Abstract:
An apparatus and method for minimizing and/or preventing thermal degradation of fuel in a fuel injector is disclosed. The body of the injector includes a fuel gallery with a contoured scarf formed therein. The scarf is configured to minimize and/or prevent fuel recirculation thus reducing the likelihood that fuel will dwell in an area long enough to sufficient to cause the degradation of the fuel.

Description:
PRIORITY CLAIM 
     This application claims the benefit of U.S. Provisional Application No. 60/851,460, filed Oct. 13, 2006, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to fuel injectors, and more particularly to reducing fuel flow stagnation regions in fuel injectors. 
     BACKGROUND 
     Fuel injectors are used to deliver fuel into a combustor wherein the fuel is burned to produce power in an engine. A variety of engines use fuel injectors including internal combustion engines, both spark ignited and diesel, gas turbine engines, pulse detonation engines, wave rotors, and the like. When hydrocarbon based fuels are exposed to high temperatures over a period of time, the fuel will thermally degrade or pyrolyse to form tars, lacquers, and coke. The degraded fuel will reduce the performance of the fuel injector and can eventually clog at least a portion of the fuel passages within the injector. To prevent thermal degradation, fuel injectors must be thermally isolated and/or have fuel flow velocities that are high enough to prevent excessive heat build up in the fuel. The present invention contemplates a novel and unobvious way to minimize thermal degradation of fuel in a fuel injector. 
     SUMMARY 
     One embodiment of the present invention is a unique fuel injector. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for altering a fuel flow within a fuel injector. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
         FIG. 1  is a cross sectional view of a fuel injector and engine support structure. 
         FIG. 2  is a perspective view of the fuel injector in  FIG. 1  with an outer housing removed. 
         FIG. 3  is a cross-sectional schematic of the fuel injector of  FIG. 1  showing fuel streamlines. 
         FIG. 4  is an end view schematic of fuel streamlines as they enter the injector and flow around the fuel gallery. 
         FIG. 5  is a perspective view of the fuel injector of  FIG. 1  with an outer housing removed. 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     The inventions disclosed herein include means for reducing thermal degradation of fuel in fuel injectors used in engines powered by hydrocarbon based fuels. Fuel injectors typically operate in a hot environment because they are positioned adjacent combustion chambers. If the fuel does not move through the fuel injector at relatively high velocities then the heat load will cause the fuel to degrade and eventually can clog the injector nozzle. In one scenario where the fuel actually re-circulates in a stagnation region of the injector, it will only be a matter of time before the fuel injector needs to be replaced. The inventors have found that stagnation regions form most often in injectors when a fuel delivery manifold is not in line with the longitudinal flow axis of the injector. As the fuel turns from the entry angle defined by the fuel manifold toward the longitudinal flow axis of the fuel injector, a stagnation region can form at the opposing or distal side of the injector relative to the fuel inlet location. 
     Referring to  FIG. 1 , a fuel injector  10  is illustrated in one embodiment of the invention. The fuel injector  10  can be held in position by an engine support structure  20  which will not be described in detail, because the particular design configuration of the surrounding support structure  20  does not affect the present invention. A fuel inlet manifold  30  can extend from the engine support structure  20  to hold the fuel injector  10  in a desired position. The fuel inlet manifold  30  is operable for delivering fuel from a source (not shown) to an injector body  40  of the fuel injector  10 . The fuel injector body  40  generally extends along an extension axis denoted as X in  FIG. 1 . The fuel injector  10  includes an outer housing  50  and an exit end  60  of the injector connected thereto. Although not illustrated in detail, a combustor or combustion chamber  70  is typically positioned downstream of the fuel injector  10 . 
