Abstract:
One embodiment of the present disclosure is a gas turbine engine. Another embodiment is a unique combustion system. Another embodiment is a unique engine. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for employing continuous detonation combustion processes. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/798,779, filed 15 Mar. 2013, the disclosure of which is now expressly incorporated herein by reference, and claims priority to and the benefit of U.S. Provisional Patent Application No. 61/801,481, filed 15 Mar. 2013, the disclosure of which is now expressly incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to heat engines. More particularly, the present disclosure relates to heat engines employing continuous detonation combustion. 
       BACKGROUND 
       [0003]    Engine and combustion systems that effectively employ continuous detonation combustion processes remain an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
       SUMMARY 
       [0004]    One embodiment of the present disclosure is a gas turbine engine. Another embodiment is a unique combustion system. Another embodiment is a unique engine. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for employing continuous detonation combustion processes. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0006]      FIG. 1  schematically depicts some aspects of a non-limiting example of an engine in accordance with an embodiment of the present disclosure; 
           [0007]      FIG. 2  schematically depicts some aspects of a non-limiting example of a combustion system in accordance with an embodiment of the present disclosure; 
           [0008]      FIGS. 3-5  schematically depict some aspects of a non-limiting example of a fluid diode in accordance with an embodiment of the present disclosure; 
           [0009]      FIG. 6  schematically depicts some aspects of a non-limiting example of a combustion system in accordance with an embodiment of the present disclosure; 
           [0010]      FIGS. 7 ,  7 A and  7 B schematically depict some aspects of a non-limiting example of a fluid diode in accordance with an embodiment of the present disclosure; 
           [0011]      FIG. 8  schematically depicts some aspects of a non-limiting example of a fluid diode in accordance with an embodiment of the present disclosure at two different time periods during operation; 
           [0012]      FIG. 9  schematically depicts some aspects of a non-limiting example of a fluid diode in accordance with an embodiment of the present disclosure, illustrating regions of alignment and misalignment; 
           [0013]      FIG. 10  schematically depicts  2  rotating detonation combustion waves; 
           [0014]      FIG. 11  schematically illustrates some aspects of a non-limiting example of a combustion system in accordance with an embodiment of the present disclosure; 
           [0015]      FIG. 12  schematically illustrates some aspects of a non-limiting example of a fluid diode structure in accordance with an embodiment of the present disclosure; 
           [0016]      FIG. 13  schematically illustrates some aspects of a non-limiting example of a fluid diode structure in accordance with an embodiment of the present disclosure; 
           [0017]      FIG. 14  schematically illustrates some aspects of a non-limiting example of two fluid diode structures in accordance with an embodiment of the present disclosure; 
           [0018]      FIG. 15  schematically illustrates some aspects of a non-limiting example of rotating regions and pressure zones generated in accordance with an embodiment of the present disclosure; 
           [0019]      FIG. 16  schematically illustrates some aspects of a non-limiting example of fluid diodes in accordance with an embodiment of the present disclosure; 
           [0020]      FIG. 17  schematically illustrates some aspects of a non-limiting example of a drive system in accordance with an embodiment of the present disclosure; 
           [0021]      FIG. 18  schematically illustrates some aspects of a non-limiting example of a drive system in accordance with an embodiment of the present disclosure; 
           [0022]      FIG. 19  schematically illustrates some aspects of a non-limiting example of an indexing mechanism in the form of an indexing coupling in accordance with an embodiment of the present disclosure; 
           [0023]      FIG. 20  schematically illustrates some aspects of non-limiting examples of diode structures in accordance with embodiments of the present disclosure are schematically depicted; 
           [0024]      FIG. 21  schematically illustrates some aspects of non-limiting examples of diode structures in accordance with embodiments of the present disclosure are schematically depicted; 
           [0025]      FIG. 22  schematically illustrates some aspects of non-limiting examples of diode structures in accordance with embodiments of the present disclosure are schematically depicted; 
           [0026]      FIG. 23  schematically illustrates some aspects of non-limiting examples of diode structures in accordance with embodiments of the present disclosure are schematically depicted; 
           [0027]      FIG. 24  schematically illustrates some aspects of non-limiting examples of diode structures in accordance with embodiments of the present disclosure are schematically depicted; 
           [0028]      FIG. 25  schematically illustrates some aspects of non-limiting examples of diode structures in accordance with embodiments of the present disclosure are schematically depicted; and 
           [0029]      FIG. 26  schematically depicts  2  rotating detonation combustion waves. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    For purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the disclosure is intended by the illustration and description of certain embodiments of the disclosure. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present disclosure. Further, any other applications of the principles of the disclosure, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the disclosure pertains, are contemplated as being within the scope of the present disclosure. 
         [0031]    Referring to the drawings, and in particular  FIG. 1 , some aspects of a non-limiting example of an engine  10  in accordance with an embodiment of the present disclosure is schematically depicted. In one form, engine  10  is a gas turbine engine. Engine  10  includes a compressor system  12 , a combustion system  14  in fluid communication with compressor system  12 , and a turbine system  16  in fluid communication with combustion system  14 . In one form, compressor system  12 , combustion system  14  and turbine system  16  are disposed about an engine centerline  18 , e.g., the axis of rotation of compressor  12  and turbine  16 . In other embodiments, other arrangements may be employed. In various embodiments, engine  10  may or may not have a compressor system and/or a turbine system, or may have additional turbomachinery components in addition to a compressor system and/or a turbine system. In some embodiments, engine  10  may be a direct propulsion engine that produces thrust directly from combustion system  14 , e.g., wherein engine  10  may not include a turbine system  16 . In other embodiments, combustion system  14  may form a gas generator for a gas turbine propulsion system, or may be employed in a gas turbine engine topping cycle. In still other embodiments, engine  10  may be one or more of other types of engines that may employ combustion systems such as combustion system  14 , such as, for example, a rocket engine. In yet still other embodiments, combustion system  14  may be configured as a direct propulsion engine, and may not include a compressor, e.g., except for engine starting purposes. 
         [0032]    Referring to  FIG. 2  in conjunction with  FIG. 1 , some aspects of a non-limiting example of combustion system  14  in accordance with an embodiment of the present disclosure are described. In one form, combustion system  14  is a pressure-gain combustion system. In other embodiments, combustion system  14  may not be a pressure-gain combustion system. In one form, combustion system  14  is a continuous detonation combustion system. In other embodiments, combustion system  14  may not be a continuous detonation combustion system. 
         [0033]    Combustion system  14  includes a supply portion  20 , a fluid diode  22  and a combustion chamber  24 . In one form supply portion  20  is configured to supply a fuel/oxidant mixture to fluid diode  22 . The fuel/oxidant mixture is supplied from supply portion  20  to fluid diode  22  generally in a primary flow direction  26 . In other embodiments, supply portion  20  may be configured to supply only a fuel or only an oxidant to fluid diode  22 . Combustion takes place in combustion chamber  24  on the opposite side of fluid diode  22  from supply portion  20 . In one form, combustion chamber  24  is a walled annular chamber. In other embodiments, combustion chamber  24  may take other forms. 
         [0034]    Fluid diode  22  is configured to allow a fluid flow in primary flow direction  26  to supply the fluid flow into combustion chamber  24  for use by the combustion process(es) taking place in combustion chamber  24 . In one form, the fluid flow is a fuel/oxidant mixture flow. In other embodiments, the fluid flow may be a fuel flow only, e.g., a gaseous and/or vaporous fuel flow, without an oxidant added thereto. In still other embodiments, the fluid flow may be an oxidant flow only, without a fuel added thereto. Fluid diode  22  is configured to prevent or reduce fluid flow in a back-flow direction  28  opposite to primary flow direction  26  at the location(s) of the combustion process(es). In one form, the fuel is a conventional fuel typically employed in gas turbine engines. In other embodiments, one or more other fuel types may be employed in addition to or in place of conventional gas turbine engine fuel. In one form, the oxidant is air. In other embodiments, one or more other oxidants may be employed in addition to or in place of air. 
         [0035]    In one form, fluid diode  22  is disposed in an annulus  30  downstream of compressor  12 . In other embodiments, fluid diode  22  may be disposed at other locations. In one form, fluid diode  22  includes a diode structure  32  and a diode structure  34  positioned adjacent to diode structure  32 . In other embodiments, more than two diode structures e.g., akin to diode structure  32  and diode structure  34 , may be employed. In one form, diode structure  32  is positioned immediately adjacent to diode structure  34 , e.g., with a small gap between diode structure  32  and diode structure  34  to limit contact between diode structure  32  and diode structure  34 . The size of the gap may vary with the needs of the application. In other embodiments, diode structure  32  may be spaced apart from diode structure  34  by some larger amount. In some embodiments, e.g., embodiments employing low friction materials, diode structure  32  and diode structure  34  may be positioned to allow contact therebetween, thereby eliminating or reducing any gap therebetween. 
         [0036]    Referring to  FIGS. 3-5 , some aspects of non-limiting examples of diode structure  32  and diode structure  34  in accordance with an embodiment of the present disclosure are described. In one form, diode structure  32  and diode structure  34  are rings or disks disposed in annulus  30 . In other embodiments, one or both diode structures  32  and  34  may take other forms, and may be, for example, cylinders, conical structures or may have any shape defined as a body of revolution. In still other embodiments, diode structures  32  and  34  may take any shape, and may or may not be disposed in an annulus. In one form, diode structures  32  and  34  are formed of a metal alloy, e.g., such as the types of alloys employed in the manufacture of turbine disks. In other embodiments, diode structures  32  and  34  may be formed of one or more other materials, e.g., one or more composite materials and/or a matrix composite materials in addition to or in place of a metal or metal alloy. 
         [0037]    Diode structures  32  and  34  include a plurality of fluid flow passages interspersed with a plurality of fluid flow blockages. In the example illustrated in  FIG. 3 , diode structure  32  includes three (3) circumferential rows of fluid flow passages  36 ,  38  and  40  interspersed with three circumferential rows of fluid flow blockages  42 ,  44  and  46 . In other embodiments, any number and orientation of rows of fluid flow passages and fluid flow blockages may be employed. In one form, fluid flow passages  36 ,  38  and  40  are equally spaced circumferentially around diode structure  32 , and fluid flow blockages  42 ,  44  and  46  are equally spaced circumferentially around diode structure  32 . In other embodiments, the fluid flow passages and/or the fluid flow blockages may not be equally spaced. 
         [0038]    Fluid flow passages  36 ,  38  and  40  are configured to permit fluid flow through diode structure  32  at the locations of fluid flow passages  36 ,  38  and  40 , e.g., in primary flow direction  26 . Fluid flow blockages  42 ,  44  and  46  are configured to prevent flow through diode structure  32  at the locations of fluid flow blockages  42 ,  44  and  46 . In one form, fluid flow passages  36 ,  38  and  40  are in the form of circular holes in diode structure  32 , whereas the fluid flow blockages  42 ,  44  and  46  are in the form of the physical material of diode structure  32  that extends circumferentially between respective fluid flow passages  36 ,  38  and  40 . In other embodiments, the fluid flow passages and the fluid flow blockages may take other geometric forms or shapes, e.g., depending upon the needs of the particular application. For example, some embodiments may include fluid flow blockages in the form of spokes of a diode structure in the form of a spoked rotor, whereas the fluid flow passages of such an embodiment may be the spaces between the spokes. 
