Abstract:
A method for operating a pulse detonation system. The method includes providing a pulse detonation chamber including a plurality of detonation tubes extending therein, and detonating a mixture of fuel and air within each detonation tube such that at least a first tube is detonated at a different time than at least a second detonation tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/929,910, filed Aug. 30, 2004, now U.S. Pat. No. 7,007,455 which claims priority to U.S. Pat. No. 6,813,878, issued Nov. 9, 2004, both of which are hereby incorporated by reference and are assigned to assignee of the present invention. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines and more particularly, to a pulse detonation system for a gas turbine engine. 
   At least some known pulse detonation systems use a series of repetitive detonations within a detonation chamber to produce a high pressure exhaust. More specifically, a fuel and air mixture is periodically detonated within a plurality of tubes within the detonation chamber to create hot combustion gases which cause pressure waves to propagate at supersonic speeds within the tubes and chamber. The pressure waves compress the hot combustion gases, which increases a pressure, density, and a temperature of the gases to produce thrust as the pressure waves pass the exit of an open end of the detonation chamber. 
   Gas turbine engines producing thrust using pulse detonation systems typically have a higher thrust to weight ratio because they are generally smaller and weigh less than conventional gas turbine engines. In addition, pulse detonation engines may include fewer rotating parts, produce lower emissions, and be more fuel efficient than conventional gas turbine engines. Pulse detonation engines also may not suffer stall and startup problems that may be experienced by some known gas turbine engines because of separation in and around compressor blades within the conventional engines. 
   However, pressures generated within the detonation chamber of some known pulse detonation systems may cause at least some known pulse detonation engines to be very loud and may facilitate structural failures within the engines. More specifically, each detonation tube has a firing frequency that is dependent upon the dynamics of detonation and a geometry of the tube. While conventional detonation chambers create thrust by imparting overall pressure rise the hot combustion gases, known pulse detonation tubes also have a dynamically varying positive pressure rise and fall in each tube as each tube repeatedly fires. The dynamic periodicity of such pressures may induce dynamic pressure loads to the pulse detonation system which may propagate from the system as acoustic pressure waves, i.e., noise. 
   BRIEF SUMMARY OF THE INVENTION 
   In one aspect, a method is provided for operating a pulse detonation system. The method includes providing a pulse detonation chamber including a plurality of detonation tubes extending therein, and detonating a mixture of fuel and air within each detonation tube such that at least a first tube is detonated at a different time than at least a second detonation tube. 
   In another aspect, a control system is provided for a pulse detonation system including a plurality of detonation tubes. The control system includes a processor that is programmed to control detonation of a mixture of fuel and air within each detonation tube, such that at least a first detonation tube is detonated at a time that is different from a time of detonation of at least a second detonation tube. 
   In yet another aspect, a pulse detonator is provided for a pulse detonation system. The chamber includes an inner casing, and an outer casing that is substantially coaxial with the inner casing, and is spaced radially outwardly from the inner casing. The inner and outer casings define a detonation chamber therebetween. A plurality of detonation tubes extend at least partially within the detonation chamber. At least a portion of at least a first detonation tube is stacked radially outwardly from at least a portion of at least an adjacent second detonation tube, such that a first central axis of the first detonation tube is spaced radially outwardly from a second central axis of the adjacent second detonation tube. 
   In even another aspect, a pulse detonation system is provided that includes a pulse detonator including a plurality of detonation tubes extending at least partially within the pulse detonator, and a control system that includes a processor programmed to control the detonation of a mixture of fuel and air within each detonation tube such that at least a first detonation tube is detonated at a time that is different from a time of detonation of at least a second detonation tube. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an exemplary gas turbine engine; 
       FIG. 2  is a schematic illustration of an exemplary pulse detonation system for use with the gas turbine engine shown in  FIG. 1 ; and 
       FIG. 3  is a cross-sectional view of a portion of a detonator shown in  FIG. 2  and taken alone line  3 — 3 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The term computer, as used herein, means any microprocessor-based system including systems using microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. 
     FIG. 1  is a schematic illustration of a gas turbine engine  10  including a low pressure compressor  12 , a high pressure compressor  14 , and a pulse detonation system  16 . Engine  10  also includes a high pressure turbine  18 , and a low pressure turbine  20 . Compressor  12  and turbine  20  are coupled by a first shaft  24 , and compressor  14  and turbine  18  are coupled by a second shaft  26 . In one embodiment, engine  10  is a F110/129 engine available from General Electric Aircraft Engines, Cincinnati, Ohio. 
