Patent Publication Number: US-6698208-B2

Title: Atomizer for a combustor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to atomizers and, more particularly, to airblast atomizers used in combustors for gas turbine engines. 
     2. Description of the Prior Art 
     The use of air to atomize liquids, such as fuel for combustion in gas turbines, is well known and the methods employed vary widely depending on the desired results, which are influenced by the fineness of atomization, the properties of liquid fuel, the availability of air for the atomizing process and the homogenity of the fuel/air mixture, referred to as F/A mixedness. 
     For example, where compressed air can be supplied from an external source, a device such as that disclosed in U.S. Pat. No. 3,474,970 can be employed, in which high velocity air is applied to one side of a conical fuel sheet produced by the discharge of a conventional spin-chamber or “Simplex” nozzle and flowing on the interior surface of a cone. The application of this principal, however, is limited to relatively low fuel flow rates, and the nozzle operates on a conventional fuel pressure atomizer at a high flows produced using compressed air. In certain applications the use of compressed air is not feasible and is preferred to employ the air which is fed into the combustion chamber from the engine compressor to atomize the fuel. This method is disclosed in U.S. Pat. No. 3,283,502 which describes generally spreading the fuel into a thin film on the surface and atomizing the fuel sheet as it leads the edge of the surface. U.S. Pat. No. 3,530,667 also shows the fuel being spread over a relatively large surface, developing a thin sheet of fuel, for ease of mixing with air, with the air being applied to both sides of the fuel sheet leaving the edge of the surface. Such fuel nozzles are described as the “prefilming” type. In both of these cases, it is evident that the success of the atomization process can be effected by the behavior of the liquid film since in general the size of the atomized drop produced is dependent on the thickness of the fuel film at the point of breakup. Variations of fuel film thickness can occur for various reasons, and this could give rise to poor atomization performances. Optimum atomization of the fuel/air mixture is important in controlling the flame temperature during combustion. The highest source of NO x  is a high flame temperature. Maintaining a homogeneous fuel/air mixture (good mixedness) prior to combustion provides a much higher level of control for a desired flame temperature. 
     An atomizer is desired that will promote uniform atomization of a homogenous fuel/air mixture for combustion, thereby promoting low micron-size fuel particles and allowing closer control of the flame temperature, which in turn produces a more efficient engine cycle while at the same time minimizing the level of undesirable NO x  and other emission species 
     SUMMARY OF THE INVENTION 
     One embodiment of the subject invention is directed to an atomizer for use with a combustor in a gas turbine, wherein the atomizer is comprised of: 
     a body; 
     fuel passageway within the body extending along a passageway centerline, wherein the fuel passageway has an entry end and a discharge end; and 
     a plurality of channels extending within the body about the passageway centerline and spaced around the discharge end of the fuel passageway, wherein at the discharge end of the passageway the channels are oriented along a circumferential angle about the passageway centerline to deliver air at the discharge end of the passageway centerline to deliver air at the discharge of the passageway with a whirling motion and wherein the channels are simultaneously oriented along an axial angle about the passageway centerline thereby converging toward the passageway centerline to deliver air at the discharge end toward the passageway centerline. 
     Another embodiment of the subject invention is directed to an atomizer for use with a combustor in a gas turbine, wherein the atomizer is comprised of: 
     a) providing a stream of fuel against a fuel passageway such that the fuel conforms to the wall of the passageway and exits in a shape conforming to the wall; 
     b) providing a flow of air which both rotates and diverges toward and intersects with the stream of fuel thereby atomizing the stream of fuel. 