     Referring to  FIG. 2 , the fuel injector  10  is shown with the outer housing  50  removed thereby depicting internal features of the injector  10 . With the outer housing  50  removed, an inner housing  80  can be viewed. The inner housing  80  is shown with a substantially cylindrical shape extending along an extension axis denoted as X in  FIG. 2 , which corresponds to axis X in  FIG. 1 . Two additional axes are depicted in  FIG. 2  and denoted as Z and Y to provide an arbitrary but useful reference system for some of the discussion below. In addition to the cylindrical shape depicted in  FIG. 2 , the inner housing  80  can have other geometric configurations as would be known to those skilled in the art. 
     While detailed understanding of the fuel injector  10  is not required to fully appreciate the disclosed invention, a few of the internal features can be observed. The inner housing  80  can have a relatively large diameter  90  at a first end  92  and can neck down through a transition  94  to a relatively smaller diameter  96  at a second end  98 . The transition  94  in the illustrated embodiment is shown having a circumferentially and axially symmetric neck down between transition ends  212   a  and  212   b , but in other embodiments may have an irregular and/or non-constant neck down. For example, the transition end  212   b  may vary in a sinusoidal pattern over the circumferential distance of transition  94 , to set forth just one nonlimiting example. The inner housing  80  has a plurality of guide vanes  99  operable to control the flow of fuel, air and/or air/fuel mixture within the injector body  40 . Guide vanes  99 , however, may not be used in some embodiments. 
     A scarf  100  is positioned adjacent the first end  92  of the fuel injector  10 . The scarf  100  advantageously facilitates fuel flow movement from the first end  92  to the second end  98  of the fuel injector  10  as will be described hereinbelow. The scarf  100  includes a wall  101  having a first width W 1  adjacent a first side  110  which is proximate the fuel inlet manifold  30  (best seen in  FIG. 3 ) and a second larger width W 2  located at an opposing or distal side  120  from the first side  110 . In some applications the first side  110  may be referred to as a top side and the distal side  120  may be referred to as a bottom side. However, it will be understood that the terms “top” and “bottom” do not necessarily refer to the relative location of the fuel injector within the confines of a combustor. The terms are merely meant to aid in distinguishing various features of the instant application. 
     The scarf  100  has an annular wall  210  of thickness TH 1  that extends between an outer surface  130  of the inner housing  80  to the inner surface (not shown) of the outer housing  50  (also not shown). The annular wall  210  has a substantially constant thickness TH 1  in the illustrated embodiment around the circumference of the fuel gallery  170 , but in other embodiments may have a varying thickness TH 1  corresponding to changes in the relative distance between the inner surface of the outer housing  50  and the outer surface  130  of the inner housing  80 . The annular wall  210  forms a fuel flow boundary in the illustrated embodiment as will be described hereinbelow. 
     A first edge  140  of the scarf  100  is positioned adjacent an end wall  150  at the first end  92  of the fuel injector  10 . A second edge  160  of the scarf  100  extends from the first edge  140  at the first width W 1  proximate the first side  110  down to the distal side  120  at the second width W 2  as defined from the end wall  150 . The scarf  100  can be symmetrical about a vertical axis or can vary three dimensionally along any major axis of the injector  10 . The second edge  160  can be substantially linear and/or can be arcuate depending on the particular injector design criteria relative to radial and axial fuel velocity requirements. 
     In alternate embodiments, the scarf  100  can take other forms such as having a thickness TH 1  less that the distance between the inner and outer housings  80  and  50 , respectively. Furthermore, the scarf may not necessarily extend 360 degrees around the inner housing  80 . The scarf  100  may instead be positioned locally in the stagnation region as a plug or a deflector to prevent fuel from entering the stagnation region. In one form the function of the scarf  100  is to facilitate transition of the fuel flow direction from any angle relative to the longitudinal axis of the injector  10  to a direction substantially parallel to the longitudinal axis of the injector  10 . 
