Abstract:
An ignition system for a combustor includes a resonance system which generates an oscillation pressure force by a resonant flow interaction between two parallel interconnected flow passages which carry an incompressible flow. A piezoelectric system driven by said resonance system. An igniter powered by said piezoelectric system.

Description:
BACKGROUND 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 11/333,691, filed Jan. 17, 2006. 
     
    
       [0002]    The present disclosure relates to a piezo-resonance igniter system for passive auto ignition of a rocket engine, and more particularly to a method which utilizes the pressure energy in the propellants themselves to excite piezoelectric crystals such that high voltage electrical pulses are created to generate a spark in an igniter system. 
         [0003]    Various conventional ignition systems have been used for ignition of a propellant mixture in a combustion chamber of a rocket engine. These ignition systems generally employed a spark induced by an electrical current from a source of electricity and a control for sensing when to supply and discontinue the spark. These conventional systems, although effective, tend to be relatively complex, heavy, and may not provide restart capability. 
         [0004]    With the need for safe storable propellant systems such as Gaseous Oxygen (GOx) and Methane combinations, an uncomplicated fully passive auto ignition system is desired to complement the advantages of the safe storable propellants by reducing ignition system complexity, weight, and cost with increased safety and reliability. 
       SUMMARY 
       [0005]    An ignition system for a combustor according to an exemplary aspect of the present disclosure includes a resonance system which generates an oscillation pressure force by a resonant flow interaction between two parallel interconnected flow passages which carry an incompressible flow. A piezoelectric system driven by said resonance system. An igniter powered by said piezoelectric system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0007]      FIG. 1  is a general perspective view an exemplary of rocket engine embodiment for use with the present disclosure; 
           [0008]      FIG. 2A  is a schematic view of an ignition system of the present disclosure; 
           [0009]      FIG. 2B  is an expanded view of the ignition system components illustrated in  FIG. 2A ; 
           [0010]      FIG. 3  is a schematic view of a flight ready ignition system of the present disclosure with an indirect piezo-resonance module; 
           [0011]      FIG. 4  is a schematic view of a flight ready piezo-resonance module ignition system of the present disclosure utilizing a direct spark torch approach mounted directly within a combustion chamber; and 
           [0012]      FIG. 5  is a schematic view of a flight ready piezo-resonance module ignition system of the present disclosure for use with an incompressible fluid flow. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  illustrates a general schematic view of a rocket engine  10 . The engine  10  generally includes a thrust chamber assembly  12 , a fuel system  14 , an oxidizer system  16  and an ignition system  18 . The fuel system  14  and the oxidizer system  16  provide a gaseous propellant system of the rocket engine  10 , however, other propellant systems such as liquid will also benefit from present disclosure. 
         [0014]    A combustion chamber wall  20  about a thrust axis A defines the nozzle assembly  12 . The combustion chamber wall  20  defines a thrust chamber  22 , a combustion chamber  24  upstream of the thrust chamber  22 , and a combustion chamber throat  26  therebetween. The thrust chamber assembly  12  includes an injector  12 A with an injector face  28  which contains a multitude of fuel/oxidizer injector elements  30  (shown somewhat schematically) which receive fuel which passes first through the fuel cooled combustion chamber wall  20  fed via fuel supply line  14 A of the fuel system  14  and an oxidizer such as Gaseous Oxygen (GOx) through an oxidizer supply line  16 A of the oxidizer system  16 . 
         [0015]    The ignition system  18  generally includes a resonance system  36  in communication with one of the propellants such as the oxidizer system  16 , a piezoelectric system  38 , and an electrical conditioning system  40  to power an igniter  42  mounted within the injector  12 A to ignite the fuel/oxidizer propellant flow from the fuel/oxidizer injector elements  30 . The oxidizer is fed to the igniter via a dedicated line  16 B in this embodiment, and the fuel is also fed to the igniter torch via a dedicated line  14 B. It should be understood that various propellant flow paths may be usable with the present disclosure so long as at least one propellant flow is in communication with the resonance system  36 . Ignition of the fuel/oxidizer propellant flow from the fuel/oxidizer injector elements  30  with the igniter  42  is conventional and need not be described in further detail herein. It should also be understood that while the current focus of this disclosure is a rocket ignition, other applications for power generation and ignition of other combustion based devices will also be usable with the present disclosure. 
