Patent Publication Number: US-8966908-B2

Title: Phase and amplitude matched fuel injector

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a fuel injector for a turbine engine, and more particularly, to a phase and amplitude matched fuel injector for a turbine engine. 
     BACKGROUND 
     During operation, turbine engines exhaust a complex mixture of air pollutants. These air pollutants may include oxides of nitrogen (NO x ). Exhaust emission standards regulate the amount of NO x  emitted to the atmosphere from a turbine engine depending on the type, size, and/or class of the engine. It is known that a well-distributed flame having a low flame temperature may help to reduce NO x  emission to levels compliant with emission regulations. One way to generate a flame with a low temperature is to premix fuel and air to a create a lean fuel-air mixture. However, naturally occurring combustion induced pressure fluctuations within the combustor of the turbine engine can be amplified during operation of the engine under lean conditions. These amplified pressure fluctuations may induce mechanical vibrations that can damage the turbine engine. 
     One method to provide a lean fuel-air mixture to a turbine engine while minimizing the harmful vibrations is described in U.S. Patent Publication No. US 2007/0074518 A1 (“the &#39;518 publication”) assigned to the assignee of the current application. In the &#39;518 publication, the length of different regions of a fuel nozzle is adjusted such that a magnitude of the fuel to air equivalence ratio reaching the flame front is a minimum when a pressure pulse at the flame front is a maximum. While the method described in the &#39;518 publication is suitable to reduce mechanical vibrations in many applications, other applications may benefit from other means of reducing mechanical vibrations. 
     The disclosed fuel injector is directed to overcoming one or more of the problems set forth above. 
     SUMMARY 
     In one aspect, a fuel injector for a turbine engine is disclosed. The fuel injector includes a body member disposed about a longitudinal axis, and a barrel member located radially outwardly from the body member. The fuel injector may also include an annular passageway extending between the body member and the barrel member from a first end to a second end. The first end may be configured to be fluidly coupled to a compressor of the turbine engine and the second end may be configured to be fluidly coupled to a combustor of the turbine engine. The fuel injector may also include a perforated plate positioned proximate the first end of the passageway. The perforated plate may be configured to direct compressed air into the annular passageway with a first pressure drop. The fuel injector may also include at least one fuel discharge orifice positioned downstream of the perforated plate. The at least one orifice may be configured to discharge a fuel into the annular passageway with a second pressure drop. The second pressure drop may have a value between about the first pressure drop and about 1.75 times the first pressure drop. 
     In another aspect, a method of operating a turbine engine including a fuel injector fluidly coupling a compressor and a combustor of the turbine engine is disclosed. The method includes directing a compressed air stream into an upstream end of the fuel injector with a first pressure drop. The method may also include directing a fuel with a second pressure drop into the compressed air stream at a location less than or equal to about 0.75 inches downstream of the upstream end. The second pressure drop may have a value between about the first pressure drop and about 1.75 times the first pressure drop. The method may further include delivering the fuel and the compressed air stream to the combustor as a fuel-air mixture. 
     In yet another aspect, a method of operating a turbine engine is disclosed. The turbine engine may be configured to have a combustion induced pressure wave induced in a combustor of the turbine engine during operation. The method may include directing a fuel-air mixture to the combustor through a fuel injector that has a longitudinal axis. Directing the fuel-air mixture may include directing compressed air into the fuel injector through a perforated plate having a plurality of perforations arranged substantially symmetrically around the longitudinal axis. The compressed air may be subject to a first pressure drop across the perforated plate. Directing the fuel-air mixture may also include directing a fuel into the fuel injector through a plurality of orifices positioned at a first length downstream of the perforated plate. The first length may be less than or equal to about 4% of a wavelength of the pressure wave induced in the combustor. The fuel may be subject to a second pressure drop across the orifices. The second pressure drop may have a value between about the first pressure drop and about 1.75 times the first pressure drop. Directing the fuel-air mixture may also include mixing the fuel in the compressed air to create the fuel-air mixture. The method may further include combusting the fuel-air mixture in the combustor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cutaway-view illustration of an exemplary disclosed turbine engine; 
         FIG. 2A  is a cross-sectional illustration of an exemplary fuel injector of the turbine engine of  FIG. 1 ; 
         FIG. 2B  is a perspective view of the exemplary fuel injector of  FIG. 2A ; and 
         FIG. 3  is a pictorial representation of an exemplary disclosed operation of the fuel injector of  FIG. 2A . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary turbine engine  100  that may be associated with a stationary or mobile machine. For example, turbine engine  100  may embody a power source of a generator set that produces electrical power output, or a power source of an earth-moving machine, a passenger vehicle, a marine vessel, or any other type of machine known in the art. Turbine engine  100  may include a compressor section  10 , a combustor section  20 , a turbine section  70 , and an exhaust section  90 . 
