TECHNICAL FIELD

This invention relates to devices in gas turbine engines that aid in containing and producing the combustion of a fuel and air mixture. Such devices include but are not limited to fuel-air nozzles, combustor liners and casings and flow transition pieces that are used in military and commercial aircraft, power generation, and other gas turbine related applications.

BACKGROUND ART

Gas turbine engines include machinery that extracts work from combustion gases flowing at very high temperatures, pressures and velocity. The extracted work can be used to drive a generator for power generation or for providing the required thrust for an aircraft. A typical gas turbine engine consists of a multistage compressor where the atmospheric air is compressed to high pressures. The compressed air is then mixed at a specified fuel/air ratio in a combustor wherein its temperature is increased. The high temperature and pressure combustion gases are then expanded through a turbine to extract work so as to provide the required thrust or drive a generator depending on the application. The turbine includes at least a single stage with each stage consisting of a row of blades and a row of vanes. The blades are circumferentially distributed on a rotating hub with the height of each blade covering the hot gas flow path. Each stage of non-rotating vanes is placed circumferentially, which also extends across the hot gas flow path. The included invention involves the combustor of gas turbine engines and components that introduce the fuel and air into the said device.

The combustor portion of a gas turbine engine can be of several different types: can/tubular, annular, and a combination of the two forming a can-annular combustor. It is in this component that the compressed fuel-air mixture passes through fuel-air swirlers or nozzles and a combustion reaction of the mixture takes place, creating a hot gas flow causing it to drop in density and accelerate downstream. The can type combustor typically comprises of individual, circumferentially spaced cans that contain the flame of each nozzle separately. Flow from each can is then directed through a duct and combined in an annular transition piece before it enters the first stage vane. In the annular combustor type, fuel-air nozzles are typically distributed circumferentially and introduce the mixture into a single annular chamber where combustion takes place. Flow simply exits the downstream end of the annulus into the first stage turbine, without the need for a transition piece. The key difference of the last type, a can- annular combustor, is that it has individual cans encompassed by an annular casing that contains the air being fed into each can. Each variation has its benefits and disadvantages, depending on the application.

In combustors for gas turbines, it is typical for the fuel-air nozzle to introduce a swirl to the mixture for several reasons. One is to enhance mixing and thus combustion, another reason is that adding swirl stabilizes the flame to prevent flame blow out and it allows for leaner fuel-air mixtures for reduced emissions. A fuel air nozzle can take on different configurations such as single to multiple annular inlets with swirling vanes on each one.

As with other gas turbine components, implementation of cooling methods to prevent melting of the combustor material is needed. A typical method for cooling the combustor is effusion cooling, implemented by surrounding the combustion liner with an additional, offset liner, which between the two, compressor discharge air passes through and enters the hot gas flow path through dilution holes and cooling passages. This technique removes heat from the component as well as forms a thin boundary layer film of cool air between the liner and the combusting gases, preventing heat transfer to the liner. The dilution holes serve two purposes depending on its axial position on the liner: a dilution hole closer to the fuel-air nozzles will aid in the mixing of the gases to enhance combustion as well as provide unburned air for combustion, second, a hole that is placed closer to the turbine will cool the hot gas flow and can be designed to manipulate the combustor outlet temperature profile.

One can see that several methods and technologies can be incorporated into the design of combustors for gas turbine engines to improve combustion and lower emissions. While gas turbines tend to produce less pollution than other power generation methods, there is still room for improvement in this area. With government regulation of emissions tightening in several countries, the technology will need to improve to meet these requirements. DISCLOSURE OF THE INVENTION

