Abstract:
A tuned cavity rotating detonation combustion system includes a an annular chamber having an inlet and an outlet; a valve plate at the inlet of the annular chamber and comprising a plurality of openings spaced circumferentially around the inlet; a plurality of tubes each having an open end in communication with a corresponding opening of the valve plate and a closed end forming a tuned cavity, and a first opening between the open end and the closed end for injection of air; and a plurality of fuel injectors corresponding to the plurality of tubes, each fuel injector being configured to inject fuel into the tube between the first opening and the open end. Each of the tuned cavities has a length sized to resonate at a same frequency as a continuous detonation frequency of at least one detonation wave in the annular chamber. Alternately, or additionally, a plurality of flame arresters corresponding to the plurality of tubes are configured to arrest the at least one detonation wave generated in the detonation chamber from travelling into the tube.

Description:
BACKGROUND 
       [0001]    The present technology relates generally to tuned cavity rotating detonation pressure gain combustion systems, and more particularly, to a system for liquid fuel injection into a tuned cavity rotating detonation combustion system. 
         [0002]    Rotating, or continuous, detonation pressure gain combustion systems are expected to have significant advantage over pulse detonation pressure gain combustors as the net non-uniformity of flow entering the turbine is expected to be lower by a factor of 2-10. One of the limitations of a rotating detonation combustor is inlet valving. The inlet valving has to work at kilohertz frequency range rather than the tens of hertz frequency range of the pulse detonation combustors. Mechanical valves that operate at such high frequencies are not practical. 
       BRIEF DESCRIPTION 
       [0003]    In accordance with one example of the technology disclosed herein, a rotating detonation combustion system comprises an annular chamber having an inlet and an outlet; a valve plate at the inlet of the annular chamber and comprising a plurality of openings spaced circumferentially around the inlet; a plurality of tubes each having an open end in communication with a corresponding opening of the valve plate and a closed end forming a tuned cavity, and a first opening between the open end and the closed end for injection of air; and a plurality of fuel injectors corresponding to the plurality of tubes, each fuel injector being configured to inject fuel into the tube between the first opening and the open end, wherein each of the tuned cavities has a length sized to resonate at a same frequency as a continuous detonation frequency of a detonation wave in the annular chamber. 
         [0004]    In accordance with another example of the technology disclosed herein, a rotating detonation combustion system comprises a detonation chamber having an inner wall, an outer wall, an inlet and an outlet; a valve plate at the inlet of the annular chamber and comprising a plurality of openings spaced around the inlet; a plurality of tubes each having an open end in communication with a corresponding opening of the valve plate and a closed end forming a tuned cavity, and a first opening between the open end and the closed end for injection of a fuel/air mixture; and a plurality of flame arresters corresponding to the plurality of tubes, each flame arrester being configured to arrest at least one detonation wave generated in the detonation chamber from travelling into the tube, wherein each of the tuned cavities has a length sized to resonate at a same frequency as an effective continuous detonation frequency of at least one detonation wave in the annular chamber. 
         [0005]    In accordance with another example of the technology disclosed herein, a method of combustion comprises introducing a plurality of fuel/air plumes into an annular chamber from a plurality of tubes at in inlet side of the annular chamber, each of the plurality of tubes having an open end at the inlet side and a closed end opposite the open end forming a tuned cavity; and igniting a fuel/air mixture formed by the plumes to generate a detonation wave in the annular chamber, wherein each of the tuned cavities has a length sized to resonate at a same frequency as a continuous detonation frequency of a detonation wave in the annular chamber. 
         [0006]    Referring to  FIG. 1 , a current rotating detonation combustor  2  includes an annulus having an outer wall  8  and an inner wall  10 . The annulus  8 ,  10  has an inlet end  4  in which a fresh fuel/air mixture  20  enters and an outlet end  6  from which an exhaust flow  22  exits. A detonation wave  16  travels in the circumferential direction  17  of the annulus  8 ,  10  consuming the incoming fuel/air mixture  18  and providing a high pressure region  14  in an expansion region  12  of the combustion. The burned fuel/air mixture (i.e. combustion gases)  19  exit the annulus  8 ,  10  and are exhausted with the exhaust flow  22 . The region  14  behind the detonation wave  16  has very high pressures and this pressure can feed back into an upstream chamber from which the air and fuel are introduced and form an unburnt fuel/air mixture  20 . Current designs of rotating detonation combustion systems attempt to overcome the inlet valve limitation by increasing the pressure drop across the valve to a 20% to 50% range to prevent the detonation pressure wave  16  from travelling into the incoming fuel/air mixture  18  and to ensure that the fuel/air mixture  18  flow does not reverse in the region following the detonation wave. However, this compromises the benefits of pressure gain of the detonation wave phenomena. 
