US20160281978A1

US20160281978A1 - Fuel Nozzle With Multiple Flow Divider Air Inlet

Info

Publication number: US20160281978A1
Application number: US14/669,089
Authority: US
Inventors: Luiz Claudio FERNANDES; Brian Richardson; Peter Stuttaford; Sumit Soni; David SCHLAMP; Chiluwata LUNGU; Justin Bosnoian; Nicolas Demougeot; Kevin B. Powell; Brandon HILL; Marc PASKIN
Original assignee: Individual
Current assignee: Ansaldo Energia Switzerland AG
Priority date: 2015-03-26
Filing date: 2015-03-26
Publication date: 2016-09-29

Abstract

The present invention discloses a novel apparatus and way for directing a supply of compressed air into a fuel nozzle assembly for mixing with a fuel source. The apparatus comprises a fuel nozzle assembly having one or more coaxial flow dividers and radially-extending swirler vanes for directing a supply of fuel to a mixing tube. Compressed air is directed to flow in a primarily axial direction by passing through one or more coaxial flow dividers spaced axially and radially about the air inlet region of the fuel nozzle assembly so as to form a non-uniform radial distribution of compressed air to the inlet region of the fuel nozzle assembly.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

TECHNICAL FIELD

The present invention relates generally to an apparatus and method for directing a flow of compressed air into a fuel nozzle assembly. More specifically, a fuel nozzle assembly is provided with a flow directing device at an air inlet region.

BACKGROUND OF THE INVENTION

In an effort to reduce the amount of pollution emissions from gas-powered turbine engines, governmental agencies have enacted numerous regulations requiring reductions in the amount of oxides of nitrogen (NOx) and carbon monoxide (CO) produced. Lower combustion emissions can often be attributed to a more efficient combustion process, with specific regard to fuel injector location, airflow rates, and mixing effectiveness.
Early combustion systems utilized diffusion type nozzles, where fuel is mixed with air external to the fuel nozzle by diffusion, proximate the flame zone. Diffusion type nozzles historically produce relatively high emissions due to the fact that the fuel and air burn essentially upon interaction, without mixing, and stoichiometrically at high temperature to maintain adequate combustor stability and low combustion dynamics.
An enhancement in combustion technology is the concept of premixing fuel and air prior to combustion to form a homogeneous mixture that burns at a lower temperature than a diffusion type flame and thereby produces lower NOx emissions. Premixing can occur either internal to the fuel nozzle assembly or external thereto, as long as it is upstream of the combustion zone. An example of a premixing combustor has a plurality of fuel nozzle assemblies, each injecting fuel into a premix chamber where fuel mixes with compressed air from a plenum before entering a combustion chamber. Premixing fuel and air together before combustion allows for the fuel and air to form a more homogeneous mixture, which, when ignited will burn more completely, resulting in lower emissions. However, the thoroughness and completeness of the mixing and resulting burning of the fuel-air mixture depends on the effectiveness of the mixing.

SUMMARY

The present invention discloses an apparatus and method for improving the air injection process for mixing with fuel injected through a fuel nozzle assembly. More specifically, in an embodiment of the present invention, a fuel nozzle assembly is disclosed comprising a plurality of concentric tubes forming first, second and third passageways. The fuel nozzle assembly also comprises a premix tube coaxial to and radially outward of the third tube, the premix tube having a plurality of swirler vanes contained therein for inducing a swirl into a passing flow of air and fuel. The fuel nozzle assembly further comprises one or more coaxial flow dividers spaced axially and radially and extending around an inlet end of the premix tube towards a base of the fuel nozzle. The one or more coaxial flow dividers split and direct a passing airflow into the premix tube of the fuel nozzle assembly.
In an alternate embodiment of the present invention, an air conditioning device for use in a fuel nozzle assembly is disclosed. The air conditioning device comprises a premix tube and one or more coaxial flow dividers positioned at an air inlet region of the fuel nozzle assembly. The one or more coaxial flow dividers each have a cylindrical portion and an air inlet portion that is turned radially outward from a center axis of the fuel nozzle assembly so as to form a plurality of annular air inlets, with the air inlets having unequal radial air flow distributions.
In yet another embodiment of the present invention, a method of conditioning an incoming air stream entering a fuel nozzle assembly is disclosed. The method generally comprises providing a fuel nozzle assembly having one or more coaxial flow dividers positioned at the air inlet region of the fuel nozzle assembly. A flow of compressed air is provided to the air inlet region and the coaxial flow dividers direct the compressed air through the areas formed between the coaxial flow dividers, where the areas formed generate a non-uniform radial distribution of compressed air to the air inlet region of the fuel nozzle assembly.
Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The instant invention will now be described with particular reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a cross section of a fuel nozzle assembly in accordance with the prior art.