         [0039]    In some embodiments, the fluid flow passages may be configured for a greater pressure drop in one direction than the opposite, e.g., for a greater pressure drop in back-flow direction  28  than in primary flow direction  26 . For example, entrance and exit effects, such as rounded and sharp corners, may be formed on appropriate ends of the fluid flow passages to yield a higher pressure drop in back-flow direction  28  than in primary flow direction  26 . In addition, the shape of the fluid flow passages may be otherwise configured to yield a higher pressure drop in back-flow direction  28  than in primary flow direction  26 , e.g., such as having or including a conical shape and/or hemispherical or partial hemispherical shape and/or any other desired shape that yields a higher pressure drop in back-flow direction  28  than in primary flow direction  26 . In various embodiments, the fluid flow passages may be angled, e.g., may have centerlines that are not parallel to the axis of rotation of the diode structure in which the fluid flow passages are formed, which in the depicted embodiment is engine centerline  18 , e.g., in order to reduce losses in the fluid flow passing through diode  22  in primary flow direction  26 . Also, in some embodiments, the fluid flow passages may have other shapes or features configured to enhance flow through fluid diode  22  in primary flow direction  26  and/or inhibit flow through fluid diode  22  in back-flow direction  28 . Further, in some embodiments, fluid flow passages  36 ,  38  and  40  may take the form of passages that extend in more than one dimension, e.g., having centerlines that extend in two (2) and/or three (3) directions; and/or may vary in direction through diode structure  32  as needed for the particular application. 
         [0040]    In the example illustrated in  FIG. 4 , diode structure  34  includes three (3) circumferential rows of fluid flow passages  56 ,  58  and  60  interspersed with three circumferential rows of fluid flow blockages  62 ,  64  and  66 . In other embodiments, any number and orientation of rows of fluid flow passages and fluid flow blockages may be employed. In one form, fluid flow passages  56 ,  58  and  60  are equally spaced circumferentially around diode structure  34 , and fluid flow blockages  62 ,  64  and  66  are equally spaced circumferentially around diode structure  34 . In other embodiments, the fluid flow passages and/or the fluid flow blockages may not be equally spaced. Fluid flow passages  56 ,  58  and  60  are configured to permit fluid flow through diode structure  34  at the locations of fluid flow passages  56 ,  58  and  60 , e.g., in primary flow direction  26 . Fluid flow blockages  62 ,  64  and  66  are configured to prevent flow through diode structure  34  at the locations of fluid flow blockages  62 ,  64  and  66 . 
         [0041]    In one form, fluid flow passages  56 ,  58  and  60  are in the form of circular holes in diode structure  34 , whereas the fluid flow blockages  62 ,  64  and  66  are in the form of the physical material of diode structure  34  that extends circumferentially between respective fluid flow passages  56 ,  58  and  60 . In other embodiments, the fluid flow passages and the fluid flow blockages may take other geometric forms or shapes, e.g., depending upon the needs of the particular application. For example, some embodiments may include fluid flow blockages in the form of spokes of a diode structure in the form of a spoked rotor, whereas the fluid flow passages of such an embodiment may be the spaces between spokes of the rotor. 
         [0042]    In some embodiments, the fluid flow passages may be configured for a greater pressure drop in one direction than the opposite, e.g., for a greater pressure drop in back-flow direction  28  than in primary flow direction  26 . For example, entrance and exit effects, such as rounded and sharp corners, may be formed on appropriate ends of the fluid flow passages to yield a higher pressure drop in back-flow direction  28  than in primary flow direction  26 . In addition, the shape of the fluid flow passages may be otherwise configured to yield a higher pressure drop in back-flow direction  28  than in primary flow direction  26 , e.g., such as having or including a conical shape and/or hemispherical or partial hemispherical shape and/or any other desired shape that yields a higher pressure drop in back-flow direction  28  than in primary flow direction  26 . In various embodiments, the fluid flow passages may be angled, e.g., may have centerlines that are not parallel to the axis of rotation of the diode structure in which the fluid flow passages are formed, which in the depicted embodiment is engine centerline  18 , e.g., in order to reduce losses in the fluid flow passing through diode  22  in primary flow direction  26 . Also, in some embodiments, the fluid flow passages may have other shapes or features configured to enhance flow through fluid diode  22  in primary flow direction  26  and/or inhibit flow through fluid diode  22  in back-flow direction  28 . Further, in some embodiments, fluid flow passages  56 ,  58  and  60  may take the form of passages that extend in more than one dimension, e.g., having centerlines that extend in two (2) and/or three (3) directions; and/or may vary in direction through diode structure  34  as needed for the particular application. 
         [0043]    Diode structures  32  and  34  are configured for relative motion between each other, e.g., via a drive mechanism (not shown). In one form, the motion between diode structures  32  and  34  is a rotating motion, e.g., about engine centerline  18 . In other embodiments, other forms of motion may be employed in addition to or in place of rotation, e.g., including translation in one or more directions and oscillatory motion in one or more directions. In addition, the rotating motion or rotation motion component may be about an axis other than engine centerline  18 . In one form, both diode structures  32  and  34  are in motion during the operation of combustion system  14 , e.g., rotational motion. In other embodiments, only one of diode structures  32  and  34  may be in motion. In embodiments having more than two diode structures, at least one of the diode structures is in motion during the operation of combustion system  14 . In some embodiments having more than two diode structures, more than one or all of the diode structures may be in motion during the operation of combustion system  14 . In one form, both diode structures  32  and  34  rotate in the same direction. In other embodiments, diode structures  32  and  34  may rotate in opposite directions. 
         [0044]    Diode structures  32  and  34  rotate at different speeds, yielding relative motion between them. In addition, the number of fluid flow passages  36 ,  38  and  40  per circumferential row, respectively, and the number of fluid flow passages  56 ,  58  and  60  per circumferential row, respectively, are different, and hence, the number of fluid flow blockages  42 ,  44  and  46  per row and the number of fluid flow blockages  62 ,  64  and  66  per row are also different. The relative motion between diode structures  32  and  34 , in conjunction with the number and spacing of fluid flow passages and fluid flow blockages, yields moving regions of relative alignment and misalignment of fluid flow passages  36 ,  38  and  40  in diode structure  32  with corresponding fluid flow passages  56 ,  58  and  60  in diode structure  34 . In one form, the regions of alignment and misalignment rotate around fluid diode  22 , e.g., about engine centerline  18  in the depicted embodiment. The rotating regions of relative alignment and misalignment rotate at a different speed than the rotational speed of either diode structure  32  or diode structure  34 . In particular, the rotating regions of relative alignment and misalignment rotate substantially faster than diode structures  32  and  34 . The rotational speed of the regions of alignment and misalignment are dependent various factors, which in the present embodiment include the number of fluid flow passages (and corresponding fluid flow blockages) in each of diode structures  32  and  34 , and the rotational speed of each of diode structures  32  and  34 . In other embodiments, other factors may be involved determining the speed of rotation and/or other type of motion of regions of alignment and misalignment, e.g., depending upon the type or types of relative motion that takes place between the diode structures. The regions of relative misalignment of the fluid flow passages (relative alignment of fluid flow blockages with fluid flow passages) are employed to block one or more rotating continuous detonation waves, i.e., to reduce or prevent flow in back-flow direction  28  in the vicinity of the rotating continuous detonation wave(s). The regions of relative alignment of the fluid flow passages (with corresponding relative alignment of fluid flow blockages) are employed to allow fluid flow through fluid diode  22  in primary flow direction  26  at locations spaced apart, e.g., circumferentially, in the depicted embodiment, from the rotating continuous detonation wave(s). 
         [0045]    For example, referring also to  FIG. 6 , some aspects of a non-limiting example of combustion system  14  in accordance with an embodiment of the present disclosure are described. During operation, combustion system  14  includes a plurality of rotating continuous detonation waves  70 . In the depicted embodiment, two rotating continuous detonation waves  70  are formed. Other embodiments may employ a single rotating continuous combustion wave or a plurality of rotating combustion waves greater in number than two. Rotating continuous detonation waves  70  are referred to as “rotating” because they rotate around annulus  30 , e.g., rotating or spinning about engine centerline  18  in a generally circumferential direction  72 . Rotating continuous detonation waves  70  are referred to as “continuous” because they are continuous combustion processes, as opposed pulsed combustion processes, such as those exhibited by pulse detonation systems. Rotating continuous detonation waves  70  are referred to as “detonation” waves because they have flame fronts that progress at speeds associated with detonation combustion, as opposed to the lower speeds associated with deflagration combustion. For instance, in one example, detonation waves  70  move at approximately 6,000 linear feet per second. In other embodiments, detonation waves  70  may move at other speeds associated with detonation combustion. 
         [0046]    Fluid diode  22  is configured to permit and restrict flow through various portions thereof, e.g., as discussed herein. For example, in one form, fluid diode  22  is configured to form rotating regions  74  and rotating regions  76 . Rotating regions  76  are interspersed between rotating regions  74 . Rotating regions  74  correspond to areas of relative misalignment of a subset of the fluid flow passages of diode structure  32  with a subset of the fluid flow passages of diode structure  34  (relative alignment of a subset of the fluid flow passages of diode structure  32  with a subset of the fluid flow blockages of diode structure  34 , and relative alignment of a subset of the fluid flow passages of diode structure  34  with a subset of the fluid flow blockages of diode structure  32 ). Rotating regions  76  correspond to areas of relative alignment of a subset of the fluid flow passages of diode structure  32  with a subset of the fluid flow passages of diode structure  34  (relative alignment of a subset of the fluid flow blockages of diode structure  32  with a subset of the fluid flow blockages of diode structure  34 ). Some embodiments may employ only a single region  74  and a single region  76 . The quantities of regions  74  and  76  may vary with the needs of the application. 
         [0047]    Fluid diode  22  is configured to rotate rotating regions  74  and  76  at the same speed as rotating continuous detonation waves  70 , wherein rotating region  74  is positioned and remains adjacent to rotating continuous detonation waves  70 , and wherein rotating regions  76  are disposed between, e.g., circumferentially, rotating continuous detonation waves  70 . Rotating regions  74  have, on average, a flow area that is less than the flow area of rotating regions  76 . In one form, rotating regions  74  include the smallest regional flow area through fluid diode  22 , whereas rotating regions  76  include the largest regional flow area through fluid diode  22 . In some embodiments, the flow area through some or all of regions  74  may be zero or nearly so. 
         [0048]    Rotating continuous combustion waves  70  form rotating higher pressure zones  78  in the vicinity of the flame fronts. Higher pressure zones  78  have a higher pressure than that of the fuel/oxidant supply mixture. Lower pressure zones  80  are formed between rotating continuous detonation waves  70 . The pressure in combustion chamber  24  decreases with increasing distance from the combustion wave fronts of rotating continuous combustion waves  70 . Because rotation regions  74  are positioned adjacent to rotating continuous detonation waves  70 , higher pressure zones  78  are generally in the same locations as rotating regions  74 . Similarly, lower pressure zones  80  are generally in the same locations as rotating regions  76 , which are spaced apart from the higher pressures associated with detonation waves  70 . The pressure in lower pressure zones  80  between rotating continuous combustion waves  70  is less than the supply pressure of the fuel/oxidant mixture. That is, the supply pressure of the fuel/oxidant mixture is selected to be higher than the pressure in pressure zones  80 . 
