Patent Publication Number: US-2011073071-A1

Title: Internally Nested Variable-Area Fuel Nozzle

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 exposed 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 injector geometry and 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 in some flow conditions than typical pressure-swirl and plain-orifice atomizers. 
     With the increasing cost and complexity of new engine designs, there may be instances when a decrease in the size of fuel nozzles is desired due to space limitations within the engine and/or combustion region. 
     It would therefore be desirable to have a variable-area fuel nozzle that is more compact, lighter in weight, and potentially less costly, than conventional variable-area fuel nozzles. Embodiments of the invention provides such a fuel nozzle. 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 nested fuel injector that includes an injector housing having a bore longitudinally therethrough, and a pintle assembled to the housing and positioned substantially within the bore. The pintle has a head located at an end of a cylindrical portion, wherein the head is seated in one end of the bore, and the seating of the head defines a variable-area exit orifice. A wave spring is assembled onto the pintle and configured to urge the pintle into the seating position. The bore is configured for the passage of a pressurized flow of fuel. The fuel pressure urges the pintle head away from the exit orifice to permit the pressurized fuel to flow from the bore out through the exit orifice 
     In another aspect, embodiments of the invention provide a fuel injector that includes a body that includes a cylindrical threaded portion, and a variable-area injector arrangement having a pintle, a wave spring, and a retaining plate operatively connected to the injector body. The wave spring urges a head of the pintle to seal against a variable-area exit orifice of the body. The bore is configured such that a flow of pressurized fuel within the bore of the body causes the head of the pintle to move out of contact with the variable-area exit orifice. This provides a passage for fuel through the variable-area exit orifice about the head of the pintle, such that the flow rate of fuel through the variable-area exit orifice increases with the fuel pressure. Furthermore, the retaining plate is configured to place a pre-load on the wave spring. 
     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 fuel injector according to an embodiment of the invention; 
         FIG. 2  is a cross-sectional view of the fuel injector of  FIG. 1 ; 
         FIG. 3  is an end view of a retaining plate, according to an embodiment of the invention; 
         FIG. 4  is a cross-sectional view of a fuel injector according to an embodiment of the invention different from the embodiment in  FIG. 2 ; 
         FIG. 5  is a cross-sectional view of a fuel injector according to yet another embodiment of the invention; 
         FIGS. 6 and 7  are plan views of a fuel injector, according to another embodiment of the invention; and 
         FIG. 8  is a cross-sectional view of the fuel injector shown in  FIGS. 6 and 7 . 
     
    
    
     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 
     With respect to variable-area fuel nozzles, generally the largest dimension of the device is along the longitudinal axis of the nozzle. Therefore, to significantly reduce the size of the fuel nozzle, it is most productive to reduce the fuel nozzle&#39;s axial length. Additionally, to increase engine performance and reduce engine cost, reductions in weight and complexity are highly desired. 
     One of the major contributors to the axial length of conventional variable-area fuel nozzles is the metering spring. Typically, the metering spring is comprised of a coil spring. To achieve the desired stroke and loading, it is often necessary to have a metering spring of a relatively long length. Additionally, a retaining assembly may be required to give the spring a positive stop. 
     Embodiments of the present invention address the aforementioned issue of fuel injector size and the effects associated therewith as related to fuel injection in air-breathing propulsion systems, and particularly in ramjets, scramjets, and gas turbine engines, by providing an exemplary compact fuel injector design, which is illustrated in  FIG. 1 . One way to achieve such compactness in fuel injector design is to reduce the axial length of the fuel injector by replacing the conventional pintle spring with a more compact component. When such a change is accompanied by a corresponding reduction in the axial length of the pintle, a substantial reduction in the axial length of the fuel injector may be realized. 
