Patent Publication Number: US-8539752-B2

Title: Integrated deflagration-to-detonation obstacles and cooling fluid flow

Description:
BACKGROUND 
     The present disclosure generally relates to cyclic pulsed detonation combustors (PDCs) and more particularly, enhancing the deflagration-to-detonation transition (DDT) process by integrating a cooling fluid flow with the initiation obstacles. 
     In a generalized pulse detonation combustor, fuel and oxidizer (e.g., oxygen-containing gas such as air) are admitted to an elongated detonation chamber at an upstream inlet end. An igniter is used to initiate this combustion process. Following a successful transition to detonation, a detonation wave propagates toward the outlet at supersonic speed causing substantial combustion of the fuel/air mixture before the mixture can be substantially driven from the outlet. The result of the combustion is to rapidly elevate pressure within the combustor before substantial gas can escape through the combustor exit. The effect of this inertial confinement is to produce near constant volume combustion. Such devices can be used to produce pure thrust or can be integrated in a gas-turbine engine. The former is generally termed a pure thrust-producing device and the latter is termed a pulse detonation turbine engine. A pure thrust-producing device is often used in a subsonic or supersonic propulsion vehicle system such as rockets, missiles and afterburner of a turbojet engine. Industrial gas turbines are often used to provide output power to drive an electrical generator or motor. Other types of gas turbines may be used as aircraft engines, on-site and supplemental power generators, and for other applications. 
     The deflagration-to-detonation (DDT) process begins when a fuel-air mixture in a chamber is ignited via a spark or other ignition source. The subsonic flame generated from the spark accelerates as it travels along the length of the chamber due to various chemical and flow mechanics. As the flame reaches critical speeds, “hot spots” are created that create localized explosions, eventually transitioning the flame to a super sonic detonation wave. The DDT process can take up to several meters of the length of the chamber, and efforts have been made to reduce the distance required for DDT by using internal initiation obstacles in the flow. The problem with obstacles for cyclic detonation devices is that they create a pressure drop within the chamber during the fill process and require cooling of the obstacles to enable long life. Initiation obstacles that include an integrated cooling system and minimize pressure drops during the fill process are desirable. 
     As used herein, a “pulse detonation combustor” is understood to mean any device or system that produces pressure rise, temperature rise and velocity increase from a series of repeating detonations or quasi-detonations within the device. A “quasi-detonation” is a supersonic turbulent combustion process that produces pressure rise, temperature rise and velocity increase higher than pressure rise, temperature rise and velocity increase produced by a deflagration wave. Embodiments of pulse detonation combustors include a fuel injection system, an oxidizer flow system, a means of igniting a fuel/oxidizer mixture, and a detonation chamber, in which pressure wave fronts initiated by the ignition process coalesce to produce a detonation wave or quasi-detonation. Each detonation or quasi-detonation is initiated either by external ignition, such as spark discharge or laser pulse, or by gas dynamic processes, such as shock focusing, autoignition or by another detonation (cross-fire). As used herein, a detonation is understood to mean either a detonation or quasi-detonation. The geometry of the detonation combustor is such that the pressure rise of the detonation wave expels combustion products out the pulse detonation combustor exhaust to produce a thrust force. Pulse detonation combustion can be accomplished in a number of types of detonation chambers, including shock tubes, resonating detonation cavities and tubular/tuboannular/annular combustors. As used herein, the term “chamber” includes pipes having circular or non-circular cross-sections with constant or varying cross sectional area. Exemplary chambers include cylindrical tubes, as well as tubes having polygonal cross-sections, for example hexagonal tubes. 
     BRIEF SUMMARY 
     Briefly, in accordance with one embodiment, a detonation chamber for a pulse detonation combustor is provided. The detonation chamber includes a plurality of initiation obstacles disposed on at least a portion of an inner surface of the detonation chamber, each of the plurality of initiation obstacles defining a low-pressure region at a trailing edge. The pulse detonation combustor further includes at least one injector in fluid flow communication with each of the plurality of initiation obstacles. The plurality of initiation obstacles enhance a turbulence of a fluid flow and flame acceleration through the detonation chamber. The at least one injector provides a cooling fluid flow through each of the plurality of initiation obstacles. 