         [0049]    By positioning regions  74  adjacent to rotating continuous detonation waves  70 , back-flow resulting from the higher pressure zones  78  associated with the detonation combustion waves is reduced or eliminated. By positioning regions  76  in lower pressure zones  80  away from rotating continuous detonation waves  70 , where the fuel/oxidant supply pressure is higher than the pressure in lower pressure zones  80 , flow into combustion chamber  24  is permitted. Thus, in various embodiments, one or more portions of fluid diode  22  may restrict or prevent flow in back-flow direction  28 , while at the same time one or more other portions of fluid diode  22  permit flow through to combustion chamber  24  in primary flow direction  26 , e.g., depending upon circumferential location in a moving reference frame associated with rotating continuous detonation waves  70  and regions  74  and  76 . The fuel/oxidant mixture admitted into combustion chamber  24  is combusted upon the approach of the next rotating continuous detonation waves  70  to arrive at the location of the admitted fuel/oxidant mixture, thus continuing the detonation process. 
         [0050]    Referring now to  FIGS. 7 ,  7 A and  7 B, some aspects of a non-limiting example of fluid diode  22  in accordance with an embodiment of the present disclosure are schematically depicted.  FIGS. 7 ,  7 A and  7 B represent developed sectional views taken circumferentially from the indicated dashed circular line of  FIG. 6 , illustrating portions of rotating regions  74  ( FIG. 7A) and 76  ( FIG. 7B ) at the middle rows of the fluid flow passages and the fluid flow blockages of diode structures  32  and  34 . A rotating continuous detonation wave  70  is illustrated as proceeding in circumferential direction  72 . Adjacent to diode structure  32  is the fuel/oxidant mixture  82  that is supplied at pressure to fluid diode  22 . The fuel/oxidant pressure may vary with the needs of the application. 
         [0051]    At regions  74 , wherein fluid diode  22  is exposed to the higher pressure zones  78  in the vicinity of detonation waves  70 , which are at a higher pressure than the fuel/oxidant  82  supply pressure, the relative misalignment of fluid flow passages  38  of diode structure  32  with fluid flow passages  58  of diode structure  32  prevents or reduces the back-flow of gases and combustion products from the combustion detonation waves  70  through regions  74 . Some back-flow may occur due to a gap  84  between diode structures  32  and  34 , indicated by arrows  86 . Some back-flow may also occur at locations where there is not a complete overlap of the fluid flow passages with the fluid flow blockages. Some embodiments may provide complete overlap of fluid flow passages with fluid flow blockages at one or more locations, whereas other embodiments may not. Thus, in some embodiments, little or no back-flow may be realized, e.g., at locations of complete overlap and where gap  84  is small or non-existent, whereas in other embodiments, some greater, although acceptable, amount of back-flow may occur. In one form, the degree of misalignment of fluid flow passages of diode structure  32  and diode structure  34  varies from a maximum at the center of regions  74  to a minimum at the designated boundaries of regions  74 . In other embodiments, the degree of misalignment may be constant or may vary in one or more other directions, e.g., depending upon the numbers and sizes of the fluid flow passages and fluid flow blockages on diode structures  32  and  34 , and the type or types of relative motion between diode structures  32  and  34 . 
         [0052]    At regions  76 , wherein fluid diode  22  is exposed to the lower pressure zones  80  between detonation waves  70 , which are at a lower pressure than the fuel/oxidant  82  supply pressure, the relative alignment of fluid flow passages  38  of diode structure  32  with fluid flow passages  58  of diode structure  32  allows fuel/oxidant mixture  82  to flow through regions  76  in primary direction  26  through diode  22  and into combustion chamber  24 . The fuel/oxidant  82  flow is indicated in  FIG. 7B  with arrows  88 . In one form, the degree of alignment between fluid flow passages of diode structure  32  and diode structure  34  varies from a maximum at the center of regions  76  to a minimum at the designated boundaries of regions  76 . In other embodiments, the degree of alignment may be constant or may vary in one or more other directions, e.g., depending upon the numbers and sizes of the fluid flow passages and fluid flow blockages on diode structures  32  and  34 , and the type or types of relative motion between diode structures  32  and  34 . 
         [0053]    Although rotating regions  74  and  76  rotate at a speed to match the speed of rotation of rotating continuous detonation waves  70  through annulus  30 , e.g.,  6 , 000  linear feet per second, e.g., at the radially outermost portion of detonation waves  70 , neither of diode structure  32  and  34  rotate at such a speed. Rather the number and spacing of fluid flow passages and the relative rotation rate between diode structure  32  and diode structure  34  form the rotating regions with a higher rate of rotation than either of diode structure  32  and diode structure  34 , akin to the operation of a vernier scale, wherein regions of alignment and misalignment of two different scales traverse a greater distance than the distance traversed by one or both of the scales. 
         [0054]    The number of fluid flow passages per row for each of diode structures  32  and  34  and the speed of rotation of diode structures  32  and  34  may be determined by various means, e.g., depending upon the configuration of the fluid diode. One way of making such a determination is via Equation 1, below: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       N 
                       1 
                     
                     
                       N 
                       2 
                     
                   
                   = 
                   
                     
                       ω 
                       - 
                       
                         ω 
                         2 
                       
                     
                     
                       ω 
                       - 
                       
                         ω 
                         1 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0055]    Wherein, N 1  is the number of holes per row of diode structure  32 ; N 2  is the number of fluid passages per row of diode structure  34 ; ω is the rotational speed of rotating continuous detonation waves  70 ; ω 1  is the rotational speed of diode structure  32 , and ω 2  is the rotational speed of diode structure  34 . The rotational speeds and number of fluid passages may be readily determined using Equation 1. In the present example, N 1  is 28, N 2  is 30, ω 1  is 2ω/7 and ω 2  is ω/3, which is one of many potential solutions to Equation 1. Thus, in the depicted example, diode structure  32  rotates at one third of the rotation rate of the rotating continuous detonation waves  70 , and diode structure  34  rotates at two-sevenths of the rotation rate of the rotating continuous detonation waves  70 . Other embodiments may employ other solutions to Equation 1. In still other embodiments, N 1 , N 2 , ω 1  and ω 2  may be determined in one or more other manners. Assuming a tip speed of 6000 feet per second for rotating continuous detonation waves  70 , the above solution to Equation 1 yields a tip speed of 2000 feet per second for diode structure  32 , and 1714 feet per second for diode structure  34 , both of which are within the capabilities of current gas turbine engine high strength metallic alloys and composite or matrix composite materials. 
         [0056]    Referring to  FIG. 8 , some aspects of a non-limiting example of fluid diode  22  in accordance with an embodiment of the present disclosure are schematically illustrated.  FIG. 8  is not drawn to scale.  FIG. 8  illustrates, in a developed view, the alignment/misalignment of one row of fluid flow passages of diode structure  32  with a corresponding row of fluid passages of diode structure  34  at a time T 1 , and the alignment/misalignment of the same row of fluid flow passages of diode structure  32  with the same row of fluid flow passages of diode structure  34  at a time T 2 . In the illustration of  FIG. 8 , the middle rows of fluid flow passages of diode structures  32  and  34  are shown, that is fluid flow passages  38  of diode structure  32  and fluid flow passages  58  of diode structure  34 . 
         [0057]    The rotational speed of diode structure  34  is 6/7 of the rotational speed of diode structure  32 , since ω 1 /ω 2 =(2ω/7)/(ω/3)=6/7, as set forth in the above example. As illustrated in  FIG. 8 , at time T 1 , fluid flow passages  38  and  58  are aligned at the left end of the view. At time T 2 , diode structure  32  has moved a unit distance of 1. Since the rotational speed of diode structure  34  is 6/7 of the rotational speed of diode structure  32 , at time T 2 , diode structure  34  has moved 6/7 of a unit distance. However, at time T 2 , the next alignment of fluid flow passages  38  and  58  occurs 3 units of distance from the initial point of alignment at time T 1 . Thus, between time T 1  and T 2 , the region of alignment has moved 3 times the distance of diode structure  32 , and 3/(6/7)=(21/6) times the distance of diode structure  34 . As is illustrated in  FIG. 8 , the regions of misalignment of the fluid flow passages moves in the same manner, that is 3 times the rate of diode structure  32  and (21/6) times the rate of diode structure  34 . Accordingly, in the depicted embodiment, regions  74  and  76  rotate around fluid diode  22  in annulus  30  at three times the speed of the fastest spinning diode structure. One or more control systems (not shown) employing one or more sensors, such as position sensors, pressure sensors, vibration sensors, acoustic sensors, temperature sensors and/or other sensors may be used to control the speed and position of diode structures  32  and  34  to ensure that regions  74  are positioned adjacent to detonation waves  70  (i.e., to ensure that regions  74  rotate with and remain at the same circumferential locations as rotating continuous detonation waves  70 ) in order to present the maximum impediment to back-flow in back-flow direction  28 . In some embodiments, diode structures  32  and  34  may be coupled at a fixed ratio, e.g., via one or more gear sets, to ensure, without external control, the relative speed between diode structures  32  and  34 . In some embodiments, the relative speed of diode structures  32  and  34  and/or the absolute speed of diode structures  32  and/or  34  may be controlled to vary, e.g., depending on operating conditions, such as based on a measured or calculated speed of detonation waves  70 , e.g., under different operating conditions. 
         [0058]    Referring to  FIG. 9 , a developed view of another example of diode members in the form of disks is illustrated, each disk having 7 rows of fluid flow passages, e.g., the top rows of which include passages  100  of a disk  1  (28 fluid flow passages  100  per circumferential row of disk  1 , interspersed with fluid flow blockages) and passages  102  of a disk  2  (30 fluid flow passages  102  per circumferential row of disk  2 , interspersed with fluid flow blockages).  FIG. 9  illustrates regions of alignment of fluid flow passages alternating with regions of misalignment of fluid flow passages. 
         [0059]    Various embodiments of the present disclosure include a fluid diode that provides one or more regions of reverse flow control that traverse circumferentially (spin) in a typically, but not exclusively, annular shaped region for a continuous detonation combustor. The fluid diode restricts back or reverse flow in one of more moving regions immediately adjacent to the traveling detonation or detonations of a continuous detonation combustor. The fluid diode operates on the principle of two (or more) disks or plates or spoked rotors or other fluid diode elements having sets of holes, slots, or openings through the plate, which move relative to each other. They move at different but related mechanical speeds. The difference in speeds together with the number, spacing and patterns of the openings creates open and closed regions that travel around the annulus or other combustion area shape at a speed greater than either of the disks. Thus the speed of the region of closed area may be made to match the speed of the detonation wave without requiring either of the plates to travel at the speed of the detonation wave. The characteristics can be used to adjust the relative sizes of the open and closed regions by adjusting the elongation of the openings in the direction of travel of these members. The fluid diode works on the principles akin to the vernier scale in which the position of markings in alignment moves a greater distance than the traveling distance of the sliding element. In embodiments of the present disclosure, the position of holes or features in alignment (or greatest misalignment) moves a greater distance than the plates having the holes. It is envisioned that the flow direction through the fluid diode may either be predominately axial or predominately radial, or a combination of both (also with some amount of swirl, in some embodiments). It is also envisioned that the orientation of the plates, disks, or elements may be either flat plate, cylinder, conical or other body of revolution configuration including curved surfaces for any of the types. One of the elements may be stationary. Although rotation is envisioned as the primary method of achieving the intended motion, methods other than rotation or used in combination with rotation are envisioned. Furthermore, the rotation or translation of one or more of the plates relative to each other is envisioned to be either in the same direction or counter in direction to each other. 