     Compressor section  10  may include components rotatable to compress inlet air. Specifically, compressor section  10  may include a series of rotatable compressor blades about a central shaft  12 . As the central shaft  12  is rotated, the compressor blades draw air into turbine engine  100  and pressurize the air. This pressurized air may then be directed to an enclosure  72  of the combustor section  20  for mixture with a liquid and/or gaseous fuel. Combustor section  20  includes one or more fuel injectors  26  arranged about the central shaft  12 . Compressed air from the enclosure  72  is drawn into these fuel injectors  26 , mixed with a fuel, and directed into a combustion chamber (hereinafter “combustor  50 ”) extending around the central shaft  12 . In the combustor  50 , the fuel-air mixture may combust to produce combustion gases at a high pressure and temperature. These combustion gases are directed to the turbine section  70 . Turbine system  70  extracts energy from these combustion gases, and directs the exhaust gases to the atmosphere through exhaust section  90 . The layout of the turbine engine  100  illustrated in  FIG. 1 , and described above, is only exemplary, and fuel injectors  26  of the current disclosure may be used with any configuration and layout of turbine engine  100 . 
       FIG. 2A  illustrates a cross-sectional view of an exemplary fuel injector  26  that may be used in turbine engine  100  of  FIG. 1 . The fuel injector  26  may include components that cooperate to inject gaseous and/or a liquid fuel into the combustor  50 . Specifically, each fuel injector  26  may include a barrel housing  34  connected at one end to an air inlet duct  35  for receiving compressed air from enclosure  72 , and on the opposing end to the combustor  50 . Fuel injector  26  may also include a central body  36 , a pilot fuel injector  38 , and an air swirler  40 . Central body  36  may be disposed radially inwardly of barrel housing  34  and aligned along a longitudinal axis  42  of the fuel injector  26 . Pilot fuel injector  38  may be located within the central body  36  and configured to inject a pilot stream of pressurized fuel through a tip end  44  of central body  36  into combustor  50 . The pilot stream of fuel may facilitate engine starting, idling, cold operation, and/or lean burn operations of turbine engine  100 . Air swirler  40  may be annularly disposed between barrel housing  34  and central body  36  in the air inlet duct  35 . 
     Barrel housing  34  may be a tubular member disposed radially outwardly of the central body  36  to define an annular passageway  32  therebetween. The annular passageway  32  may receive a fuel-air mixture from the air inlet duct  35  at an upstream end and discharge the fuel-air mixture into the combustor  50  at a downstream end. The air inlet duct  35  may be a tubular member configured to receive compressed air from the enclosure  72  at an upstream end, mix the compressed air with fuel, and discharge the fuel-air mixture into the annular passageway  32  at a downstream end. The air inlet duct  35  may include a perforated plate  60  at the upstream end opposite the barrel housing  34 . The perforated plate  60  may control the amount of air that enters the fuel injector  26  from the enclosure  72 . 
       FIG. 2B  illustrates a perspective view of the upstream end of fuel injector  26  when viewed from enclosure  72  (see  FIG. 1 ). In the discussion that follows, reference will be made to both  FIGS. 2A and 2B . The perforated plate  60  may include a plate  63  having a plurality of annularly positioned perforations that direct air into the air inlet duct  35 . Radially inwardly of the annularly positioned perforations, the perforated plate  60  may include a central opening  62 . When attached to the fuel injector  26 , the pilot fuel injector  38  may pass through the central opening  62  to define an annular opening between the plate  63  and the pilot fuel injector  38 . Compressed air from the enclosure  72  may enter the fuel injector  26  through this annular opening, and flow into the combustor  50  through an annular passageway formed between the central body  36  and the pilot fuel injector  38 . 