     In accordance with another embodiment, a detonation chamber for a pulse detonation combustor is provided. The detonation chamber includes a plurality of initiation obstacles disposed on at least a portion of an inner surface of the detonation chamber and defining a low-pressure region at a trailing edge of each of the plurality of initiation obstacles. The plurality of initiation obstacles are configured to enhance a turbulence of a fluid flow and flame acceleration through the detonation chamber. The pulse detonation chamber further includes an inlet and an outlet, wherein the plurality of initiation obstacles are disposed between the inlet and the outlet and at least one injector in fluid flow communication with each of the plurality of initiation obstacles, wherein the at least one injector provides a cooling fluid flow to each of the plurality of initiation obstacles. The cooling fluid flow passes through each of the initiation obstacles and into the detonation chamber at the trailing edge of each of the initiation obstacles. 
     In accordance with another embodiment, a pulse detonation combustor is provided. The pulse detonation combustor includes at least one detonation chamber; an oxidizer supply section for feeding an oxidizer into the detonation chamber; a fuel supply section for feeding a fuel into the detonation chamber; and an igniter for igniting a mixture of the gas and the fuel in the detonation chamber. The detonation chamber further comprises a plurality of initiation obstacles disposed on an inner surface of the detonation chamber and defining a low pressure region at a trailing edge of each of the plurality of initiation obstacles, wherein the plurality of initiation obstacles are configured to enhance a turbulence of a fluid flow and flame acceleration through the detonation chamber; and at least one injector in fluid flow communication with each of the plurality of initiation obstacles, wherein the at least one injector provides a cooling fluid flow through each of the plurality of initiation obstacles. 
     These and other advantages and features will be better understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the subsequent detailed description when taken in conjunction with the accompanying drawings, wherein like elements are numbered alike in the several FIGs, and in which: 
         FIG. 1  is a schematic view illustrating a structure of a hybrid pulse detonation turbine engine system; 
         FIG. 2  is a schematic view illustrating a structure of a single detonation chamber of the pulse detonation combustor of  FIG. 1 ; 
         FIG. 3  is a schematic view illustrating an improved pulse detonation combustor in accordance with exemplary embodiments; 
         FIG. 4  is a schematic view illustrating an improved pulse detonation combustor in accordance with exemplary embodiments; 
         FIG. 5  is a schematic view illustrating an improved pulse detonation combustor in accordance with exemplary embodiments; 
         FIG. 6  is a schematic view illustrating an improved pulse detonation combustor in accordance with exemplary embodiments; and 
         FIG. 7  is a schematic view illustrating an improved pulse detonation combustor in accordance with exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, one or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. Illustrated in  FIGS. 1 and 2 , are various pulse detonation engine systems  10  that convert kinetic and thermal energy of the exhausting combustion products into motive power necessary for propulsion and/or generating electric power. Illustrated in  FIG. 1  is an exemplary embodiment of a pulse detonation combustor  14  in a pulse detonation turbine engine concept  10 . Illustrated in  FIG. 2  is an exemplary embodiment of a pulse detonation combustor  14  in a pure supersonic propulsion vehicle. The pulse detonation combustor  14 , shown in  FIG. 1  or  FIG. 2 , includes a detonation chamber  16  having an oxidizer supply section (e.g., an air intake)  30  for feeding an oxidizer (e.g., oxidant such as air) into the detonation chamber  16 , a fuel supply section (e.g., a fuel valve)  28  for feeding a fuel into the detonation chamber  16 , and an igniter (for instance, a spark plug)  26  by which a mixture of oxidizer combined with the fuel in the detonation chamber  16  is ignited. 
     In exemplary embodiments, air supplied from an inlet fan  20  and/or a compressor  12 , which is driven by a turbine  18 , is fed into the detonation chamber  16  through an intake  30 . Fresh air is filled in the detonation chamber  16 , after purging combustion gases remaining in the detonation chamber  16  due to detonation of the fuel-air mixture from the previous cycle. After the purging the pulse detonation combustor  16 , fresh fuel is injected into pulse detonation combustor  16 . Next, the igniter  26  ignites the fuel-air mixture forming a flame, which accelerates down the detonation chamber  16 , finally transitioning to a detonation wave or a quasi-detonation wave. Due to the detonation combustion heat release, the gases exiting the pulse detonation combustor  14  are at high temperature, high pressure and high velocity conditions, which expand across the turbine  18 , located at the downstream of the pulse detonation combustor  16 , thus generating positive work. For the pulse detonation turbine engine application with the purpose of generation of power, the pulse detonation driven turbine  18  is mechanically coupled to a generator (e.g., a power generator)  22  for generating power output. For a pulse detonation turbine engine application with the purpose of propulsion (such as the present aircraft engines), the turbine shaft is coupled to the inlet fan  20  and the compressor  12 . In a pure pulse detonation engine application of the pulse detonation combustor  14  shown in  FIG. 2 , which does not contain any rotating parts such as a fan or compressor/turbine/generator, the kinetic energy of the combustion products and the pressure forces acting on the walls of the propulsion system, generate the propulsion force to propel the system. 
