Abstract:
A fuel swirler plate for improving atomization of fuel in a fuel injector. A plurality of identical fuel supply passages is formed in the plate, each passage including an outer fuel reservoir region; a region having converging walls wherein fuel is accelerated and turned partially tangential to the axis of the plate and fuel injector; a metering region wherein flow is regulated; and an exit region wherein the fuel is combined with similar fuel flows from the other passages to form a high velocity swirl annulus between the swirler plate and a pintle ball of the fuel injector. An advantage of the novel swirl plate over prior art plates is that, when the injector valve is closed, only a very small volume of fuel resides in the swirl annulus between the pintle ball and the exit region of the plate, and such residual fuel is urged rotationally and becomes the leading edge of a new vortex the next time the valve is opened, thus minimizing SAC spray formation. The present invention is useful in fuel cells, burners, and in both direct injection and port injection fuel injectors of internal combustion engines.

Description:
[0001]     The present application draws priority from a U.S. Provisional Application Ser. No. 60/391,007, filed on Jun. 24, 2002. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates generally to fuel injectors for injecting liquid fuel into internal combustion engines or fuel reformers; more particularly, to fuel injectors having pressure-swirl atomizers for providing a finely atomized fuel spray; and most particularly, to a pressure-swirl atomizer including a flat plate having converging swirler passages for providing an improved level of atomization.  
       BACKGROUND OF INVENTION  
       [0003]     Fuel injectors are well known for supplying metered amounts of fuel to combustors such as internal combustion engines, and reformers such as hydrogen/reformate generators for fuel cells. In either case, it is highly desirable that the fuel spray created by these injectors be well atomized for essentially instantaneous vaporization upon entering the spray chamber, whether it be the injection port or firing chamber of an engine or the vaporizer chamber of a catalytic reformer. In a fuel cell, for example, this is a desirable since the liquid fuel is thereby inhibited from contacting the hot metal surfaces of the vaporizer chamber, thus preventing undesirable carbon formation and uncontrolled combustion.  
         [0004]     Conventional port fuel injectors operate at lift pump pressures of less than 400 kPa and employ director-style spray tips. A conventional fuel director can have one to ten or more holes that define a spray pattern and flow rate of the injector. As the size and/or number of holes in the director is increased, the flow rate of the injector at a given pressure also increases. The diameter of the hole also determines the spray droplet size. As the hole diameter decreases, the droplet size also decreases desirably at a given pressure; however, if the hole diameter is too small, the holes are susceptible to plugging from fuel and combustion deposits. Therefore, the minimum practical lower limit for a director hole diameter is approximately 100 microns (0.1 mm). This hole size limits the minimum spray droplet size at a 400 kPa lift pump pressure to dv90&#39;s of approximately the diameter of the hole; and in practice most droplets are larger. Therefore, a physical barrier (hole diameter) limits the minimum droplet size obtainable with a director style injector spray tip. In addition, the director style spray tip generates sprays that are non-uniform and stringy in comparison to sprays generated by apparatus in accordance with the invention as detailed hereinbelow.  
         [0005]     Pressure-swirl atomizers, capable of generating sprays in continuous systems such as paint sprayers and gas turbine nozzles, are well known. Pressure-swirl atomizers have also been applied to pulsed-spray applications, such as fuel cells and high-pressure gasoline fuel injectors, to provide finely atomized sprays.  
         [0006]     A pressure-swirl atomizer has several advantages over director-plate atomizers traditionally used for pulsed spray applications. First, pressure-swirl atomizers can produce smaller droplets. This is especially evident at lower pressures, as required by port fuel injection systems. Also, pressure-swirl atomizers are less susceptible to plugging than director type atomizers. Additionally, pressure-swirl atomizers can generate uniform hollow-cone sprays that are most desirable in a direct cylinder injection application.  