FIG. 2 is a perspective view of a fuel nozzle assembly in accordance with an embodiment of the present invention.

FIG. 3 is a cross section of the fuel nozzle assembly of FIG. 2 in accordance with an embodiment of the present invention.

FIG. 4 is a perspective view of a portion of the fuel nozzle assembly in accordance with an embodiment of the present invention.

FIG. 5 is a cross section view through the portion of the fuel nozzle assembly of FIG. 4 in accordance with an embodiment of the present invention.

FIG. 6 is an exploded view of the fuel nozzle assembly of FIG. 2 in accordance with an embodiment of the present invention.

FIG. 7A is a perspective view of a fuel nozzle assembly in accordance with an alternate embodiment of the present invention.

FIG. 7B is a cross section of the fuel nozzle assembly of FIG. 7A in accordance with an alternate embodiment of the present invention.

FIG. 8A is a perspective view of a fuel nozzle assembly in accordance with yet another alternate embodiment of the present invention.

FIG. 8B is a cross section of the fuel nozzle assembly of FIG. 8A in accordance with yet another alternate embodiment of the present invention.

FIG. 9A is a perspective view of a fuel nozzle assembly in accordance with a further alternate embodiment of the present invention.

FIG. 9B is a cross section of the fuel nozzle assembly of FIG. 9A in accordance with a further alternate embodiment of the present invention.

FIG. 10 is a diagram depicting a method of conditioning an incoming airflow entering a fuel nozzle assembly in accordance with an embodiment of the present invention.

FIG. 11 is a cross section of an alternate embodiment of the fuel nozzle assembly of FIG. 2.

