Patent Publication Number: US-2011047961-A1

Title: Pulse detonation inlet management system

Description:
BACKGROUND 
     With the development of pulse detonation combustors (PDCs) and engines (PDEs), various efforts have been made to use this technology in practical applications. An example of such a practical application is the development of a “hybrid” engine that uses a combination of both conventional gas turbine engine technology and PDE technology to maximize operation efficiency. Other examples include use in aircrafts, missiles, and rockets. 
     Pulse detonation combustors are used, for example, in pulse detonation engines. In pulse detonation engines, thrust is generated by the supersonic detonation of fuel in a detonation chamber. The supersonic detonation increases the pressure and temperature in the detonation chamber until it is released resulting in thrust. The detonation process is efficient since all of the charge is burned while inside the detonation chamber. As with any engine that intakes air, inlet stability is an important aspect of maintaining proper operation of a pulse detonation engine. This presents a particular challenge in pulse detonation engines, which use open inlet tubes. 
     The operation of pulse detonation engines creates extremely high pressure peaks and oscillations within the combustor that may travel to upstream components, and generates high heat within the combustor and surrounding components resulting in damage and malfunction of the upstream components. Consequently, various valving techniques are being developed to provide inlet control and prevent the high pressure peaks from traveling to the upstream components. 
     For these and other reasons, there is a need for the present invention. 
     SUMMARY 
     A pulse detonation combustor valve assembly is provided that includes a fixed valve portion having an inlet and a reciprocating valve portion. The valve assembly is coupled to a pulse detonation combustor. The reciprocating valve portion is exterior to the fixed valve portion and coaxially aligned with the fixed valve portion. The reciprocating valve portion is arranged to reciprocate with respect to the fixed valve portion to control inlet flow through the inlet of the valve assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are better understood with reference to the following drawings. Like reference numerals represent corresponding parts. 
         FIGS. 1A-1C  show cross-sectional views of an exemplary embodiment of a pulse detonation combustor valve assembly; 
         FIGS. 2A-2C  show cross-sectional views of another exemplary embodiment of a pulse detonation combustor valve assembly; 
         FIGS. 3A and 3B  show a cross-sectional view yet another embodiment of a pulse detonation combustor valve assembly; 
         FIG. 4  shows an exemplary embodiment of sealing elements; 
         FIG. 5  shows another exemplary embodiment for fuel injection; 
         FIG. 6  shows the operational stages of an exemplary embodiment of a pulse detonation combustor valve assembly; 
         FIG. 7  shows the operating stages of an exemplary embodiment of a pulse detonation combustor valve assembly; and 
         FIG. 8  shows an exemplary operating cycle of a pulse detonation combustor valve assembly. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, a “pulse detonation combustor” (PDC) is understood to mean any device or system that produces both a pressure rise and velocity increase from a series of repeated detonations or quasi-detonations within the device. A “quasi-detonation” is a supersonic turbulent combustion process that produces a pressure rise and velocity increase higher than the pressure rise and velocity increase produced by a deflagration wave. Embodiments of PDCs include a means of igniting a fuel/oxidizer mixture, for example a fuel/air mixture, and a detonation chamber, in which pressure wave fronts initiated by the ignition process coalesce to produce a detonation or quasi-detonation. Each detonation or quasi-detonation is initiated either by external ignition, such as spark discharge or laser pulse, or by gas dynamic processes, such as shock focusing, auto ignition or by another detonation (i.e. cross-fire). PDCs are used in pulse detonation engines (PDEs), for example. As used herein, “engine” means any device used to generate thrust and/or power. As used herein, “detonation” includes both detonations and quasi-detonations. 
     Embodiments of the present invention will be explained in further detail by making reference to the accompanying drawings in which like reference numerals indicate corresponding parts. The drawings do not limit the scope of the invention in any way. 
       FIGS. 1A-1C  depict a pulse detonation combustor valve assembly  100  according to an exemplary embodiment of the present invention. The assembly  100  includes a fixed valve portion  103  and a reciprocating valve portion  104 . The fixed valve portion  103  includes a fixed base member  101  and a fixed end cap  102 , as shown in  FIG. 1B . In the embodiment shown, the fixed base member  101  and the fixed end cap  102  are axially aligned. The reciprocating valve portion  104  reciprocates with respect to the fixed valve portion  103  to periodically occlude an inlet  108 . Seal elements, such as labyrinth seals shown in  FIG. 4 , are arranged between the fixed valve portion and the reciprocating valve portion  104 . The seal elements can be any suitable seal element to accomplish the desired seal. The inlet  108  provides for the flow of an oxidizer, such as air, through the assembly. The invention is not limited to controlling the flow of oxidizer. The valve assembly can also used to control the flow of fuel or a fuel and oxidizer mixture through the inlet. 