         [0007]     A disadvantage of prior art pressure-swirl atomizers is that large droplets of fuel, known in the art as a “SAC” spray, are released into the spray chamber at the beginning of each injection pulse. When the injector first opens, the fuel located between the swirler and the valve seat does not have rotational velocity. This fuel exits the injector axially in mostly non-atomized large droplets, not in a finely atomized cone. These large droplets in the SAC spray are undesirable because the fuel contained therein is generally non-metered and can also reach chamber surfaces where it can produce carbon formation in fuel cells, as well as higher emissions from internal combustion engines. Therefore, it is desirable to use an optimized swirler/nozzle design to produce very small droplets in a conical spray pattern as the fuel exits the injector.  
         [0008]     Conventional pressure-swirl atomizers typically include a complex swirler constructed of powdered metal. Manufacturing costs associated with the use of powdered metal swirlers are relatively high. Other types of pressure-swirl atomizers utilize flat-plate swirlers stamped from sheet metal. This process typically limits their geometry to simple circular and straight-line passages to keep the stamping tool simple and durable. However, such limitations restrict the performance of the part. Additionally, this process can also result in sharp edges and abrupt transitions that can induce the flow to separate undesirably from the edges, resulting in cavitation erosion of the swirler and unpredictable flow patterns. Such flow separation is quite sensitive to edge conditions such as sharpness or burrs. Slight variations in edges can translate into non-uniformity in the produced parts and resulting flow variations.  
         [0009]     What is needed is a pressure-swirl plate for a fuel injector that reduces the cost, flow variation, and transient spray development problems associated with prior art swirl plates, while maintaining their advantages over director-style atomizers.  
         [0010]     It is a principal object of the present invention to optimize flat swirler plate geometry to optimize performance of a pressure-swirl atomizer.  
         [0011]     It is a further object of the invention to simplify the construction and reduce the cost of producing a swirler-plate nozzle atomizer.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0012]     Briefly described, a fuel swirler plate for improving atomization of fuel in a fuel injector includes a plurality, preferably six, of identical fuel supply passages formed in the plate. Each passage includes an outer reservoir region wherein fuel is received from a source; an inwardly converging region having converging passage walls wherein fuel from the reservoir region is both accelerated and turned partially in a direction tangential to the axis of the plate and fuel injector; a metering cross-section formed as a minimum cross-sectional area in the converging region; and an exit region wherein the fuel dispensed from each passage combines with similar fuel flows from the other passages to form a high velocity swirl annulus between the swirler plate and a pintle ball of the fuel injector valve. The valve seat is conical below the ball, such that the swirl annulus, in descending the seat toward the exit from the fuel injector body, is further accelerated into a vortex having a very high angular velocity. Upon exiting the fuel injector, the fuel vortex spreads substantially instantaneously into a predictable, controlled hollow cone wherein the fuel may become vaporized before striking a surface. An advantage of the novel swirler plate over prior art plates is that, when the injector valve is closed, only a very small volume of fuel resides upstream of the valve seat in the annular region between the pintle ball and the exit region of the plate; and further, such residual fuel, which can cause large SAC sprays in prior art arrangements, is urged rotationally and becomes the leading edge of a new vortex each time the valve is opened, thus minimizing SAC spray formation.  
         [0013]     The present invention may be usefully applied to fuel cells, burners, high pressure (10-20 MPa) gasoline direct injection fuel injectors, and low pressure (200-400 kPa) port fuel injectors, and may also be applied to other continuous flow pressure-swirl atomizer applications. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which:  
         [0015]      FIG. 1  is an elevational cross-sectional view, taken along line  1 - 1  in  FIG. 2 , of a fuel injector nozzle, including a flat pressure-swirl plate in accordance with the invention;  
         [0016]      FIG. 2  is a top view of the apparatus shown in  FIG. 1 ;  
         [0017]      FIG. 3  is an equatorial cross-sectional view of the swirl plate shown in  FIG. 1 ;  
         [0018]      FIG. 4  is an axial view from below showing the relationship between the swirl plate, a swirl plate retainer, and a pintle ball valve head;  
         [0019]      FIG. 5  is a second embodiment of a swirl plate; and  
         [0020]      FIG. 6  is a third embodiment of a swirl plate. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Referring now to the drawings, and particularly to  FIGS. 1 and 2 , nozzle  10  for incorporation into a fuel injector (shown schematically as  12 ) for an internal combustion gasoline or diesel engine, or a fuel reformer for a fuel cell (not shown). Nozzle  10  includes a nozzle body  14  having a bore  16  for receiving fuel  18  from a source in known fashion. Bore  16  terminates in a plate seat  20  which is preferably slightly undercut  22  at its juncture with bore wall  24 . Coaxial with bore  16  and plate seat  20  is a frusto-conical valve seat  26  terminating in a cylindrical outlet passage  28  which opens axially through an end wall  30  of body  14 . Valve seat  26  preferably has an included cone angle  32  of about 90°.  