     The scarf may be integrally formed with the body  40  of the injector  10  or may be formed as a separate piece. In one non limiting embodiment, the scarf  100  is formed integrally with the end wall  150  of the injector  10 . In another embodiment, the scarf is attached to the body of the injector via welding, brazing, or mechanical means. In still another embodiment, the scarf is formed integrally with the body of the injector via casting, forging, and/or machine work. In yet another embodiment, the scarf is formed from different material than the material used to form the body of the injector. 
     Referring to  FIG. 3 , a cross-sectional view of one embodiment of the injector  10  schematically illustrates fuel streamlines flowing from the fuel inlet manifold  30 , through inlet  200 , and then in to a fuel gallery  170 . The fuel inlet manifold  30  is shown having an axis of extension F generally aligned with the Z-axis such that fuel enters inlet  200  along a path generally aligned with the Z-axis. In some embodiments, however, the fuel inlet manifold  30  may not be aligned with the Z-axis. 
     The annular wall  210  extends in a curvilinear manner from the first side  110  to the distal side  120 , as seen in the side view of  FIG. 3  along the Y axis. The curvilinear shape of annular wall  210  may also be referred to as a variably arcuate shape. In some embodiments, the annular wall  210  may extend in a straight line or may take on any other shape configured to prevent and/or minimize a stagnation region. 
     The fuel gallery  170 , located between the inner housing  80  and the outer housing  50 , permits the fuel to enter the injector  10  and circumferentially follow along the second edge  160  of the scarf  100 . In one embodiment, the fuel gallery  170  can entirely encompass the inner housing  80 . The fuel gallery  170  operates to direct fuel from the first end  92  toward the second end  98  of the injector  10 . Without the scarf  100 , a fuel gallery  170  may have a naturally occurring stagnation region located at or near the distal side  120  opposite from the fuel inlet manifold  30 . If not for a scarf  100  positioned in or adjacent the natural stagnation region, a fuel recirculation zone would form and cause the re-circulating fuel to thermally degrade due to the prolonged exposure to a heat load. Therefore, it will be appreciated that the scarf  100  is positioned and oriented in the illustrated embodiment to minimize or prevent a stagnation region from forming. If the fuel manifold  30  and fuel flow rates and conditions change in other embodiments then different shapes, positions, and orientations of scarf  100  can be used. 
     The fuel injector  10  can be formed of material or combinations of material designed to withstand the temperatures and pressures required under engine operating conditions. Typically the majority of the material selected would be from a metal such as stainless steel or nickel based alloys. Alternatively the material could be at least partially formed of ceramic and/or composites. It should be appreciated, that the scarf  100  may be formed from a different material than used in the body  40  of the injector. 
     Turning now to  FIG. 4  and with continuing reference to  FIG. 3  above, a front view of a fuel flow path is depicted with a view along the X axis. In operation, the fuel is delivered from the fuel inlet manifold  30  to the fuel gallery  170 . The fuel streamlines  180  then flow circumferentially around the fuel gallery  170  along the second edge  160  of the scarf  100 . After filling the fuel gallery  170  circumferentially near the first end  92  of the injector  10 , the fuel will be forced to flow toward the second end  98  and exit through the exit end  60  (see  FIG. 1 ) and mix with combustion air in the combustor  70 . At the distal side  120  of the injector body  40  the fuel streamlines  180  are urged to flow in a longitudinal axial direction relative to the injector body  40  due to the location and design shape of the scarf  100 . Thus, scarf  100  effectively prevents and/or minimizes flow recirculation in the area of the distal side  120  formed when streamlines  181   a  and  181   b  coalesce relative to a configuration without scarf  100 . In this manner, thermal degradation of the fuel due to recirculation is eliminated. It will be understood, however, that scarf  100  may be used anywhere a fuel flow stagnation region develops, whether caused by the manner described above or other mechanisms. For example, scarf  100  could be used in an adverse pressure gradient region to minimize and/or prevent the formation of separated flow. 
