Abstract:
According to one aspect of the invention, a pulse detonation combustor chamber is provided having an ignition chamber and a detonation chamber. The cross-sectional area of the ignition chamber is greater than the cross-sectional area of the detonation chamber. A flame is generated in the ignition chamber upon ignition of a flammable mixture. The flame flows into the detonation chamber and detonates within the detonation chamber.

Description:
BACKGROUND 
       [0001]    In pulse detonation combustors, a mixture of fuel and oxidizer, such as air, is ignited and is transitioned from deflagration to detonation, so as to produce detonation waves, which can be used to provide thrust, among other functions. This deflagration to detonation transition (DDT) typically occurs in a tube or pipe structure, having an open end through which the exhaust exits. 
         [0002]    The deflagration to detonation process begins when a fuel-oxidizer mixture in a tube is ignited via a spark or other source. The subsonic flame generated from the spark accelerates as it travels along the length of the tube due to various flow mechanics. As the flame reaches sonic velocity, shocks are formed which reflect and focus creating “hot spots” and localized explosions, eventually transitioning the flame to a supersonic detonation wave. 
         [0003]    As indicated previously, the above-described process takes place along the length of a tube, and is often referred to as the run-up to detonation, i.e. the distance/time from spark to detonation. 
         [0004]    However, a problem with existing smooth walled tube structures is the relatively long run-up length necessary to achieve detonation of the fuel-air mixture. In fact, in many applications the run-up length, up to detonation, can be such that the ratio L/D (i.e. tube length over tube diameter) is greater than 100. This run-up length is problematic when trying to incorporate the pulse detonation combustor in applications where space and weight are important factors, such as aircraft engines. Efforts have been made to reduce the run-up length to detonation by using obstacles within the flow, in an effort to enhance mixing of the fuel-oxidizer mixture, and typical run-up lengths with obstacles is around L/D of 30. However, there still exists a need to reduce the run-up length and accelerate the development of the flame kernel around the spark or ignition source. 
         [0005]    For these and other reasons, there is a need for the present invention. 
       SUMMARY 
       [0006]    According to one aspect of the invention, a pulse detonation combustor chamber is provided having an ignition chamber and a detonation chamber. The cross-sectional area of the ignition chamber is greater than the cross-sectional area of the detonation chamber. A flame is generated in the ignition chamber upon ignition of a flammable mixture. The flame propagates into the detonation chamber and detonates within the detonation chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The nature and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments of the invention which are schematically set forth in the figures. Like reference numerals represent corresponding parts. 
           [0008]      FIG. 1  illustrates a cross-sectional view of a pulse detonation combustor according to an exemplary embodiment of the present invention; 
           [0009]      FIG. 2  illustrates a cross-sectional view of a pulse detonation combustor according to another exemplary embodiment of the present invention; 
           [0010]      FIG. 3  illustrates a cross-sectional view of a pulse detonation combustor according to yet another exemplary embodiment of the present invention; 
           [0011]      FIG. 4  illustrates a cross-sectional view of a pulse detonation combustor according to a further exemplary embodiment of the present invention; 
           [0012]      FIG. 5  illustrates a pulse detonation combustor according to an alternative exemplary embodiment of the present invention; 
           [0013]      FIG. 6  illustrates a pulse detonation combustor according to another exemplary embodiment of the present invention; and 
           [0014]      FIG. 7  illustrates a pulse detonation combustor according to a further alternative exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    As used herein, a “pulse detonation combustor” PDC is understood to mean any device or system that produces both a pressure rise and velocity increase from a series of repeated detonations or quasi-detonations within the device. A “quasi-detonation” is a supersonic turbulent combustion process that produces a pressure rise and velocity increase higher than the pressure rise and velocity increase produced by a deflagration wave. Embodiments of PDCs include a means of igniting a fuel/oxidizer mixture, for example a fuel/air mixture, and a detonation chamber, in which pressure wave fronts initiated by the ignition process coalesce to produce a detonation and quasi-detonation. Each detonation or quasi-detonation is initiated either by external ignition, such as spark discharge or laser pulse, or by gas dynamic processes, such as shock focusing, auto ignition or by another detonation (i.e. cross-fire). Pulse detonation may be accomplished in a number of types of detonation chambers including detonation tubes, shock tubes, resonating detonation cavities, for example. In addition, a PDC can include one or more detonation chambers. 
         [0016]    Pulse detonation combustors are used for example in aircraft engines, missiles, and rockets. As used herein, “engine” means any device used to generate thrust and/or power. As used herein, “detonation” includes both detonations and quasi-detonations. 
         [0017]    Embodiments of the present invention will be explained in further detail by making reference to the accompanying drawings, which do not limit the scope of the invention in any way. 