DETAILED DESCRIPTION

The present invention discloses a fuel nozzle assembly for use in a gas turbine combustion system for use in a premix combustion system to help reduce emissions from the combustion system as shown in detail in FIGS. 2-10. The fuel nozzle assembly as shown in FIGS. 2-9B is not to scale but merely intended to represent the present invention. As one skilled in the art understands, a gas turbine engine typically incorporates a plurality of combustors. Generally, for the purpose of discussion, the gas turbine engine may include low emission combustors such as those disclosed herein and may be arranged in a can-annular configuration about the gas turbine engine. One type of gas turbine engine (e.g., heavy duty gas turbine engines) may be typically provided with, but not limited to, six to eighteen individual combustors, each of them fitted with the components outlined above. Accordingly, based on the type of gas turbine engine, there may be several different fuel circuits utilized for operating the gas turbine engine. Each combustor includes one or more fuel nozzle assemblies for supplying the fuel for generating the hot combustion gases.
Emissions from a combustion system are based in part on how completely the fuel and air mix and then burn, or combust. In order to minimize the emissions and maximize the burning of the fuel that is being injected, it is preferable that the fuel and air are thoroughly mixed. To ensure thorough mixing, one factor considered is the condition of the air mixing with the fuel.
Referring initially to FIG. 1, a fuel nozzle assembly 100 of the prior art is shown in cross section. The fuel nozzle assembly 100 is similar to that of U.S. Pat. No. 6,438,961 assigned to the General Electric Co. The fuel nozzle assembly provides a swirler 102 for injecting fuel into a passing air flow and an inlet flow conditioner 104 for directing the flow radially inward through a series of holes 106. The inlet flow conditioner 104 comprises a cylindrical wall portion and an end wall perpendicular to the cylindrical portion. The flow, is turned axially through a plurality of turning vanes 108. However improved conditioning of the incoming airflow to the fuel nozzle assembly can be achieved through a simpler geometry.
An improved way of treating the incoming air flow to a fuel nozzle assembly is discussed below with respect to FIGS. 2-10. The fuel nozzle assembly 200 is in accordance with an embodiment of the invention. More specifically, referring to FIGS. 2 and 3, the fuel nozzle assembly 200 comprises a first tube 202 extending along a center axis A-A and having a first passageway 204 formed within the first tube 202. The first passageway 204, depending upon the operation of a combustion system contains a liquid, gas, air, or mixture thereof for purging the first passageway 204, where the contents of the first passageway 204 are directed towards a tip region 205 of the fuel nozzle assembly 200. Depending on the configuration of the fuel nozzle assembly, the first tube 202 can also include a blank or dual fuel cartridge extending within the first tube 202 and along the center axis A-A that may be purged with air. The cartridge, although not depicted, is sized to then also aid in establishing the correct size of the corresponding first passageway 204 for the gas or purge air.
Coaxial to and radially outward of the first tube 202 is a second tube 206. A second passageway 208 is formed between the first tube 202 and the second tube 206. The second passageway 208 extends coaxial to the first passageway 204 to within approximately swirler vanes 220, as discussed below. The second passageway 208 contains fuel, air, or a mixture thereof directed to the swirler vanes 220, as discussed below.
The fuel nozzle assembly 200 also comprises a third tube 210 which is coaxial to and radially outward of the second tube 206, thereby forming a third passageway between a portion of the second tube 206 and the third tube 210 as well as between a portion of the first tube 202 and the third tube 210. That is, the third passageway is split into two portions, 212A and 212B, which do not communicate with each other. A first portion 212A extends from a base 224 of the fuel nozzle assembly 200 to proximate the swirler vanes 220. A second portion 212B extends from proximate the swirler vanes 220 to the tip region 205 of the fuel nozzle assembly 200. Through the first portion 212A flows a gas, where the gas initially travels axially through the first portion 212A and then radially outward through the swirler vanes 220, where it is injected into a surrounding air stream. The second portion 212B flows air, gas, or a mixture thereof, which is drawn into the second portion 212B at the region adjacent to the swirler vanes 220, through air inlet holes 221. The air, fuel, or mixture thereof then passes axially through the second portion 212B to the tip region 205 of the fuel nozzle assembly 200, where it serves to mix with the liquid, air, gas, or a mixture thereof from the first passageway 204 proximate the tip region 205.
In an alternate embodiment of the present invention, a fuel-air mixture can be provided to second portion 212B for injection through the tip of the fuel nozzle assembly. This is shown in FIGS. 3 and 6. The second portion 212B can flow a gaseous fuel, air, or mixture thereof. In order to supply second portion 212B with a flow of fuel, it is necessary for the second portion 212B to be in fluid communication with the fuel-air mixture resulting from the plurality of swirler vanes 220. A fuel mixture can be supplied to the second portion 212B through one or more holes 213 located in the third tube 210. The one or more holes 213 can be oriented at an angle or perpendicular to the surface of the third tube 210.