       FIG. 5  depicts another embodiment of the instant application. Fuel injector  10  has been rotated about the X axis to better show a view along the Z axis. Scarf  100  has been added to outer surface  130  and is located proximate distal side  120 . Depending on the flow properties and relative location of fuel inlet manifold  30 , scarf  100  may be placed at other locations within fuel gallery  170 . Scarf  100  has a shark&#39;s tooth shape with rounded plateau  220  that is configured to engage the inner surface (not shown) of the outer housing  50  (also not shown). The apex  222  of the plateau  220  tapers down to the outer surface  130  of the inner housing  80  at a vertex  224 . Scarf  100  serves as a plug or deflector in distal side  120  to prevent and/or minimize a fuel recirculation region from developing. 
     One aspect of the invention contemplates a fuel injector comprising: an injector body having first and second ends connected to a fuel inlet manifold; an inner housing; an outer housing spaced apart from the inner housing to form a fuel gallery within the injector body; and a scarf positioned within the fuel gallery proximate the first end of the injector body, the scarf is adapted to urge the fuel to flow generally in a longitudinally axial direction relative to the injector body, the scarf operable to prevent a fuel stagnation region from forming in the fuel gallery. Another aspect of the present invention provides that the scarf comprises: a wall having a first edge spaced axially apart from a second edge defined by a first width proximate the fuel inlet and a second width proximate a side opposite of the fuel inlet, wherein the second width is greater than the first width. Yet another aspect of the present invention provides that the second edge of the scarf is substantially linear. Yet another aspect of the present invention provides that the second edge of the scarf is variably arcuate. Yet another aspect of the present invention provides that the scarf has a thickness that substantially extends from an inner wall of the outer housing to an outer wall of the inner housing. Yet another aspect of the present invention provides that the inner and outer housings are substantially circular in cross-section and substantially concentric relative to one another. Yet another aspect of the present invention provides that the scarf is attached to the body of the injector via welding, brazing, or mechanical means. Yet another aspect of the present invention provides that the scarf is formed integrally with the body of the injector via casting, forging, and/or machine work. Yet another aspect of the present invention provides that the scarf is formed from different material than the material used to form the body of the injector. 
     Another aspect of the present invention contemplates a fuel injector comprising: a fuel gallery formed internal to the injector connected to a fuel inlet; and a scarf positioned in the fuel gallery such that the fuel is prevented from re-circulating and forced to traverse axially along a longitudinal axis of the fuel injector. Yet another aspect of the present invention contemplates that the scarf comprises: a first side having a first width proximate to a fuel inlet extending to a second side having a second width larger than the first width, the second side positioned at a distal side of the fuel gallery relative to the fuel inlet. Yet another aspect of the present invention contemplates that the scarf extends substantially linearly between the first and second sides. Yet another aspect of the present invention contemplates that the scarf extends in an arcuate path between the first and second sides. Yet another aspect of the present invention contemplates that the scarf extends less than 360 degrees around an inner housing of the fuel injector. Yet another aspect of the present invention contemplates an injector further comprising: a pair of spaced apart walls with substantially circular cross-sections forming the fuel gallery. Yet another aspect of the present invention contemplates that the scarf has a thickness substantially equal to the distance between the spaced apart walls. Yet another aspect of the present invention contemplates that the scarf is attached to the injector via welding, brazing, or mechanical means. Yet another aspect of the present invention contemplates that the scarf is formed integrally with the injector via casting, forging, and/or machine work. 
     Another aspect of the present invention contemplates a method of preventing thermal degradation of fuel in a fuel injector comprising: delivering fuel to a fuel gallery defined between an inner wall and an outer wall of a fuel injector body; and preventing fuel from entering a stagnation region of the fuel gallery. Yet another aspect of the present invention contemplates the preventing step comprises: forming a scarf in the stagnation region of the fuel gallery to urge the fuel generally along a longitudinal axis of the injector. Yet another aspect of the present invention contemplates that the preventing step comprises: turning the fuel flow direction from a defined angle of entry into the fuel. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.