Abstract:
A fuel injector having a body with a bore, which defines a fuel manifold. The injector also has a variable-area injector arrangement having a pintle with a conical head and a pintle spring connected to the body. The pintle spring urges a tip of the pintle to seal against an exit orifice of the body, such that application of pressurized fuel within the body causes the pintle to move. Above some threshold pressure, the pressurized fuel causes the conical head to move out of contact with the exit orifice of the body. This, in turn, provides a corresponding variable area for passage of the pressurized fuel through the exit orifice about the conical head of the pintle. The injector further includes a swirler configured to create a swirling action in the flow of pressurized fuel through the fuel manifold, wherein the manifold is upstream of the exit orifice.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to fuel delivery systems, and, more particularly, to fuel injectors for delivering fuel to the combustion chambers of combustion engines. 
     BACKGROUND OF THE INVENTION 
     Variable-area fuel injectors have been used in many applications relating to air-breathing propulsion systems, including, for example, in ramjets, scramjets, and in gas turbine engines such as those used in aviation. Ramjets, scramjets, and gas turbine engines typically include a section for compressing inlet air, a combustion section for combusting the compressed air with fuel, and an expansion section where the energy from the hot gas produced by combustion of the fuel is converted into mechanical energy. The exhaust gas from the expansion section may be used to achieve thrust or as a source of heat and energy. 
     Generally, some type of fuel injector is used in the combustion section for spraying a flow of fuel droplets or atomized fuel into the compressed air to facilitate combustion. In some applications of air-breathing propulsion systems including ramjets, scramjets, and particularly in gas turbine engines, which must run at variable speeds, variable-area fuel injectors have been used because they provide an inexpensive method to inject fuel into a combustor, while also metering the fuel flow without the need for an additional metering valve. 
     Typically, the fuel flow rate is controlled by the combination of a spring, the fuel pressure, and an annular area, which is increasingly enlarged as the fuel pressure is increased. This is unlike the operation of pressure-swirl atomizers where the pressure-flow characteristics are static, and are determined solely by the fixed injector geometry and the variable injection pressure. Generally, variable-area fuel injectors provide good atomization over a much wider range of flow rates than do most pressure-swirl atomizers. Additionally, with variable-area fuel injectors, the fuel pressure drop is taken at the fuel injection location, thus providing better atomization than typical pressure-swirl and plain-orifice atomizers. 
     However, throughout its operational pressure range, most variable-area fuel injectors do not provide optimal spray circumferential uniformity, or patternation. Typically, these conventional variable-area fuel injectors have slots or holes used to feed fuel to the fuel manifold which is upstream of the exit area. In general, this configuration does not prevent the formation of wakes in the fuel flow downstream of these slots or holes. Optimal patternation is desirable in order to avoid non-uniform fuel distribution, which can cause hot spots in air-breathing engines resulting in thermal distress and failure of the engine itself. Good patternation also helps avoid regions of high fuel concentration (i.e., rich regions) in combustors, which reduces fuel efficiency and leads to poor emissions quality. 
     In applications not related to air-breathing engines, poor patternation can also lead to failure of the device. One such application is the automotive engine exhaust treatment process in which fuel is used to increase the temperature of the engine exhaust. By increasing the temperature of the exhaust, downstream post-engine exhaust treatment devices, such as dosers and diesel particulate filters can operate more effectively. However, poor patternation can cause hot-spots in the matrix of both the doser and the diesel particulate filter, thus reducing the life of the matrix. 
     Therefore, it would be desirable to have a variable-area fuel injector that provides superior patternation throughout the operational fuel flow range. Embodiments of the invention provide such a variable-area fuel injector. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, embodiments of the invention provide a fuel injector having a body with a bore, which defines a fuel manifold. The injector has a variable-area injector arrangement having a pintle with a conical head and a pintle spring connected to the body. The pintle spring urges a tip of the pintle to seal against an exit orifice of the body, such that application of pressurized fuel within the body causes the pintle to move. Above some threshold pressure, the pressurized fuel causes the conical head to move out of contact with the exit orifice of the body. This, in turn, provides a corresponding variable area for passage of the pressurized fuel through the exit orifice about the conical head of the pintle. The injector further includes a fuel swirler configured to create a swirling action in the flow of pressurized fuel through the fuel manifold, wherein the manifold is upstream of the exit orifice. 