         [0016]    Referring to  FIG. 2A , one ignition system  18  includes a housing  32  which defines a resonance cavity  44  having an inlet  34  incorporating a supersonic inlet nozzle  46  to receive a flow of propellant such as the oxidizer from the oxidizer supply line  16 B of the oxidizer system  16 . An outlet  16   a  from the resonance system  36  includes an outlet nozzle  50  to maintain pressure in the resonance cavity  44  at a predetermined level. Although the illustrated embodiment of the oxidizer is a gaseous propellant (compressible flow) resonance configuration, it should be understood that resonant pressure pulses from incompressible liquid flow as well as from other propellant sources will likewise be usable with the present disclosure. 
         [0017]    The resonance system  36  is in communication with the piezoelectric system  38  through a gas resonance tube  52 . It should be understood that in  FIG. 2A  the piezoelectric system  38  is illustrated in a schematic form in what may be considered a ground based configuration which may include adjustment features that may or may not be required. That is, other even less complicated piezoelectric systems are achievable as illustrated in the following embodiments. 
         [0018]    The gas resonance tube  52  is located through an opening  54  in the resonance cavity  44  opposite the supersonic inlet nozzle  46 . The oxidizer entering through the supersonic inlet nozzle  46  as underexpanded flow is directed at the gas resonance tube  52  causing an oscillating detached shock  56  to form upstream of the entrance  56 N to the gas resonance tube  52 . Reflected shocks within the gas resonance tube  52  couple and reinforce the detached shock  56  and interact with the flow within the gas resonance tube  52  such that the successive cycles of shocks cause the formation of a series of unstable zones of elevated pressure within the gas resonance tube  52 . Physical criteria for the interaction may be defined by: “d” the diameter of the supersonic inlet nozzle  46 ; “G” the distance between the throat of the inlet nozzle  46  and the entrance  56 N of the gas resonance tube  52 ; “Dtube” the internal diameter of gas resonance tube  52  and “DMC” which is the throat diameter of the outlet nozzle  50 . A constant diameter gas resonance tube  52  is depicted; however, it is understood that stepped, conical or other shaped resonance tubes may alternatively be utilized with the present disclosure. 
         [0019]    The gas resonance tube  52  is sealed at an end opposite the entrance  56 N with a force transmission diaphragm  58  (also illustrated in  FIG. 2B ). A force transfer member  60  includes a force transfer rod  62  and a force transfer platen  64  in contact with the force transmission diaphragm  58 . The force transfer platen  64  is of a larger diameter than the force transfer rod  62  so as to increase the surface area in contact with the force transmission diaphragm  58  and react pressure loads from the oscillating pressures in the gas resonance tube  52 . The sizing of the force transmission diaphragm  58  allows the resonance pressure pulses to act over a relatively large effective area, increasing the net force output for a given gas resonance tube  52  diameter (Dtube) and supply pressure. Flow relief passages  52   a  ( FIG. 2B ) may be incorporated into the mating faces of the gas resonance tube  52  and the end segment  70  to increase working fluid transfer across the face of the force transmission diaphragm  58  during the relatively short resonant pressure pulses in the gas resonance tube  52 . 
         [0020]    The force transfer rod  62  is received within a guide sleeve  65 . The guide sleeve  65  contains a piezoelectric crystal stack  66  mounted in contact with the force transfer rod  62 . The oscillating pressure force in the gas resonance tube  52  is transmitted to the piezoelectric crystal stack  66  through the force transfer member  60  to generate electrical pulses. The wire harness  67  is connected directly to the igniter  42 , eliminating the electrical conditioning system  40 . The oscillating force drives the direct spark ignition, in which each pressure pulse results in a spark, offering a persistent source of ignition. 
         [0021]    Alternatively or in addition thereto, the electrical pulses are communicated to the igniter  42  through a wire harness  67  and the electrical conditioning system  40 . An energy storage system  68 A (illustrated schematically) such as an electrical capacitor or battery and a voltage multiplier system  68 B (illustrated schematically) within the electrical condition system  40  may condition the spark to a desired spark output energy and frequency independent of the crystal output. This permits the system to be sized to suit any application. In other words, the electrical condition system  40  may include various electrical subsystems such as storage capacitors or voltage amplifiers to specifically tailor the ignition system to provide various outputs. 