     A third embodiment of the subject invention is directed to an annular combustor comprising: 
     a) a combustion chamber; 
     b) at least one atomizer for receiving and mixing fuel and air for introduction to the combustion chamber; 
     c) wherein the atomizer is comprised of 
     1) a body, 
     2) a fuel passageway within the body extending along a passageway centerline, wherein the fuel passageway has an entry end and a discharge end; and 
     3) a plurality of channels extending within the body about the passageway centerline and spaced around the discharge end of the fuel passageway, wherein at the discharge end of the passageway the channels are oriented along a circumferential angle about the passageway centerline to deliver air at the discharge end of the passageway with a whirling motion and wherein the channels are simultaneously oriented along an axial angle about the passageway centerline thereby converging toward the passageway centerline to deliver air at the discharge end toward the passageway centerline. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view of a compressor/turbine including a combustor with an atomizer in accordance with the present invention; 
     FIG. 2 is a perspective view of a combustor having an atomizer in accordance with the present invention; 
     FIG. 3 is a perspective view of an atomizer in accordance with the present invention; 
     FIG. 3A is a cut-away perspective view identical to that in FIG. 3; 
     FIG. 4 is a cross-sectional side view of the atomizer illustrated in FIG. 3 along lines IV—IV; 
     FIG. 4A is a cross-sectional view identical to that in FIG. 4 showing air and fuel flow through the atomizer and including a fuel injector which provides fuel to the atomizer; 
     FIG. 5 is an end view of the atomizer illustrated in FIG. 3 along lines V—V; 
     FIG. 6 is a cross-sectional side view of the atomizer tip and 
     FIG. 7 is an end view of the atomizer tip along lines VII—VII in FIG.  6 ; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an annular combustor  10  connected to a compressor/turbine arrangement  100 . The compressor/turbine arrangement  100  includes compressor blades  102 , a diffuser  103 , turbine blade nozzle channels  104 , and turbine blades  105  positioned around a rotary drive shaft (not shown), which rotates about a central axis (not shown). The combustor  10 , further illustrated in FIG. 2, is comprised of an annular inner shell  115  and a co-axial annular outer shell  120 . A dome end wall  130  connects the inner shell  115  and the outer shell  120 , wherein the inner shell  115 , the outer shell  120  and the dome end wall  130  define an annular combustion chamber  35 . 
     Returning to FIG. 1, within the compressor/turbine arrangement  100 , an annular housing wall  108  is positioned opposite to the exit end  40  of the combustor  10  to enclose the combustion chamber  35 . 
     Air entering the air intake passage  110  positioned adjacent to the compressor blades  102  is directed through passageway  118  along the exterior surface of the combustor  10 , and is introduced into the combustion chamber  35  through a number of passageways  125 ,  128 ,  130  and openings  80  (FIG. 2) extending through the walls of the combustor  10 . Furthermore air is introduced to the combustion chamber  35  at the end  122  of passageway  118 . The combustion chamber  35 , the air path  118  and the turbine blades  105  are in fluid communication with each other. A plurality of fuel/air atomizers  200  extend through the wall of the combustor  10  to provide fuel delivery to the chamber  35 . The fuel/air atomizers  200 , which are tubular in shape, are adapted to direct liquid or gas fuel from fuel injectors  135  and compressed air or oxygen into the combustion chamber  35 . An igniter  140  passes through the combustor  10  and into the combustion chamber  35 , where it may ignite the air/fuel mixture within the chamber  35  until the combustion is self-sustaining. Of significant importance in providing a homogeneous combustion is the design of the atomizers  200 . 
     Directing attention to FIGS. 3 and 3A, an atomizer  200  for use with a combustor in a gas turbine is comprised of a body  205  with a fuel passageway  210  within the body  205  extending along a passageway centerline  215 . The fuel passageway  210  has an entry end  212 , and a discharge end  214 . 
     A plurality of channels  220  (FIGS. 3A and 7) extend within the body  205  about the passageway centerline  215  are spaced around the discharge end  214  of the fuel passageway  210 . At the discharge end  214  of the passageway  210 , channels  220  are oriented along a circumferential angle CA (FIG.  7 ), about the passageway centerline  215  to deliver air at the discharge end  214  of the passageway  210  with a whirling motion. The channels  220  are simultaneously oriented along an axial angle AA (FIG.  6 ), about the passageway centerline  215  and converge toward the passageway centerline  215  to deliver air at the discharge end  214  in a direction approximately tangential to the wall  211  of the fuel passageway  210 . 
     The circumferential angle CA may be between 5° and 60° and preferably is approximately 30°. 
     The channels  220  may diverge toward the passageway centerline  215  at an axial angle AA of between 5° and 60° with a preferred angle of approximately 30°. 
     Each of the channels  220  may follow a helix about the passageway centerline  215  as illustrated in FIG.  7 . Additionally, as a variation that may be easily envisioned from FIG. 7, the channels  220  may follow a linear path about the passageway centerline  215 . 
     As seen in FIG. 7, the channels  220  may be evenly spaced about the periphery of the body  205 . As further illustrated in FIGS. 3,  4  and  6 , the channels  220  may be contained within a conical shaped tip  225  at the discharge end  214  of the passageway  210 . Furthermore, as illustrated in FIGS. 3 a  and  7 , the channels  220  may be located on the interior surface  227  of the tip  225 . 