     In another aspect, embodiments of the invention provide the aforementioned fuel injector, wherein the amount of pressure needed to move the conical head of the pintle out of contact with the variable-area exit orifice is determined by a pre-load placed on the pintle spring. 
     In yet another aspect, embodiments of the invention provide the aforementioned fuel injector, wherein the pre-load is placed on the pintle spring by a retaining nut assembly, and the fuel swirler is configured to hold the pintle substantially centered within the injector body 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a plan view of a variable-area fuel injector according to an embodiment of the invention; 
         FIG. 2  is a cross-sectional view of the variable-area fuel injector of  FIG. 1 ; 
         FIG. 3  is a perspective view of a fuel swirler according to an embodiment of the invention; 
         FIG. 4A  is a perspective view of a fuel swirler according to another embodiment of the invention; 
         FIG. 4B  is a plan view of the fuel swirler of  FIG. 4A  showing an end of the fuel swirler hidden in the perspective view of  FIG. 4A ; 
         FIG. 4C  is a cross-sectional view of the fuel swirler of  FIG. 4A ; and 
         FIG. 5  is a plan view of the fuel swirler of  FIG. 4A  assembled into a fuel injector according to an embodiment of the invention. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention address the aforementioned problem of poor patternation and the effects associated therewith as related to fuel injection, particularly in gas turbine and other air-breathing engines. To understand the solution to this problem, it is helpful to understand some of the causes. Poor patternation in fuel injectors may result from lack of concentricity between the fuel injector body and the fuel injector pintle. Also, wakes, present in the fuel flow, due to the geometry upstream of the fuel injector exit orifice can have a significant effect on fuel spray quality. 
     According to an embodiment of the invention, a variable-area injector  100 , as illustrated in  FIGS. 1 and 2 , has a body  102  having a bore or opening  120  along a longitudinal axis  103  of the injector  100 , and which includes a hexagonal outer surface  104 , a sealing surface  106 , and a threaded portion  108 . In alternate embodiments, the outer surface  104  may be square, lobe-shaped, or of some other suitable shape that permits installation of the body using some type of readily available wrench or similar tool. In embodiments of the invention, a fuel swirler  110  is attached at a first end  112  of the body  102  in the longitudinal opening  120 . This attachment of the fuel swirler  110  in the longitudinal opening  120  of the body  102  may be effected by brazing or welding. It is also contemplated that the fuel swirler  110  may be threaded or press fit into the opening  120 , or keyed into the opening  120  via slots formed or machined into the walls of the opening  120 . However, in alternate embodiments, the fuel swirler  110  is not fixedly attached to the body  102 . During operation, the fuel swirler  110  is held in place by pressure from a spring  124 , and by the fuel pressure. The variable-area injector  100  further includes a pintle  114 , which, in this embodiment, has a relatively long, small-diameter cylindrical portion  116  and a conical head  118  at one end of the cylindrical portion  116 . In one embodiment, a lower portion  119  of the cylindrical portion  116  is threaded 
     During assembly of the variable-area injector  100 , the pintle  114  will be inserted into the longitudinal opening  120  in the body  102 . As explained above, the fuel swirler  110  is attached to the body  102  inside the longitudinal opening  120  at the first end  112 . Typically, the cylindrical portion  116  of the pintle is inserted initially at a second end  122  of the body  102 , such that when the pintle  114  is fully inserted, the cylindrical portion  116  is substantially centered in the longitudinal opening  120  and in a central opening in the fuel swirler  110 , and the conical head  118  is seated in a variable-area exit orifice  134  at the second end  122  of the body  102 . 