         [0022]     A flat pressure-swirl plate  34  in accordance with the invention is coaxially disposed on plate seat  20  and is retained thereupon by plate retainer  36  which is press-fit into bore  16  and itself has a central bore  37 . The upper portion  38  of retainer  36  has a plurality of cylindrical faces  40 , preferably three, four, or six, (six shown) separated by flats  41  and having a diameter slightly greater than the diameter of bore  16  for engaging wall  24  and for forming fuel flow passages  42  around retainer  36 . The lower portion  44  of retainer  36  is preferably cylindrical and has a smaller diameter than upper portion  38  such that an annular fuel supply chamber  46  is formed adjacent plate  34 , chamber  46  being in fluid communication with passages  42 . The lower axial surface  48  of lower portion  44  is planar, as is the surface of plate seat  20 , such that plate  34  is tightly sandwiched therebetween. Undercut  22  ensures that the swirl plate rests flatly in the counterbore.  
         [0023]     Preferably, once body  14 , plate  34 , and retainer  36  are assembled, they are heat-treated as an assembly and diffusion bonded together. Then bore  37  and valve seat cone  26  are finish ground coaxially to precise size and roundness dimensions. The order of the process steps and the optional heat treat may be varied within the scope of the invention.  
         [0024]     A valve head, preferably a spherical pintle ball  50 , and attached pintle shaft  52  are disposed within bore  37  and through a central opening  54  in plate  34  such that ball  50  forms a valve seal with valve seat  26 . The center  56  of sphere  50  is preferably slightly above the upper surface  58  of plate  34 . The diameters of bore  37  and ball  50  are selected such that a very small annulus  60  exists therebetween, the preferred clearance being no more than about 5 μm, to minimize fuel leakage which would thereby bypass the swirl plate. Ball  50  is actuated axially of nozzle  10  to open and close the valve preferably via a conventional solenoid valve actuator (not shown), as is well known in the prior art.  
         [0025]     Referring now to  FIG. 3 , a flat pressure-swirl plate  34  in accordance with the invention is formed as by stamping or chemical etching from sheet stock, preferably full-hard stainless steel. The plate is relatively small and delicate, and its form must be accurately maintained during assembly of the nozzle. Plate  34  is circular in outline and during assembly is located concentrically on seat  20  in counterbore  16  by a plurality of spring bumps  62 , preferably three equilaterally arranged, formed on the outer rim  64  of plate  34  that are compressed slightly against wall  24 . Outer rim  64  of plate  34  flexes and acts as a spring so that the swirl plate is centered in the nozzle to prevent skewing of the fuel spray during operation of the fuel injector. Minor variations in diameter of bore  16  are compensated for by the compression of these springs.  
         [0026]     Plate  34  comprises a metal tracery outlining a plurality of identical fuel flow passages  66 , preferably six as shown in  FIGS. 3 and 4 , hexagonally arranged about central opening  54  described above. Passages  66  are bounded axially by plate seat  20  and lower surface  48 , as described above, and are bounded equatorially by outer rim  64  and first and second walls  68 , 70 , respectively of lands  72  that extend inwards of outer rim  64 . Each passage  66  includes several flow regions: an outer reservoir region  74  wherein fuel is received from annular chamber  46 ; an inwardly converging region  76  wherein walls  68 , 70  converge and wherein fuel from the reservoir region is both accelerated and turned partially in a direction tangential to the axis of the plate and fuel injector; a metering region  78  formed as a minimum cross-sectional area at the end of converging region  76 , wherein the walls are substantially parallel and the ratio of length to width of the region is preferably about 1:1; and an exit region  80  wherein the fuel dispensed from each metering region  78  combines with similar fuel flows from the other passages to form a high velocity swirl annulus  82  between swirler plate  34  and pintle ball  50 , as shown in  FIG. 4 .  