     According to an embodiment of the invention, a variable-area injector  100 , as illustrated in  FIGS. 1 and 2 , has a body, or housing,  102  having a bore or opening  103  along a longitudinal axis  104  of the injector  100 , and which includes a hexagonal outer surface  106 , a sealing surface  108 , and a threaded portion  110 . In alternate embodiments, the outer surface  106  may be square, lobe-shaped, or of some other suitable shape that permits installation of the body, for example into the combustion chamber of a ramjet, scramjet or gas turbine engine, using some type of readily available wrench or similar tool. The variable-area injector  100  further includes a pintle  114 , which, in this embodiment, has a small-diameter cylindrical portion  116  and a conical head  118  at one end of the cylindrical portion  116 . In an embodiment of the invention, the cylindrical portion  116  of the pintle  114  is threaded. It is also contemplated that the pintle head could have a shape other than the conical shape shown in  FIG. 2 . For example, a spherical-shaped head could be used according to an embodiment of the invention. With the appropriate changes to the exit orifice  119 , a variety of pintle head shapes could be used. 
     During assembly of the variable-area injector  100 , the pintle  114  will typically be inserted into the longitudinal opening  103  in the body  102 . Typically, the cylindrical portion  116  of the pintle is inserted initially at an end  120  of the body  102 , such that when the pintle  114  is fully inserted, the conical head  118  is seated in an exit orifice  119  in the longitudinal opening  103  at the second end  120  of the body  102 . A wave spring  122  is assembled into the opening  103  over the cylindrical portion  116  of the pintle  114  until it abuts a substantially vertical portion  124  of the wall of the opening  103 . 
     A wave spring is coiled flat wire with waves added to give the wire a spring effect. Wave springs may, in certain applications, provide the same force as a coil spring of larger size. This not only offers the potential for space savings, but also for smaller assemblies that use less materials, and, therefore, reduce production costs. As will be explained more fully below, a wave spring can be used to exert a force, or pre-load, on a part or assembly to keep selected components in relatively constant contact. The selected components will remain in contact until the application of a counteracting force greater than that of the pre-load separates these selected components. 
     As shown in  FIGS. 1 and 2 , the wave spring  122  has an axial length, which is substantially less than the axial length of an equivalent coil spring. In some embodiments, one or more shims  126  may be assembled over the cylindrical portion  116  of the pintle  114  up to the wave spring  122 . The wave spring  122  and optional shim(s)  126  are held in place by a retaining plate  128 . The retaining plate  128  can be attached to the pintle  114  by welding, brazing, or by any other suitable method. For example, the cylindrical portion  116  of the pintle  114  could be threaded such that the retaining plate  128  could be threaded onto the pintle  114  to hold the wave spring  122  and shim(s)  126  in place. After the retaining plate  128  is assembled onto the pintle  114 , the threads on the cylindrical portion  116  can be intentionally damaged so that the position of the retaining plate  128  cannot be changed, thus maintaining the same pre-load on the wave spring  122 . In an alternate embodiment, a lock nut (not shown) may be assembled onto the pintle  114  to fix the position of the retaining plate  128 . 
     In operation, pressurized fuel is introduced into the opening  103 . In an embodiment of the invention, the retaining plate places a pre-load on the wave spring  122 , which urges the pintle  114  in a manner that keeps the conical head  118  seated in the exit orifice  119  when no fuel is flowing. The force of the pressurized fuel flow against the conical head  118  causes the pintle  114  to axially translate in the direction of the flow and, in turn, causes the conical head  118  to lift out of the exit orifice  119 . This causes the retaining plate  128  to axially translate in the same direction and further compress the pre-loaded wave spring  122 . One or more openings in the retaining plate  128  allow the fuel to flow through the opening  103  out through the exit orifice  119 . The exit orifice  119  is a variable-area orifice, in that as the fuel pressure increases, the wave spring  122  is increasingly compressed and the conical head  118  moves farther away from the exit orifice  119 . As the distance of the conical head  118  from the exit orifice  119  increases, the exit orifice area increases, thus allowing for a resulting increase in the rate of fuel flow through the fuel injector  100 . The use of the wave spring  122 , instead of the coil spring used in conventional fuel injectors allows the pintle  114  to be shortened substantially, such that all of the components of the fuel injector  100  are substantially contained within the injector housing  102 . 