     The fuel swirler  110  is configured to hold the pintle  114  substantially in place during fuel-injector operation. The spring  124  is assembled over the cylindrical portion  116  until it abuts the fuel swirler  110 . A retaining nut  126  and washer  128  are assembled onto the lower portion  119  of the pintle  114  such that the washer  128  abuts the spring  124 . An optional lock nut  130  is assembled onto the lower portion  119  of the pintle  114  to ensure that the retaining nut  126  does not loosen. In an embodiment of the invention, the lower portion  119  is threaded allowing the retaining nut  126  to be threaded onto the pintle  114 . In alternate embodiments of the invention, the retaining nut  126  is attached to the lower portion  119  by welding, brazing or other suitable means. The washer  128 , retaining nut  126 , and optional lock nut  130  are assembled to the pintle  114  so as to place a pre-load on the spring  124 . The pre-load on spring  124  serves to keep the conical head  118  seated in the variable-area exit orifice  134 . 
     In an embodiment of the invention, the variable-area fuel injector  100  is threaded into the wall of the combustor or of some other pressurized vessel, for example, the wall of the combustion chamber of a gas turbine engine (not shown), via the threaded portion  108  of the body  102 . The outer surface  104 , whether hexagonal, square, or lobe-shaped is configured to be gripped by a wrench, socket wrench, or some similar tool to facilitate assembly of the fuel injector  100  to the wall of the combustion chamber. The sealing surface  106  of the body  102  is configured to seal against the wall of the combustion chamber (not shown). 
     In operation, the conical head  118 , the second end  122  of the body  102 , and the outer surface  104  are exposed to the fuel-air combustion inside the combustion chamber. The threaded portion  108  of the body  102 , the fuel swirler  110 , the spring  124 , cylindrical portion  116  of the pintle  114 , along with the nuts  126 ,  130  and washer  128  are all exposed to pressurized fuel. When the fuel pressure is below some threshold value, the spring  124  keeps the conical head  118  of the pintle  114  seated in the longitudinal opening  120 , such that no fuel flows into the combustion chamber. The threshold value is related to the amount of pre-load that has been applied to the spring  124  by the retaining nut  126  during assembly. However, when the fuel pressure exceeds the threshold value, the spring  124  is compressed as the conical head  118  is lifted away from the longitudinal opening  120 , thus allowing fuel to flow through a fuel manifold  132 , out of the variable-area exit orifice  134  surrounding the conical head  118  and into the combustion chamber (not shown). 
     The flow of pressurized fuel through the opening between the exit orifice  134  and the conical head  118  results in a “hollow cone” spray pattern of fuel from the fuel injector  100  into the combustion chamber (not shown). As the fuel pressure increases causing the conical head  118  of the pintle  114  to move further away from the longitudinal opening  120 , the small diameter of the cylindrical portion  116  substantially replaces the larger conical head  118  in the exit orifice  134 , thus increasing the flow area of the exit orifice. As a result of this variable-area feature, the size of the area available for fuel flow at the exit orifice  134  increases as the fuel pressure increases, thereby allowing fuel to flow into the combustion chamber at an increasing rate. 
     To prevent the formation of wakes, which cause poor patternation, in the fuel as it flows through the fuel manifold  132 , the fuel swirler  110  causes the fuel to move in a spiraling motion as it moves through the fuel manifold  132 , thus reducing or eliminating non-uniformities in the fuel flow. Additionally, the swirling action created by the fuel swirler  110  improves atomization of the fuel by thinning out the liquid sheet as it flows out of the variable-area injector  100  through the exit orifice  134 . Further, the swirling action of the fuel flow helps to center the pintle  114  within the body  102  producing a more uniform spray pattern as a result of the vortex that forms in the fuel manifold  132  and exit orifice  134 . 