     
    
     
       DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present technology will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1  schematically illustrates a current rotating detonation combustor; 
           [0009]      FIG. 2  schematically illustrates a tuned cavity rotating detonation combustion system according to one example of the present invention; 
           [0010]      FIG. 3  is a cross-sectional view of the tuned cavity rotating detonation combustion system along line  3 - 3  of  FIG. 2 ; 
           [0011]      FIG. 4  schematically illustrates a perspective view of the tuned cavity rotating detonation combustion system of  FIG. 2 ; 
           [0012]      FIG. 5  schematically illustrates the working principle of the tuned cavity rotating detonation combustion system of  FIGS. 2-4 ; 
           [0013]      FIG. 6  schematically illustrates a tuned cavity according to another example of the present invention; 
           [0014]      FIG. 7  schematically illustrates a tuned cavity rotating detonation combustion system according to another example of the present invention; 
           [0015]      FIG. 8  schematically illustrates a flame arrester configuration for a tuned cavity rotating detonation combustion system according to an example of the present invention; 
           [0016]      FIG. 9  schematically illustrates a flame arrester configuration for a tuned cavity rotating detonation combustion system according to an example of the present invention; 
           [0017]      FIG. 10  schematically illustrates a flame arrester configuration for a tuned cavity rotating detonation combustion system according to an example of the present invention; 
           [0018]      FIG. 11  is a cross-sectional view of a valve plate of a tuned cavity rotating detonation combustion system according to an example of the present invention along line  8 - 8  as shown in  FIG. 7 ; 
           [0019]      FIG. 12  is a schematic illustration of a detonation chamber according to an example of the present invention; 
           [0020]      FIG. 13  is a schematic illustration of a detonation chamber according to an example of the present invention; 
           [0021]      FIG. 14  is a schematic illustration of a detonation chamber according to an example of the present invention; and 
           [0022]      FIG. 15  is a schematic illustration of a detonation chamber according to an example of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Referring to  FIGS. 2-5 , a rotating detonation combustion system  2  according to an example of the present technology may include a rotatable detonation annulus having an outer wall  8  and an inner wall  10 . It should be appreciated that the walls  8 ,  10  of the annulus may form a cylindrical annulus as shown in  FIG. 1 , but that walls  8 ,  10  may also be curved, or may define a conical annulus. As shown in  FIGS. 2 and 3 , a stationary valve plate  30  with a plurality of holes  46  corresponding to a plurality of tubes  34  is positioned adjacent to the inlet end of the annulus  8 ,  10  and an exhaust nozzle  24  is provided to the exit end of the annulus  8 ,  10 . The exhaust nozzle  24  may include an outer wall  28  and an inner wall  26  configured to direct the exhaust from the annulus  8 ,  10 . An igniter  32  may be provided in the outer wall  28  to ignite the fuel/air mixture to provide combustion gases. Although one igniter  32  is shown in the drawing, it should be appreciated that more than one igniter may be provided. The operation of the igniter(s)  32  may be controlled by a controller  58 . The controller  58  may be a computer processor or other logic-based device, software components (e.g., software applications), and/or a combination of hardware components and software components (e.g., a computer processor or other logic-based device and associated software application, a computer processor, or other logic-based device having hard-wired control instructions, or the like). 
         [0024]    As shown in  FIG. 4 , the plurality of tubes  34  are distributed circumferentially around the inlet end of the annulus  8 ,  10  and are closed at ends  35  as shown in  FIGS. 2 and 5  to form tuned cavities. Although the tubes  34  are shown in  FIG. 4  as having a circular cross section, it should be appreciated that other cross sectional shapes, for example, rectangular, may be used. The length L of the tuned cavity is designed to reflect a pressure wave from the detonation to reach the inlet of the rotating annulus  8 ,  10  to coincide with the approach of the next detonation wave. Fuel injectors  36 , for example liquid fuel injectors, are connected to each of the tuned cavity tubes  34  and supported by a fuel manifold (not shown). It should be appreciated that for clarity, only one fuel injector  36  is shown in  FIGS. 2 and 4 , and that in  FIG. 4  the fuel and air manifolds  38  are omitted for clarity. The tubes  34  are supported by the air manifold  38  and air  40  is injected into the tuned cavity tubes  34  at pressure antinodes  39  in the tubes  34 . As shown in  FIG. 2 , a static pressure  41  in the tube  34  is formed from sound pressure that increases in the direction shown by arrow  42 . The static pressure is lowest at the pressure antinode  39  where the injected air  40  is introduced to the tube  34  (i.e. where the velocity of the injected air  40  is highest) and the static pressure is highest at the closed end  35  of the tube  34  and at the entrance to the stationary valve plate  30  (i.e. where the velocity of the air and the air/fuel mixture is lowest). It should be appreciated that the injected air  40  may be introduced into the tubes  34  in a continuous stream and does not need to be turned on and off or otherwise cycled. The injectors  36  may be configured to inject fuel into the air  40  to create mixtures with an equivalence ratio between about 0.4 to about 1.4. 