     In some embodiments, position of the retaining plate  128  may be fixed. For example, the threads on the cylindrical portion  116  of the pintle  114  could end at a certain distance from wave spring  122  such that the retaining plate  128  does not abut the wave spring  122 . In such an instance, one or more shims  126  could be assembled to the pintle  114  such that the shim(s) abut the wave spring  122  and the retaining plate  128 . Additional shims  126  could be added to such an assembly when an increase in the pre-load is desired. In an alternate embodiment, the cylindrical portion  116  of the pintle may have a step feature which acts as a stop for the retaining plate  128 . The retaining plate  128  could be welded or brazed to this step feature, and one or more shims  126  would be assembled between the wave spring  122  and retaining plate  128  to control the amount of pre-load on the wave spring  122 . 
       FIG. 3  shows an exemplary embodiment of the retaining plate  128  including three openings  132 . However, alternate embodiments of the retaining plate may greater or fewer than three openings. The retaining plate  128  of  FIG. 2  also includes a central opening  134  configured to accept the pintle  114  during assembly. In some embodiments, the central opening  134  may be threaded to facilitate assembly to the pintle  114 . During operation, the three openings  132  provide a path for the flow of pressurized fuel through the fuel injector  100 . The diameter of the retaining plate  128  is such that an outer perimeter  136  of the perimeter  128  is in close proximity to a wall  138  (shown in  FIG. 2 ) of the injector bore  103 . 
     In the embodiment illustrated in  FIG. 4 , a fuel swirler  202  is assembled to a fuel injector  200  over the pintle  114  into the opening  103 . The fuel injector  200  includes the injector body  102  with hexagonal portion  106  and threaded portion  110 . In the embodiment of  FIG. 4 , the fuel swirler  202  is assembled into the opening  103  after (i.e., upstream from) the wave spring  122 , any optional shims  126 , and the retaining plate  128  such that the fuel swirler  202  is positioned closer to an end  204  of the body  102  than to the substantially vertical portion  124  of the wall of the opening  103 . As in the previous embodiment, the wave spring  122  biases the conical head  118  of the pintle  114  into the exit orifice  119 , cutting off the flow of fuel from the fuel injector  200 . In an embodiment of the invention, both the wall of the opening  103  and an outer surface of the fuel swirler  202  are threaded to facilitate assembly. In such an embodiment, the cylindrical portion  116  of the pintle  114  and the retaining plate  128  could also be threaded to facilitate assembly. However, other embodiments of the invention include equally suitable means for attaching the retaining plate  128  to the pintle  114 , and for attaching the fuel swirler  202  to the opening  103  in the body  102  including, but not limited to, press-fit, welding and brazing may be used. 
     In at least one embodiment, the fuel swirler  202  has a generally cylindrical body (not shown) which has one or more vanes (not shown) that spiral around the outer surface of the cylindrical body. In some embodiments, the vanes are integral (i.e., not separable) with the cylindrical body, though it is contemplated that a fuel swirler  202  having a cylindrical body with non-integral vanes could be used. Typically, in this embodiment, each of the one or more vanes has a raised portion (not shown) configured to engage the wall  206  of the fuel injector bore  103  when the fuel swirler  202  is assembled to the body  102 . The swirler  202  geometry can also include other designs. For examples, the vanes could be helical or straight, and the swirler  202  could be a “plug” with various orifices having angled geometries, or slots oriented to induce swirl into the fuel flow. 
     In operation, when pressurized fuel flows into the fuel injector  200  and around the fuel swirler  202  towards the exit orifice  119 , the fuel begins to swirl due to the spiraling shape of the one or more vanes. As a result of this swirling action, non-uniformities, such as those caused by upstream wakes, in the fuel flow are reduced or eliminated. This 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. The pressurized fuel flows through openings  132  (shown in  FIG. 3 ) in the retaining plate  128  and counteracts the preload placed on the pintle  114  due to biasing by the wave spring  122 . When the fuel pressure exceeds a threshold level, the conical head  118  moves away from the exit orifice  119 , thus allowing fuel to flow from the fuel injector  200 . 
