Patent Grant
6899290
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.
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.
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'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.
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.
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.
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.
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.
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.
It is a principal object of the present invention to optimize flat swirler plate geometry to optimize performance of a pressure-swirl atomizer.
It is a further object of the invention to simplify the construction and reduce the cost of producing a swirler-plate nozzle atomizer.
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.
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.
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:
Referring now to the drawings, and particularly to
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.
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.
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.
Referring now to
Plate 34 comprises a metal tracery outlining a plurality of identical fuel flow passages 66, preferably six as shown in
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.
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.
Referring to
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 vertically 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.
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.
Although
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.
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.
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
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
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.
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.
The present application draws priority from a U.S. Provisional Application, Ser. No. 60/391,007, filed on Jun. 24, 2002.
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| Number | Date | Country | |
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| Number | Date | Country | |
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| 60391007 | Jun 2002 | US |