         [0025]    The fuel injectors  36  are turned on and off by valves  60  under the operation of the controller  58  with a specific phased relationship of the detonation wave(s)  16  rotating in the detonation annulus  8 ,  10 . In particular, the length L of the tubes  34  is sized to resonate at the same frequency as a continuous detonation frequency. It should be appreciated that the continuous detonation frequency is the effective frequency of the detonation wave or waves in the chamber. For example, if there is a single detonation wave in the chamber, the effective continuous detonation frequency is the frequency of the single wave. However, if multiple detonation waves are in the chamber, the effective continuous detonation frequency is that multiple times the frequency of a single wave. For example, if two continuous detonation waves each having a frequency of 1 kHz are in the chamber, the effective frequency is 2 kHz. 
         [0026]    The fuel injector  36  injects fuel, for example liquid fuel, in short, timed bursts to coincide with the forward propagating detonation pressure wave(s)  16 . Referring to  FIG. 5 , the fuel injectors  36  are turned on (indicated by the solid circle) and off (indicated by the non-solid circle) in sequence to develop a combustible mixture  20  for the detonation wave(s)  16  to propagate into. The pattern of the fuel injectors  36  that are turned on rotates in synchronization with the detonation wave(s)  16  with an appropriate phase lag. As shown to the left in  FIG. 5 , a fuel/air mixture  18  plume emanating from each tube  34  makes up the combustible mixture for the detonation wave(s)  16  to propagate into. As shown to the left and right in  FIG. 5 , buffer air  54  separates the incoming fresh fuel/air mixture  18  plume from a high temperature burned gas region  44  defined by expansion fans  52 . A high pressure region  48  exists behind the detonation wave(s)  16 , which is the same as the high pressure region  14  in  FIG. 1 , and a pressure wave  50  is generated in the tubes  34 . 
         [0027]    Referring to the lower left portion of  FIG. 5 , some of the fuel injectors  36  below the fresh fuel/air mixture  20  are turned off to ensure that the airflow underneath the detonation annulus  8 ,  10  is unfueled. This ensures that the flame does not propagate into the mixing section when the detonation wave  16  passes by. Referring to the lower middle portion of  FIG. 5 , some of the fuel injectors  36  behind the detonation wave  16  are turned on at an appropriate time with respect to the propagating detonation wave  16  to inject fuel into the airstream such that the mixture propagates into the detonation annulus  8 ,  10 . The tuned cavity tubes  34  are designed to reflect and return the pressure wave  50  in phase with the detonation wave  16  which reduces, or eliminates, ingestion of burned mixture into the inlet cavities. By utilizing the tuned cavities  34  at the inlet to the combustion system, the pressure energy in the detonation wave  16  is reflected back into the inlet plane of the combustor to reduce the pressure drop requirements of the system. It should also be appreciated that the controller  58  may turn alternate fuel injectors  36  on and off to throttle the combustion system. 
         [0028]    Referring to  FIG. 6 , in an alternate/additional feature of the present technology, a piston  56  is provided with a control system to change the tuned length L of the cavity tubes  34  to match the detonation frequency as the inlet mixture temperature changes with operating conditions amongst other things that could change the rotating detonation frequency. The position of the piston  56  may be adjusted by an actuator  62  that is controlled by the controller  58 . The actuator  62  may be, for example, a linear motor, a screw drive, or a hydraulic piston. The tuned length of the tube  34  may be changed to account for changes in the inlet mixture temperature and the detonation frequency. 
         [0029]    Referring to  FIG. 7 , a tuned cavity rotating combustion system according to another example does not include fuel injectors. Instead, a fuel/air mixture  64  is introduced into each tube  34  at a pressure antinode  39  of the static pressure wave  41  in the tube  34 . The fuel/air mixture  64  may be a lean mixture and its composition may be controlled by the controller  58 . The fuel/air mixture  64  may be continuously introduced into the tubes  34 . In other words, the fuel/air mixture  64  may be fed into the tubes  34  without the use of injectors or valves that are turned on and off (opened and closed). Of course, the source of the fuel/air mixture  64  may be turned on and off to initiate and end the supply of the mixture as needed to control the operation of the combustion system, but in the combustion system shown in  FIG. 7  no injectors or valves are necessary to control the flow of the mixture  64  from its introduction into the tubes  34  from the manifold  38  and into the combustion chamber from the tubes  34 . 