     The plurality of perforations of the plate  63  may include a plurality of first perforations  64   a , a plurality of second perforations  64   b , and a plurality of third perforations  64   c . The first perforations  64   a , the second perforations  64   b , and the third perforations  64   c  may be annularly positioned about the longitudinal axis  42 . In some embodiments, the second perforations  64   b  may be positioned radially outwardly of the third perforations  64   c , and radially inwardly of the first perforations  64   a . In some embodiments, the first, second, and third perforations  64   a ,  64   b ,  64   c  may be substantially circular. In some embodiments, the diameter of second perforations  64   b  may be greater than the diameter of the third perforations  64   c  and smaller than the diameter of the first perforations  64   a . As the compressed air flows into the air inlet duct  35  through the first, second, and third perforations  64   a ,  64   b ,  64   c , the compressed air will experience a pressure drop ΔP air  and an increase in velocity due to flow restrictions caused by the perforated plate  60 . The geometry of the perforated plate  60  may be such that pressure fluctuations within air inlet duct  35  are minimized to provide a uniform flow of air through air inlet duct  35 . The arrangement of the first, second, and third perforations  64   a ,  64   b ,  64   c  on the perforated plate  60  may reduce the distortions (or skew) in the velocity profile of the air in the air inlet duct  35 . 
     With reference to  FIG. 2A , air swirler  40  may be positioned in the air inlet duct  35  downstream of the perforated plate  60 . The air swirler  40  may include an annulus with a plurality of vanes  54  connected thereto. As the compressed air flows across the vanes  54 , a swirl may be imparted to the compressed air. Some or all of vanes  54  may include a plurality of gaseous fuel orifices  58  at the upstream side (or the leading edge) of the vanes  54 . The number and arrangement of the orifices  58  in a vane  54  may depend upon the application. Although, in general, fuel injector  26  may include any number of vanes  54  and any number or orifices  58  per vane  54 , in some embodiments, the air swirler  40  may include twelve vanes  54 , and each vane may include forty orifices  58 . The orifices  58  may direct a gaseous fuel (hereinafter “fuel”) into the air stream flowing in the air inlet duct  35 . Any type of gaseous fuel, such as, for example, natural gas, landfill gas, bio-gas, or any other suitable gaseous fuel may be directed into the fuel injector  26  through the orifices  58 . Each of the orifices  58  may be in communication with a gaseous fuel gallery  59  that receives the gaseous fuel from an external source (not shown). The orifices  58  may have a geometry that induces a pressure drop ΔP gas  in the fuel entering the fuel injector  26 . As the fuel enters the air inlet duct  35  through the orifices  58 , the fuel mixes with the compressed air flowing across the air swirler  40  to form a fuel-air mixture. This fuel-air mixture enters the combustor  50  through the annular passageway  32  of the barrel housing  34 . In embodiments where the fuel injector  26  is configured to operate on both a liquid fuel and a gaseous fuel (that is, a dual fuel injector), some or all of these vanes  54  may also include liquid fuel jets (not shown) that are configured to inject a liquid fuel into the air stream in the air inlet duct  35 . While the current disclosure is applicable to a fuel injector that delivers a gaseous fuel and/or a liquid fuel to the combustor  50 , for the sake of brevity, an exemplary embodiment of a fuel injector  26  that delivers a gaseous fuel to the combustor  50  is discussed herein. 
     Combustor  50  (referring to  FIG. 1 ) may house the combustion process. Combustor  50  may be configured to receive the mixed fuel-air mixture through the barrel housing  34  of each fuel injector  26 . This fuel-air mixture may be ignited and combusted within the combustor  50 . As the fuel-air mixture combusts, an expanding flame front is created. Due to the variations in the fuel-air mixture directed into the combustor  50  through different fuel injectors  26 , circumferential pressure fluctuations may be induced in the combustor  50 . These pressure fluctuations emanate from the flame front and propagate as a sinusoidal pressure wave into the fuel injectors  26  against the flow of fuel and air. In general, the frequency of the pressure wave depends on the application (such as, for example, the geometry of the combustor, etc.). As the pressure wave moves past the orifices  58  and the perforated plate  60 , the flow of fuel and air into the fuel injector  26  may be affected. 