         [0060]    The performance of a continuous detonation engine or pressure gain combustor was previously held to a low level by employing a high level of flow restriction, resulting in unnecessary pressure loss in the downstream direction required in any diode valve or controlling orifice (aero valve) of previous design. Embodiments of the present disclosure may allow the back-flow region adjacent to the detonation to be sufficiently blocked locally to allow proper combustor and/or engine operation, while also providing a relatively low level of flow restriction (pressure loss) to the fresh incoming fuel, air, or fuel and air mixture (as compared to previous detonation combustion systems). This causes the pressure onto which the detonation adds (that is the pressure into which the detonation travels) to be significantly higher than is previously attainable for a given supply pressure. This higher initial pressure causes a higher post detonation pressure. Thus, this well know limiter of continuous detonation engine performance is mitigated, and combustion systems in accordance with embodiments of the present disclosure may enable a new class of engines (both gas turbine and direct thrust producing) to be developed using this higher pressure gain across the engine or combustor using the constant volume combustion principles of the continuous detonation type. 
         [0061]    The low flow loss characteristic of embodiments of the present disclosure in the region or regions of inflow of unburned reactants allows a higher through flow of mass per unit cross sectional area of the device, thus creating a more compact unit, relative to previous detonation combustion systems. In addition, the low flow loss characteristic of embodiments of the present disclosure in the region or regions of inflow of unburned reactants allows the detonation wave which travels into the flow to be oriented in a manner more normal to the direction into which the combusted gas is intended to travel, thus creating a momentum component to the flow more in line with the engine axis. This may increase the performance potential of the combustion system relative to previous combustion systems. 
         [0062]    Although it may be possible to employ a moving mechanical blocker traveling at the speed of the detonate wave, such an approach may include tip speeds of approx. 6000 feet per second in the annulus, and is thus undesirable because the resulting stresses in the moving mechanical blocker may be higher than those allowable by known materials under the expected operating conditions. In embodiments of the present disclosure, the regions of translating or rotating high flow restriction and low flow restriction are made to travel at a velocity equal to that of the detonation wave without causing a mechanical component to travel at such high velocities, which would result in high, likely prohibitively high, stress levels in the moving mechanical component. Through the use of embodiments of the present disclosure, it is anticipated that the stresses within the mechanical components may be made to be within those of known design practice using known materials. 
         [0063]    In addition, a moving mechanical blocker traveling at the speed of the detonation wave would experience a continuously high heat flux from the detonative combustion wave that it would be blocking. However, embodiments of the present disclosure contemplated herein do not have that continuous high heat flux on any given location of the fluid diode, since at no given location on the structure does the detonation continuously reside. Thus in embodiments of the present disclosure, no location on the structure of the fluid diode is continuously heated by the detonation wave but instead all positions are intermittently heated by the passing detonation wave and then cooled by the arriving flow of unburned reactants traversing through the fluid diode. 
         [0064]    The fluid diode may utilize the rotation of the disk or plate on the same or differing axis of rotation to create the intended motion of the single or multiple regions. The relative rotational position of the two or multiple disks or plates or other-shaped fluid diode elements may be indexed (made to have required relative positions) either mechanically or by position control in order to create the desired regions of relatively more open area and relatively more closed area traversing the annulus. Also the fluid diode may utilize the simultaneous translation and rotation of the disks, plates or other shaped diode elements to create the traveling regions of greater fraction of open area and greater fraction of closed area. In this way the fluid diode creates the regions of relatively more open area and relatively more closed area traversing an annulus or other combustion zone shape at velocities sufficient to correspond to the tangential velocity of the traveling or spinning detonation wave(s) in the continuous detonation combustor, while the disks or plates or elements travel at a lower tangential velocity than that of the detonation event or events. The speeds or motion of the disks, plates or other fluid diode elements may be driven by known methods, and may be controlled by sensors detecting the velocity and/or position of the detonation of detonations via known techniques to match either the velocity, position or both of the regions with that of the detonation or detonations. This allows the fluid diode which creates the preferred regions to couple with the spinning detonation in the continuous detonation combustor and to act to restrict the backflow of combusted gasses produced by the detonation in the region adjacent to and trailing the detonation wave or waves. 
         [0065]    The fluid diode then carries or reacts the pressure forces generated by the detonation wave and pressure field trailing it via the more closed region having high flow pressure loss characteristics, and thus transmits the reacted forces to the non rotating structure of the combustor by bearings or other known means. The moving more open or less restrictive regions created by the fluid diode are similarly coupled with the inflow of unreacted fuel, air or oxidizer, or un-reacted fuel and air mixture admitted ahead of the spinning detonation and downstream of the fluid diode prior to arrival of the spinning detonation wave which then combusts the mixture. In summary, by this unique means the fluid diode creates single or multiple regions of relatively more open area (less restrictive to fluid flow) and relatively more closed area (more restrictive to fluid flow) that traverse the annulus or other combustion zone and couple with the single spinning detonation wave or multiple detonation waves in the continuous detonation combustor. 
         [0066]    The fluid diode may be part of a continuous detonation thrust producing engine, a continuous detonation pressure gain combustor, or any other device utilizing continuous detonation traveling in a continuous path. It is intended to include oxidizers other than air in its application. 
         [0067]    The spacing of the open areas within the elements is intended to be highly regular and even with deviations from this tolerated by the design. This allows creation of the more open and closed regions to travel at a near constant velocity. It is envisioned that irregular spacing together with an oscillatory component to the various element&#39;s speed could be used to create a near constant velocity of the regions. 
         [0068]    The distance between open areas in the direction of detonation wave travel is targeted to be near that of the open area or less to give the greatest available open area in the regions of alignment and near alignment of the areas. Lesser spacing is preferred in some embodiments, in that complete blockage of flow in the regions of misalignment of areas is not required. The areas of open flow may be circular, oval, slot, or of other shape consistent with creating a low stress rotating fluid diode elements or set of rotating fluid diode elements. Across the width of the flow channel, the rows of holes may be spaced in an inline or staggered arrangement, with staggered giving a relatively higher percentage of open area in some embodiments. 
         [0069]    Referring now to  FIGS. 10-25 , some aspects of non-limiting examples of embodiments of the present disclosure, which in some respects are built at least in part on the embodiments set forth above, are described. 
         [0070]    Throttling of a continuous detonation combustor, such as combustion system  14 , also known as a rotating detonation combustor or rotating continuous detonation combustor, may be accomplished by continually introducing a region of dilution air behind the detonative event between the vitiated gases produced by the detonative event, and simultaneously supplying fuel into a region into which the detonative combustion event is moving. This region is caused by the introduction of a transiently moving fuel supply pattern created by application of a valve, similar to that described above as fluid diode  22 . It is also envisioned that such a valve may be used to control fuel flow, either together with or separate from the previously invented air valve, fluid diode  22 , which acts on the bulk of the combustor flow. The hereinafter described valve application may be employed to control only the addition of dilution air, e.g., by controlling where fuel flow is initiated after the end of the detonative events or continuous detonation waves, and is also envisioned in applications where fuel is introduced in manners set forth above. 
         [0071]    The particular application of the valve device, or fluid diode, described below, is to schedule fuel introduction into one or more moving regions immediately adjacent to and behind or ahead of the traveling detonation or detonations, also referred to herein as detonation waves, continuous detonation waves, and rotating continuous detonation waves, of a continuous detonation combustor. The valve operates on the principle of two (or more) diode structures in the form of disks, plates, spoked rotors, cylinders or elements of other shapes having sets of holes, slots or other openings through such diode structures, which move relative to each other. They move at different but closely matched mechanical speeds. The difference in speeds together with the number, spacing and patterns of the openings creates open and closed regions that travel around the annulus at a speed greater than either of the diode structures. Thus the speed of the region of closed area and open area can be made to match the speed of the detonation without requiring either of the plates to travel at the speed of the detonation. The valve works using principles similar to those of the vernier scale, in which the position of markings in alignment moves a greater distance than the traveling distance of the sliding element. In embodiments of the present disclosure, the position of holes or features in alignment (or greatest misalignment) moves a greater distance than the plates having the holes. It is envisioned that the flow direction through the valve may either be predominately axial or predominately radial, or a combination of both (also with some amount of swirl). It is also envisioned that the orientation of the diode structures, e.g., plates, disks, or elements may be for example, flat plate, cylinder, or conical configuration, including curved surfaces for any of the types, and that the diode structures may be in the form of any suitable bodies of revolution. One of the elements may be stationary. Although rotation is envisioned as the primary method of achieving the intended motion, methods other than rotation or used in combination with rotation are envisioned. Furthermore, the rotation and/or translation of one or more of the diode structures relative to each other is envisioned to be either in the same direction or counter in direction relative to each other. 
         [0072]    The application of the valve utilizes the opening and closing of the passages to introduce fuel into air, including stratification of charge, to promote detonation and/or to create a non-fueled or very lean layer of fuel/air between sequenced detonations. This also serves to eliminate or reduce deflagrative burning at the interface of combusted and non combusted fuel/air mixture, as commonly occurs in these devices. The valve acts to introduce fuel within the flowpath of the combustor only after some air only (i.e., air without fuel) has been introduced after the detonation wave has passed. When used with the previously described embodiments, this sequence of no or reduced fuel addition occurs or is located after the closed period (e.g., rotating region  74 , described above) of the air valve (fluid diode). The net effect of the introduction of the additional or un-fueled air is the lowering of the overall fuel air ratio of the combustor and hence the lower of the bulk mixed exiting temperature of the gases produced by the combustor, and thus acts to provide a throttling feature to a continuous detonation combustor. 
         [0073]    Thus, embodiments of the present disclosure include controlling the flow of fuel of a continuous detonation combustor, also known as a rotating detonation combustor, so that the overall fuel/air ratio of the combustor can be reduced significantly below the stoichiometric ratio, thus, in some embodiments, adding a throttling ability, which is not believed by the Inventor to have ever been before identified as possible for a continuous detonation combustor/engine. Also the introduction of a region of low or non-fueled oxidant (e.g., air) region also acts to reduce or eliminate the deflagrative burning that occurs in some continuous detonation combustors, thus improving the pressure gain potential for a given fuel consumption. The allowable fuel/air ratios over which a potential continuous detonation combustor/engine or pressure gain combustor is held to a very restrictive range by the known detonability limits particular to the fuel and air combination and the very near the stoichiometric fuel air ratio. The ability to throttle allows the device to be applicable for use as the main combustor of a gas turbine engine whose turbine inlet temperature is required to be below the level of stoichiometric fuel air ratio, or requires modulation in the power or thrust output level. Some embodiments of the present disclosure allow the fueled region into which the detonation wave continually travels to be within the allowable range for detonation while allowing a portion of air to act as dilution without interfering with the continuous detonation properties. The dilution air is presented as layers within the gas moving downstream of the combustion region and hence mixes with the vitiated gas products due to turbulence. Because it is introduced within a region of relatively low pressure behind the detonation wave, the pressure of supply is below that of the region of pressure gain across the combustor. This dilution air region is acted upon by the shock process created as a result of the detonation in the downstream region and is thereby indirectly compressed by the detonative combustion event, and thus attains the pressure gain state. The density gradient at the interfaces between the hot vitiated products of detonative combustion and the cooler dilution gas, when experiencing the passing motion of the strong pressure gradient from the shock, experiences strong generation of vorticity at the interface due to known baroclinic instabilities. This vorticity created strong mixing at the interfaces also. 