     Turning now to  FIGS. 3-7 , illustrated are schematic views of alternate embodiments of an improved pulse detonation combustor. The schematic views illustrate an inside of an improved detonation chamber, generally similar to detonation chamber  16  of  FIG. 2 , by removing the top 50% of the chamber, or tube, surface. More specifically, illustrated in  FIG. 3  is an improved pulse detonation combustor, generally depicted as  40 , similar to the pulse detonation combustor  14  of  FIGS. 1 and 2 . The improved pulse detonation combustor  40  is illustrated having a detonation chamber  41  defined by sidewalls  47 . The improved detonation chamber  41  includes an inlet  42  and an outlet  44 , through which a fluid flows from upstream towards downstream, as indicated by the directional arrows  43 . The improved detonation chamber  41  also includes a plurality of initiation obstacles  46  for deflagration-to-detonation transition. The initiation obstacles  46  may be disposed on an inner surface  32  of the improved detonation chamber  41  and extend into the detonation chamber  41 . Alternately, the initial obstacles  46  may be formed integral with the detonation chamber sidewalls  47 . The pulse detonation combustor  40  may further include proximate the inlet  42  of the detonation chamber  41 , an air intake valve  52 . 
     In the embodiment depicted in  FIG. 3 , each of the plurality of initiation obstacles  46  includes an integrated injector  54  configured for the injection of a cooling fluid flow  49  into the detonation chamber  41 . In this exemplary embodiment, provided are a plurality of injectors  54  configured to aid in supplying a proper fuel-to-air mixture to the detonation chamber  41 . Each of the plurality of injectors  54  provides the injection of fuel through the initiation obstacle  46  to which it is integrated. By integrating the injection, and thus supply, of fuel with the initiation obstacles  46 , the fuel may be used as the cooling fluid flow  49  to maintain an appropriate temperature of each initiation obstacle  46 . The integration of the injection of the cooling fluid flow  49  with the initiation obstacles  46  minimizes the need for a secondary cooling airflow path dedicated to the initiation obstacles  46  and at the same time creates viable locations for fuel injection into the detonation chamber  46 . Injection of the required fuel for the combustion process through the initiation obstacles  46  provides for cooling of the initiation obstacles  46  to improve longevity and reduce maintenance cycles. In addition, by injecting the fuel through each of the initiation obstacles  46  the fuel is spread out over an entire length “L” of the detonation chamber  41 . The initiation obstacles  46  create turbulence in the flow, so by injecting the fuel at these locations, the fuel is introduced at locations of high mixing. 
     The injectors  54  are positioned to inject a fluid flow  49 , which in this particular embodiment is fuel, at a trailing edge  48  of each obstacle  46  where a low-pressure region is created during a fill process. The injection of fuel at the trailing edge  48  of the obstacles  46  enables the low-pressure region to be reduced during the fill process. By reducing this low-pressure region, the filling losses in the detonation chamber  41  are reduced. 
     In order to ensure the proper mixture of fuel and air in the detonation chamber  41 , the injection of the fluid flow  49  through the obstacles  46  will need to be controlled, including, but not limited to, staging of the injection, timing of the injection and duration of the injection. In an exemplary embodiment, the injection of the fluid flow  49  will be pulsed and timed with the frequency of combustor operation (air valve, ignition source, etc.). For pulsed applications the injectors  54  can be timed together, staged, or operated individually to achieve the desired fuel-to-air mixture. 
     The plurality of integrated initiation obstacles  46  and injectors  54  are disposed on the inner surface  32  of the improved detonation chamber  41  to enhance and accelerate the turbulent flame speed, while limiting the total pressure loss in the pulse detonation combustor  40  and providing cooling to the initiation obstacles  46  for durability. The plurality of initiation obstacles  46  also enhance turbulence flame surface area by providing increased turbulence which allow the flame front to stretch at a greater rate compared to the flame surface area in a combustor chamber with smooth walls. A plurality of circumferentially and axially spaced apart integrated initiation obstacles  46  and injectors  54  were found to be necessary in the illustrated embodiments to affect the transition of the accelerating turbulent flame into a detonation wave  58 . 