       FIG. 3  shows a perspective view of the fuel swirler  110  incorporated into the fuel injector  100  of  FIG. 2 , according to an embodiment of the invention. The fuel swirler  110  has a generally cylindrical body  140  which has a plurality of integral vanes  142  that spiral around the outer surface of the cylindrical body  140 . Each of the plurality of integral vanes  142  has a raised portion  144  configured to engage the wall of the opening  120  when the fuel swirler  110  is assembled to the body  102 . The fuel swirler  110  includes a central opening  146  to accommodate the pintle  114  when the fuel swirler  110  is assembled into the body  102 . When pressurized fuel flows around the fuel swirler  110  and into the fuel manifold  132 , the fuel begins to swirl due to the spiraling shape of the plurality of integral vanes  142 . As a result of this swirling action, non-uniformities, such as those caused by upstream wakes, in the fuel flow are reduced or eliminated. As mentioned above, the swirling action, especially at high flow rates, also tends to thin out the liquid sheet as it flows through the exit orifice  134 , thus improving atomization of the fuel, which, in turn, improves combustion, leading to increased engine efficiency and less pollution. It is also contemplated that embodiments of the invention includes swirlers having a cylindrical body, in which the one or more vanes spiraling around the outer surface of the cylindrical body are not integral with the cylindrical body. The swirler  110  geometry can also include other designs. For examples, the vanes could be helical or straight, and the swirler  110  could be a “plug” with various orifices having angled geometries, or slots oriented to induce swirl into the fuel flow. 
       FIGS. 4A, 4B, and 4C  illustrate one such alternate embodiment of a fuel swirler  150 .  FIG. 4A  is a perspective view of the fuel swirler  150 , which is essentially a cylindrical plug with a plurality of angled holes  152 . At one end  154  of the fuel swirler  150  the plurality of angled holes  152  are drilled, or formed, in the side of a raised portion  156 . At the other end  158  of the fuel swirler  150 , shown in  FIG. 4B , the plurality of angled holes  152  are located at evenly spaced intervals around the circumference of an end face  160 .  FIG. 4C  is a cross-sectional view of the fuel swirler  150  that shows the path of the plurality of angled holes  152  through the body of the fuel swirler  150 , according to an embodiment of the invention. It should be noted that the cross-section shown in  FIG. 4C  is not through the center of the fuel swirler  150 . The plurality of angled holes  152  must be drilled, or formed, so as not to go through the center of the fuel swirler  150  due to the presence of the central opening  161 . 
       FIG. 5  illustrates an exemplary fuel injector  200  incorporating the fuel swirler  150 , according to an embodiment of the invention. During assembly, a cylindrical portion  162  of the fuel swirler  150  is inserted into the longitudinal opening  120  of the body  102  at the end  112 . The fuel swirler  150  includes a central opening  161  to accommodate the cylindrical portion  116  (shown in  FIG. 2 ) of the pintle  114  when the fuel swirler  150  is assembled into the body  102 . A shoulder portion  164  is configured to abut the end  112  of the body  102  during assembly. The shoulder portion  164  can be attached to the body  102  by brazing, or by welding. In an alternate embodiment, the fuel swirler  150  can be press-fit, or threaded, into the longitudinal opening  120  of the body  102 . The spring  124  will abut the raised portion  156 . As in  FIGS. 1 and 2 , the washer  128 , retaining nut  126 , and optional lock nut  130  are assembled to the pintle  114  so as to place a pre-load on the spring  124 . The pre-load on spring  124  serves to keep the conical head  118  seated in the variable-area exit orifice  134 . 
     Referring still to  FIG. 5 , in operation, pressurized fuel enters the plurality of angled holes  152  on the side of the raised portion  156  of the fuel swirler  150 . The pressurized fuel exits through each of the plurality of angled holes  152  at the end face  160 . The pressurized fuel exits at an angle sufficient to cause the desired swirling action, which reduces or eliminates non-uniformities in the fuel flow. 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.