allows the primary pilot fuel flow to be broken down into a relatively small flow number, aiding in ignition, weak stability and low power emission. It also allows the secondary pilot fuel flow to have a comparatively large flow number allowing for higher power operation while not causing requirements for severely high fuel delivery pressures. This provides for operation of a gas turbine engine up to 50%-70% or greater throttle level without activating main fuel circuit 112, while allowing for lower fuel delivery pressure requirements compaired to conventional pilot stages operating at similar levels.
Another exemplary way of accomplishing this is to have a relatively low flow number on the centerline, again for ignition, weak stability and lower power emission, and to place radially outboard of that a prefilming airblast atomizer with a larger flow number. Such a configuration will also allow for lower requirements for fuel delivery pressure while allowing pilot-only operation up to elevated throttle levels. An example of an injector with such a configuration is described below.
Referring to
Injector 200 differs from injector 100 because, among other things, secondary fuel circuit 218 in injector 200 includes a prefilming atomizer instead of a pressure swirl atomizer. As such, injector 200 includes two pilot air circuits, namely inner and outer pilot air circuits, whereas injector 100 does not include an inner pilot air circuit. The prefilming atomizer of secondary pilot fuel circuit 218 is described below.
Inside intermediate air swirler 234 is an outer pilot air swirler 238, with an outer pilot air circuit 240 defined therebetween, much like pilot air circuit 140 described above. A pilot prefilmer 270 inside outer pilot air swirler 238 combines with secondary pilot fuel swirler 272 to form a prefilming chamber for secondary pilot fuel circuit 218. A conical pilot wall 273 is provided radially inward from swirler 272 for directing air through a secondary inner air circuit 274 radially outward against fuel issued from the prefilming chamber of secondary pilot fuel circuit 218. The upstream portion of conical pilot wall 273 includes swirl vanes 276 on its radially inward surface to provide swirl to air passing through primary inner pilot air circuit 278. Secondary pilot fuel circuit 218, outer pilot air circuit 240, and secondary inner air circuit 274 form a diverging pilot air-blast atomizer, which in many ways is a small scale version of the main air-blast atomizer of main fuel circuit 212.
As can be seen in
Thermal management of the three fuel circuits in injectors 100, 200 can be accomplished by cooling with fuel flowing through at least the primary pilot fuel circuit during low power engine operation to cool the other two fuel circuits when they are inactive. In general, in the feed arm 102, 202, the primary pilot fuel circuit 116, 216 should be outboard of the other two fuel circuits 112, 212, and 118, 218, and can be kept in close proximity with the other two fuel circuits 112, 212, and 118, 218 within the nozzle body, respectively. Such thermal management techniques are disclosed in commonly assigned U.S. Pat. No. 7,506,510, which is incorporated by reference herein in its entirety. The ordering of the fuel circuits described herein is exemplary and those skilled in the art will readily appreciate that the fuel circuits can be reordered as appropriate for specific applications without departing from the spirit and scope of the invention.
Injector 100 of
The methods and systems of the present invention, as described above and shown in the drawings, provide for fuel injectors with superior properties including staged operation in a pilot only mode for a substantial portion of the operating thrust. This is accomplished while having lower requirements of fuel delivery pressure and reducing the chance of carbon formation due to thermal breakdown of fuel.
While the apparatus and methods of the subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject invention.