     As previously described, the embodiment depicted in  FIG. 3 , integrates a single injector  54  with each of the plurality of initiation obstacles  46 . Referring now to  FIG. 4 , illustrated is an alternate embodiment of an improved pulse detonation combustor, generally depicted as  50 , and similar to pulse detonation combustor  40  of  FIG. 3 . For ease of illustration, the same numerals may be used to indicate similar elements in the figures. In this exemplary embodiment, and in contrast to the embodiment of  FIG. 3 , the pulse detonation combustor  40  includes a single fuel modulator, or injector,  55  that is integrated with two or more of the initiation obstacles  46 . More specifically, as illustrated a single injector  55  is integrated and in fluidic communication via fluid lines  56  with at least two or more of the plurality of initiation obstacles  46 . Alternatively, more than one injector  55  may be included wherein each is integrated with two or more initiation obstacles  46 . The initiation obstacles  46  and injector  55  are integrated as previously described with regard to  FIG. 3  so as to deliver a cooling fluid flow  49  at a trailing edge  48  of each of the initiation obstacles  46  and operate in a similar manner. The integration of a single injector/modulator  55 , or more than one initiation obstacle  46  per injector  55 , provides for a pulse detonation combustor  40  in which less system components are required. 
     Referring now to  FIG. 5 , illustrated is an alternate embodiment of an improved pulse detonation combustor, generally depicted  60 , and similar to pulse detonation combustor  40  of  FIG. 3 . In the embodiment illustrated in  FIG. 5 , the integrated initiation obstacle and fuel injector system provide for the injection of a fluid flow  49  that includes both fuel and air. More specifically, in contrast to the previously disclosed embodiment, provided is the injection of a fluid flow  49  that includes a flow  51  of both air and fuel. The flow  51  is injected though a plurality of integrated initiation obstacles  46  and a plurality of injectors  62  via fluidic communications  56 . It should be noted that, illustrated are a plurality of injectors  62  configured in fluidic communication with a first set of initiation obstacles  53  and a second set of initiation obstacles  57 . Alternately, the injection of the flow  51  of fuel and air may be accomplished by fewer or greater numbers of injectors, such as configurations similar to the described embodiments illustrated in  FIGS. 3 and 4 . 
     The plurality of injectors  62  are configured to inject the flow  51  of the fuel and air mixture into the detonation chamber  41  at a trailing edge  48  of each initiation obstacle  46 . In this exemplary embodiment, the individual flows of the fuel and air may be configured on separate circuits or injected in a spray blast atomization configuration. When injecting the fuel and air on separate circuits, the equivalence ratio can be tailored along the length of the detonation chamber  41  (for example: phi=1 at head end→phi=0.7 at aft) by changing the injection timing/duration for each individual injector  62 . The spray blast enables creation of the proper droplet size for liquid fuels and therefore may be advantageous. In an alternate embodiment, the integrated initiation obstacles  46  and injectors  62  may be configured to inject more than one type of fuel through a single injector  62 . The injection of more than one type of fuel, such as a gaseous fuel and a liquid fuel, may allow for ease in detonation. 
     Referring now to  FIG. 6 , illustrated is an alternate embodiment of an improved pulse detonation combustor, and more particularly an integrated initiation obstacle and cooling fluid injector, generally depicted as  70 . System  70  is generally similar to pulse detonation combustor  40  of  FIG. 3 . In the embodiment illustrated in  FIG. 6 , the detonation chamber  41  is surrounded by a plenum  72  providing a flow of air  78  to the detonation chamber  41 . More specifically, the plenum  72  supplies the flow of air  78  to the detonation chamber  41  via a plurality of openings  74  formed in the sidewall  47  of the detonation chamber  41 . A cooling fluid flow  49 , such as a gaseous and/or liquid fuel, is injected though a plurality of integrated initiated obstacles  46  and injectors  75 , similar to the embodiment illustrated in  FIG. 3 . It should be noted that, while a plurality of injectors  75  are illustrated, with each injector  75  integrated with a single initiation obstacle  46 , a fewer number of injectors/modulators each configured integral with two or more initiation obstacles  46 , such as that illustrates in  FIGS. 4 and 5 , is anticipated. 
     The plurality of injectors  75  are configured to inject the cooling fluid flow  49  into the detonation chamber  41  at a trailing edge  48  of each initiation obstacle  46 . The injection of the flow of air  78  via plenum  72  and openings  74 , is distributed substantially equally along an entire surface of the detonation chamber  41  with the cooling fluid flow  49  being injected simultaneously along the chamber  41 . The distributed airflow  78  injection via openings  74  provides a faster fill of the chamber  41  so as to reduce fill time and enable higher frequency operation of the pulse detonation combustor  70 . 