     The fixed valve portion  103  is axially aligned with the reciprocating valve  104 . The shape and size of the fixed valve portion  103  and the reciprocating valve portion  104  can be determined based upon the desired performance characteristics and the application. In the exemplary embodiment, the fixed valve portion  103  and the reciprocating valve portion  104  are cylinders arranged concentrically. In addition, fuel is supplied axially from a fuel injector  110  via a passage  102   a  arranged in the fixed valve portion  103 .  FIG. 1A  shows the valve assembly  100  where the reciprocating valve portion  104  is open, and  FIG. 1C  illustrates the valve assembly  100  where the reciprocating valve portion  104  is closed blocking the inlet  108 . 
     In  FIGS. 1A-1C , the inlet  108  is formed from an annular arrangement of the fixed base member  101  and the fixed end cap  102 . However, the inlet  108  can also be formed as holes, slots, or any other suitable openings in the fixed base member  101 . A fluidic device (not shown) can be provided at the inlet to reduce pressure drop at the inlet  108  by avoiding flow separation. 
     Actuation of the reciprocating valve portion  104  can be accomplished by any suitable means including mechanical (cam, scotch yoke, spring-mass-damper systems), pneumatic, electromagnetic, hydraulic, etc. For purposes of discussion, push-rods  106  are shown as part of an exemplary actuation device. The valve assembly  100  can be supported by any suitable support structure. 
     In  FIGS. 1A-1C , fuel is injected axially from the fuel injector  110 . However, fuel can be injected through an opening arranged on the side of the fixed base member  101 . Fuel can be injected downstream from the inlet  108  or upstream of the inlet  108 . Fuel can either be liquid fuel or gaseous fuel. 
       FIGS. 2A and 2B  depict another embodiment of a pulse detonation combustor valve assembly. The assembly  200  includes the fixed valve portion  103 , the reciprocating valve portion  104 , an inlet passage  202 , and an inlet  208 . As in the previous embodiment, fuel is supplied from the fuel injector  110  via a passage  102   a  in the fixed valve portion  103 . In this embodiment, the fixed base member  101  includes a receptacle  101   a . The receptacle  101   a  is arranged in the fixed base member  101  opposite the reciprocating valve portion  104 . The receptacle  101   a  receives the reciprocating valve portion  104  during valve operation to prevent flow through the inlet  208 . 
     The reciprocating valve portion  104  reciprocates with respect to the receptacle  101   b  in the fixed base member  101  to periodically occlude the inlet  208  to control flow through the valve assembly. In  FIG. 2A , the reciprocating valve portion  104  is shown in the open position, while in  FIG. 2B , the reciprocating valve portion  104  is shown in the closed position. Actuation of the reciprocating valve portion  104  can be accomplished by any suitable means as described with respect to previous embodiments. For purposes of discussion, push-rods  106  are shown as part of an exemplary actuation device. 
     Each of the valve assemblies shown in  FIGS. 1A-1C  and  2 A- 2 B can be used in any device requiring valve operation to control inlet flow. For example, the valve assemblies can be used in any combustion/detonation device. In a more specific example, the valve assembly is coupled to a pulse detonation combustor  112 , as shown in  FIG. 1A . The fixed base member  101  of the assembly  100  can be attached to the pulse detonation combustor by any suitable means such as by flanges, welding, etc. Alternatively, the fixed base member  101  of the valve assembly can be formed as an integral part of a pulse detonation combustor  112 . More specifically, the fixed base member  101  and the pulse detonation combustor  112  can be formed as a continuous structure, as shown in  FIG. 2C . Operation of the valve assembly in  FIG. 2C  is the same as in  FIGS. 2A and 2B . 
       FIGS. 3A and 3B  illustrate another exemplary embodiment of the present invention. In this embodiment, the fixed base member  101  tapers to an aerodynamic member  101   b  that includes the receptacle  101   a . In addition, the inlet passage  202  is replaced with an annulus or inlet passage  302  that is curved to correspond to the aerodynamic member  101   b  of the fixed base member  101 . In addition, the fixed end cap  102  of the fixed valve portion  103  in this embodiment includes a curved portion  102   b . The curved portion  102   b  continues the curve of the inlet passage  302 . The curved portion  102   b  also corresponds to the curve of the aerodynamic member  101   b . As in previous embodiments, the reciprocating valve portion  104  reciprocates with respect to the fixed valve portion  103  to periodically occlude the inlet passage  302 . The reciprocating valve portion  104  is open in  FIG. 3A , and closed in  FIG. 3B . 
     The inlet passage  302  is not limited to an annular structure, and can be formed in any manner suitable to the application. Further, the inlet passage  302  can include one or more vanes  304 . The vanes  304  provide structural support to the inlet passage  302  and can be configured to induce swirl in the incoming airflow. The swirl together with the aerodynamic member  101   b  and the curved portion  102   b  serve to prevent flow separation and thus reduce aerodynamic losses. The amount of swirl and the geometry of the aerodynamic member  101   b  can be adjusted to improve fuel-air mixing and promote more efficient detonations. 
