Patent Publication Number: US-6666018-B2

Title: Combined cycle pulse detonation turbine engine

Description:
This is a continuation in part of application Ser. No. 10/074,072, filed Feb. 12, 2002 now U.S. Pat. No. 6,550,235, which is a divisional application of U.S. Pat. No. 6,442,930 corresponding to Ser. No. 09/540,566 and filed on Mar. 31, 2000, which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to gas turbine engines, and more particularly, to a pulse detonation system for a turbofan engine. 
     Variable cycle turbofan ramjet engines may be used to provide aircraft flight speeds between low subsonic Mach numbers to high supersonic Mach numbers of about Mach 6. Known engines, as described in U.S. Pat. No. 5,694,768, include a core engine system and a dual mode augmentor. The dual mode augmentor provides additional heat to exhaust airflow exiting the core engine system to increase engine thrust. The core engine system provides power to drive a fan assembly and typically includes in serial, axial flow relationship, a compressor, a combustor, a high pressure turbine, and a low pressure turbine. The dual mode augmentor is positioned downstream from the core engine and receives air from the core engine and a bypass duct surrounding the core engine. 
     Known engines can operate over a wide range of flight speed operations if several different combustion systems are utilized. During flight speed operations from takeoff to approximately Mach 3, the core engine and an engine fan system provide airflow at a pressure and quantity used by the augmentor to produce thrust for the engine. To maintain flight speed operations between Mach 3 and Mach 6, the core engine system is shut-down and ram air flow is introduced into the dual mode augmentor either by windmilling the fan system or by utilizing an auxiliary ram duct. To sustain flight speed operations above Mach 6, either a separate supersonic combustion system, i.e., a scramjet, is used, or a separate rocket-based thrust producing system is used. To achieve flight speed operations in space, the rocket-based thrust producing system is used. As a result, for an engine to operate efficiently over a wide range of operating flight speeds, several different combustion systems are used. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment, a pulse detonation system for a turbofan engine is disclosed. The turbofan engine includes a fan assembly and a turbine sub-system. The turbine sub-system includes at least one turbine. The pulse detonation system is configured to create a temperature rise and a pressure rise within the turbofan engine and to generate thrust for the turbofan engine. The pulse detonation system includes a pulse detonation core replacement assembly comprising at least one detonation chamber configured to detonate a fuel mixture. The pulse detonation core replacement assembly is positioned between the fan assembly and the turbine sub-system. 
     A turbofan engine embodiment is also disclosed. The turbofan engine includes a fan assembly, at least one turbine downstream from the fan assembly, an inlet portion upstream from the fan assembly, an exhaust portion positioned co-axially with the inlet portion, and a pulse detonation system positioned between the fan assembly and the turbine. The pulse detonation system is configured to create a temperature rise and a pressure rise to generate engine thrust for the turbofan engine. The pulse detonation system includes a pulse detonation core assembly comprising at least one detonation chamber configured to detonate a fuel mixture. The pulse detonation core assembly is positioned between the fan assembly and the turbine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view of a turbofan engine including a pulse detonation system; 
     FIG. 2 is a cross-sectional view of a pulse detonation augmentor used with the pulse detonation system shown in FIG. 1 taken along lines  2 — 2 ; 
     FIG. 3 is a cross-sectional side view of an alternative embodiment of a turbofan engine in a low flight speed mode of operation; 
     FIG. 4 is a cross-sectional view of another embodiment of a turbofan engine including a pulse detonation core replacement augmentor assembly used to replace a core engine shown in FIG. 1; 
     FIG. 5 is a cross-sectional view of the turbofan engine shown in FIG. 4 in a ram duct mode of operation; and 
     FIG. 6 is a cross-sectional view of the turbofan engine shown in FIG. 4 in a rocket mode of operation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a cross-sectional side view of a turbofan engine  10  including a pulse detonation system  12 . FIG. 2 is a cross sectional view of a pulse detonation augmentor  13  taken along lines  2 — 2  shown in FIG.  1 . In one embodiment, turbofan engine  10  is an F110/129 engine available from General Electric Aircraft Engines, Cincinnati, Ohio. Engine  10  has a generally longitudinally extending axis or centerline  14  extending in a forward direction  16  and an aft direction  18 . Engine  10  includes a core engine  30  which includes a high pressure compressor  34 , a combustor  36 , a high pressure turbine  38 , and a power turbine or a low pressure turbine  39  all arranged in a serial, axial flow relationship. In alternative embodiments, engine  10  includes a core fan assembly (not shown). 
     Pulse detonation system  12  is disposed downstream from both core engine  30  and receives core engine combustion gases from core engine  30 . Pulse detonation system  12  creates a temperature rise and a pressure rise within engine  10  without the use of turbomachinery included within core engine  30  to generate thrust from engine  10 . Pulse detonation system  12  includes pulse detonation augmentor  13  which includes an inlet side  70 , an outlet side  72 , and a shock tube sub-system  74 . Inlet side  70  is upstream from outlet side  72  and circumferentially surrounds an engine centerbody  76 . 
     Shock tube sub-system  74  includes a plurality of shock tubes  78  extending between pulse detonation augmentor inlet side  70  and pulse detonation augmentor outlet side  72 . Shock tubes  78  permit fuel and air entering pulse detonation system  12  to mix and detonate. Each shock tube  78  has a circular cross-sectional profile and shock tube subsystem  74  has a circular cross-sectional profile. In one embodiment, shock tube sub-system has a non-circular cross-sectional profile. As known to those skilled in the art, pulse detonation may be accomplished in a number of types of detonation chambers, including detonation tubes, resonating detonation cavities and annular detonation chambers. As used herein, the terms “shock tube” and detonation chamber are used interchangeably. Shock tubes  78  extend from core engine  30  to a converging-diverging exhaust nozzle  84 . Exhaust nozzle  84  is disposed downstream from pulse detonation system  12  and shock tubes  78 . 
     During operation, airflow enters engine  10  and fuel is introduced to core engine  30 . The air and fuel are mixed and ignited within core engine  30  to generate hot combustion gases. Specifically, pressurized air from high pressure compressor  34  is mixed with fuel in combustor  36  and ignited, thereby generating combustion gases. Such combustion gases drive high pressure turbine  38  which drives high pressure compressor  34 . The combustion gases are discharged from high pressure turbine  38  into low pressure turbine  39 . The core airflow is discharged from low pressure turbine  39 . 
     The combined airflow is channeled into pulse detonation system  12  and mixed with additional fuel introduced to engine  10 . Pulse detonation system  12  detonates the mixture to create a temperature rise and a pressure rise within engine  10 , thus generating thrust from engine  10 . In one embodiment, system  12  is controlled with a very high speed valving system capable of operating at between 500 and 1000 cycles per second or higher and a spark or plasma ignition system. In another embodiment, system  12  is controlled with a continuous detonation valveless system that incorporates a pre-burning device. In yet another embodiment, system  12  utilizes a variable geometry mixer/injector to control off-design tailoring of outlet gases within shock tube sub-system  74 . Alternatively, system  12  incorporates elements of the previous three embodiments for control. 
     As used herein, “detonating” refers both detonations and quasi-detonations. A “quasi-detonation” is a combustion process that produces a pressure rise and velocity increase higher than the pressure rise and velocity increase produced by a deflagration wave. In contrast, deflagrations result in a loss of pressure. The detonations or quasi-detonations are 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). 
     FIG. 3 is a cross-sectional side view of an alternative embodiment of a turbofan engine  100  including a pulse detonation system  102  in a low flight speed mode of operation. Engine  100  has a generally longitudinally extending axis or centerline  104  extending in a forward direction  106  and an aft direction  108 . Engine  100  includes a core engine  110  which includes a high pressure compressor  114 , a combustor  116 , a high pressure turbine  117 , and a power turbine or a low pressure turbine  118  all arranged in a serial, axial flow relationship. In an alternative embodiment, engine  100  also includes a core engine including a core fan assembly. 