Referring to FIG. 11, yet another alternate embodiment of the fuel nozzle assembly is depicted. As discussed above, second portion 212B can pass a fuel-air mixture to the tip region 205. However, this fuel can be provided to second portion 212B through an alternate means, such as through holes 211 in the first tube 202. As such, fuel from first passageway 204 passes through holes 211 and into second portion 212B.
Referring back to FIG. 3, the fuel nozzle assembly 200 also comprises a premix tube 214 positioned coaxial to and radially outward of the third tube 210. The premix tube 214 has an inlet end 216 and an opposing outlet end 218. A plurality of swirler vanes 220 extend radially between the third tube 210 and premix tube 214. As it can be seen from FIGS. 3-5, the inlet end 216 of the premix tube 214 has a flared edge directed generally radially outward from the center axis A-A. The plurality of swirler vanes 220 are positioned about the center core of coaxial tubes of the fuel nozzle assembly 200 and provide a way of injecting and mixing fuel and air together to induce a swirl, as discussed further below.
The fuel nozzle assembly 200 also comprises one or more coaxial flow dividers 222 for dividing an incoming airflow stream, as shown in FIG. 5. The exact quantity of coaxial flow dividers can vary, but for the embodiment of the present invention depicted in FIGS. 2-9, there are two coaxial flow dividers, a first flow divider 222A and a second flow divider 222B that work together with the inlet end 216 of the premix tube 214 and the base region 224 to split and direct the flow of compressed air into the fuel nozzle assembly 200. More specific features of the coaxial flow dividers 222 can be seen in FIGS. 4 and 5. For example, each coaxial flow divider 222 (and therefore 222A and 222B) include a cylindrical portion 226 having an axial length and an inlet region portion 228, where the inlet region portion 228 is turned radially outward from the center axis A-A.
As discussed above, the one or more coaxial flow dividers direct a supply of compressed air into the fuel nozzle assembly 200. The coaxial flow dividers 222 are spaced apart in a radial and axial positioning to create a series of annular openings through which the air flows. The effective area of these openings, which regulates the amount of air that can pass therethrough, is controlled by this axial and radial positioning of the coaxial flow dividers 222. More specifically, for the embodiment of the fuel nozzle assembly depicted in FIG. 3, there are three air inlet areas generated by the plurality of coaxial flow dividers 222 and the premix tube 214. A first air inlet area 230 is formed between third tube 210/base 224 of the fuel nozzle assembly 200 and the first flow divider 222A. A second air inlet area 232 is formed between the first flow divider 222A and the second flow divider 222B. Finally, for the embodiment depicted in FIG. 3, a third air inlet area 234 is formed between the second flow divider 222B and the inlet end 216 of the premix tube 214.
The series of air inlets 230, 232, and 234 form a series of co-annular flows of compressed air directed axially towards the plurality of swirler vanes 220. However, the inlet areas 230, 232, and 234 to do not provide a uniform radial air flow distribution due to the size of the respective openings. More specifically, the radial air flow distribution of the first air inlet 230 has a different radial air flow distribution than that of the second air inlet 232. However, for one embodiment of the present invention, the radial air flow distribution of the first air inlet 230 is similar to that of the radial air flow distribution for the third air inlet 234. Accordingly, for an embodiment of the present invention, the radial air flow distributions of the first air inlet 230 and third air inlet 234 are each greater than the second air inlet area 232. The one or more coaxial flow dividers 222 generate different volumes of air passing therethrough such that a greater amount of air is biased to an inner diameter and outer diameter regions of the premix tube 214. For example, for one embodiment of the present invention, the second air inlet area 232 has a radial air flow distribution that is approximately 85% of that of either the first air inlet area 230 or third air inlet area 234. However, the air inlet areas may vary based on downstream fuel input.
Another feature of the present invention is the ability to expand the air flow after it has passed through the one or more coaxial flow dividers 222 and corresponding air inlet areas (230, 232, and 234) and passes through premix tube 214. In an embodiment of the invention depicted in FIGS. 3 and 5, the premix tube 214 tapers radially outward at a region 215 to increase the volume within the premix tube 214. As such, the geometry of the premix tube 214 provides a way of expanding or diffusing the compressed air immediately downstream of the second flow divider 222B. The exact geometry of the premix tube and coaxial flow dividers may vary to avoid flow separation.
The overall shape of the coaxial flow dividers 222 and premix tube 214 together provide a smooth way of transitioning the airflow into a uniform axial flow direction. The shape and orientation of the one or more coaxial flow dividers 222 provides a way to change the flow direction of the compressed air while minimizing pressure loss. As one skilled in the art understands, flow passing through a screen, such as that of the prior art shown in FIG. 1 undergoes a pressure loss. The present invention produces a slight squeeze to the compressed air and then permits expansion of the compressed air to the desired geometry of the premix tube 214 and plurality of swirler vanes 220.