     Again directing attention to FIG. 7, the width W of each channel  220  increases to W′ at the outer most radial point of that channel  220  to define an enlarged portion  222 . This enlarged portion  222  permits easier alignment of the channel  220  with the passageways that supply air to them and yields a dependable flow area supply to the passageway of the channels  220 . 
     As shown in FIG. 4, the body  205  is comprised of the tip  225  and a cylindrical base  230  directly behind the tip  225 . Air is supplied to each channel  220  by a plurality of peripheral air passageways  235 . The air passageways  235  extend through the base  230  and may be parallel to the passageway centerline  215 . The peripheral passageways  235  are in fluid communication with the channels  220 . As illustrated in FIG. 5, there may be ten peripheral passageways  235  equally spaced within the base  230  around the fuel passageway  210 . Air is introduced to the air passageways  235  and travels through the channels  220 . The number of peripheral passageways  235  is a function of the desired cooling and the desired flow. 
     The combustion chamber of the annular combustor may be exposed to temperatures in excess of 3000° Fahrenheit. Therefore, it is imperative to provide a mechanism to cool the atomizers  200 . The air flowing through the air passageways  235 , and subsequently through the channels  220 , prior to the air being mixed with the fuel provides such cooling. To further enhance this cooling, an accumulating chamber  240  (FIGS. 3A and 4A) may be introduced between the air passageways  235  and the channels  220 . This accumulating chamber  240  not only permits a longer residence time of the air within the body  205 , but also makes it unnecessary to exactly align each air passageway  235  with a respective channel  220 . 
     As illustrated in FIG. 4, the tip  225  may be a discrete part from the base  230 . However, the tip  225  is integrally secured to the base  230  using conventional techniques such as welding. 
     The atomizer  200  has an enlarged conical portion  245  (FIGS. 3A and 4A) at the entry end  212  of the fuel passageway  210 . A fuel injector  135  (FIG. 4A) is angled such that the flow of fuel from the injector  135  is directed against the enlarged conical portion  245  and forms a thin film on the surface on the wall  211  of the fuel passageway  210  to form the shape of a hollow cylinder  252 . This thin film of fuel travels through the fuel passageway  210  and at the discharge end  214  is discharged. On the other hand, air traveling through the air passageway  235  and the channels  220  is directed in a rotating divergent path, which intersects with, and atomizes the thin film of fuel exiting from the fuel passageway  210 . A portion of the air traveling through the channels  220  may be deflected by the hollow cylinder of fuel  252  to a direction diverging from the passageway centerline  215 . Nevertheless, for the most part, the converging air flow merges with the hollow cylinder  252  of fuel. It is through this simple mechanism the atomizer  200 , in accordance with the subject invention is believed to provide improved atomization of the air/fuel mixture using a low pressure fuel supply jet and as a result provides a greater level of homoganarity of the air/fuel mixture prior to the combustion chamber  35 , thereby promoting better control of the combustion temperature and as a result, controlling the level of undesirable NO x  and other emission species. 
     The subject invention is also directed to this method of atomizing fuel and mixing it with air for an annular combustor in a gas turbine engine. In particular, directing attention to FIG. 4A, a stream of fuel  250  is directed against the enlarged conical portion  245  of the fuel passageway wall  211 , such that the fuel conforms to the wall  211  on the passageway  210  and, through air pressure differential across the combustor, exits in a shape conforming to the wall  211  in the approximate shape of a sleeve. Simultaneously, a flow of air  255  is provided through the air passageways  235  and into the channels  220  where it both rotates and converges toward and intersects in a shearing manner with the stream of fuel  250 , thereby atomizing the stream of fuel  250  and, in a diverging swirling form, exiting at the discharge end  214 . 
     The rotation and convergence imparted to the flow of air  255  by the atomizer tip  225  directs the air at an axial angle AA relative to the passageway centerline  215  of between 5° and 60°, preferably about 30°, and a circumferential angle CA relative to a line extending radically from the passageway centerline  215  of between 5° and 60°, preferably about 30°. 
     It is thought the present invention and many of its intended advantages will be understood from the foregoing description and that it will be apparent that various changes may be made in the form, construction and arrangement of the parts thereof, without departing from the spirit and scope of the invention, or sacrificing all of its material advantages, the form herein before described merely preferred or exemplary embodiments thereof.