     An auxiliary ram duct and valving system  150  is disposed radially outward from core engine  110  and extends from an inlet side  152  of engine  100  to pulse detonation system  102 . Auxiliary ram duct and valving system  150  includes an auxiliary ram duct  154  and a ram air valve  156 . Ram duct  154  includes an inlet  157  for receiving air. Inlet  157  is annular and is in flow communication with ram duct  154 . Ram air valve  156  is disposed within ram duct  154  and is selectable to control a flow of ram air through auxiliary ram duct and valving system  150 . During low flight speed modes of operation, ram air valve  156  is closed to prevent ram air from flowing through ram duct  154  into engine  100 . During moderate supersonic Mach number flight speed operations between Mach 3 and Mach 5, ram air valve  156  is open to permit ram air to flow through ram duct  154  into engine  100 . Ram air valve  156  is also positionable at intermediate positions to control an amount of airflow channeled into ram duct  154 . 
     Pulse detonation system  102  is disposed downstream from core engine  110  and auxiliary ram duct and valving system  150 . During operation, pulse detonation system  102  receives airflow from ram duct  154  and core engine combustion gases from core engine  110 . Pulse detonation system  102  creates a temperature rise and a pressure rise within engine  100  without the use of turbomachinery to generate thrust from engine  100 . Pulse detonation system  102  includes a pulse detonation augmentor  168 , which includes an inlet side  170 , an outlet side  172 , and a shock tube sub-system  174 . Inlet side  170  is upstream from outlet side  172  and circumferentially surrounds an engine centerbody  176 . Shock tube sub-system  174  includes a plurality of shock tubes (not shown) extending between pulse detonation augmentor inlet side  170  and pulse detonation augmentor outlet side  172 . Fuel and air are mixed and detonated within shock tube sub-system  174 , which extends from core engine  110  to an exhaust nozzle  180 . 
     During low flight speed operation, airflow enters engine  100  and fuel is introduced to core engine  110 . Specifically, pressurized air from high pressure compressor  114  is mixed with fuel in combustor  116  and ignited, thereby generating combustion gases. Such combustion gases drive high pressure turbine  117  which drives high pressure compressor  116 . The combustion gases are discharged from high pressure turbine  117  into low pressure turbine  118 . The core airflow is discharged from low pressure turbine  118 . The airflow is channeled into pulse detonation system  102  and mixed with additional fuel introduced to engine  100 . Pulse detonation system  102  creates a temperature rise and a pressure rise within engine  100  to generate thrust from engine  100 . 
     During moderate supersonic Mach number flight speed operations between Mach 3 and Mach 5, ram air valve  156  is placed in an open position to permit ram air to enter ram duct  154  and flow to pulse detonation system  102 . Fuel is introduced to pulse detonation system  102  and is mixed with ram air exiting ram duct  154 . The fuel/air mixture is ignited to produce combustion gases and thrust for engine  100 . 
     FIG. 4 is a cross-sectional view of another embodiment of a turbofan engine  200  including a pulse detonation system  202 . Engine  200  has a generally longitudinally extending axis or centerline  204  extending in a forward direction  206  and an aft direction  208 . Engine  200  includes a fan assembly  212 , which includes a forward fan  214  disposed in an inlet duct  216  of engine  200 . Fan  214  includes a plurality of blades  218  circumferentially spaced around engine centerline  204 . Inlet guide vanes  220  are disposed in inlet duct  216  upstream from forward fan  214  and extend between an engine hub  222  and an engine casing  224 . Engine  200  also includes a turbine sub-system  230  disposed in flow communication with forward fan  214 . Turbine sub-system  230  includes a turbine  232  disposed in flow communication with forward fan  214  and including a plurality of blades  234  extending radially outward from engine centerline  204 . 
     Pulse detonation system  202  creates a temperature rise and a pressure rise within engine  200  without the use of turbomachinery to generate thrust for engine  200 . Pulse detonation system  202  includes a pulse detonation augmentor  240  and a pulse detonation core replacement augmentor assembly  242 . Pulse detonation augmentor  240  includes an inlet side  250 , an outlet side  252 , and a shock tube sub-system  254 . Inlet side  250  is upstream from outlet side  252  and circumferentially surrounds an engine centerbody  256 . Shock tube subsystem  254  includes a plurality of shock tubes (not shown) extending between pulse detonation augmentor inlet side  250  and pulse detonation augmentor outlet side  252 . The shock tubes permit fuel and air entering pulse detonation system  202  to mix and detonate to provide thrust from engine  200 . 
     Pulse detonation core replacement augmentor assembly  242  (or pulse detonation core assembly  242 ) includes an inlet side  260 , an outlet side  262 , and a shock tube sub-system  264 . Inlet side  260  is upstream from outlet side  262  and circumferentially surrounds an engine centerbody  266 . Inlet side  266  includes an annular inlet  268 , which permits airflow to enter pulse detonation core replacement augmentor assembly  242 . Shock tube sub-system  264  includes a plurality of shock tubes (not shown) extending between pulse detonation core replacement augmentor assembly inlet side  260  and pulse detonation core replacement augmentor assembly outlet side  262  and circumferentially disposed around engine centerline  204 . 
     The shock tubes permit fuel and air entering pulse detonation system  202  to mix and detonate. The shock tubes also direct the hot combustion gases to pulse detonation augmentor  240 . Pulse detonation core replacement augmentor assembly  242  replaces a core engine, such as core engine  110  (shown in FIG. 3) of engine  100  (shown in FIG.  3 ). By “replacing a core engine,” it should be understood that pulse detonation core replacement assembly may replace either the high pressure turbine, compressor and combustor forming a core engine, or may replace only the combustor of a core engine. 
     Turbine sub-system  230  is disposed between pulse detonation augmentor  240  and pulse detonation core replacement augmentor assembly  242 . Accordingly, turbine subsystem turbine  232  is in flow communication with pulse detonation augmentor  240  and pulse detonation core replacement augmentor assembly  242 . A cooling air pump  270  is disposed radially inward from pulse detonation core replacement augmentor assembly  242  and provides cooling air to turbine sub-system  230 . Cooling air pump  270  is disposed on a shaft (not shown), which connects turbine  232  with forward fan  214 . Alternatively, cooling air pump  270  may be disposed radially outward from pulse detonation core replacement assembly  242 . 
     Engine  200  also includes an ejector/mixer  272  disposed upstream from turbine sub-system turbine  232 . Ejector/mixer  272  controls the mixture of hot high pressure gases exiting pulse detonation core replacement augmentor assembly  242  and flowing to turbine  232 . Ejector/mixer  272  also controls an amount of cooling air flowing through pulse detonation core replacement augmentor assembly  242 , thus permiting turbine  232  to operate efficiently from engine start-up operating conditions to engine full-power operating conditions. Beneficially, controlling the amount of high pressure gas exiting pulse detonation core replacement assembly  242  and flowing to turbine  232  facilitates augmenting the thrust generated by the turbofan. In one embodiment, engine  200  also incorporates a shock tube flow adjustment schedule (not shown) and an inlet flow/shock tube operating band schedule (not shown) to enable turbine  232  to function through a complete range of engine operating conditions. 
     An auxiliary ram duct and valving system  280  is disposed radially outward from pulse detonation system  202  and extends from an inlet side  282  of engine  200  to pulse detonation augmentor  240 . Auxiliary ram duct and valving system  280  includes an auxiliary ram duct  284  and a ram air valve  286 . Ram duct  284  surrounds inlet guide vanes  220 , and forward fan  214 , and includes an inlet  287  for receiving air upstream from inlet guide vanes  220 . Inlet  287  is annular and is in flow communication with ram duct  284 . Ram air valve  286  is disposed within ram duct  284  and is selectable to control a flow of ram air through auxiliary ram duct and valving system  280 . During low flight speed modes of operation, ram air valve  286  is closed to prevent ram air from flowing through ram duct  284  into engine  200 . During moderate supersonic Mach number flight speed operations between Mach 3 and Mach 5, ram air valve  286  is opened to permit ram air to flow through ram duct  284  into engine  200 . Ram air valve  286  is also positionable at intermediate positions to control an amount of airflow channeled into ram duct  284 . 
