Patent Application
20110073071
This invention generally relates to fuel delivery systems, and, more particularly, to fuel injectors for delivering fuel to the combustion chambers of combustion engines.
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.
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.
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:
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.
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'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
According to an embodiment of the invention, a variable-area injector 100, as illustrated in
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
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.
In the embodiment illustrated in
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
In operation, pressurized fuel enters the fuel injector 300 via bore 303 flowing through the openings 132 (shown in
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
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.