Referring to FIGS. 4 and 5, another feature of the present invention is a plurality of pins 240 positioned about and between the one or more coaxial flow dividers 222. The plurality of pins 240 aid in holding the one or more coaxial flow dividers 222 together while also maintaining the air inlet areas 230, 232, and 234 previously discussed. The plurality of pins 240 are secured to the one or more coaxial flow dividers 222 by a means such as welding or brazing. As such, the pins are generally fabricated from a material similar in thermal and mechanical properties to that of the one or more coaxial flow dividers 222.
Alternate embodiments of the present invention are depicted in FIGS. 7A-9D. Generally speaking, these alternate embodiments provide additional ways of securing the one or more coaxial flow dividers to the fuel nozzle assembly while also maintaining the air inlet areas previously discussed. Referring initially to FIGS. 7A and 7B, a fuel nozzle assembly 700 is disclosed, which is generally similar in structure and operation to the fuel nozzle assembly of FIGS. 2-6. The fuel nozzle assembly 700 includes a premix tube 714, one or more coaxial flow dividers 722 and a plurality of pins 740. To enhance the structural rigidity of the fuel nozzle assembly 700 and the one or more coaxial flow dividers 722, a plurality of struts 742 are positioned extending between and secured to the one or more coaxial flow dividers 722 at the radially outermost point and the inlet end 716 of the premix tube 714. The plurality of struts 742 are secured to the one or more coaxial flow dividers 722 and premix tube 714 by a means such as welding or brazing. The exact size, quantity and spacing of the plurality of struts 742 will vary depending on a number of factors such as the size and number of coaxial flow dividers 722 and size of the air inlet areas.
An alternate embodiment of the fuel nozzle assembly having improved structural integrity at the air inlet region is shown in FIGS. 8A and 8B. A fuel nozzle assembly 800 is depicted in FIGS. 8A and 8B, and is generally similar in structure and operation to the fuel nozzle assembly 200 of FIGS. 2-6. The fuel nozzle assembly 800 includes a premix tube 814, one or more coaxial flow dividers 822 and a plurality of pins 840. To enhance the structural rigidity of the fuel nozzle assembly 800 and the one or more coaxial flow dividers 822, a plurality of struts 842 extend across the edge or inlet region of each of the coaxial flow dividers 822, where the plurality of struts 842 are secured to the one or more coaxial flow dividers 822 and the inlet end 816 of the premix tube 814. The plurality of struts 842 are secured to the coaxial flow dividers 822 and premix tube 814 preferably by a weld or braze. The exact size, quantity and spacing of the plurality of struts 842 will vary depending on a number of factors such as the size and number of coaxial flow dividers 822 and size of the air inlet areas.
A further alternate embodiment of the present invention is depicted in FIGS. 9A and 9B. This embodiment also provides a way of improving the structural integrity at the air inlet of the fuel nozzle assembly. A fuel nozzle assembly 900 is depicted in FIGS. 9A and 9B, and is generally similar in structure and operation to the fuel nozzle assembly 200 of FIGS. 2-6. The fuel nozzle assembly 900 includes a premix tube 914, one or more coaxial flow dividers 922 and a plurality of pins 940. To enhance the structural rigidity of the fuel nozzle assembly 900 and the one or more coaxial flow dividers 922, a plurality of struts 942 extend through a portion of the flow dividers 922 and a portion of the premix tube 914. The plurality of struts 942 extend through the coaxial flow dividers 922 by passing through one or more holes in the flow dividers 922. The coaxial flow dividers 922 are then secured to the one or more coaxial flow dividers 922 and the inlet end 916 of the premix tube 914 by a means such as brazing or welding. The exact size, quantity and spacing of the plurality of struts 942 will vary depending on a number of factors such as the size and number of coaxial flow dividers 922 and size of the air inlet areas.
Referring now to FIG. 10, another embodiment of the present invention is disclosed. A method 1000 of conditioning an incoming air stream entering a fuel nozzle assembly is disclosed. In a step 1002, a fuel nozzle assembly is provided having one or more coaxial flow dividers positioned at an air inlet region of the fuel nozzle assembly with the coaxial flow dividers spaced axially and radially at the air inlet region. The spacing of the coaxial flow dividers creates a plurality of areas. In a step 1004, a flow of compressed air is provided to the air inlet region of the fuel nozzle assembly. Once the flow of compressed air is provided, in a step 1006, the compressed air is directed through each of the plurality of areas formed by the coaxial flow dividers with the air flowing in a direction that is coaxial to a center axis. The coaxial flow dividers are spaced and oriented so as to provide a non-uniform radial distribution of compressed air to the inlet region of the fuel nozzle assembly. Upon exit from the coaxial flow divider region, the compressed air is oriented in primarily an axial direction.
While the invention has been described in what is known as presently the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, is intended to cover various modifications and equivalent arrangements within the scope of the following claims. The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive.
From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.