     Referring now to  FIG. 7 , illustrated is an alternate embodiment of an improved pulse detonation combustor, generally depicted  80 . In contrast to the previously disclosed pulse detonation combustors in which the cooling fluid flow  49  included fuel or a fuel/air mixture, in this exemplary embodiment only air is injected though a plurality of integrated initiated obstacles  46  and injectors  82 . It should be noted that, illustrated are a plurality of injectors  82  each configured in fluidic communication and integral a single initiation obstacles  46 . Alternately, the injection of the air may be accomplished by fewer or greater numbers of injectors, such as configurations similar to the described embodiments illustrated in  FIGS. 3 and 4 . 
     The plurality of injectors  82  are configured to inject air into the detonation chamber  41  at a trailing edge  48  of each initiation obstacle  46 . In this exemplary embodiment, the air may be pulsed or steady and operates to cool the initiation obstacles  46 . Fuel injection into the detonation chamber  41  would occur separate from injectors  82 . 
     In each of the embodiments illustrated in  FIGS. 3-7 , the plurality of initiation obstacles  46  may be arranged as depicted and disposed in any number of rows and columns. More specifically, the columns may be spaced axially along the improved detonation chamber  41 , and the rows may be spaced circumferentially along the improved detonation chamber  41 . Additionally, the number of rows and columns and the spacing between each may be varied to achieve detonations or quasi-detonations in varying fuel-air systems. In other exemplary embodiments, the plurality of integrated initiation obstacles  46  and injectors may be disposed in a number of rows and columns and having staggered or inline arrangement along the axial direction. In further exemplary embodiments, the plurality of integrated initiation obstacles  46  and injectors may have varying density on the interior surface  32  of the detonation chamber  41 . In the exemplary embodiments illustrated in  FIGS. 3-7 , the plurality of integrated initiation obstacles  46  and injectors are disposed in one or more circumferential arrays  90  ( FIG. 3 ), each including the plurality of integrated initiation obstacles  46  and injectors wherein each circumferential array  90  is axially spaced as indicated at “A”, relative to another circumferential array  90 , along at least a portion of the inner surface  32  of the detonation chamber  41  from the inlet  42  to the outlet  44 . The plurality of integrated initiation obstacles  46  and injectors may have various possible configurations within the detonation chamber  41 , further including odd as well as even numbers thereof; unequal as well as equal circumferential spacing; and unequal as well as equal size, geometry, and position of the initiation obstacles  46  around the inner surface  32  of the detonation chamber  41  as desired to enhance deflagration-to-detonation transition (DDT), minimize aerodynamic performance losses and provide an integrated cooling system to the initiation obstacles  46 . 
     Referring still to  FIGS. 3-7 , the plurality of the plurality of integrated initiation obstacles  46  and injectors may be disposed in a wide variety of arrangements on the inner surface  32  of the detonation chamber  41 , between the inlet  42  and the outlet  44 . In the exemplary embodiments, the initiation obstacles  46  are arranged in corresponding rows in the detonation chamber  41  in single planes along a length of the detonation chamber  41 . 
     The improved detonation chamber  41  may be constructed in a variety of ways including, but not limited to, casting, welding or molding initiation obstacles  46  to form the structures protruding from the surface  32  of the detonation chamber  41  and having integrated therewith the injectors. The plurality of initiation obstacles  46  may be formed as commonly used DDT geometries such as spirals, regularly spaced blockage plates, or as shaped walls. These various configurations are shown in the FIGs. as an expedient of presentation only, and actual use and design of the various initiation obstacles  46  will depend on actual combustor design and aerodynamic cycles. 
     Accordingly, by the introduction of relatively simple and small initiation obstacles on an interior surface of the detonation chamber between the inlet and the outlet and having integrated therewith at least one injector for the injection of cooling fluid flow, such as a fuel, a combination of fuels, a fuel/air mixture, or air, provides: (i) significant enhancement in the turbulence of the fluid flow within the detonation chamber; (ii) enhancement of the deflagration-to-detonation transition; (iii) cooling of the initiation obstacles; (iv) minimization of pressure drops during the fill process; and (v) creates viable locations for fuel injection into the detonation chamber. The integrated initiation obstacles and injectors may have various configurations represented by various permutations of the various features described above as examples. 
     While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.