With regard to present invention, there is provided a novel and improved combustor design that is capable of operating in a typical fashion while minimizing the pollutant emissions that are a result of combustion of a fuel and air mixture and address other issues faced by such devices. The invention consists of a typical can-annular combustor with fuel and air nozzles and/or dilution holes that introduce the compressor discharge air and pressurized fuel into the combustor at various locations in the longitudinal and circumferential directions. The original feature of the invention is that the fuel and air nozzles are placed in such a way as to create an environment with enhanced mixing of combustion reactants and products. Staging the fuel and air nozzles to have upstream nozzles inject mainly fuel and another set of nozzles downstream which inject mainly air enhances the mixing of the combustion reactants and creates a specific oxygen concentration in the combustion region that greatly reduces the production of NO _x . In this device, there is no attached/anchored flame, but rather a region in the can near the front wall where diffusion combustion occurs. The novel configuration of separate fuel and air nozzles means that air that is injected downstream and propagations upstream will be diluted, thus reducing the oxygen concentration the flame sees and reducing peak flame temperatures. This is what makes the said invention capable of reducing emissions. In addition, the introduction of compressor discharge air downstream of the combustion region allows for any CO produced during combustion to be burned/consumed before entering the first stage turbine. In effect, the combustor will improve gas turbine emission levels, thus reducing the need for emission control devices as well as minimize the environmental impact of such devices. In addition to this improvement, the tangentially firing fuel and fuel-air nozzles directs any initial flame fronts to the adjacent burner nozzles in each can, greatly enhancing the ignition process of the combustor.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings:

FIG. 1 is a two-dimensional sketch showing the can-annular arrangement with the nozzles that attach to the outer can liner injecting fuel and air into a common plane;

FIG. 2 is a two-dimensional sketch showing the general idea of the tangential nozzles applied to the can in a can-annular combustor; FIG. 3 is an isometric side view of the upstream portion of an example configuration of the said invention;

FIG. 4A is an isometric cutaway view of the invention;

FIG. 4B is a close up view of the image from FIG. 4A;

FIG. 5 is a section view showing section A- A as defined in FIG. 3 ; and

FIG. 6 is a section view showing section B-B as defined in FIG. 3.

BEST MODES FOR CARRYING OUT THE INVENTION FIG. 1 shows an example of the general arrangement of a can-annular combustor with the can 1 spaced circumferentially on a common radius, all cans of which are enclosed between a cylindrical outer liner 2 and a cylindrical inner liner 3. The FIG. also shows the tangential nozzle arrangement of the cans. FIG. 2 shows the can in more detail. A can liner 4 forms the can volume, with fuel/air nozzles 5 injecting either fuel or air. The nozzles form an angle 8 between the nozzle centerline 6 and a line tangent to the can liner 4 that intersections with the nozzle centerline 6. This angle defines the circumferential direction of the nozzles.

FIG. 2 also shows the general operation of the can in the example can-annular combustor configuration, where the fuel or air 9 is injected into the cans 1 at an angle 8. A flame 10, that is not anchored in this invention, forms and travels through the can in a path 11 that follows the can liner. These tangentially directed nozzles result in flow from each nozzle interacting with the downstream and adjacent nozzle. This key feature enhances ignition and reduces the issue of piloting multiple burner nozzles by allowing the flame to be directed from one nozzle to ignite the fuel at the adjacent and downstream nozzle.

FIG. 3 shows the beginning or upstream portion of an example can with the downstream portion excluded. The said invention will have a plurality of nozzle rows that are spaced along the longitudinal direction of the can. Each row of nozzles 12, 13 may have at least one nozzle and can be offset by a circumferential angle from adjacent nozzle rows. In particular, the nozzles 12 in the row close to the front wall 15 inject pure/mostly fuel into the can in a manner previously described, where as nozzles 13 downstream of these inject pure compressor discharge air or a fuel-air mixture into the can in a similar manner. The can may also have several rows of circumferentially spaced holes 14 or passages for cooling air to enter the can at any location. FIGS. 4 A and 4B show the most upstream face 15 of the can, which may have holes 16 similar to dilution holes that allow compressor discharge air to enter the can. FIGS. 5 and 6 show how nozzles 12, 13 from each set of nozzles may be offset by a circumferential angle. The different rows of nozzles allows for the separate injection of the fuel and air creating a zone of combusting reactants near the front wall that does not see a high oxygen concentration, which in effect will reduce peak flame temperatures. Flue gases that travel upstream towards the front wall will be diluted from combustion products, making it possible for the combusting reactants to see a lower oxygen concentration. This combustion environment created by the staged fuel and air nozzles makes the reduced emissions possible.

The present invention is described above with reference to a preferred embodiment. However, those skilled in the art will recognize that changes and modifications may be made in the described embodiment without departing from the nature and scope of the present invention. Various changes and modifications to the embodiment herein chosen for purposes of illustration will readily occur to those skilled in the art. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof.

Having fully described the invention in such clear and concise terms as to enable those skilled in the art to understand and practice the same, the invention claimed is: