Patent Application
20070186556
This invention relates generally to turbine engines, more particularly to methods and apparatus for operating a pulse detonation engine.
Known pulse detonation engines generally operate with a detonation process having a pressure rise, as compared to engines operating within a constant pressure deflagration. As such, pulse detonation engines may have the potential to operate at higher thermodynamic efficiencies than may generally be achieved with deflagration-based engines.
At least some known hybrid pulse detonation-turbine engines have replaced the steady flow constant pressure combustor within the engine with a pulse detonation combustor that may include at least one pulse detonation chamber. Although such engines vary in their implementation, a common feature amongst hybrid pulse detonation-turbine engines is that air flow from a compressor is directed into the pulse detonation chamber wherein the air is mixed with fuel and ignited to produce a combustion pressure wave. The combustion wave transitions into a detonation wave followed by combustion gases that are used to drive the turbine.
However, known pulse detonation engines generally do not include pulse detonation chamber designs that are optimized to direct steady and spatially uniform flows to the turbine. Rather, with at least some known pulse engines, an output flow from the pulse detonation chamber generally varies over time in both temperature and pressure. Reducing the number of flow variations from the pulse detonation chamber generally improves the performance of pulse detonation engines. More specifically, reduced flow variations may be critical to reducing flow losses, increasing engine efficiency, and increasing power.
In one aspect, a method for operating a pulse detonation engine is provided. The method includes channeling air flow from a pulse detonation combustor into a flow mixer having an inlet portion, an outlet portion, and a body portion extending therebetween. The method also includes channeling ambient air past the flow mixer and mixing the air flow discharged from the pulse detonation combustor with the ambient air flow such that a combined flow is generated from the flow mixer that has less flow variations than the air flow discharged from the pulse detonation combustor.
In another aspect, a flow mixer for use with a pulse detonation combustor coupled to an axial turbine is provided. The flow mixer includes an inlet portion, an outlet portion, and a body portion extending therebetween. The inlet portion is configured to receive air flow discharged from the pulse detonation combustor and the body portion is configured to channel a bypass air flow circumferentially around the body portion. The outlet portion facilitates mixing pulse detonation combustor air flow with bypass air flow to produce a steady, uniform air flow towards the turbine.
In a further aspect, a pulse detonation engine is provided. The engine includes a pulse detonation combustor including at least one pulse detonation chamber that is configured to channel pulse detonation combustor air flow and bypass air flow towards an axial turbine. The engine also includes a flow mixer that is configured to receive and to mix the pulse detonation combustor air flow and the bypass air flow from the chamber to facilitate producing a steady, uniform air flow towards the turbine.
In operation, air flows through fan 14, booster 16, and high pressure compressor 18, being pressurized by each component in succession. At least a portion of the highly compressed air is delivered to PDC 20 and secondary or bypass portion flows over each component to facilitate cooling each component. Hot exhaust flow from PDC 20 drives turbines 22 and/or 24 before exiting gas turbine engine 10.
As used herein, the term “pulse detonation combustor” (“PDC”) is understood to mean any combustion device or system wherein a series of repeating detonations or quasi-detonations within the device generate a pressure rise and subsequent acceleration of combustion products as compared to pre-burned reactants. The term “quasi-detonation” is understood to mean any combustion process that produces a pressure rise and velocity increase that are higher than the pressure rise and velocity produced by a deflagration wave. Typical embodiments of PDC include a means of igniting a fuel/oxidizer mixture, for example a fuel/air mixture, and a confining chamber, in which pressure wave fronts initiated by the ignition process coalesce to produce a detonation wave. Each detonation or quasi-detonation is initiated either by an external ignition, such as a spark discharge or a laser pulse, and/or by gas dynamic processes, such as shock focusing, auto-ignition or through detonation via cross-firing. The geometry of the detonation chamber is such that the pressure rise of the detonation wave expels combustion products from the PDC exhaust to produce a thrust force. As known to those skilled in the art, pulse detonation may be accomplished in a number of types of detonation chambers, including detonation tubes, shock tubes, resonating detonation cavities and annular detonation chambers.