         [0018]      FIGS. 1 through 7  depict cross-sectional side views of a pulse detonation combustor chamber for a pulse detonation combustor according to various exemplary embodiments of the present invention. The pulse detonation combustor chamber  100  includes an ignition chamber  10  and a detonation chamber  12 . The ignition chamber  10  and the detonation chamber  12  can be discrete chambers or formed as a contiguous chamber. In  FIGS. 1-3 , an oxidizer, e.g., air, is supplied to the ignition chamber  10  via inlet  14 , while in  FIGS. 4-7  the oxidizer is supplied via inlet passage  24 . A fuel injector  16  is provided to supply fuel into the ignition chamber  10 . The fuel injector can be arranged in various locations of the ignition chamber such as co-axial to the flow, perpendicular to the flow, at a tangential angle to the flow (to induce swirl), or at an angle in conjunction with a suitably shaped wall to help promote mixing. Any known mechanism for fuel injection can be used such as air-blast atomization, pressure-atomization, etc. The fuel and oxidizer mixture in the ignition chamber  10  is ignited by an ignition source  18 , such as a spark plug, for example. Any suitable ignition source can be used. The location of the ignition source  18  can be arranged based upon the optimum ignition location for fuel-oxidizer mixing. In the exemplary embodiment, the ignition source  18  is placed downstream of the fuel injection. This arrangement allows time for the fuel to mix with the oxidizer and evaporate a bit. Overall, the ignition source  18  can be placed between the point of fuel injection and the beginning of any obstacles that may be arranged in the detonation chamber. Although a single ignition source  18  is shown in the exemplary embodiments, multiple ignition sources could also be used. 
         [0019]    In the embodiments shown, the detonation chamber  12  includes an obstacle field or center body  20  to promote turbulence within the detonation chamber  12 . The center body  20  is often referred to as deflagration to detonation transition (DDT) geometry. DDT geometry enhances the deflagration to detonation transition process by increasing turbulence in the detonation chamber  12 . There are a variety of DDT geometries. The overall length and diameter of the center body  20  is determined based on operational parameters and characteristics to optimize performance. It is to be noted that the invention is not limited to the use of the center body  20  or DDT geometry. 
         [0020]    In each of the exemplary embodiments shown in  FIGS. 1-7 , the ignition chamber  10  is larger than the detonation chamber  12 . More specifically, the cross-sectional area of the ignition chamber  10  is larger than the cross-sectional area of the detonation chamber  12 . For example, the volume of the detonation chamber  12  can be two times that of the ignition chamber  10 . The ratio can be set to optimize the performance based upon the application. The cross-sectional area of the ignition chamber  10  with respect to that of the detonation chamber  12  can be selected to control the flow resistance and/or the temperature/pressure profile exiting the ignition chamber  10 . 
         [0021]    The enlarged ignition chamber  10  slows the oxidizer flow to promote fuel-oxidizer mixing, flame kernel growth and serves to prevent liquid fuel from wetting the walls of the ignition chamber  10 . More particularly, by injecting fuel and oxidizer in the enlarged ignition chamber  10 , the mixture velocity is slow at the point of ignition. This allows the flame kernel plenty of time to grow, even in relatively high bulk velocities. The mixture velocity then increases as the mixture transitions to the smaller detonation chamber  12 . This transition increases turbulent mixing and promotes DDT. Cross-sectional area variations in the ignition chamber  10  and the detonation chamber  12  allow for control of the bulk flow velocity. This enhances liquid fuel injection, fuel-air mixing, initial flame kernel growth, DDT turbulence, and minimizes loads on the upstream components in the assembly. 
         [0022]    The enlarged ignition chamber  10  allows for larger fuel spray without wetting the walls of the chamber. In addition, the enlarged ignition chamber  10  increases the residence time of the fuel-air mixture in the ignition chamber  10 , which results in greater evaporation of the fuel and enables stable flame kernel growth. The enlarged ignition chamber  10  also reduces pressure drop and aerodynamic flow losses. 
         [0023]    By transitioning from a large ignition chamber  10  to a smaller detonation chamber  14 , the run-up distance and time are reduced and the overall pulse detonation combustor chamber length is reduced. This allows for the possibility of more practical applications of pulse detonation combustors, such as use in hybrid turbine engines. Other arrangements require a combustor length to diameter ratio (L/D) up to as much as 30 to transition to detonation, while the embodiments disclosed herein require L/D ratios of 20 or less, for example. 
         [0024]    Reduced run-up length results in reduced run-up time. Reduced run-up time enables the combustor to operate at higher frequencies. Higher frequency will generate more pressure rise and increase the usable output of the PDE device. 
         [0025]    Turning now to  FIG. 1 , an exemplary embodiment of the present invention is shown. In this embodiment, the ignition chamber  10  steps-down to the smaller detonation chamber  12 . Fuel is injected co-axially from fuel injector  16 . The co-axial injection of fuel reduces wall wetting and allows for a wider spray angle of fuel. Oxidizer is supplied to the ignition chamber  10  downstream of the fuel injection via opposing inlets  14 . The detonation chamber  12  includes DDT geometry such as Schelkin spiral geometry, for example. Any suitable DDT geometry can be used to increase turbulence. Alternatively, the detonation chamber  12  can be arranged without DDT geometry. In addition, the fuel-oxidizer ratio can be supplied so that there is a slightly fuel-rich mixture in the ignition chamber  10  to improve the DDT process. This can be accomplished by controlling the flow of fuel and oxidizer into the ignition chamber  10 . 