         [0074]    The low flow loss characteristic of the above-disclosed fluid diode embodiments allows a low pressure loss method of introduction of this dilution air. The inventor is not aware of any method of throttling of a continuous detonation combustor beyond the narrow range of detonable limits, other than that disclosed and claimed herein. 
         [0075]    A moving mechanical feature accomplishing the same functions as the fluid diodes disclosed herein, but traveling at the speed of the detonation wave instead of the reduced speeds of the diode structures disclosed herein that generate moving regions at the speed of the detonation wave, may be considered. However, such a scheme would require tip speeds of approximately 6000 feet per second in the annulus, which would yield stresses that are believed to exceed the capabilities of current state-of-the-art materials. Embodiments of the present disclosure provide the regions of translating (rotating) fueled and un-fueled regions are made to move at a velocity equal to that of the detonation wave, but without causing a structure to travel at such high velocities. Thus, with embodiments of the present disclosure, it is anticipated that the stresses within the structures, e.g. the diode structures, can be made to be within those of known design practice using known materials. 
         [0076]    Continuous detonation combustion provides continuously high heat flux from the detonative combustion process. Some embodiments of the present disclosure reduce the average level of high heat flux by introduction of the un-fueled region. All positions are intermittently heated by the passing combustion wave, and are then cooled by the arriving flow of non-vitiated flow traversing the combustor. As described, mixing of the two regions occurs as a consequence of the flow traversing to the combustor exit including known mechanisms of turbulence of various scales. Additional mixing features of various techniques, including known techniques, can be used to further enhance mixing as needed. 
         [0077]    Referring to  FIG. 10 , two rotating continuous detonation waves  70 A and  70 B are illustrated in a laid-out or developed view. The direction of propagation of the rotating continuous detonation waves is indicated by arrow  114 , which corresponds to circumferential direction  72 . The direction of provision of fuel and oxidant in the depiction of  FIG. 10  is indicated by arrows  116 . It will be understood that fuel and/or oxidant may be provided from various directions in various embodiments. Each detonation wave has a flame front  118 , otherwise referred to herein as wavefront  118  or leading edge  118 , and a trailing or aft end  120 . Flame fronts  118  proceed circumferentially around the annular combustion chamber. In the depiction of  FIG. 10 , fuel and oxidant are provided into combustion chamber  24  via one or more fluid diodes in manner described above, at least insofar as fuel and oxidant are supplied in certain zones, and neither fuel nor oxidant are supplied in other zones. Air is supplied into lower pressure zones  80  via fluid diode  22 , as previously described. Fuel is supplied via a fluid diode  23 , described below, in a rotating fuel introduction zone  81 . Rotating lower pressure zone  80  and fuel introduction zone  81  advance in front of each rotating continuous detonation wave, into which the detonative combustion wavefront  118  moves, detonatively combusting the fuel/oxidant mixture; the fuel and oxidant mixture is continuously supplied in advance of the rotating continuous detonation wave, thereby continuously maintaining the rotating continuous detonation wave. For example, in one embodiment, fluid diode  23  is configured to supply fuel in fuel introduction zone  81 , and fluid diode  22  is configured to supply air into lower pressure region  80 , e.g., in direction  26 , although it will be understood that in various embodiments of the present disclosure, including those illustrated and described herein, fuel and/or oxidant may be supplied in direction  26  and/or other directions, e.g., directions transverse to direction  26 . Similarly, as in the manner described above, fluid flow from the rotating continuous detonation waves at higher pressure zones  78  in backflow direction  28  is prevented or reduced via one or more fluid diodes in manner described above. In the depiction of  FIG. 10 , higher pressure zones  78  and lower pressure zones  80  are depicted as being of different lengths, e.g., circumferential lengths or arc lengths (degrees of arc). It will be understood that  FIG. 10  is diagrammatic in nature, and not to scale; and further, that the relative sizes or lengths (circumferential or arc and/or radial) of higher pressure zones  78  and lower pressure zones  80  may vary depending upon the needs of the particular application, e.g., in the manner set forth below, and may or may not be the same size/length. In the description that follows, reference is made to circumferential length, which in most cases is synonymous with arc length, or degrees of arc, and hence is generally referred to simply as circumferential length. 
         [0078]    Under certain circumstances, such as operation at stoichiometric fuel/oxidant conditions or near stoichiometric fuel/oxidant conditions, deflagrative combustion may take place at the aft end  120  of each rotating continuous detonation combustion wave in the vicinity of the interface  122  between combusted and non combusted fuel/air mixture, effectively forming a deflagrative zone in the vicinity of the interface  122 , which may also thus be referred to as deflagrative zone  122 . In order to prevent incoming fuel and oxidant supplied at low pressure zone  80  from generating deflagrative combustion at interface  122 , it is desirable to delay the provision of fuel so as to create a dilution layer, e.g., a layer of only air, behind the detonation wave in the vicinity of interface  122 . The fuel introduction lag, i.e., wherein the fuel introduction in lower pressure zone  80  lags the air introduction in low pressure zones  80 , creates an air/fuel interface  124  that is spaced apart from deflagrative zone or interface  122 , forming a dilution air layer or dilution layer  126 . Thus, dilution layer  126  is a result of lagging the fuel introduction, which is depicted as fuel lag  83  or fuel introduction lag  83 , which is formed or generated in accordance with embodiments of the present disclosure. Accordingly, whereas the embodiments described with respect to  FIGS. 1 to 9  introduced fuel and air throughout the lower pressure zone  80 , the embodiments described with respect to  FIGS. 11-25  lag the fuel introduction relative to the air introduction, and hence, have a reduced fuel introduction region, illustrated in  FIG. 10  as fuel introduction zone  81 . The air introduction region occurs in lower pressure zones  80 , both during the region of fuel introduction lag  83  and during the fuel introduction zone  81 . Various embodiments of the present disclosure are configured to generate the fuel introduction lag, some of which are described as follows. In some embodiments, the fuel introduction lag may be varied, and/or the stoichiometry of the detonation waves may be varied, and hence dilution layer  126  and fuel introduction region  81  may be varied, thereby reducing or eliminating deflagrative combustion at or in the vicinity of interface  122 , and throttling the output of the continuous detonation combustion system  15 . 
         [0079]    In the depiction of  FIG. 10 , detonation wave  70 A is considered generally to be a detonation wave with rotating regions  74  and  76 , and higher and lower pressure zones  78  and  80 , respectively, of the sort produced by or associated with the embodiments of  FIGS. 1-9 , whereas detonation wave  70 B is considered generally to be a detonation wave with rotating regions  75 ,  77  and  79 ; and higher and lower pressure zones  78  and  80 , respectively; of the sort produced by or associated with the embodiments of  FIGS. 11-25 . Rotating regions  77  and  79  form fuel introduction zones and zones of fuel introduction lag, referred to herein as fuel introduction zone  81  and fuel introduction lag  83 , respectively. In one form, circumferential length of the combination of fuel introduction zone  81  and fuel introduction lag  83  is equal to the circumferential length of lower pressure region  80 . In other embodiments, fuel introduction zone  81  and fuel introduction lag  83  may not be equal in circumferential length to that of lower pressure region  80 , and may vary, e.g., based on the fuel supply pressure, and the alignment and misalignment of fluid supply passages. Higher pressure zone  78  is illustrated as being at the forward portion of the detonation wave, wherein fuel and oxidant are not supplied, and lower pressure zone  80  trails the higher pressure portion of the detonation wave, and has a sufficiently low pressure relative to the supply pressures of the fuel and oxidant to allow the entry of fuel and oxidant into combustion chamber  24 . 
         [0080]    Referring to  FIG. 11 , some aspects of non-limiting example of a combustion system  15  in accordance with embodiments of the present disclosure are schematically illustrated. In one form, combustion system  15  is a pressure-gain combustion system. In other embodiments, combustion system  15  may not be a pressure-gain combustion system. In one form, combustion system  15  is a continuous detonation combustion system. In other embodiments, combustion system  15  may not be a continuous detonation combustion system. It will be understood that combustion system  15  may be employed in engine  10  of  FIG. 1  in addition to or in place of combustion system  14 . Moreover, it will be understood that combustion system  15  includes many of the same or similar components as described above with respect to combustion system  14 , in which case like reference numbers/characters will be employed in the following description. 
         [0081]    Combustion system  15  includes supply portion  20 , first fluid diode  22 , a second fluid diode  23  and combustion chamber  24 . It will be understood that the use of the terms, “first,” “second,” and the like, when describing components of combustion system  15  are not intended to imply any sequence, order of priority, order of arrangement, order of flow, or the like, but rather, are merely intended to numerically differentiate one such component from another for ease of introduction of such components. In one form supply portion  20  is configured to supply an oxidant to fluid diode  22  and a fuel to fluid diode  23 . In one form, the oxidant is air, and the fuel is conventional gas turbine engine fuel. In other embodiments, other oxidants may be used in addition to or in place of air, and/or other fuels may be used in addition to or in place of conventional gas turbine engine fuel. In some other embodiments, supply portion  20  may be configured to supply only a fuel or only an oxidant to fluid diode  22 , and to supply only of fuel or only an oxidant to fluid diode  23 . In some embodiments, supply portion  20  may be configured to supply a fuel/air mixture to fluid diode  22 , and also a fuel/air mixture to fluid diode  23 . For example, in some embodiments, it may be desirable to supply a substantially substoichiometric fuel/air mixture to fluid diode  22 , and to supply more of fuel/air mixture having higher stoichiometry, e.g. near stoichiometric, to fluid diode  23 , wherein the fuel/air mixture supplied to fluid diode  22  is insufficient for combustion, but in conjunction with the fuel/air mixture supplied to fluid diode  23  is sufficient for combustion. The stoichiometry of the final fuel/air mixture may vary with the needs of the application, and may be stoichiometric or substoichiometric with the stoichiometry being sufficient to achieve desired detonation combustion properties. 
         [0082]    The fuel and oxidant may be supplied from supply portion  20  to first fluid diode  22  and fluid diode  23  generally in primary flow direction  26 , such as is depicted in  FIG. 11 . In some embodiments, fuel and/or oxidant may be supplied in or from other directions e.g., radially inward. Combustion takes place in combustion chamber  24  on the opposite side of fluid diode  22  and fluid diode  23  from supply portion  20 . In one form, combustion chamber  24  is a walled annular chamber. In other embodiments, combustion chamber  24  may take other forms. 
         [0083]    First fluid diode  22  is configured, as set forth previously, to allow a fluid flow, such as an oxidant flow, in primary flow direction  26  to supply the fluid flow into combustion chamber  24  for use by the detonative combustion process(es) taking place in combustion chamber  24 . In addition, fluid diode  22  is configured, as set forth previously, to prevent or reduce fluid flow in a back-flow direction  28  opposite to primary flow direction  26  at the location(s) of the detonative combustion process(es). 