Claims

1. A fuel nozzle assembly comprising:

a first tube extending along a center axis and having a first passageway therein;

a second tube coaxial to and radially outward of the first tube and forming a second passageway between the first tube and the second tube;

a third tube coaxial to and radially outward of the second tube and forming a third passageway between the second tube and a portion of the third tube and a portion of the first tube and the third tube;

a premix tube coaxial to and radially outward of the third tube, the premix tube having an inlet end and an opposing outlet end, the premix tube having a plurality of swirler vanes positioned between the third tube and premix tube, the plurality of swirler vanes configured to inject fuel and induce a swirl into a passing flow of fuel and air; and,

one or more coaxial flow dividers, each of the coaxial flow dividers having a cylindrical portion and an inlet region portion, where the inlet region portion is turned radially outward from the center axis;

wherein the one or more coaxial flow dividers split and direct a passing airflow into the premix tube.

2. The fuel nozzle assembly of claim 1, wherein the first tube contains a cartridge for supplying purge through a first passageway.

3. The fuel nozzle assembly of claim 2, wherein the first passageway contains either liquid, gas, air, or a mixture thereof.

4. The fuel nozzle assembly of claim 3, wherein the second passageway contains air, fuel, or a mixture thereof.

5. The fuel nozzle assembly of claim 4, wherein the third passageway is divided into a first portion and a second portion, the first portion extending from proximate a base of the fuel nozzle assembly to proximate the plurality of swirler vanes, while the second portion extends from proximate the plurality of swirler vanes to proximate a tip region of the fuel nozzle assembly, where the first portion is not in fluid communication with the second portion.

6. The fuel nozzle assembly of claim 5, wherein the first portion of the third passageway contains gas and the second portion of the third passageway contains air, gas, or a mixture thereof.

7. The fuel nozzle assembly of claim 1, wherein the inlet end of the premix tube tapers radially outward from the center axis.

8. The fuel nozzle assembly of claim 1, further comprising a plurality of struts extending between and secured to the one or more coaxial flow dividers and the premix tube.

9. The fuel nozzle assembly of claim 8, wherein the plurality of struts extend through a portion of the coaxial flow dividers and a portion of the premix tube.

10. The fuel nozzle assembly of claim 8, wherein the plurality of struts extend across the inlet region of each of the coaxial flow dividers.

11. An air conditioning flow device for use in a fuel nozzle assembly comprising:

a premix tube having an inlet end turned radially outward from a center axis of the fuel nozzle assembly; and,

one or more coaxial flow dividers positioned at an air inlet region of the fuel nozzle assembly, each coaxial flow divider having a cylindrical portion extending an axial length and an air inlet portion turned radially outward, the one or more coaxial flow dividers spaced axially and radially so as to form a plurality of annular air inlet areas therebetween, so as to form an unequal radial air flow distribution between the coaxial flow dividers.

12. The air conditioning flow device of claim 11, wherein the plurality of coaxial flow dividers comprise a first and second flow divider.

13. The air conditioning flow device of claim 12, wherein a first air inlet area is formed between a third tube of the fuel nozzle assembly and the first flow divider, a second air inlet flow area is formed between the first and second flow dividers, and a third air inlet area is formed between the second flow divider and the inlet end of the premix tube.

14. The air conditioning flow device of claim 13, wherein the first air inlet area has a different radial air flow distribution than the second air inlet area.

15. The air conditioning flow device of claim 14, wherein the first air inlet area has a similar radial air flow distribution to the third air inlet area.

16. The air conditioning flow device of claim 15, wherein the first air inlet area and third air inlet area each have a radial air flow distribution that is greater than the second air inlet area.

17. The air conditioning flow device of claim 13 further comprising a plurality of struts extending between and secured to the one or more coaxial flow dividers and the premix tube.

18. A method of conditioning an incoming air stream entering a fuel nozzle assembly comprising:

providing the fuel nozzle assembly having one or more coaxial flow dividers positioned at an air inlet region of the fuel nozzle assembly and spaced axially and radially at the air inlet region;

providing a flow of compressed air to the air inlet region of the fuel nozzle assembly; and,

directing the compressed air through each of a plurality of areas formed by the one or more coaxial flow dividers and in a direction coaxial to a center axis of the fuel nozzle assembly;

wherein the plurality of areas provide a non-uniform radial distribution of compressed air to the air inlet region of the fuel nozzle assembly.

19. The method of claim 18, wherein the coaxial flow dividers further comprise a plurality of radially extending support pins positioned radially between adjacent coaxial flow dividers.

20. The method of claim 18, wherein the compressed air is oriented in primarily an axial direction upon exiting the coaxial flow dividers and entering the premix tube of the fuel nozzle assembly.