In the exemplary embodiment, body portion 46 has substantially the same shape as inlet portion 42 and has a diameter 56 that is substantially constant from inlet portion 42 to outlet portion 44 along a length 58 of body portion 46. Specifically, in the exemplary embodiment, body diameter 56 is approximately equal to body diameter 54. In alternative embodiments, body portion diameter 56 is variable along body length 58.
In the exemplary embodiment, outlet portion 44 transitions from the substantially circular shape of body portion 46 to a lobed or “daisy” shape gradually that facilitates channeling hot exhaust flow from chamber 30 towards turbine 22 (shown in
Peaks 64 and troughs 66 facilitate mixing cool ambient or bypass air flow 70 with hot exhaust gas flow 72 to form a steady and spatially uniform combined air flow 74. Specifically, peaks 64 enable higher temperature or hot flow 72 to be channeled in a generally axial direction along centerline axis 48 while, simultaneously, troughs 66 direct lower temperature or cool flow 70 toward centerline axis 48 and towards hot flow 72, thus resulting in mixing the flows 70 and 72 to form a combined flow 74.
In the exemplary embodiment, each peak 64 has a height 80 measured between centerline axis 48 and outlet portion 44. Moreover, in the exemplary embodiment, outlet portion 44 has a diameter 82 defined by diametrically opposite peaks 64, for example. In the exemplary embodiment, outlet diameter 82 is larger than body diameter 54. In alternative embodiments, outlet diameter 82 is smaller than, or approximately the same size as, body diameter 54. In the exemplary embodiment, outlet portion 44 is oriented such that each peak 64 is angled outward from body 46 at an angle 84 and each trough 66 is angled inward from body 46 at an angle 86. Angles 84 and 86 are variable depending on the various engine parameters, engine demands, or specific engine requirements.
In operation, air flow 70 is directed along body 46 and around peaks 64 and through troughs 66 where at least a portion of air flow 70 is directed towards axis 48, simultaneously, air flow 72 is directed through body 46 and through peaks 64 and around troughs 66 where at least a portion of air flow 72 is directed towards axis 48. Peaks 64 and troughs 66 substantially “slice” each respective air flow 70 and 72 which facilitates mixing flows 70 and 72 into combined flow 74 that is cooler than hot flow 72. In one embodiment, peaks 64 and troughs 66 are angled to facilitate generating counter-rotating vortices which enhances mixing of flows 70 and 72 into combined flow 74 that is cooler than hot flow 72.
In the exemplary embodiment, body portion 146 has substantially the same shape as inlet portion 142 such that inlet portion 142 transitions gradually to outlet portion 144 along a length 158 of body portion 146. Specifically, in the exemplary embodiment, body portion 146 has a minor axis (not shown) that is shorter than inlet minor axis 154 and a major axis (not shown) that is longer than inlet major axis 155. In alternative embodiments, body portion 146 minor axis is longer than inlet minor axis 154 and body portion 146 major axis is smaller than inlet major axis 155.
In the exemplary embodiment, outlet portion 144 transitions gradually from the substantially elliptical shape of body portion 146 to a lobed shape that facilitates channeling the hot exhaust flow from chamber 30 towards turbine 22 (shown in
Peaks 164 and troughs 166 facilitate mixing cool ambient or bypass air flow 170 with hot exhaust gas flow 172 to form a steady and spatially uniform combined air flow 174. Specifically, peaks 164 enable higher temperature or hot flow 172 to be channeled along centerline axis 148 while, simultaneously, troughs 166 direct lower temperature or cool flow 170 toward centerline axis 148 towards hot flow 172, thus resulting in mixing the flows 170 and 172 to form a combined flow 174.