     Engine  200  also includes an oxidizer injection system (not shown in FIG.  4 ). The oxidizer injection system is upstream from first pulse detonation augmentor  240  and in flow communication with pulse detonation augmentor  240  and permits an oxidizer (not shown) to be introduced into engine  200  to enable engine  200  to operate in a rocket mode of operation for flight altitudes at the edge of space and beyond. In one embodiment, the oxidizer is liquid oxygen. Alternatively, the oxidizer is liquid air. 
     During powered fan modes of operation or low flight speed modes of operation, ram air valve  286  is closed to prevent airflow from entering ram duct  284  and instead airflow enters engine  200  and passes through forward fan  214 . Airflow is discharged axially from forward fan  214  into pulse detonation core replacement augmentor assembly inlet  268 . As air enters pulse detonation core replacement augmentor assembly  242 , fuel is introduced into pulse detonation core replacement augmentor assembly  242 . The pulse detonation core replacement augmentor assembly shock tubes combine the air and fuel and detonate the mixture, thus increasing the temperature and pressure of the flow through pulse detonation core replacement augmentor assembly  242 . 
     During powered fan modes of operation, ejector/mixer  272  tailors the mixture of hot high pressure gases exiting pulse detonation core replacement augmentor assembly  242  and flowing to turbine  232 . Ejector/mixer  272  also tailors an amount of cooling air flowing through pulse detonation core replacement augmentor assembly  242  to permit turbine  232  to operate within engine  200 . Accordingly, during such powered fan modes of operation, a portion of the hot gases are directed through ejector/mixer  272  around turbine  232  to permit turbine  232  to operate from engine start-up operating conditions through engine full-power operating conditions. During such modes of operation, turbine  232  drives forward fan  214 . 
     The hot gases are discharged from pulse detonation core replacement augmentor assembly  242  into pulse detonation augmentor  240 . Additional fuel is introduced into pulse detonation augmentor  240 , which mixes the hot gas mixture and the fuel and detonates the mixture. Detonating the mixture creates an additional temperature and pressure rise, resulting in thrust from engine  200 . The powered fan mode of operation permits engine  200  to produce thrust for flight speed operations to about Mach 3. 
     FIG. 5 is a cross-sectional view of turbofan engine  200  in a ram duct mode of operation. The ram duct mode of operation permits engine  200  to operate with flight speeds between approximately Mach 3 and Mach 6. During the ram duct mode of operation, inlet guide vanes  220  are rotated to a closed position to substantially prevent airflow from entering forward fan  214  and to substantially cocoon forward fan  214  and turbine sub-system  230 . Ram air valve  286  is rotated opened to permit ram air to enter ram duct  284  and flow to pulse detonation system  202 . Fuel is introduced to pulse detonation system  202  within pulse detonation augmentor  240  and is mixed with ram air exiting ram duct  284 . The fuel/air mixture is ignited to produce combustion gases and thrust for engine  200 . An auxiliary heat exchanger (not shown) provides cool air to cool cocooned forward fan  214  and turbine subsystem  230 . 
     FIG. 6 is a cross-sectional view of turbofan engine  200  shown in a rocket mode of operation and including an oxidizer injection sub-system  290 . The rocket mode of operation permits engine  200  to operate with flight altitudes at the edge of space and flight speeds greater than Mach 6. During the rocket mode of operation, inlet guide vanes  220  remain rotated in a closed position to substantially prevent airflow from entering forward fan  214  and turbine sub-system  230 . Ram air valve  286  is rotated closed to prevent ram air from entering ram duct  284  and pulse detonation system  202 . Oxidizer injection system  290  introduces an oxidizer (not shown) to pulse detonation system  202  and directs the oxidizer downstream towards pulse detonation augmentor  240 . The oxidizer, combined with injected fuel, produces thrust from engine  200  and helps to cool engine  200  during operation. 
     The above-described pulse detonation system includes a pulse detonation core replacement assembly, which produces engine thrust. The pulse detonation system permits an engine to operate with a high efficiency and performance over a wide range of operating flight speeds. 
     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.