BACKGROUND
The present invention relates to seals for a pulse detonation engine. It finds particular application in conjunction with seals to limit or retard leakage between detonation tubes of a pulse detonation engine and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other applications.
Turbojet engines are typically directly attached to aircraft inlets without an interface being required. A pulse detonation engine (PDE), on the other hand, includes an interface between the engine and an aircraft inlet. Pulse detonation engines impose different airflow demands on a high-speed inlet than do conventional turbojet engines. Turbojet engine systems require a constant and near-uniform airflow supply. The airflow demand of a detonation tube for a PDE is in a cyclic “on/off” manner. A valve distributes airflow by opening chambers to prevent the “on/off” airflow demand of each individual tube from causing a transient into the approaching airflow.
A combustion chamber of a pulse detonation engine is similar to a piston of an automobile gasoline engine. Air and fuel are injected into a chamber to form a combustible mixture with a detonation initiated by a spark source. In the case of a pulse detonation engine, the explosion creates a high-pressure wave that moves down the combustion tube to the exit. The large increase in pressure in the chamber results in propulsive thrust.
The cycle for each combustion chamber of the pulse detonation engine is as follows: airflow (oxidizer) fill, fuel injection, entrance close, and ignition. At the beginning of the propulsive cycle, the combustion chamber is opened to the inlet airflow supply. The chamber is then closed to the incoming airflow, thus eliminating the demand of airflow from the inlet. Fuel is injected into the combustion chamber and the mixture is ignited. The chamber then is re-opened for additional airflow for the next combustion cycle. A high-speed valve, such as a high-speed rotary airflow control, typically provides this opening and closing of the airflow supply port. A high-speed valve is used because high engine efficiency typically requires high combustion frequencies. U.S. Pat. No. 6,637,187 discloses such a high-speed rotary airflow control.
A seal is needed between the high-speed valve and an associated engine frame.
The present invention provides a new and improved apparatus and method for creating a seal between the high-speed valve and the associated engine frame.
SUMMARY
In one aspect of the present invention, a system of controlling airflow into a pulse detonation engine is contemplated. The system includes a rotary airflow controller valve receiving air from a high-speed inlet. An engine frame includes a plurality of detonation chambers. A sealing mechanism is between the rotary airflow controller valve and the engine frame. The sealing mechanism is associated with the engine frame and limits leakage of a gas from a first of the detonation chambers to a second of the detonation chambers.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to exemplify the embodiments of this invention.
FIG. 1 is a schematic view of a high-speed propulsion system for a pulse detonation engine in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 2 is a schematic view of the high-speed propulsion system of FIG. 1 indicating a detail section;
FIG. 3 is a perspective view of a rotary airflow controller and engine frame shown in the detail section of FIG. 2 in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIGS. 4 and 5 are perspective top and bottom views, respectively, of the rotary airflow controller of FIG. 3 in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 6 is a perspective view of the engine frame of FIG. 3 in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 7 is an exploded perspective view of the arrangement of the rotary airflow controller and engine frame of FIG. 3 in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 8 is an exploded perspective view of the arrangement of a rotary airflow controller, sealing section, and engine frame in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 9 is a perspective view of the sealing section of FIG. 8 in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 10 is a top view of the sealing section of FIG. 8 with the integration of a sealing material in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIGS. 11, 12, and 13 are schematic views of sections A-A, B-B, and C-C, respectively, of FIG. 10 in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 14 is a schematic cross-sectional view of an integration of a rotary valve and a seal in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 14
a illustrates an enlarged view of the seal region within the dashed circle shown in FIG. 14 in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 15 is a schematic view of an attachment method of a sealing section to an engine frame in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 16 is a schematic view of an attachment method of a sealing section to an engine frame in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 17 illustrates a seal design with a high-temperature thermoplastic resin used as the sealing material in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIG. 18 illustrates a seal design with brass used as the sealing material in accordance with one embodiment of an apparatus illustrating principles of the present invention;
FIGS. 19 through 21 illustrate a seal design in accordance with one embodiment of an apparatus illustrating principles of the present invention where the sealing section is a honeycomb structure;
FIGS. 22 and 23 illustrate a seal design for directing gases to effectively limit or retard leakage of gases between adjacent detonation chambers in accordance with one embodiment of an apparatus illustrating principles of the present invention; and
FIG. 24 illustrates a seal design for using suction to effectively limit or retard leakage of gases between adjacent detonation chambers in accordance with one embodiment of an apparatus illustrating principles of the present invention.