         [0084]    As set forth previously, first fluid diode  22  is disposed in annulus  30  downstream of compressor  12 , but in other embodiments may be disposed at other locations. In one form, first fluid diode  22  includes first diode structure  32  or first rotating diode structure  32 ; and second diode structure  34  or second rotating diode structure  34 , each of which may be disposed relative to each other, or otherwise configured or arranged as previously described. In some embodiments, one or more seals may be disposed between diode structure  32  and diode structure  34 . In some embodiments, fluid diode  22  may employ one or more additional diode structures of the form previously described as with respect to diode structure  32  and diode structure  34 . 
         [0085]    Second fluid diode  23  is configured, in the same manner as previously set forth above with respect to fluid diode  22 , to allow a fluid flow, such as a fuel flow, in primary flow direction  26  to supply the fluid flow into combustion chamber  24  for use by the detonative combustion process(es) taking place in combustion chamber  24 . In addition, fluid diode  23  is configured, in the same manner as previously set forth above with respect to fluid diode  22 , to prevent or reduce fluid flow in a back-flow direction  28  opposite to primary flow direction  26  at the location(s) of the detonative combustion process(es). In one form, fluid diode  23  is positioned radially outward of fluid diode  22 , and is disposed or otherwise positioned to receive fuel from an annulus portion  31  of annulus  30 . In other embodiments, fluid diode  23  maybe arranged differently than that illustrated in  FIG. 11 . For example, in some embodiments, fluid diode  23  may take the form of a cylinder, a cone or conical section, or any body of revolution. 
         [0086]    In one form, fluid diode  23  includes a third diode structure  33  or a third rotating diode structure  33  and a fourth diode structure  34  or fourth rotating diode structure  34  positioned adjacent to diode structure  33 . In other embodiments, more than two diode structures e.g., akin to diode structure  33  and diode structure  35 , may be employed. In one form, diode structure  33  is positioned immediately adjacent to diode structure  35 , e.g., with a small gap between diode structure  33  and diode structure  35  to limit contact between diode structure  33  and diode structure  35 . The size of the gap may vary with the needs of the application. In other embodiments, diode structure  33  may be spaced apart from diode structure  35  by some larger amount. In some embodiments, e.g., embodiments employing low friction materials, diode structure  33  and diode structure  35  may be positioned to allow contact therebetween, thereby eliminating or reducing any gap therebetween. In some embodiments, one or more seals may be disposed between diode structure  33  and diode structure  35 . 
         [0087]    Referring to  FIGS. 12-14 , some aspects of non-limiting examples of diode structure  33  and diode structure  35  in accordance with an embodiment of the present disclosure are described. In one form, diode structure  33  and diode structure  35  are rings or disks disposed in annulus  30  e.g., referred to as diode structure  33 A and diode structure  35 A. In other embodiments, one or both diode structures  33  and  35  may take other forms, and may be, for example, cylinders, conical structures or may have any shape defined as a body of revolution. For example, some embodiments described and illustrated herein include diode structure  33 B in diode structure  35 B in the form of cylindrical structures. However, for the sake of the convenience of the reader, the written description generally refers to the aforementioned fluid flow passages simply as fluid flow passages  33  and  35 . In still other embodiments, diode structures  33  and  35  may take any shape, and may or may not be disposed in an annulus. Diode structures  33  and  35  may be formed of the same material described above as with respect to diode structure  32  and  34 , or may be formed of any material suited to the temperatures and stresses and other environmental factors associated with a combustion system, such as combustion system  15 . In the depictions of  FIGS. 12-14 , diode structures  33 A and  35 A are illustrated as extending from diode structures  32  and  34  respectively. Dashed lines  37  and  39  respectively indicate that diode structures  33  and  35  may be formed integrally with or attached to respective diode structures  32  and  34 , or may be separate components that rotate in direction  72  at the same speed as, and in maintained orientation relative to diode structures  32  and  34 . 
         [0088]    Diode structures  33  and  35  include a plurality of fluid flow passages interspersed with a plurality of fluid flow blockages. Diode structures  33  and  35  include fluid flow passages  41  and  45 . In some embodiments, fluid flow passages  41  are employed in conjunction with diode structure  32 , and fluid flow passages  45  are employed in conjunction with diode structure  34 . In such cases, fluid flow passages  41  may be illustrated as fluid flow passages  41 A, and fluid flow passages  45  are illustrated as fluid flow passages  45 A. In some embodiments, fluid flow passages  41  may be employed in conjunction with diode structure  34 , and fluid flow passages  45  may be employed in conjunction with diode structure  32 . In such cases, fluid flow passages  41  are illustrated as fluid flow passages  41 B, and fluid flow passages  45  are illustrated as fluid flow passages  45 B. However, for the sake of the convenience of the reader, the written description generally refers to the aforementioned fluid flow passages simply as fluid flow passages  41  and  45 . Accordingly, in the example illustrated in  FIGS. 12-14 , diode structure  33  includes a single circumferential row of fluid flow passages  41  interspersed with a single circumferential row of fluid flow blockages  43 ; and diode structure  35  includes a single circumferential row of fluid flow passages  45  interspersed with a single circumferential row of fluid flow blockages  47 . In one form, the number of fluid flow passages  41  is the same as the number of fluid flow passages  36 ,  38  and  40 ; and the number of fluid flow blockages  43  is the same as the number of fluid flow blockages  42 ,  44  and  46 . In addition, the number of fluid flow passages  45  is the same as the number of fluid flow passages  56 ,  58  and  60 ; and the number of fluid flow blockages  47  is the same as the number of fluid flow blockages  62 ,  64  and  66 . In other embodiments, the number of fluid flow passages  41  and  45 , and the number of fluid blockages  43  and  47  may not be the same in number as the corresponding fluid flow passages and fluid flow blockages of diode structures  32  and  34 . In various embodiments, any number, circumferential length, size and orientation of rows of fluid flow passages and fluid flow blockages may be employed in accordance with the principles disclosed herein, so as to yield the rotating regions  75 ,  77 ,  79 , fuel introduction zones  81  and zones of fuel introduction lag  83  disclosed herein. In one form, fluid flow passages  41  and  45  are equally spaced circumferentially, and fluid flow blockages  43  and  47  are equally spaced circumferentially. In other embodiments, the fluid flow passages and/or the fluid flow blockages may not be equally spaced. For the sake of convenience of illustration, only a portion of the circumference of each of diode structures  33  and  35  (diode structures  33 A and  35 A) is illustrated. It will be understood that diode structures  33  and  35  continue circumferentially around the periphery of diode structures  32  and  34 , respectively. 
         [0089]    Fluid flow passages  41  and  45  are configured to permit fluid flow through respective diode structures  33  and  35  at the locations of respective fluid flow passages  41  and  45 , e.g., in primary flow direction  26 . Fluid flow blockages  43  and  47  are configured to prevent flow through respective diode structures  33  and  35  at the locations of fluid flow blockages  43  and  47 . In one form, fluid flow passages  41  are in the form of slots, and fluid flow passages  45  are in the form of holes, e.g. circular holes, whereas the fluid flow blockages  43  and  47  are in the form of the physical material of respective diode structures  33  and  35  that extend circumferentially between respective fluid flow passages  41  and  45 . In some embodiments, fluid flow passages  41  may be in the form of slots, and fluid flow passages  45  may be in the form of holes. In other embodiments, the fluid flow passages and the fluid flow blockages may take other geometric forms or shapes, e.g., depending upon the needs of the particular application. For example, some embodiments may include fluid flow blockages in the form of spokes of a diode structure in the form of a spoked rotor, whereas the fluid flow passages of such an embodiment may be the spaces between the spokes 
         [0090]    In some embodiments, the fluid flow passages may be configured for a greater pressure drop in one direction than the opposite, e.g., for a greater pressure drop in back-flow direction  28  than in primary flow direction  26 . For example, entrance and exit effects, such as rounded and sharp corners, may be formed on appropriate ends of the fluid flow passages to yield a higher pressure drop in back-flow direction  28  than in primary flow direction  26 . In addition, the shape of the fluid flow passages may be otherwise configured to yield a higher pressure drop in back-flow direction  28  than in primary flow direction  26 . In various embodiments, the fluid flow passages may be angled, e.g., may have centerlines that are not parallel to the axis of rotation of the diode structure in which the fluid flow passages are formed, which in the depicted embodiment is engine centerline  18 , e.g., in order to reduce losses in the fluid flow passing through diode  23  in primary flow direction  26 . Also, in some embodiments, the fluid flow passages may have other shapes or features configured to enhance flow through fluid diode  23  in primary flow direction  26  and/or inhibit flow through fluid diode  23  in back-flow direction  28 . Additionally, in some embodiments the orientation of the fluid diode structures may be reversed relative to the depicted embodiment, e.g., wherein diode structures  34  and  35  are positioned to be exposed to fuel and/or oxidant prior to diode structures  32  and  33  being exposed to fuel and/or oxidant. 
         [0091]    Diode structures  33  and  35  are configured for relative motion between each other in the same manner and variations thereof as described previously as with respect to diode structures  32  and  34 . In one form, both diode structures  32  and  34  rotate in the same direction. In other embodiments, diode structures  32  and  34  may rotate in opposite directions. As with diode structures  32  and  34 , diode structures  33  and  35  rotate at different speeds, yielding relative motion between them. In addition, the number of fluid flow passages  41  and  45  per circumferential row, and hence, the number of fluid flow blockages  43  and  47  per row are also different. In some embodiments, the fluid flow passages may be configured for a greater pressure drop in one direction than the opposite, e.g., for a greater pressure drop in back-flow direction  28  than in primary flow direction  26 , as set forth above with respect to fluid diode  22 . The relative motion between diode structures  33  and  35 , in conjunction with the number and spacing of fluid flow passages and fluid flow blockages, yields moving regions of relative alignment and misalignment of fluid flow passages  41  in diode structure  33  with corresponding fluid flow passages  45  in diode structure  35 . In one form, the regions of alignment and misalignment rotate around fluid diode  23 , e.g., about engine centerline  18  in the depicted embodiment. The rotating regions of relative alignment and misalignment rotate at a different speed than the rotational speed of either diode structure  33  or diode structure  35 . In particular, the rotating regions of relative alignment and misalignment rotate substantially faster than diode structures  33  and  35 , and are configured to rotate at the same speed as the rotating continuous detonation wave in the same manner as that described above with respect to fluid diode  22 . The rotational speed of the regions of alignment and misalignment are dependent various factors, which in the present embodiment include the number of fluid flow passages (and corresponding fluid flow blockages) in each of diode structures  33  and  35 , and the rotational speed of each of diode structures  33  and  35 . In other embodiments, other factors may be involved determining the speed of rotation and/or other type of motion of regions of alignment and misalignment, e.g., depending upon the type or types of relative motion that takes place between the diode structures. The regions of relative misalignment of the fluid flow passages (relative alignment of fluid flow blockages with fluid flow passages) are employed to block one or more rotating continuous detonation waves, i.e., to reduce or prevent flow in back-flow direction  28  in the vicinity of the higher pressure regions rotating continuous detonation wave(s). The regions of relative alignment of the fluid flow passages (with corresponding relative misalignment of fluid flow blockages) are employed to allow fluid flow through fluid diode  23  in primary flow direction  26  and lower pressure regions. The areas of alignment and misalignment are spaced apart circumferentially. 