       FIG. 5  shows an alternate embodiment of the fuel injector  300  in which the fuel swirler  202  is located in a bore  303  downstream of the wave spring  122 , the retaining plate  128 , and any optional shims  126 . The fuel injector  300  includes an injector body, or housing  302  with hexagonal portion  106  and threaded portion  110 . The wave spring  122  urges the conical head  118  of the pintle  114  to seat in the exit orifice  119 . During assembly, the pintle  114  is assembled into the bore  303  of the injector body  302 , and the fuel swirler  202  is assembled onto the pintle  114 , within the bore  303 . In one embodiment, an angled portion  304  of the bore wall serves as a physical stop for the fuel swirler  202 , though, as can be seen from the embodiment of  FIG. 5 , the fuel swirler  202  does not have to abut the angled portion  304 . The fuel swirler  202  may be threaded into the bore  303 , though other suitable means of attachment, including, but not limited to, press-fit, brazing and welding, may be used as well. The wave spring  122  and retaining plate  128 , along with any optional shims  126 , are assembled onto the cylindrical portion  116  of the pintle  114 , within the bore  303 . The retaining plate  128  can be assembled to the pintle  114 , using threaded means or other suitable attachment means such as brazing or welding. 
     In operation, pressurized fuel enters the fuel injector  300  via bore  303  flowing through the openings  132  (shown in  FIG. 3 ) in the retaining plate  128 . The pressurized fuel then flows through the fuel swirler  202 , creating a swirling action in the fuel flow that aids in the uniformity of the fuel spray from the fuel injector  300 . When the fuel pressure on the conical head  118  exceeds a threshold level, the conical head  118  moves away from the exit orifice  119 , thus allowing fuel to flow from the fuel injector  300 . 
       FIGS. 6 and 7  are plan views of an exemplary embodiment of a fuel injector  400  having a body, or housing,  402 , which omits the hexagonal portion shown in previous embodiments, instead having a cylindrical threaded portion  404 . As a result, this embodiment has the potential to be even more compact than previous embodiments. As can be seen in  FIG. 8 , the length of both the body  402  and a pintle  414 , specifically a cylindrical portion  416  of the pintle  414 , can be made shorter than in embodiments where the body includes a hexagonal and a threaded portion. As shown in  FIG. 6 , the body  402  further includes two holes  406  drilled, or formed, into an end, or axial face,  408  of the body  402 , wherein the two hole  406  are configured to accommodate a spanner wrench (not shown) or similar tool. The spanner wrench is inserted into holes  406  to assemble the fuel injector  400  into a threaded opening in the combustion chamber (not shown) of an engine (not shown). 
       FIG. 8  is a cross-sectional view of the fuel injector  400  shown in  FIGS. 6 and 7 . The pintle  414  has a conical head  418  at one end of the cylindrical portion  416 , and is assembled from the end  408  into a bore  410  of the body  402 . The conical head  418  is seated in the exit orifice  119 . The wave spring  122  is assembled onto the cylindrical portion  416  of the pintle  414  in the bore  410  and abuts a substantially vertical portion  420  of the wall of the bore  410 . One or more optional shims  126  and the retaining plate  128  are then assembled onto the cylindrical portion  416  of the pintle  414  inside the bore  410 . The fuel swirler  202  is then assembled into the bore  410  upstream of the wave spring  122  and retaining plate  128 . The cylindrical portion  416  of the pintle  414  and the retaining plate  128  may be threaded to facilitate assembly, or other suitable means such as brazing, press-fit, or welding may be used to assemble these components. Similarly, the wall of the bore  410  and an outer surface of the fuel swirler  202  may be threaded to facilitate assembly, or the fuel swirler  202  may be press-fit, brazed or welded into the bore  410 . In alternate embodiments of the invention, the fuel swirler  202  is assembled into the bore  410  downstream of the wave spring  122 , shims  126 , and retaining plate  128 . In yet another embodiment of the invention, the fuel injector  400  does not include a fuel swirler  202 . 
     In operation, pressurized fuel enters the bore  410  flowing through the fuel swirler  202 , which creates a swirling action in the fuel flow. The swirling action reduces or eliminates wakes, and other non-uniformities, in the fuel flow. The pressurized fuel then flows through openings  132  (shown in  FIG. 3 ) in the retaining plate  128 . When the fuel pressure on the conical head  418  exceeds some threshold level, it overcomes the force placed on the pintle  414  by the pre-loaded wave spring  122 . This lifts the conical head  418  away from the exit orifice  119 , allowing fuel to flow from the fuel injector  400  into the combustion chamber (not shown). 
     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.