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT
With reference to FIG. 1, an air breathing propulsion system 5 includes a rotary airflow controller valve 10 installed between a high-speed inlet 11 and a pulse detonation engine 7. As shown, airflow 13 in an annular duct at an exit of the high-speed inlet 11 enters the rotary controller 10 and exits into the engine 7. The portion of the high-speed propulsion system that is detailed in the following figures is indicated by the dashed circle in FIG. 2.
Views of the rotary airflow controller 10 are shown in FIGS. 3-5. The controller 10, as illustrated, is configured to control airflow into eight combustion or detonation chambers 87 in a pulse detonation engine. The controller 10 of FIGS. 3-5 is similar to a four-bladed propeller; however, each of the four (4) blades 53, 54, 55, 56 of the rotor 10 spans about 90° of the circumference. The airflow 13 approaching the rotary controller is indicated in FIG. 4. Each of the blades 53, 54, 55, 56 is attached to a center shaft 14, which includes a hole 15 for mounting the rotary controller 10 on a drive shaft. The rotary controller 10 rotates in the direction indicated by arrow 16. The blades 53, 54, 55, 56 are composed of an upstream surface 17, a downstream surface 18, an outer tip surface 19, and a sealing surface 20 (seal) (see FIG. 5). The sealing surface 20 is located at the exit plane.
The seal 20 used for a pulse detonation engine (PDE), as described and shown herein, is designed to prevent leakage of hot combustion gases from one detonation tube to an adjacent tube in the PDE. The seal 20 is typically located at an interface between the rotating airflow control valve 10 and a stationary engine frame 12 (see FIG. 6) of the pulsed detonation engine. The seal 20 between adjacent detonation chambers 87 (tubes) in FIG. 6 limits or retards the leakage of hot high-pressure gas from one detonation tube 87 to an adjacent tube 87. Such seals 20 may be designed to allow for free rotation of an airflow control valve, while being sufficiently close to the downstream flat closing surface of the rotary valve 10 to limit or retard leakage of the exhaust gases through the interface of the valve and detonation tube.
Several factors are considered in designing the rotor blades 53, 54, 55, 56. Such factors include geometry requirements (e.g., overlap for closing of the entrance to a combustion chamber), exit area of the inlet, rotor entrance to exit area ratio, engine entrance shape, valve height, valve diameter, radial position, radius of hub, rate of combustion, rotor speed, and the like. Aerodynamic factors that may influence the design of rotor blades include inlet diffuser exit airflow velocity, allowable engine entrance velocity, engine chamber pressure (during airflow injection), engine airflow demand, inlet design, inlet subsonic diffuser design, and the like. The surfaces of the rotor 10 may be designed to provide ducting of the incoming airflow from an air intake to the pulse detonation engine.
The sealing surfaces 20, shown in FIG. 5, provide a means of alternately shutting off the airflow supply to four of the combustion chambers in an eight-chamber engine. Open sectors 21 allow airflow to be supplied to the other four chambers not shut off by the sealing surfaces 20. The sealing surfaces 20 of the rotary airflow controller 10 are larger in angular extent than the open areas 21 at the exit of the airflow controller 10. This size difference allows the sealing surfaces 20 to overlap on the flange at the entrance opening to the combustion chamber to affect a closing of the entrance to the combustion chamber prior to ignition. The rotational speed of the rotor is dictated by the desired combustion rate. For instance, it is contemplated that the rotary airflow controller 10 illustrated in FIGS. 1-5 rotates around the center axis at about 600 rpm to provide a combustion rate of 40 firings per second for each of the eight chambers in the engine in which two opposite chambers fire at the same time.