       FIG. 3  illustrates the effect of the combustion induced pressure wave  82  on the time-varying flow characteristics of fuel and air through the fuel injector  26 . As pressure wave  82  moves past an orifice  58 , the pressure drop ΔP gas  across the orifice  58  changes. As a peak of the sinusoidal pressure wave  82  reaches the orifice  58 , ΔP gas  decreases, and the mass flow of fuel exiting the orifice  58  decreases. And, as a valley of the sinusoidal pressure wave reaches the orifice  58 , ΔP gas  increases, and the mass flow of fuel exiting the orifice  58  increases. Thus, because of the combustion induced pressure wave  82  in the combustor  50 , the flow of fuel entering the fuel injector  26  through the orifices  58  varies sinusoidally. Fuel curve  74  represents the time-varying flow of fuel through the fuel injector  26 . Similarly, as the sinusoidal pressure wave  82  passes the perforated plate  60 , the pressure drop ΔP air , and the flow of compressed air entering the air inlet duct  35  through the perforated plate  60  also varies sinusoidally. Air curve  76  represents the time-varying flow of compressed air through the fuel injector  26 . 
     The fuel exiting the orifices  58  mixes with the air entering the air inlet duct  35  and forms a fuel-air mixture. The ratio of fuel to air in the fuel-air mixture to the stoichiometric fuel to air ratio is referred to as the equivalence ratio. If the mass flow of fuel and air entering the fuel injector  26  is a constant over time, the equivalence ratio will be a constant. However, since the amount of fuel and air entering the fuel injector  26  varies sinusoidally, the equivalence ratio also varies sinusoidally, as represented by equivalence ratio curve  78 . Thus, the equivalence ratio of the fuel-air mixture reaching the combustor  50  may vary in a sinusoidal manner with time. When the value of equivalence ratio reaching the combustor  50  is high (compared to a time averaged value), the heat release and resulting pressure wave  82  within the combustor  50  may be high. Likewise, when the value of equivalence ratio is low, the heat release and resulting pressure wave  82  within the combustor  50  may be low. Thus, the time-varying equivalence ratio may exacerbate the combustion induced pressure waves  82  in the combustor  50 . 
     If the orifices  58  and the perforated plate  60  are positioned proximate each other compared to a wavelength (λ) of the pressure wave  82  (for example, about ≦4% of λ), the fuel curve  74  will be in phase with the air curve  76 . When the fuel and air curves  74 ,  76  are in phase, the peaks and valleys of the curves match. Matching the phase of the fuel and air curves  74 ,  76  is referred to as phase-matching. Phase-matching the fuel and air curves  74 ,  76  reduces the amplitude of the equivalence ratio curve  78 . The distance between the orifices  58  and the perforated plate  60  needed for phase-matching depends upon the application. In some embodiments of fuel injector  26 , the distance “L” between the orifices  58  and the perforated plate  60  is less than or equal to about 4% of the wavelength (λ) of the pressure wave  82 , so that the air and fuel flow through the fuel injector  26  are phase-matched. In some embodiments of fuel injector  26 , the distance L may be less than or equal to about 2% of the wavelength of the pressure wave  82 . 
     In a typical fuel injector, the pressure drop of fuel ΔP gas  is significantly higher than the pressure drop of air ΔP air  (for example, in some fuel injectors, ΔP gas  may be greater than or equal to 3ΔP air ). Because of the higher pressure drop, as is known to a person of ordinary skill in the art, the pulsation in the fuel flow caused due to the pressure wave  82  will be smaller than the pulsation in the air flow. Therefore, the amplitude of the fuel curve  74  will be smaller than the amplitude of the air curve  76 . Because of this difference in amplitudes, the mass of fuel entering the fuel injector  26  through an orifice  58 , and the mass of air entering the fuel injector  26  through the perforated plate  60 , will change differently with time. This difference in variation of the mass of fuel and air with time changes the fuel to air ratio (and therefore, the equivalence ratio) of the fuel-air mixture in the fuel injector  26 . Therefore, phase-matching the fuel and air curves  74 ,  76  may not, by itself, minimize the amplitude of the equivalence ratio curve  78 . If the magnitude of the mass pulsation of the fuel and air are the same (that is, the amplitudes of the fuel curve  74  and the air curve  76  are the same), then the ratio of the fuel and air entering the fuel injector  26  at an instant of time may be the same. Matching the phase and the amplitude of the fuel and air curves  74 ,  76  may make the equivalence ratio substantially a constant over time. 