     Referring to  FIG. 4 , seal elements  402   a  and  402   b  are provided to seal the receptacle  101   a  and the space  404  in which the reciprocating valve portion  104  reciprocates, respectively. In the exemplary embodiment shown, the seal elements  402   a  and  402   b  are labyrinth seals. However, any suitable seal elements can be used that will ensure that the pressure rise is sufficiently maintained within the pulse detonation combustor. The seal elements  402   a ,  402   b  ensure proper flow of oxidizer through inlet passage so that flow is not lost in the space  404  or in the receptacle  101   a . The seal elements prevent the pressure rise from passing to any upstream components. The location of the seal elements is not limited to those shown in  FIG. 4 . They may be positioned in any suitable location to achieve the sealing results. 
     In the previous exemplary embodiments, the fuel injector  110  is axially aligned with the fixed valve portion  103  and the reciprocating valve portion  104 . However, fuel may also be supplied downstream of the reciprocating valve portion  104  by injectors  502  arranged in the inlet passage  302 , as shown in  FIG. 5 . Of course, fuel may be injected in any manner suitable to the specific structure and application. Alternatively, fuel can be injected into the pulse detonation combustor  112 . 
     As previously noted, the actuator mechanism for each of the embodiments discussed may be selected from any number of known actuators. Also, the reciprocating valve portion  104  and the fixed valve portion  103  can be cylindrical or cylindrical through a portion of their length. However, embodiments of the invention are not limited to a cylinder and the valve assembly can be of any shape suitable for the application. 
     The embodiments described above provide for the reciprocation of the reciprocating valve portion  104  to modulate the flow through the inlet with very small pressure drop. The aerodynamic member  101   b  prevents flow separation and minimizes aerodynamic losses. 
     The reciprocating valve portion  104  and the fixed valve portion  103  according to the exemplary embodiments of the present invention significantly reduce the forces and loads experienced by upstream components, which simplifies operation and extends the operational life of the system. The valve assembly enables the detonation load to be balanced radially. Very little, if any, forces will be experienced axially. Therefore, the components coupled to the valve assembly (for example, its driving mechanism) will be shielded from the damaging pressure oscillations. 
     The valve assembly according to embodiments of the present invention enables the inlet passage to be opened and closed quickly. In operation, the reciprocating valve portion traverses a relatively short axial distance. However, the reciprocating valve portion and the fixed valve portion can have a relatively large opening. Therefore, the physical opening of the valve assembly will change rapidly with small reciprocating movement. As a consequence, flow through the valve assembly can be optimized. 
     Operation of the valve assembly will be discussed in more detail. As shown in  FIGS. 6 and 7 , the entire stroke length is represented by a+b+c. The stroke length of a, b, and c parameters can be adjusted to change the valve timing and increase/decrease the valve opening time. Variable geometry elements can be incorporated into the actuation mechanism to adjust timing on the fly if desired. In the embodiment shown, the reciprocating valve portion reciprocates from Top Dead Center (TDC) to Bottom Dead Center (BDC). 
     During the upstroke, the reciprocating valve portion begins to open as the tip exits the receptacle. The valve assembly is fully open once the tip has cleared the inlet opening and is fully open for the duration of time until the tip of the reciprocating valve portion begins to occlude the inlet, as shown in  FIG. 7 . On the downstroke, when the reciprocating valve portion enters the receptacle, it is considered fully closed. The valve assembly is fully closed for the duration of the time that the reciprocating valve portion is within the receptacle, as shown in  FIG. 7 . According to embodiments of the invention, the opening of the valve assembly can be large relative to the axial distance b traversed by the reciprocating valve portion. This provides for a smaller axial stroke and less loads or demands on the actuating mechanism to achieve optimal performance. 
     As discussed above and shown in  FIG. 8 , the valve assembly reaches fully open and fully closed positions rapidly. This allows for maximized time open. 
     Additionally, depending on the desired operational performance, the rate of reciprocation of the reciprocating valve portion can be constant or it can be variable based on various performance and operational requirements. Further, the rate of reciprocation can be changed or adjusted to change the fill profile of the combustor or other device chamber to be filled to achieve the desired operation. The rate of reciprocation can be controlled by any known means, such as through the use of a computer control system, stepper motors, and the like. 
     As described herein, embodiments of the arrangement of the valve assembly and the inlet passage provide for an efficient filling phase with very small pressure drop, which increases engine performance and/or efficiency. The valve assembly also balances mechanical loads from combustion pressure. The symmetry of the system allows for very strong components while being lightweight. 
     It is noted that the above embodiments have been shown and described with respect to a single pulse detonation combustor (or device chamber). However, the concept of the present invention is not limited to single pulse detonation combustor embodiments. 
     It is noted that although embodiments of the present invention have been discussed above with respect to aircraft and power generation applications, the present invention is not limited to this and can be in any similar detonation/deflagration device in which the benefits of the present invention are desirable. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.