In the exemplary embodiment, each peak 164 has a height 180 measured between centerline axis 148 and outlet portion 144. Moreover, in the exemplary embodiment, outlet portion 144 has a height 182 defined by opposite peaks 164. In the exemplary embodiment, outlet diameter 182 is longer than body portion 146 minor axis. In the exemplary embodiment, outlet portion 144 is oriented such that each peak 164 is angled outward from body diameter along an angle 184. In alternative embodiments, trough 166 may have an inward angle (not shown). Angle 184 is variable depending on the various engine parameters, engine demands, or specific engine requirements.
In operation, air flow 170 is directed along body 146 and around peaks 164 and through troughs 166 where at least a portion of air flow 170 is directed towards axis 148, simultaneously, air flow 172 is directed through body 146 and through peaks 164 and around troughs 166 where at least a portion of air flow 172 is directed towards axis 148. Peaks 164 and troughs 166 substantially vertically “slice” each respective air flow 172 and 170 which facilitates mixing flows 172 and 170 into combined flow 174 that is cooler than hot flow 172.
In the exemplary embodiment, body portion 246 has substantially the same shape as inlet portion 242 such that inlet portion 242 transitions gradually to outlet portion 244 along a length 258 of body portion 246. Specifically, in the exemplary embodiment, body portion 246 has a minor axis (not shown) that is shorter than inlet minor axis 254 and a major axis (not shown) that is longer than inlet major axis 255. In alternative embodiments, body portion 246 minor axis is longer than inlet minor axis 254 and body portion 246 major axis is smaller than inlet major axis 255.
In the exemplary embodiment, outlet portion 244 transitions gradually from the substantially elliptical shape of body portion 246 to a square-wave lobed shape that facilitates channeling the hot exhaust flow from chamber 30 towards turbine 22 (shown in
Peaks 264 and troughs 266 facilitate mixing cool ambient or bypass air flow 270 with hot exhaust gas flow 272 to form a steady and spatially uniform combined air flow 274. Specifically, peaks 264 enable higher temperature or hot flow 272 to be channeled along centerline axis 248 while, simultaneously, troughs 266 direct lower temperature or cool flow 270 toward centerline axis 248 and towards hot flow 272, thus resulting in mixing flows 270 and 272 to form a combined flow 274.
In the exemplary embodiment, each peak 264 has a height 280 measured between centerline axis 248 and outlet portion 244. Moreover, in the exemplary embodiment, outlet portion 244 has a height 282 defined by opposite peaks 264. In the exemplary embodiment, outlet diameter 282 is larger than body portion 246 minor axis. In the exemplary embodiment, outlet portion 244 is oriented such that each peak 264 is angled outward from body diameter along an angle 284. In alternative embodiments, trough 266 may have an inward angle (not shown). Angle 284 is variable depending on the various engine parameters, engine demands, or specific engine requirements.
In operation, peaks 264 and troughs 266 produce substantially vertical “slices” each respective of air flow 272 and 270. The vertical slices alternate and facilitate mixing flows 272 and 270 into combined flow 274 that is cooler than hot flow 272.
The above-described turbine engine is efficient, cost effective, and highly reliable. The engine includes at least one flow mixer configured to facilitate reduce flow variations generated from the pulse detonation combustor. Each flow mixer an inlet portion, an outlet portion, and a body extending therebetween configured to optimize power extraction from the pulse detonation combustor by mixing cool bypass air flow and hot pulse detonation combustor air flow. Mixing air flows facilitates reducing non-uniform flow fields generate towards downstream turbines. As a result, the described flow mixer facilitates improving overall efficiency in a cost effective and reliable manner taking advantage of the efficiency gain of pulse detonation engines.
Exemplary embodiments of flow mixers are described above in detail. The flow mixers are not limited to the specific embodiments described herein, but rather, components of the flow mixers may be utilized independently and separately from other components described herein. Each flow mixer component can also be used in combination with other turbine 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.