Referring to FIGS. 6 and 7, the engine frame 12 is illustrated including an interface plane 85. The plane 85 defines the interface between the rotary airflow controller 10 and the engine frame 12. A seal 22 along the interface 85 limits or retards leakage of gases from one of the chambers 87 to another one of the chambers 87. The seal 22 is provided along the interface 85 by either integrating the seal into the leading edge or as a separate sealing section that is attached (secured) to the leading edge of the engine frame 12. In the embodiment in which the seal 22 is integrated into the engine frame 12, it is contemplated that a gap is provided between the rotary airflow controller 10 and the seal 22 of the engine frame 12 so that the rotary airflow controller 10 rotates relative to the engine frame 12. Alternatively, it is contemplated that the rotary airflow controller 10 is positioned such that the seal 22 is in selective contact with the sealing surface 20 of the rotor 10 during rotation of the rotary valve 10 relative to the engine frame 12. The seal 22 and/or the gap act as a means for limiting leakage of a gas from one of the detonation chambers 87 to another of the detonation chambers 87.
FIG. 8 illustrates an exploded view of an engine arrangement 89 in which a seal is provided in the form of a sealing section or sealing segment 110 located between the rotary valve 10 and the fixed engine frame 12.
A description of the seal segment 110 is better understood along with a description of the rotary airflow controller 10 and the engine frame 12. With reference again to FIG. 3, a downstream view of the cross-section of the rotary airflow controller 10 at the exit plane (as shown in the bottom perspective view in FIG. 5) is shown superimposed on the engine entrance frame 12 separating the combustion chambers 87 of the engine. As shown in FIG. 4, the valve 10 rotates about a center axis in the direction indicated by the arrow 16, and alternately closes and opens airflow into the combustion chambers 87 (see FIG. 3). The flat sealing surfaces 20 (see FIG. 5) of the rotary airflow controller 10 provide for closing the entrance to the combustion chambers 87 (see FIG. 3). As shown with reference again to FIG. 6, respective cross-sections of the combustion chambers 87 are segments of a circle (e.g., pie-shaped). Each of the combustion chambers 87 is defined by a portion of a center 60, two side webs 84, and an outside surface 86. The webs 84 separate the combustion chambers 87.
With reference to FIGS. 6, 8, and 9, the sealing segment 110 is similar to the engine frame 12. Like the engine frame 12, airflow passages 47 (detonation passages) of the sealing segment 110 contain webs 44, an inner surface 48, and an outer ring 46. The leading edge surfaces 45 include the surfaces on an inner hub 40, the webs 44, and the outer ring 46. A sealing material 70 acts as the seal 22, illustrated by the dashed lines in the leading edge surfaces 45, provides for a seal between the sealing segment 110 and the rotary airflow controller valve 10.
With reference to FIG. 10, a top, downstream view of the segment 110 illustrates the sealing material 70. The sealing material 70 is placed on the leading edge 45 for providing sealing around each of the airflow passages 47. Details of the cross-sections shown in FIG. 10 are presented in FIGS. 11-13. FIG. 11 illustrates cross-section A-A of FIG. 10, showing the installation of the sealing material 70 into a seal groove 60. Similarly, the installation of sealing material in cross-sections B-B and C-C of FIG. 10 are shown in FIGS. 12 and 13, respectively.
With reference to FIGS. 8 and 10, the seal 22 (sealing material 70) is provided between the sealing section 110 and the rotary airflow controller valve 10 when the sealing section 110 is positioned sufficiently close to the downstream surface 91 of the rotary valve 10 such that the gap between the sealing section 110 and the rotary valve 10 is minimized. In one embodiment, it is contemplated that the sealing material 70 is used and the gap between the rotary airflow controller valve 10 and the sealing section 110 is less than about 0.003 inches. In this embodiment, rotary airflow controller valve 10 is able to rotate relative to the sealing section 110. Furthermore, the sealing material 70 and the gap act as a means for limiting leakage of a gas from one of the detonation chambers 87 to another of the detonation chambers 87. In another embodiment, it is contemplated that the sealing segment 110 is positioned such that the sealing material 70 is in selective contact with the sealing surface 20 of the rotor 10 during rotation of the rotary valve 10. A seal is provided by installing the sealing material 70 in the leading edge of the engine frame by using a similar method of installation of the sealing material in FIGS. 12 and 13.