   In operation, air flows through low pressure compressor  12  from an inlet side  28  of engine  10  and compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . Compressed air is then delivered to pulse detonation system  16  where it is mixed with fuel and ignited. The combustion gases are channeled from pulse detonation system  16  to drive turbines  18  and  20  and provide thrust from an outlet  30  of engine  10 . 
     FIG. 2  is a schematic illustration of an exemplary pulse detonation system  50  for use with a gas turbine engine, for example engine  10  (shown in  FIG. 1 ).  FIG. 3  is a cross-sectional view of a portion of a pulse detonator  52  for pulse detonation system  50  taken along line  3 — 3 . Pulse detonation system  50  includes a pulse detonator  52  and a control system  53 . Pulse detonator  52  includes annular outer and inner casings  54  and  56 , respectively, and a plurality of detonation tubes  58 . Outer and inner casings  54  and  56  are disposed substantially coaxially about a longitudinal centerline axis  60  of pulse detonation system  50  and are spaced radially apart such that a detonation chamber  62  is defined therebetween. Pulse detonator  52  includes an inlet end  64 , an outlet end  66 , and detonation tubes  58 . Detonation tubes  58  extend through detonation chamber  62  along axis  60 , and also extend a length  68  measured from an upstream end  70  that is adjacent chamber inlet side  64 , to a downstream end  72 . An exhaust chamber  73  is defined between detonation tube downstream ends  72  and detonator outlet end  66 . Exhaust chamber  73  includes an upstream end  74  and a downstream end  75 . 
   Detonation tubes  58  are stacked in an array  76  within detonation chamber  62  such that a plurality of tubes  58  are spaced circumferentially around axis  60 , and such that a plurality of tubes  58 , or a portion of a plurality of tubes  58 , are stacked radially outwardly from inner casing  56  to outer casing  54 . In an alternative embodiment, detonation tubes  58  are stacked within detonation chamber  62  such that a plurality of tubes  58  are spaced circumferentially around axis  60  and such that only one tube  58  is positioned radially between inner casing  56  and outer casing  54 . 
   In the exemplary embodiment, detonation tubes  58  each have a substantially circular cross-sectional geometric shape, and tubes  58  substantially occupy the space defined between inner and outer casings  56  and  54 , respectively. Furthermore, as illustrated in  FIG. 3 , tubes  58  are arranged in stacks  78  which include smaller diameter tubes  58 , and stacks  80  which include larger diameter tubes  58 . More specifically, in the exemplary embodiment, a central axis  81  of a first tube  58  is spaced radially outwardly from a central axis  83  of a second tube  58  that is adjacent the first tube  58 . However, it will be understood that the number, geometric shape, configuration, and/or diameter of tubes  58  will vary depending upon the particular application, and as described below. For example, in one embodiment, detonation tubes  58  each have approximately equal diameters. In another embodiment, detonation tubes  58  include tubes of varying diameter. Furthermore, it will be understood that a length  68  of each tube  58  will vary depending upon the particular application, and as described below. For example, in one embodiment, detonation tubes  58  each include approximately equal lengths  68 . In another embodiment, detonation tubes  58  include tubes of varying length  68 . The examples herein described are intended as exemplary only, and are not intended to limit the number, geometric shape, configuration, diameter, and/or length  68  of detonation tubes  58 . 
   Control system  53  includes a computer and/or processor  82 , a plurality of pressure feedback sensors  84 , and a firing system  86  that is coupled to detonation tubes  58  adjacent upstream ends  70 . As described below, firing system  86  charges each tube  58  with compressed air and fuel, and periodically detonates the mixture of fuel and air within each tube  58  to produce hot combustion gases within each tube  58  and exhaust chamber  73 . Sensors  84  are coupled to outer casing  54  adjacent exhaust chamber  73 , and measure a pressure of combustion gases within exhaust chamber  73 . Computer  82  is electrically coupled to sensors  84  and firing system  86 . In one embodiment, computer  82  is a multiple-input, multiple-output, (MIMO) electronic control computer. In an alternative embodiment, control system  52  includes only one pressure feedback sensor  84 . 