         [0092]    Referring to  FIG. 15 , some aspects of a non-limiting example of rotating regions of alignment of fluid flow passages and rotating regions of misalignment of fluid flow passages, and corresponding and rotating lower pressure regions and higher pressure regions, in accordance with an embodiment of the present disclosure are schematically illustrated. Fluid flow passages  41  and  45  are positioned to lag behind respective fluid flow passages  36 ,  38 ,  40  and  56 ,  58 ,  60 ; and hence fluid flow blockages  43  and  47  lag behind respective fluid blockages  42 ,  44 ,  46  and  62 ,  64 ,  66 . For example, in the depiction of  FIG. 12 , the leading edges of fluid flow passages  41  lag the leading edges of fluid flow passages  36 ,  38 ,  40  by an angle Ø1; and the leading edges of fluid flow passages  45  lag the leading edges of fluid flow passages  56 ,  58 ,  60  by an angle Ø1. The lag of fluid flow passages  41  and fluid flow passages  45 , e.g., the lag of the leading edges and/or the radial centerlines, generate the fuel introduction lag  83  depicted in  FIG. 10 . In particular, in some embodiments, the circumferential length of the openings  45  relative to the circumferential length of slots  41  forms rotating region  77 , which determines the circumferential length of the fuel introduction zone  81 , e.g., extending from the left-hand end of the fuel introduction lag  83  depicted in  FIG. 10 , and extending leftward to the left-hand end of lower pressure zone  80 . In addition, in some embodiments, the amount of lag of the fluid flow passages  41  and  45  relative to respective flow passages  36 ,  38 ,  40  and  56 ,  58 ,  60  forms rotating region  79 , which determines the point at which fuel introduction begins, e.g., relative to rotating region  76  and/or lower pressure zone  80 , and hence, determines the fuel introduction lag  83 . In addition, diode structures  33  and  35  are configured to generate rotating region  75 , in a manner the same as or similar to that described above with respect to rotating region  74  and rotating region  76 . In the depicted embodiment, rotating region  75  is illustrated as being of the same circumferential length or arc length as rotating region  74 . In other embodiments, rotating region  75  may be a different circumferential length or arc length relative to rotating region  74 . 
         [0093]    In the depiction of  FIG. 15 , the rotating regions  74  and  76  formed by fluid diode  22  are illustrated as having approximately the same circumferential length. However, it will be understood that fluid diode structures  32  and  34  may be configured to generate a rotating region  74  having a different size than rotating region  76 , e.g., by changing the circumferential length of the fluid flow passages in fluid diode structures  32  and  34 , which thus changes the circumferential length of the fluid flow blockages. In some embodiments, the circumferential length of the fluid flow passages in one of the diode structures may be changed relative to the circumferential length of the fluid flow passages in the other of the diode structures in order to generate a rotating region  74  having a different circumferential length than rotating region  76 . By creating a rotating region  74  having a different circumferential length than rotating region  76 , the respective higher pressure zones  78  and lower pressure zones  80  defined by respective rotating regions  74  and  76  will have a different circumferential length in one of the fluid diode structures relative to the other. In addition, the effective circumferential length of the fluid flow passages may be varied on-the-fly, i.e. during the operation of combustion system  14  and/or combustion system  15  by subdividing fluid diode structures  32  and/or  34  into 2 or more rotating components each, wherein one of the rotating components has fluid flow passages having a length in the circumferential direction that is different than the fluid flow passages of the other component, and by varying the relative position e.g. angular position, between the rotating components. Such a configuration is equivalent to having 2 diode structures rotating with each other at the same speed employed in conjunction with 2 other diode structures rotating with each other at the same speed, but at a different speed than the first to diode structures. The relative position may be varied, for example, by employing an indexing coupling in a drive train that drives the subdivided fluid diode structures or one or more pairs of diode structures, for example and without limitation, in a manner such as that described herein below. 
         [0094]    Fluid diode structures  33  and  35  are configured, in the same or similar manner to that set forth above with respect to fluid diode  22 , to generate rotating regions that rotate or travel at the same speed as the rotating continuous detonation wave. The rotating regions include one or more rotating regions  75  of relative misalignment of the fluid flow passages of diode structures  33  and  35 , and a corresponding number of each of rotating regions  77  and  79  of relative alignment of the fluid flow passages of diode structures  33  and  35  (similarly, one or more rotating regions of relative alignment of the fluid flow blockages of diode structures  33  and  35 , and the corresponding number of rotating regions of relative misalignment of the fluid flow blockages of diode structures  33  and  35 , respectively). The rotating regions  75 ,  77  and  79  are configured to travel or rotate at the same speed as the continuous detonation combustion wave in the same or similar manner to that described above with respect to rotating regions  74  and  76 . 
         [0095]    In the depiction of  FIG. 15 , the rotating regions  75 ,  77  and  79  formed by fluid diode  22  are illustrated as having particular proportions relative to one another. However, it will be understood that fluid diode structures  33  and  35  may be configured to form a rotating regions  75 ,  77  and  79  in any desired size wherein the combined arc length of rotating  75 ,  77  and  79  are less than 360°. In some embodiments, the circumferential length of the fluid flow passages in one of the diode structures may be changed relative to the circumferential length of the fluid flow passages in the other of the diode structures in order to generate rotating regions having different circumferential lengths relative to each other. In some embodiments, such as those described herein, the effective circumferential length of the fluid flow passages may be varied on-the-fly, i.e. during the operation of combustion system  15  by subdividing fluid diode structures  33  and/or  35  into 2 or more rotating components each, wherein one of the rotating components has fluid flow passages having a length in the circumferential direction that is different than the fluid flow passages of the other component, and by varying the relative position e.g. angular position, between the rotating components. Such a configuration is equivalent to having 2 diode structures rotating with each other at the same speed employed in conjunction with 2 other diode structures rotating with each other at the same speed, but at a different speed than the first to diode structures. The relative position may be varied, for example, by employing an indexing coupling, for example and without limitation, in a manner such as that described herein below. In some embodiments, the relative angular positions of diode structures  33  and  35  may be varied for example via the use of an indexing coupling in a drive train that drives diode structure  33  and/or diode structure  35 . 
         [0096]    As previously mentioned, pressure in lower pressure zones  80  between rotating continuous combustion waves  70  is less than the supply pressure of the oxidant supplied by fluid diode  22 , and less than the supply pressure of fuel supplied via fluid diode  23 . That is, the supply pressures of the fuel and oxidant are selected to be higher than the pressure in pressure zones  80 . 
         [0097]    By positioning regions  75  adjacent to rotating continuous detonation waves  70 , back-flow resulting from the higher pressure zones  78  associated with the detonation combustion waves is reduced or eliminated. By positioning regions  77  and  79  in lower pressure zones  80  away from rotating continuous detonation waves  70 , where the fuel supply pressure is higher than the pressure in lower pressure zones  80 , flow, e.g., of fuel, into combustion chamber  24  is permitted. Thus, in various embodiments, one or more portions of fluid diode  23  may restrict or prevent flow in back-flow direction  28 , while at the same time one or more other portions of fluid diode  23  permit flow through to combustion chamber  24  in primary flow direction  26 , e.g., depending upon circumferential location in a moving reference frame associated with rotating continuous detonation waves  70  and regions  75 ,  77  and  79 . The fuel/oxidant mixture admitted into combustion chamber  24  via fluid diodes  22  and  23  is combusted upon the approach of the next rotating continuous detonation waves  70  to arrive at the location of the admitted fuel/oxidant mixture, thus continuing the detonation process. 
         [0098]    Referring to  FIG. 16 , some aspects of a non-limiting example of fluid diodes  33  and  35  in accordance with an embodiment of the present disclosure are schematically depicted. The depiction of  FIG. 16  is schematic in nature, and illustrates the fluid flow passages of diode structures  32  and  34  as being the same size, and also illustrates fluid flow passages  41  and  45  of diode structures  33  and  35 , respectively. The alignment of the fluid flow passages and at the misalignment of the fluid flow passages are depicted, and illustrate an offset  91  in the positions of alignment and misalignment of the fluid flow passages in diode structures  33  and  35  relative to diode structure  32  and  34 , respectively. 
         [0099]    Referring to  FIG. 17 , some aspects of a non-limiting example of a drive system  200  in accordance with an embodiment of the present disclosure is schematically depicted. Drive system  200  includes a mechanical power unit  202 , such as an electrical motor, a rotor or school of a gas turbine engine, or another source of mechanical power. Mechanical power unit  202  is coupled to diode structures  32  and  33  via a drive train  204 , e.g. a shafting system and/or gear system and/or belt system, and is operative to drive diode structure  32  and  33  at the same rotational speed. Mechanical power unit  202  is coupled to diode structures  34  and  35  via a drive train  206 , e.g. a shafting system and/or gear system and/or belt system, and is configured to drive diode structures  34  and  35  at the same rotational speed, but at a different rotational speed than diode structures  32  and  33  in a manner set forth previously above. 
         [0100]    Referring to  FIG. 18 , some aspects of a non-limiting example of a drive system  210  in accordance with an embodiment of the present disclosure is schematically depicted. Drive system  210  includes a mechanical power unit  212 , such as an electrical motor, a rotor or school of a gas turbine engine, or another source of mechanical power. Mechanical power unit  212  is coupled to diode structures  34  and  35  via a drive train  214 , e.g. a shafting system and/or gear system and/or belt system, and is operative to drive diode structure  34  and  35  at the same rotational speed. Drive train  214  includes an indexing mechanism  215  that is configured to vary the angular position of diode structure  33  relative to diode structure  32  on the fly, i.e., during the operation of rotating detonation combustion system  15 . In one form, indexing mechanism  215  is an indexing coupling. In other embodiments, indexing mechanism  215  may take other forms. In some embodiments, indexing mechanism  215 , illustrated in dashed lines, may also or alternatively be employed to vary the angular position of diode structure  32  relative to diode structure  33 . Mechanical power unit  212  is coupled to diode structures  34  and  35  via a drive train  216 , e.g. a shafting system and/or gear system and/or belt system, and is configured to drive diode structures  34  and  35  at the same rotational speed, but at a different rotational speed than diode structures  32  and  33  in a manner set forth previously above. In some embodiments, drive train  216  may include indexing mechanism  215 , illustrated in dashed lines, to vary the angular position of diode structure  35  relative to diode structure  34 . In some embodiments, an indexing mechanism  215 , illustrated in dashed lines, may also or alternatively be employed to vary the angular position of diode structure  33  relative to diode structure  32  and/or very the angular position of diode structure  32  relative to diode structure  33 . By varying the angular positions of one or more diode structures relative to another one or more diode structures on-the-fly, the fuel introduction lag may be so varied, and/or the stoichiometry of the detonation waves may be so varied, and hence dilution layer  126  and fuel introduction region  81  may be so varied, thereby reducing or eliminating deflagrative combustion at or in the vicinity of interface  122 , and throttling the output of the continuous detonation combustion system  15 . 
         [0101]    Referring to  FIG. 19 , some aspects of a non-limiting example of an indexing mechanism  215  in the form of an indexing coupling in accordance with an embodiment of the present disclosure is schematically illustrated. Indexing coupling to 15 includes a shaft portion  220  and shaft portion  222  that are coupled together by a splined coupling  224 . In other embodiments, shaft portion  220  and shaft portion  222  may be coupled together by other means, for example a coupling having an angled pin and slot arrangement at one end and a straight spline or pin and slot arrangement. In the depicted embodiment, shaft  220  includes straight splines  226 , and shaft portion  222  includes angled or helical splines  228 . In other embodiments, other splined configurations may be employed for example, splines on each shaft having opposite helical angles or different helical angles. Coupling  224  includes internal straight and helical splines  230  and  232  configured to mate with the splines of shaft portion  220  and shaft portion  222 , which are illustrated in dashed lines. By moving splined coupling  224  in direction  234 , the relative angular position between shaft portion  220  and shaft  222  is varied in one direction, and by moving splined coupling  224  in opposite direction  236 , the relative angular position between shaft portion  220  and shaft  222  is varied in the opposite direction, thereby indexing shaft portion  220  relative to shaft portion  222 . 