FIG. 14 illustrates a cross-section of the installation of the sealing section 110 with the rotary valve 10. As the rotor 10 rotates in the direction of the arrow 16, the detonation chambers 47 are either sealed, as shown on the right of the figure, or are open to accept airflow 13, as shown on the left of FIG. 14. As illustrated in FIG. 14a, which shows an enlarged view of the seal region within the dashed circle shown in FIG. 14, the sealing material 70 prevents the hot gases from a detonation 96 in the right detonation chamber 47 from crossing over to the left chamber 47 and causing pre-detonation in the left chamber 47. The gases from the detonation 96 are prevented from crossing over to the adjacent chamber by placing the sealing segment 110 with the seal material 70 at a distance sufficiently close to the sealing face 20 of the rotor 10. The arrangement as shown in FIG. 14 limits or retards the leakage rate between adjacent detonation chambers 47.
With reference to FIGS. 15 and 16, the sealing section 110 is installed directly onto the engine frame 12. The sealing section 110 shown in FIG. 15 is rigidly attached (secured) to the front (leading edge) of the pulse detonation engine frame 12 such that the webs 44 of the sealing segment 110 are positioned substantially directly above the interface plane 85 of the engine frame 12 to create a straight joint 111. However, any attachment approach or method for attaching the sealing section 110 to the engine frame 12 may be used to provide a rigid attachment. For example, FIG. 16 illustrates an alternate approach in which the webs 44 overlap (are offset from) the interface planes 85 to create an offset joint 112. The overlapping approach allows additional adjustment of the distance between the sealing section 110 and the rotary valve 10. More specifically, the joint 112 offers the option of sliding the sealing section 110 relative to the engine frame 12.
Several types of materials can be used for the sealing material 70 as described herein. Examples of materials are shown in FIGS. 17-21. FIG. 17 illustrates a sealing section 110 including a sealing material 70 made with a high-temperature thermoplastic resin, such as a polyamide-imide. One such example is TORLON; however, this is only one example of a wide variety or plastics the may be used as a sealing material. FIG. 18 illustrates a sealing section 110 including a sealing material 71 made with a metal material (e.g., brass (oil impregnated)). In other embodiments, it is also contemplated that the sealing material is a carbon material.
In addition, several types of structures can be used for the sealing material 70. FIGS. 19-21 illustrate one exemplary structure. The structure shown for the sealing section 70 is a honeycomb structure, as best seen in FIG. 21. This honeycomb structure allows for relatively low weight and relatively high strength. Typical materials used to construct a honeycomb seal are aluminum or various types of steel.
Another embodiment of the present invention is illustrated in FIGS. 22 and 23. In this embodiment, a stream of high-pressure gas, such as air, is provided to limit or retard the leakage of hot combustion gases between adjacent detonation chambers of the PDE. High-pressure gas 76 from an external source is ducted through the webs 44 (struts), which in this embodiment are hollow, and through an opening 74 (orifice) in the leading edge of the strut 44. The air exiting the opening 74 substantially fills any gap present between the rotor 10 and the sealing section 110. The high pressure opposing airflow 76 limits or retards the leakage of gases escaping from the detonation chambers 47. FIG. 23 shows one arrangement of a seal in the leading edge of the sealing section 110. As shown, a system of slots 75 and the apertures 74 (openings) along with the seal act as a means for directing air to limit or retard leakage. Although FIG. 23 shows a specific arrangement of the apertures 74 and the slots 75, it should be understood that any combination of apertures, slots, or other such structures are contemplated to be arranged for providing streams of pressurized gases to limit or retard leakage between the detonation chambers 47.
An alternate embodiment for limiting or retarding the leakage of gases between chambers is shown in FIG. 24. This embodiment includes an arrangement of seals, slots, and apertures similar to that shown in FIGS. 22 and 23; however, instead of using high-pressure air, the seals, slots, and apertures are used as a means for directing air to limit or retard leakage by providing suction at the leading edge 45 of the sealing section 110. The suction captures a portion of the gas along the interface that escape from the detonation chambers 47 and exhausts the portion of the gas by directing the gas away from the interface such that leakage of the gas into adjacent chambers 47 is limited or retarded. The suction airflow 80 enters the webs 44 (struts), which are hollow, via openings 79 and passes through passages 78 in the hollow webs 44 to be exhausted.
It is to be understood that the materials, structures, and embodiments discussed with reference to FIGS. 17-24 may be used in either the embodiment including the sealing material on the engine frame or the embodiment including the sealing material on the sealing section, which is attached to the engine frame.
While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.
Patent Application
20090120059