         [0026]    The ignition source  18  in this embodiment is arranged downstream from the fuel and oxidizer inlets. As previously discussed, although a single ignition source is shown, the combustor can include multiple ignition sources including ignition sources in the detonation chamber  12 . Referring to  FIG. 2 , the pulse detonation combustor chamber  100  includes the elements shown in  FIG. 1 , with the further inclusion of a flow mixing element  22 . The flow mixing element  22  is arranged near the air inlet  14  to create a uniformly mixed flow of oxidizer and fuel into the ignition chamber  10 . The flow mixing element  22  can be a perforated plate or a geometry to induce swirl or other turbulence for example. Any suitable flow mixing element can be used to promote the uniform flow of air into the ignition chamber  10 . 
         [0027]      FIG. 3  illustrates another exemplary embodiment of the pulse detonation combustor chamber  100 . In this embodiment, the combustor chamber includes all of the elements shown in  FIG. 1 , except that the enlarged ignition chamber  10  tapers to converge with the smaller detonation chamber  12 . The taper results in lower pressure drop through the transition from large diameter to small diameter. In addition, the taper can result in a smoother flow for mixing. 
         [0028]    Referring to  FIG. 4 , another exemplary embodiment of the present invention is shown. In this embodiment, the inlets  14  of the pulse detonation combustor chamber  100  are replaced with an inlet passage  24 . The inlet passage  24  receives oxidizer from an oxidizer source through a valve  26  and supplies it to the ignition chamber  10 . The cross-sectional area of the inlet passage  24  is smaller than that of the ignition chamber  10 . The smaller cross-sectional area of the inlet passage  24  relative to the ignition chamber  10  minimizes valve inertial loads and pressure forces. However, the invention is not limited to this arrangement, and the cross-sectional area of the inlet passage can be selected based upon the application. In this embodiment, fuel is supplied from the fuel injector  16 , which is arranged perpendicular to the inlet passage  24  and to the ignition chamber  10 . The fuel injector  16  can also be arranged in the transition corner where the inlet passage  24  meets the ignition chamber  10 . 
         [0029]      FIG. 5  shows another exemplary embodiment of the pulse detonation combustor chamber  100  where the ignition chamber  10  tapers to converge with the detonation chamber  12 . The taper reduces pressure drop or aerodynamic losses. In  FIG. 6 , both transition corners are tapered. More specifically, the inlet passage  24  tapers to diverge with the ignition chamber  10  while the ignition chamber tapers to converge with the detonation chamber  12 . The arrangement of the ignition source  18  and fuel injector  16  are similar to those in  FIGS. 4-5 . Each of the embodiments shown in  FIGS. 3-6  could also include a flow mixing element to promote uniform flow into the ignition chamber  10 . 
         [0030]    Referring to  FIG. 7 , the pulse detonation combustor chamber according to this exemplary embodiment includes multiple ignition sources  18 , including one arranged within the detonation chamber  12 . As previously noted, any number and location of ignition sources may be used to achieve optimal performance. 
         [0031]    The pulse detonation combustor chamber according to the exemplary embodiments disclosed herein is configured to reduce the run-up length, and consequently, run-up time. This is achieved by including an enlarged ignition chamber with respect to the detonation chamber. This arrangement allows for the reduced length of the pulse detonation combustor chamber, and consequently, reduced length of the pulse detonation combustor. More specifically, the enlarged ignition chamber provides for slow mixture velocity at the time of ignition, which promotes stable flame kernel growth. The mixture velocity then increases as the mixture transitions to the smaller detonation chamber. This transition increases turbulent mixing and promotes DDT. Cross-sectional area variations in the ignition chamber and the detonation chamber allow for control of the bulk flow velocity. This enhances liquid fuel injection, fuel-air mixing, initial flame kernel growth, DDT turbulence, which results in reduced run-up time. 
         [0032]    The reduced length of the combustor chamber provides for more practical applications of combustors including these combustor chambers in turbine engines, for example. In addition, the reduced run-up length enables operation at higher frequencies to increase the pressure rise resulting in more output to the device and provides a higher efficiency gain when replacing a constant pressure combustor with a PDC. 
         [0033]    It is noted that the above embodiments have been shown with respect to a single pulse detonation combustor chamber. However, the concept of the present invention is not limited to single pulse detonation combustor chamber embodiments. 
         [0034]    It is noted that although embodiments of the present invention have been discussed above specifically with respect to aircraft and power generation turbine engine applications, the present invention is not limited to this and can be in any similar detonation/deflagration device in which the benefits of the present invention are desirable. 
         [0035]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.