         [0027]     When injection is desired, preferably, pintle shaft  52  is axially displaced upwards (with respect to  FIG. 1 ), thereby removing ball  50  from mating engagement with seat  26 . Ball  50  is guided straight away from the seat because of guide annulus  60 . Pressurized fuel  18  inside injector  12  can then begin to flow out of the injector. The process is reversed to end injection.  
         [0028]     The fuel flow path presented by the present invention is as follows. Fuel moves from bore  16  through passages  42  into annular chamber  46  and thence into regions  74  in swirl plate  34 . At this point in the fuel flow, fuel velocity is relatively low and the pressure drop is minimal. Fuel then turns 90 degrees toward the axis of the nozzle. Flow velocity is still quite slow at this point; hence, conditions of surfaces and edges in regions  74  do not add variation to the flow rate or pressure drop. Now fuel enters converging region  76  between walls  68 , 70 . It is an important feature of a swirl plate in accordance with the invention that fuel is prevented from losing wall contact and cavitating in this region, as occurs in prior art swirl plates. To this end, curved wall  68  is formed having a first blend radius  69  and curved wall  70  is formed having a second blend radius  71  in an opposite direction. As walls  68 , 70  converge in region  76 , the flow accelerates as fuel moves towards metering region  78 . The dimensions of metering region  78  are selected to produce the desired swirl velocity, and therefore the desired fuel spray angle at exit from outlet passage  28 . A gradual reduction in flow cross-sectional area is essential to accelerating the fuel without causing the fuel to separate from the walls, which would add flow variation. It is also desirable that acceleration happen in a simple plane without adding rotation to the fuel. In a swirl plate in accordance with the present invention, flow velocity through the flow passages is kept low in areas where it can be difficult to control quality of the cut-out edges which can disrupt flow. The velocity is also kept low at locations where the flow must change direction around corners, as in changing direction from annular chamber  46  into passages  66 . Then, in regions  76 , the flow is gently accelerated into metering region  78 . This results in repeatable flow with reduced variation part to part.  
         [0029]     Referring to  FIG. 4 , edge  84  of lands  72  is tangent to the swirl annulus  82 . The diameter of swirl annulus  82  is selected to be slightly larger than the diameter of pintle ball  50  at the axial location at which the annulus intersects the ball. As noted above, the intersection point is below the equator or center  56  of the pintle ball. This allows the equator of the pintle ball to be guided by bore  37 . In addition to guiding the pintle ball  50 , this arrangement, as noted above, also restricts fuel from bypassing the swirl plate and entering the swirl annulus  82  directly and without a tangential velocity.  
         [0030]     Fuel enters swirl annulus  82  from metering region  78  at a high velocity, on the order of 130 meters per second. The swirling flow then moves downwards vortically along conical valve seat  26  between the seat and pintle ball  50  toward outlet passage  28 . The diameter reduction as the fuel moves through the conic area further increases the rotational velocity. The fuel forms a thin sheet along the walls of outlet passage  28 . The center of the passage contains only air and fuel vapor, no liquid. As the fuel exits passage  28  through wall  30 , the fuel forms a conical spray pattern  86 . The conical spray angle is determined by the ratio of axial to tangential (swirl) velocities. The total flow rate is determined by supply pressure and by the cross-sectional area of the nozzle. Other significant flow factors include the cross-sectional area of region  78 , the diameter of swirl annulus  82 , the size of the annular gap between pintle ball  50  and valve seat  26  when the valve is open, and the exit orifice diameter of outlet passage  28 . By adjusting these parameters without undue experimentation, a desired spray angle and flow rate can be achieved.  