         [0022]    Since the spark energy production is driven by the resonance of the propellant flow, a fully passive auto-ignition system is provided. When the propellant valves are open, flow through the resonance system  36  is such that resonance occurs and spark energy is created. Once ignition occurs, the resultant backpressure within the combustion chamber  24  ( FIG. 1 ) “detunes” the resonance phenomena and spark production stops. Furthermore, should the engine flame out, spark production automatically resumes as the propellant valves remain open. Control and operation of the rocket engine is considerably simplified by the elimination of separate power supply and switching command systems in the igniter system such that the heretofore typical uncertainties in the spark duration control are obviated. This provides significant advantages for distributed multi-thruster systems, such as an attitude control system (ACS). 
         [0023]    Referring to  FIG. 2B , the force transmission diaphragm  58  is preferably sandwiched between an end segment  70  of the gas resonance tube  52  and a diaphragm support ring  72  which may be welded together through a weld W or other attachment. The force transmission diaphragm  58  preferably includes a relief feature  74  located between the diaphragm support ring  72  and the force transfer platen  64 . The relief feature  74  is preferably a circular flexed portion of the force transmission diaphragm  58  within which the force transfer platen  64  is received. The relief feature  74  minimizes tensile load losses on the force transmission diaphragm  58  thereby enhancing flexibility to maximize transfer of the oscillating pressure force to the force transfer platen  64  and thence to the piezoelectric crystal stack  66  through the force transfer rod  62 . 
         [0024]    Applicant has demonstrated relatively short ignition delay times of approximately 18 mseconds utilizing a gaseous propellant (compressible flow) resonance configuration. However, multiple approaches exist to achieve the resonant pressure pulses from incompressible liquid flow as well such that the present disclosure is adaptable to any propellants. 
         [0025]    Referring to  FIG. 3 , another ignition system  18 B is illustrated. The resonance system  36 A includes a more compact flight-ready piezoelectric system  38 A integrated with the resonance system  36 A. Such a system is readily mounted anywhere within the communicating conduits of a working fluid system such as embodied by the oxidizer system or fuel system ( FIG. 1 ). 
         [0026]    The piezoelectric system  38 A includes an electrical condition system  90 A to remotely power the igniter  92  (illustrated schematically) mounted within a piezoelectric housing  80 . The resonance system  36 A includes a resonance housing  82  which defines the resonance cavity  44  therein. Preferably, the resonance housing  82  is threaded to the piezoelectric housing  80  to provide an exceedingly compact and robust system which is readily maintained. 
         [0027]    A piezoelectric guide sleeve  84  is interfit with an insulator load reaction interface sleeve  86  and both are mounted within the piezoelectric housing  80  against a stop  88 . The force transmission diaphragm  58  is preferably sandwiched between and end segment  82   a  of the resonance housing  82  which defines the gas resonance tube  52  and the piezoelectric guide sleeve  84 . The force transmission diaphragm  58  also includes the relief feature  74  as illustrated in  FIG. 2B . 
         [0028]    A force transfer member  90  is mounted within the piezoelectric guide sleeve  84  adjacent the force transmission diaphragm  58 . The force transfer member  90  is preferably a frustro-conical member in which an apex  92  thereof is located in contact and preferably interfits with the piezoelectric crystal stack  66 . That is, the force transfer member  90  essentially combines the force transfer rod  62  and a force transfer platen  64  of the above embodiment, however operation is generally equivalent as the apex  92  is in contact with the piezoelectric crystal stack  66 . The oscillating pressure force in the gas resonance tube  52  is transmitted to the piezoelectric crystal stack  66  through the force transfer member  90  to generate electrical pulses in an electrode  94  opposite the piezoelectric crystal stack  66 . The electrical pulses from the electrode are communicated to the igniter  42  through the electrical conditioning system  90 A via a wire harness  96 . The wire harness preferably terminates in a connector  98  which permits removable attachment to a spark power cable  99  such that the system  36 A,  38 A may be readily replaced during maintenance. As discussed above, since the spark energy production is driven by the resonance of the propellant flow, a fully passive auto-ignition system is provided which is “detuned” when ignition occurs such that spark production automatically stops. 