     The variation in mass pulsations (of the fuel and air) is a function of the respective pressure drops of the fuel and air (that is, ΔP gas  and ΔP air ), and other characteristics of the fluids (such as, for example, the density). Decreasing ΔP gas  may increase the pulsation of the fuel flow and make the amplitude of the fuel curve  74  approach the amplitude of the air curve  76 . Since the orifices  58  are positioned proximate the perforated plate  60  (compared to the wavelength of the pressure wave  82 ) in fuel injectors  26  of the current disclosure, sufficient amplitude matching of the fuel and air curves  74 ,  76  may be achieved if ΔP gas  is less than or equal to about 1.75ΔP air . Decreasing the pressure drop of the fuel ΔP gas  may be achieved in any manner. In some embodiments, the size (for example, the diameter) of the orifices  58  may be increased to decrease ΔP gas . As known to a person of ordinary skill in the art, a compressible flow orifice equation may be used to calculate the pressure drop of the fuel ΔP gas  across an orifice  58  having a known size. 
     Amplitude-matching, along with phase-matching, may minimize the amplitude of the equivalence ratio curve  78 , and thereby reduce the pressure wave  82  in the combustor  50 . The exact percentage increase of ΔP gas  over ΔP air  for amplitude-matching may depend upon the application. In general, in fuel injectors  26  of the current disclosure, ΔP gas  may be between about ΔP air  and about 1.75 times ΔP air  (that is, ΔP air ≦ΔP gas ≦about 1.75 times ΔP air ) to decrease the amplitude of the equivalence ratio curve  78 . In some embodiments of fuel injector  26 , ΔP gas  is between about ΔP air  and about 1.5 times ΔP air  (that is, ΔP air ≦ΔP gas ≦about 1.5 times ΔP air ). 
     INDUSTRIAL APPLICABILITY 
     The disclosed fuel injector may be applicable to any turbine engine where reduced combustion induced oscillations are desired. Although particularly useful for low NO x -emitting turbine engines, the disclosed fuel injector may be applicable to any turbine engine regardless of the emission output of the engine. The disclosed fuel injector may reduce combustion induced oscillations by phase and amplitude matching the fuel and air flows through the fuel injector. The operation of fuel injector  26  will now be explained. 
     During operation of turbine engine  100 , air may be drawn into compressor section  10  and compressed (referring to  FIG. 1 ). This compressed air may then be directed into combustor  50  through a plurality of fuel injectors  26 . As the compressed air flows through a fuel injector  26 , fuel may be directed into the air stream through a plurality of orifices  58  of the fuel injector  26  to create a fuel-air mixture. As the fuel-air mixture enters combustor  50 , the mixture may ignite and combust. The hot expanding exhaust gases may then be directed into turbine section  70  to extract energy therefrom. 
     With reference to  FIG. 3 , variations in the fuel-air mixture directed into the combustor  50  through different fuel injectors  26  may induce a sinusoidal pressure wave  82  in the combustor  50 . This pressure wave  82  may cause the equivalence ratio of the fuel-air mixture entering the combustor  50  through a fuel injector  26  to vary sinusoidally. The variation of the equivalence ratio may be minimized by phase-matching and amplitude-matching the fuel and air flows through the fuel injector  26 . Phase-matching may be accomplished by positioning the fuel orifices  58  at a distance L of less than, or equal to, about 4% of the wavelength of the pressure wave  82  from the perforated plate  60 . Amplitude-matching may be accomplished by keeping the pressure drop of the fuel entering the fuel injector  26  (ΔP gas ) to between about ΔP air  and about 1.75 times ΔP air . 
     In some embodiments, a distance L between the orifices  58  and the perforated plate  60  of less than or equal to about 0.75 inches (19.05 mm) may result in phase matching. In an exemplary fuel injector  26  used in an application where a wavelength λ of the pressure wave  82  is about 36 inches (about 914.4 mm), a distance L between the orifices  58  and the perforated plate  60  of about 0.5 inches (12.7 mm) (that is, about 1.4% of λ) results in phase-matching. In an exemplary embodiment of a fuel injector  26  having four hundred and eighty (480) orifices  58 , each having a diameter of about 0.04 inches (about 1.02 mm), ΔP gas  is reduced from greater than about 130% of ΔP air  to about 20% of ΔP air  by increasing the diameter of each orifice  58  to about 0.05 inches (about 1.27 mm). Phase and amplitude-matching of the fuel and air flows may efficiently minimize the pressure waves without substantially increasing cost of the fuel injector and the turbine engine. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed fuel injector. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed fuel injector. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.