         [0031]     The quality of fuel atomization is determined by the flow path through a fuel injector nozzle. Because flow is rapidly pulsed in normal operation, this process is a transient process. Therefore, how quickly the swirl is established is an important performance factor. To better understand the present invention, it is helpful to consider a prior art straight swirl flow passage (not shown). At low fuel flow velocities, such as when the injector first opens, nearly 100% of the passage area is used for flow. However, as flow rate increases, fuel begins to separate from the walls near the inlet edges, creating an effectively narrower passage. This contraction can vary greatly, depending upon the condition of the inlet edges, and can reduce the flow by up to 25% from the ideal. This effect is opposite of the desired. It is preferable to have a narrower passage initially, to quickly produce high velocities for reduced SAC spray, but also a wider passage, with higher flows, for less pressure drop. The converging walls of the present invention initially produce a higher velocity even though the passage is made approximately 25% narrower than a corresponding straight passage. This is possible because the converging shape prevents flow separation at the higher velocities. Thus, the initial fuel velocity in the present invention is higher, and therefore the SAC sprays are reduced.  
         [0032]     Although  FIGS. 1 and 2  illustrate incorporation of the invention in an inwardly-opening fuel injector, the invention is also applicable to outwardly-opening fuel injectors. The swirl for outwardly opening applications is established by similar methods and geometries as detailed for the inwardly-opening injector, except that the swirl velocity is reduced as the diameter increases along the seat cone, and an air-core is not produced because there is no exit orifice.  
         [0033]     A flat swirl plate in accordance with the invention has also been applied to a port fuel injector. The resulting dv90s for this style injector are 10% to 20% smaller than that of a director style injector of similar flow. Comparable reductions in d32 numbers are also achieved. The injector fuel spray is also more uniform and cone shaped than as provided by the director style injector.  
         [0034]     The flat plate geometry of the present swirl plate has the benefit of being easily manufactured, which lowers costs. There are several methods to manufacture a flat plate swirler, including, but not limited to, stamping and photo chemically machining (PCM). Typically, complex curves are difficult to stamp, but are very easy to PCM, which process can produce flat plate swirlers with low tooling cost and has the capability to form complex curves easily. Material choice is not limited by the PCM process. A full-hard stainless steel plate is preferred for increased durability and resistance to erosion, although this material may reduce the tool life for a stamped swirler plate.  
         [0035]     These benefits allow for slight variations in swirler geometry design as desired, so that a wide range of atomizers, addressing specific performance parameters, may be produced. Three slight variations in swirler geometry have been developed to optimize specific performance parameters. In addition to the geometry variations, the metering region cross-section  78  may be varied to cover a range of spray angle and flow rate applications. The three variations can be described as: 
        1) a tangent slot swirler (shown in  FIG. 4 ) wherein the outer wall of the passage in the exit region is tangent to a diameter slightly larger than that of the pintle ball, which design produces a small SAC spray with an acceptable pressure drop;     2) an offset annulus slot swirler  34 ′ ( FIG. 5 ), having a larger swirl annulus  82 ′, wherein the outer wall  88  of the passage in the exit region is offset  90  from the swirl annulus by an additional 25%, the mean flow in the exit passage then being tangent to the pintle ball, which design has the lowest pressure drop but at the expense of increased SAC spray; and     3) a hook-slot swirler  34 ″ ( FIG. 6 ), wherein the offset  90  is the same as in the offset annulus slot swirler  34 ′ but the outer wall curves inward  92  near the tip of land  72 ′ to about the same diameter of swirl annulus  82  as in  FIG. 4 , resulting in reduced SAC spray.        
 
         [0039]     Additionally, the ratio of plate thickness and passage width is selected to minimize the cross-sectional flow area variation. Preferably, the passage width is about twice the plate thickness. This is because typical variation in plate thickness is about one half the variation in slot width for the PCM process. If a stamping process is used, then the height-to-width ratio should be adjusted accordingly to match known processes characteristics. Each plate design may be produced from sheet stock of various thicknesses and in a variety of metering region widths as required to meet the flow requirements of most known fuel injectors.  
         [0040]     While the invention has been described as having a preferred design, the present invention may be further modified within the spirit and scope of this disclosure as may occur to those skilled in the art. This application is therefore intended to cover any and all variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as may come within the known or customary practice in the art to which this invention pertains and which may fall within the limits of the appended claims.