         [0029]    Referring to  FIG. 4 , another ignition system  18 C is illustrated. The resonance system  36 B and piezoelectric system  38 B are integrated within a combustion chamber  24 B as would be preferred for a thruster system as each individual thruster system thereby includes an essentially self-contained ignition system. The resonance system  36 B is preferably defined by a resonance housing  12 B which defines the resonance cavity  44  therein. The resonance housing  12 B is attached directly to the injector  12 A through fasteners such as bolts b or the like. 
         [0030]    As the  FIG. 4  embodiment generally includes components common to that of the previous embodiments, consistent reference numeral usage will be utilized while components more specific to the  FIG. 4  embodiment will be described in detail. It will be understood that operation of the  FIG. 4  embodiment is generally as the  FIG. 3  embodiment, however, the electrode  100  of the  FIG. 4  embodiment is mounted to provide a direct spark torch approach. That is, the electrode directly communicates with the combustion chamber  24  through the injector face  28  which contains the multitude of fuel/oxidizer injector elements  30  (shown schematically) which receive fuel from the fuel cooled combustion chamber wall  20  which is fed via fuel supply line  19   a  of the fuel system  14  and an oxidizer such as Gaseous Oxygen (GOx) through an oxidizer supply line  36   a  of the oxidizer system  16  (also illustrated in  FIG. 1 ). 
         [0031]    The electrode  100  extends through an oxidizer manifold  102  and a fuel manifold  103  to generate a spark within the combustion chamber  24 . The electrode  100  is mounted within an insulator load reaction interface  104  which extends along a significant length of the electrode  100 . The insulator load reaction interface  104  is interfit with the piezoelectric guide sleeve  84  and retained within the injector  12 A. A torch housing  106  is defined about the electrode and the insulator load reaction interface  104  to define a torch oxidizer feed annulus  108 . 
         [0032]    Oxidizer is communicated form the oxidizer manifold  102  through torch oxidizer inlet ports  110  through the torch housing  106 . A multitude of fuel injection ports  112  in communication with the fuel manifold  103  communicate fuel toward the distal end of the electrode  100 . Oxidizer and fuel is thereby injected adjacent a distal end of the electrode  100  from which the ignition spark is generated to thereby ignite the mixture within the combustion chamber  24 B. As discussed above, since the spark energy production is driven by the resonance of the propellant flow, a fully passive auto-ignition system is provided which is “detuned” when ignition occurs such that spark production automatically stops. 
         [0033]    Referring to  FIG. 5 , another ignition system  18 D that utilizes an incompressible working fluid such as a liquid propellant is illustrated. The resonance system  36 C includes an incompressible fluid resonance housing  120  which defines a resonance cavity  122  therein. Preferably, the resonance housing  120  includes a threaded portion  120 A such that a piezoelectric housing  80  and associated piezoelectric system (as disclosed in  FIG. 3 ) is threaded thereto. In other words, the piezoelectric housing  80  and associated piezoelectric system (as disclosed in  FIG. 3 ) is a common system which may be driven by, for example only, either the resonance housing  82  illustrated of  FIG. 3  or the incompressible fluid resonance housing  120  illustrated in  FIG. 5  to provide an exceedingly compact and robust system. 
         [0034]    The incompressible fluid resonance housing  120  includes a split leg resonator  124  having a first leg  126 A and a second leg  126 B. The legs  126 A,  126 B split off from an incompressible fluid inlet  128  and rejoin at a common leg  126 C to form a generally triangular relationship. It should be understood that other paths will also be usable with the present disclosure. The common leg  126 C includes an incompressible fluid outlet  132  which is in communication with a combustion chamber as illustrated in  FIG. 1 . A gas resonance tube  130  is in communication with the first leg  126 A of the split leg resonator  124  to generate an oscillating pressure force within the gas resonance tube  130  due to the unstable flow oscillations between the parallel flowpaths in legs  126 A and  126 B. The oscillating pressure force generated within the gas resonance tube  130  may then utilized to drive the piezoelectric system as described above. 
         [0035]    As discussed above, since the spark energy production is driven by the resonance of the propellant flow, a fully passive auto-ignition system is provided which is “detuned” when ignition occurs such that spark production automatically stops. 
         [0036]    It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
         [0037]    It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant disclosure. 
         [0038]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
         [0039]    The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present disclosure are possible in light of the above teachings. The preferred embodiments of this disclosure have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this disclosure. It is, therefore, to be understood that within the scope of the appended claims, the disclosure may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this disclosure.