   Firing system  86  charges each detonation tube  58  with fuel, from a fuel source (not shown), and compressed air from compressors  12  and  14  (shown in  FIG. 1 ). The mixture is detonated to produce hot combustion gases within each tube  58  that flow downstream through exhaust chamber  73  and are discharged from detonation chamber outlet end  66  towards turbines  18  and  20  (shown in  FIG. 1 ) and engine outlet  30  (shown in  FIG. 1 ). In one embodiment, compressed air and fuel are mixed by firing system  86  before the mixture is supplied to each detonation tube  58 . In an alternative embodiment, compressed air and fuel are each independently supplied to each detonation tube  58  and are mixed within each detonation tube  58 . 
   Firing system  86  does not continuously detonate the mixture within tubes  58 . Rather, and as described below, firing system  86  periodically cycles the detonation of the fuel/air mixture to generate pressure waves, or pulses, that propagate through the combustion gases to facilitate increasing the pressure and temperature of the combustion gases to provide thrust. The pressure waves propagate downstream through tubes  58  and exhaust chamber  73 . 
   The methods and systems described herein facilitate containing larger dynamic pressure variations within tubes  58  and exhaust chamber upstream end  74 , such that dynamic pressure variations are reduced within exhaust chamber downstream end  75  as combustion gases exit engine exhaust  30 . More specifically, firing system  86  detonates the fuel air mixture in each tube  58 , referred to herein as filing each tube  58 , sequentially such that only a desired number of tubes  58  are fired simultaneously. In one embodiment, each tube  58  is fired independently at a different time. In an alternative embodiment, a plurality of tubes  58  are fired simultaneously, and a plurality of tubes  58  are fired non-simultaneously. 
   As each individual tube  58  fires, a positive-going pressure pulse is emitted that propagates downstream through exhaust chamber  73  from upstream end  74  to downstream end  75 . Sensors  84  sense the pressure pulses from various tubes  58  within exhaust chamber  73 . Computer  82 , using an active noise-control algorithm, determines an appropriate firing sequence for tubes  58 , based on the sensed pressure pulses, such that dynamic pressure variations are reduced within exhaust chamber  73 , while a high and steady pressure of combustion gases is exhausted through detonator outlet end  66  and ultimately, engine exhaust  30 . More specifically, computer  82  controls firing of each tube  58  within array  76  such that low, positive pressure regions of pressure pulses are substantially aligned with high, positive pressure regions of adjacent pulses. Aligning adjacent pulses in such a manner facilitates reducing pressure variations. Specifically, as pressure pulses propagate through exhaust chamber  73 , higher amplitude dynamic pressure variations are substantially smoothed out, causing the exhaust of combustion gases exiting exhaust chamber  73  and engine exhaust  30  to be at a substantially uniform and high pressure. Accordingly, high amplitude dynamic pressure variations are substantially contained within tubes  58  and exhaust chamber upstream end  74 , such that a reduction in dynamic pressure loads is induced within system  50 , and the number and intensity of acoustic pressure waves emitted by system  50  are facilitated to be reduced. As a result, structural failures associated with system  50  and a level of noise emitted by system  50  are facilitated to be reduced. 
   In one embodiment, each tube  58  within array  76  is fired such that high positive pressure regions of pressure pulses align with high positive regions of adjacent pressure pulses to facilitate increasing the positive pressure of the pressure pulses, and thereby increasing the pressure of the hot combustion gases exhaust from exhaust chamber  73 . 
   An exhaust chamber length  88 , measured between the downstream end  72  of the longest tube  58  within array  76  and detonator outlet end  66 , is variably selected to facilitate reducing dynamic pressures to a pre-determined level. More specifically, the geometry and configuration of detonation tubes  58  is also variably selected. For, example, in one embodiment, a greater number of smaller diameter tubes  58  may facilitate a shorter exhaust chamber length  88 , than a smaller number of larger diameter tubes  58 . 
   The above-described pulse detonation system facilitates reducing structural failures of the system and noise produced by the system. More specifically, by aligning low positive pressure regions with high positive pressure regions of adjacent pulses, the system facilitates reducing dynamic pressure loads within the system and facilitates reducing the number and intensity of acoustic pressure waves emitted by the system. In addition, the above-described pulse detonation system may facilitate increasing the thrust of a pulse detonation engine by aligning high positive pressure regions with high positive regions of adjacent pressure pulses. As a result, a pulse detonation system is provided which may facilitate an engine that has a longer engine life, and operates with increased thrust, increased efficiency, and reduced noise. 
   Exemplary embodiments of pulse detonation systems are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each pulse detonation system component can also be used in combination with other pulse detonation system components. 
   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.