         [0102]    Referring to  FIG. 20 , some aspects of non-limiting examples of diode structures  22  and  23  in accordance with embodiments of the present disclosure are schematically depicted. In the embodiment of  FIG. 19 , fluid diode  22  includes diode structures  32  and  34  having the same form as previously set forth, e.g., circular plates. In the embodiment of  FIG. 19 , fluid diode  23  is cylindrically shaped, whereas fluid diode structure  33 B is coupled to, affixed to or integral with diode structure  32 , or rotate with diode structure  32  but without being coupled thereto, as described previously, and as indicated by dashed lines  37  and  39 . In the illustrated embodiment, fluid diode structures  32 ,  34 ,  33 , and  35  include the same fluid flow passages described previously. In other embodiments, other fluid flow passages may be employed. In the depiction of  FIG. 20 , the cylindrical diode structures  33  and  35  extended in direction  26 . In other embodiments, the cylindrical diode structure  33  and  35 , or diode structures  33  and  35  of any body of revolution, may extend in direction  26 , direction  28  or both. In embodiments, using fuel flow within the diodes, the cooling may be enhanced by transfer from the m member to the fuel. The fuel passages may be designed so as to provide a degree of cooling uniformity and effectiveness. Fuel introduction via the side wall may add cooling tot eh side wall structure. Introduction of air flow in to the space between the rotating diodes can be made to provide additional cooling. 
         [0103]    Referring to  FIG. 21 , some aspects of a nonlimiting example of fluid diode  22  and  23  in accordance with an embodiment of the present disclosure are schematically depicted. In the embodiment of  FIG. 20 , fluid flow passages fluid diode  23 , e.g., diode structure  35 , are configured to direct fuel flow into the fluid flow passages of fluid diode  22 , e.g., diode structure  34 , which may enhance the mixing of the fuel and the oxidant, and also provide cooling to the diode structures. In some embodiments, fuel is provided through fuel transfer passages leading from the fuel feed passages to fluid flow passages in the same diode structure to introduce fuel into the air as the air travels through the fluid flow passages. In some embodiments, a single fuel valve supplies multiple rows of fluid flow passages. 
         [0104]    Referring to  FIG. 22 , some aspects of a non-limiting example of fluid diodes  22  and  23  in accordance with an embodiment of the present disclosure are schematically depicted. In the embodiment of  FIG. 21 , fluid flow passages fluid diode  23 , e.g., diode structure  35 , are configured to direct fuel flow (F2) into the fluid flow passages of fluid diode  22 , e.g., diode structure  34 , which may enhance the mixing of the fuel and the oxidant (F1), and also provide cooling to the diode structures. 
         [0105]    Referring to  FIG. 23 , some aspects of a non-limiting example of fluid diodes  22  and  23  in accordance with an embodiment of the present disclosure are schematically depicted. In the embodiment of  FIG. 22 , fluid flow passages fluid diode  23 , e.g., diode structure  35 , are configured to direct fuel flow (F2) into the fluid flow passages of fluid diode  22 , e.g., diode structure  34 , which may enhance the mixing of the fuel and the oxidant (F1), and also provide cooling to the diode structures. 
         [0106]    Referring to  FIG. 24 , some aspects of a non-limiting example of fluid diode structure  22  and  23  in accordance with an embodiment of the present disclosure are schematically depicted. Fluid flow passage  41 B is depicted in the form of a slot in diode structure  35 B, whereas fluid flow passage  45 B is depicted in the form of a circular hole in diode structure  33 B. In other embodiments, the slot may be in diode structure  35 B, and the hole may be in diode structure  33 B. In other embodiments, any suitable size shape and circumferential length of fluid flow passages may be employed in accordance with the teachings herein. 
         [0107]    Referring to  FIG. 25 , some aspects of a non-limiting example of fluid diode structures  22  and  23  in accordance with an embodiment of the present disclosure are schematically depicted. In the depiction of  FIG. 25 , slot  41  is subdivided into sub-portions  41 C,  41 D and  41 E, wherein the combined circumferential length of sub-portions  41 C,  41 D and  41 E add up to the same length as the previously described slot  41 , as configured to generate the rotating regions previously described. In other embodiments, slot  41  may be subdivided into a greater or lesser number of sub-portions. In various embodiments, one or more of sub-portions  41 C,  41 D and  41 E may be blocked, or exposed to different fixed and/or modulated fuel flow sources that alter the stoichiometry of the detonation waves  70 , thereby varying, on-the-fly, the fuel introduction lag, and/or the stoichiometry of the detonation waves, and hence dilution layer  126  and fuel introduction region  81 , thereby reducing or eliminating deflagrative combustion at or in the vicinity of interface  122 , and throttling the output of the continuous detonation combustion system  15 , without the use of an offset mechanism. The sub-portions may be supplied with fuel from separate circuits and independently controlled regarding on, off, or modulated fuel flow, including the ability to effectively throttle the engine, that is operate over a variable range of less than stoichiometric fuel air ratios. The sub-portions and the fuel feed passages may allow flexibility regarding the fueling of the traveling region of the circumference being fueled. In some embodiments, fuel is added to the air via transverse injection from the side. In other embodiments, fuel is added to the air via fuel transfer passages to the fluid flow passages in one or more of the diodes. 
         [0108]    Throttling of a continuous detonation combustor, also known as a rotating detonation combustor, may be accomplished by continually introducing a region of dilution air behind the detonative event between the vitiated gases produced by the detonative event and simultaneously supplying fuel into a region into which the detonative combustion event is moving. This region is caused by the introduction of a transiently moving fuel supply pattern created by application of a valve of like kind of the Continuous Detonation Pressure Gain Combustor Flow Diode Valve. This valve may be used to control fuel flow either together with or separate from the air valve acting on the bulk of the combustor flow. The option for the described valve application to control only the addition of dilution air is also envisioned. In which case, fuel is introduced in manners previously utilized. 
         [0109]    The particular application of the valve device schedules fuel introduction in one or more moving regions immediately adjacent to and behind or ahead of the traveling detonation or detonations of a continuous detonation combustor. The valve, as previously disclosed and recorded, operates on the principle of two or more disks or plates or spoked rotors or elements having sets of holes, slots, or openings through the plate, which move relative to each other. They may move at different, but closely matched, mechanical speeds. The difference in speeds, together with the number, spacing, and patterns of the openings, creates open and closed regions that travel around the annulus at a speed greater than either of the disks. Thus, the speed of the region of closed area and open area may be made to match the speed of detonation without requiring either of the plates to travel at the speed of the detonation. 
         [0110]    The valve works on the general principles of the Vernier scale, in which the position of markings in alignment moves a greater distance than the traveling distance of the sliding element. In this disclosure, the position of the holes or features in alignment, or greatest misalignment, moves a greater distance than the plates having the holes. It is envisioned that the flow direction through the valve may be predominately axial, predominately radial, or a combination of both (also with some amount of swirl). It is also envisioned that the orientation of the plates, disks, or elements may be either flat plate, cylinder, or conical configuration including curved surfaces for any of the types. One of the elements may be stationary. Although rotation is illustrated as the method of achieving the intended motion, methods other than rotation or used in combination with rotation are envisioned. Furthermore, the rotation or translation of one or more of the plates relative to each other is envisioned to be either in the same direction or counter in direction to each other. 
         [0111]    The application of the valve utilizes the opening and closing of the passages to introduce fuel into air, including stratification of charge, to promote detonation and/or to create a non-fueled or lean layer of air between sequenced detonations. This also serves to eliminate or reduce deflagrative burning at the interface of combustion and non-combusted fuel air mixture as commonly occurs in these devices. The valve acts to introduce fuel within the flowpath of the combustor only after some air has been introduced not having fuel added after the detonation event has passed. When used with the previously disclosed valve, this sequence of no or reduced fuel addition occurs or is located after the closed period of the air valve. The net effect of the introduction of the additional or un-fueled air is the lowering of the overall fuel air ratio of the combustor and, hence, the lowering of the bulk mixed exiting temperature of the gases produced by the combustor and, thus, acts to provide a throttling feature to a continuous detonation combustor. 
         [0112]    The disclosure relates to a device that creates the opportunity to control the flow of fuel of a continuous detonation combustor, also known as a rotating detonation combustor, so that the overall fuel air ratio of the combustor can be reduced below the stoichiometric ratio, thus adding a throttling ability. This is a feature that was previously identified as not possible for a continuous detonation engine. The introduction of a region of low or non-fueled region acts to reduce or eliminate the deflagrative burning that occurs in continuous detonation combustors of the conventional type, thus improving the pressure gain potential for a given fuel consumption. The allowable fuel air ratios over which a continuous detonation engine or pressure gain combustor is operable is held to a restrictive range by detonability limits particular to the fuel and air combination and near the stoichiometric fuel air ratio. The ability to throttle allows the device to be applicable to use as the main combustor of a gas turbine engine whose turbine inlet temperature is required to be below the level of stoichiometric fuel air ratio or requires modulation in the power or thrust output level. 
         [0113]    This device allows the fueled region, into which the detonation continually travels, to be within the allowable range for detonation while allowing a portion of air to act as dilution without interfering with the continuous detonation properties. The dilution air is presented as layers within the gas moving downstream of the combustion region and mixes with the vitiated gas products due to turbulence. Because it is introduced within a region of relatively low pressure behind the detonation wave, the pressure of supply is below that of the region of pressure gain across the combustor. This dilution air region is acted upon by the shock process created as a result of the detonation in the downstream region and thereby indirectly compressed by the detonative combustion event and, thus, attained the pressure gain state. The density gradient at the interfaces between the hot vitiated products of detonative combustion and the cooler dilution gas, when experiencing the passing motion of the strong pressure gradient from the shock, experiences strong generation of vorticity at the interface due to baroclinic instabilities. This vorticity creates strong mixing at the interfaces. The low flow loss characteristic of the previously disclosed valve allows a low pressure loss method of introduction of the dilution air. 
         [0114]    A moving mechanical feature accomplishing the same function when traveling at the speed of the detonation can be suggested. This may include speeds of approximately 6000 feet per second in the annulus. In this disclosure, the regions of translating fueled and un-fueled regions may move at a velocity equal to that of the detonation without causing a structure to travel at such velocities which would result in high or prohibitively high stress levels in the moving structure. Through the use of the device, it is anticipated that the stresses within the structure may be within those of known design practice suing known materials. 
         [0115]    Some continuous detonation combustors experience continuously high heat flux from the detonative combustion. The device described may reduce the average level of high heat flux by introduction of the un-fueled region. Positions are intermittently heated by the passing combustion and then cooled by the arriving flow of non-vitiated flow traversing the combustor. Mixing of the two regions occurs as a consequence of the flow traversing to the combustor exit including, but not limited to, known mechanisms of turbulence of various scales. Additional mixing features can be used to enhance mixing as needed. 
         [0116]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the disclosure is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the disclosure, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.