         [0030]    Referring to  FIG. 8 , in order to prevent the combustion wave(s) from entering into and travelling down the tubes  34 , the ends of the tubes  34  adjacent the valve plate  30  may have a converging opening  66 . The holes  46  in the valve plate  30  may have diverging openings  68 . The converging openings  66  at the end of the tubes  34  and the diverging openings  68  of the openings  46  in the valve plate  30  operate as flame arresters to prevent the detonation wave(s) from entering and travelling into the tubes  34 . As discussed above with respect to  FIG. 5 , the tuned cavity tubes  34  are designed to reflect and return the pressure wave in phase with the detonation wave(s)  16  which reduces, or eliminates, ingestion of burning or burned mixture into the inlet cavities. 
         [0031]    Referring to  FIG. 9 , in accordance with another example, the valve plate  30  may include openings  46  that include converging and diverging sections, e.g. are hour glass shaped. The openings  46  act as flame arresters in a manner similar to that discussed above with respect to  FIG. 8 . Referring to  FIG. 10 , the openings  46  in the valve plate  30  may include converging and diverging sections similar to those in  FIG. 9 . Additionally, the openings  46  may be provided to inject the fuel/air mixture  64  at an acute angle to the propagation  17  of the detonation wave(s)  16  to impart momentum to the mixture  64  entering the detonation chamber. The valve plate  30  may also have a thermal barrier coating (TBC) applied to its surface to protect the valve plate from the temperature of the detonation wave(s)  16 . It should be appreciated that the flame arresters shown in  FIGS. 8-10  may also be used in the combustion systems shown in  FIGS. 2-6 . It should also be appreciated that the closed ends  35  of the tubes  34  may have cross sections that are smaller or larger than the openings  46  in the valve plate  30 . 
         [0032]    The openings  46  in the valve plate  30  may have a shape other than circular as shown in  FIG. 3 . Referring to  FIG. 11 , the openings  46  in the valve plate may have, for example, a rectangular or square shape. Other shapes are also possible, including for example oval or elliptical or other polygonal shapes. 
         [0033]    The combustion chamber may also have a shape other than annular as shown in  FIG. 2 . Referring to  FIG. 12 , a combustion chamber  3  having a conical shape defined by an inner wall  5  and an outer wall  7 , which correspond to the inner and outer walls  8 ,  10  of  FIG. 1 , may be used in the combustion systems described herein. As shown in  FIGS. 13 and 14 , the combustion chamber may have curved inner and outer walls  5 ,  7  that are either concave or convex, respectively. Polygonal combustion chambers  3  are also possible for use with the combustion systems described herein. For example as shown in  FIG. 15 , a combustion chamber  3  may have a square shape defined by inner and outer walls  5 ,  7 . Other polygonal shapes, for example rectangular, may also be used. 
         [0034]    By utilizing the tuned cavities at the inlet to the combustion system, the pressure energy in the detonation wave is reflected back into the inlet plane of the combustor to reduce the pressure drop requirements of the system. The tuned cavity rotating detonation combustion system may release ten times the amount of heat per unit volume in comparison to standard combustion systems. Thus a combustor made with the rotating detonation technology may be substantially smaller than a conventional combustion system. The present technology also allows liquid fuel to be injected into the incoming air stream to create a mixture in which the detonation will propagate. The specific arrangement of the injectors along with a control system will enable a liquid fueled system that will not have the auto-ignition issue which can limit the upper temperature limit for the incoming air for previously disclosed rotating detonation combustion systems. 
         [0035]    In addition the tuned cavity rotating detonation combustion system of the present technology may result in a pressure gain and thus improved fuel burn of up to 5% in a modern high pressure ratio gas turbine engines. These advantages may be very significant to both military and commercial gas turbine engines. The present technology may also be used to design compact augmentors for gas turbine engines and ram burners for missiles or rockets as well, for example as shown in  FIG. 2 . It should be appreciated that instead of the exhaust nozzle  26 ,  28  as shown in  FIG. 2 , in the case of the rotating detonation combustion system used in a gas turbine engine, the exhaust gases of the system may be used to drive a high pressure turbine. 
         [0036]    It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular example. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
         [0037]    While only certain features of the present technology have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes.