Abstract:
A pulse combustion device has a number of combustors with upstream bodies and downstream nozzles. Coupling conduits provide communication between the combustors. For each given combustor this includes a first communication between a first location upstream of the nozzle thereof and a first location along the nozzle of another. There is second communication between a second location upstream of the nozzle and a second communication between a second location upstream of the nozzle of a second other combustor and a second nozzle location along the nozzle of the given combustor.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to pulse combustion devices, and more particularly to pulse combustion engines. 
   Diverse pulse combustion technologies exist. Pulse detonation engines (PDE&#39;s) represent areas of particular development. In a generalized PDE, fuel and oxidizer (e.g. oxygen-containing gas such as air) are admitted to an elongate combustion chamber at an upstream inlet end. The air may be introduced through an upstream inlet valve and the fuel injected downstream thereof to form a mixture. Alternatively, a fuel/air mixture may be introduced through the valve. Upon introduction of this charge, the valve is closed and an igniter is utilized to detonate the charge (either directly or through a deflagration to detonation transition process). 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 chamber before substantial gas can escape inertially through the outlet. The effect of this inertial confinement is to produce near constant volume combustion as distinguished, for example, from constant pressure combustion. Exemplary pulse combustion engines are shown in U.S. Pat. Nos. 5,353,588, 5,873,240, 5,901,550, and 6,003,301. 
   Additionally, pulse combustion devices have been proposed for use as combustors in hybrid turbine engines. For example, the device may replace a conventional turbine engine combustor. Such proposed hybrid engines are shown in U.S. Pat. No. 3,417,564 and U.S. Publication 20040123583 A1. 
   BRIEF SUMMARY OF THE INVENTION 
   One aspect of the invention involves a pulse combustion device having a circular array of combustion conduits. Each conduit includes a wall surface extending from an upstream inlet to a downstream outlet. At least one valve is positioned to admit at least a first gas component of a propellant to the combustion conduit inlets. The device includes an outlet end member. The array and outlet end member are rotatable in at least a first direction relative to each other. Means are provided at least partially in the outlet end member for providing a circumferentially varying effective nozzle geometry. 
   In one or more implementations, the means may provide a circumferentially varying effective throat area. The outlet end member may be essentially fixed and the array may rotate. Alternatively, the array may be essentially fixed and the outlet end member may rotate. The means may include a passageway through the outlet end member. The outlet end member may further include an igniter. The inlet valve may comprise an inlet end member non-rotating relative to the outlet end member. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view of a gas turbine engine. 
       FIG. 2  is a sectional view of a combustor of the engine of  FIG. 1 , taken along line  2 - 2 . 
       FIG. 3  is a sectional view of a combustor of the engine of  FIG. 1 , taken along line  3 - 3 . 
       FIG. 4  is a longitudinal sectional view of a conduit array and nozzle of the combustor of  FIG. 2 , taken along line  4 - 4 . 
       FIG. 5  is a longitudinal sectional view of a conduit array and nozzle of the combustor of  FIG. 2 , taken along line  5 - 5 . 
       FIG. 6  is a partially schematic unwrapped longitudinal circumferential sectional view of the combustor of the engine of  FIG. 1 . 
       FIG. 7  is rear view of an alternative nozzle. 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a gas turbine engine  20  having a central longitudinal axis  500 . From upstream to downstream, the exemplary engine  20  includes a fan section  22 , at least one compressor section  24 , a pulse combustion combustor section  26 , and a turbine section  28 . The exemplary combustor  26  includes a circumferential array of longitudinally-extending conduits  30  ( FIG. 2 ) mounted within an engine case  32  for rotation about the axis  500  (e.g., supported or formed on a carousel structure  34  which may be on one of the compressor/turbine spools or a separate free spool). 
   The exemplary combustor array includes eighteen combustor conduits  30  (shown for illustration as straight passages oriented longitudinally and having a transverse cross-section of an annular sector). Alternative cross-sections including circular sections are possible, as are non-longitudinal orientations and non-straight configurations. The direction of rotation is labeled as  506 . The exemplary passageways are formed between inner and outer walls  36  and  38  spanned by radial walls  40 . 
     FIG. 6  shows further details of the exemplary combustor  26  during steady-state operation. Positions of the conduits at an exemplary point in the cycle are respectively designated as  30 A- 30 R. Each exemplary conduit  30  has an upstream inlet  42  and a downstream outlet  43 . For ease of reference, the conduits will be identified by the reference numerals associated with the illustrated positions. Fixed inlet (upstream) and outlet (downstream) end members  44  and  45  are positioned respectively upstream and downstream of the conduit array and have respective open areas  46  and  47  for admitting gas to the conduits and passing gas from the conduits. As is discussed in further detail below, member  45  serves as a nozzle structure and its open area  47  serves as a nozzle aperture. 
   At the illustrated instance in time, a last bit of a purge flow  50  of combustion products is exiting the outlet  43  of the conduit  30 A at a first end  51  of the open area  47 . A slug of a buffer gas  52  is in a downstream end portion of the conduit  30 A following right behind the purge flow  50 . A propellant charge  54  follows behind the buffer slug  52 , being delivered by a propellant fill flow  56  through the inlet  42 . An exemplary propellant flow includes a gaseous oxidizer (e.g., air) and a fuel (e.g., a gaseous or liquid hydrocarbon). In the exemplary turbine engine embodiment, the air may be delivered from the compressor  24  and the fuel may be introduced by fuel injectors (not shown). 
   At the illustrated point in time, the next conduit  30 B has just had its outlet closed by passing in front of an upstream face  58  along a blocking portion  60  of the downstream member/nozzle  45 . At the point of closure/occlusion, some or all of the buffer slug  52  may have exited the conduit outlet. The buffer slug  52  serves to prevent premature ignition of the charge  54  due to contact with the combustion gases. The closure of the outlet port causes a compression wave  62  to be sent in a forward/upstream direction  510  through the charge  54  leaving a compressed portion  63  of said charge in its wake. 
   This compression process continues through the position approximately shown for conduit  30 C. At some point (e.g., as shown for the conduit  30 D) the conduit outlet becomes exposed to the operative end  64  of an ignition source  66  (e.g., a spark ignitor in the member  45 ). The ignitor  66  ignites the compressed charge  63  causing detonation and sending a detonation wave  68  forward/upstream after the compression wave  62  (e.g., as shown for conduits  30 D,  30 E, and  30 F). The combustion products  70  are left in the wake of the detonating wave. 
   A surface  80  of a main portion of the combustor upstream member  44  is positioned to block the conduit inlets during a main portion of the combustion process. In the exemplary implementation, the surface  80  (a downstream face) is positioned to block the inlets  42  to prevent upstream expulsion of the charge  54  as the compression wave  62  approaches. The surface  80  is also positioned to prevent upstream discharge of combustion products during a high pressure interval thereafter. An exemplary circumferential extent of the surface  80  is between 40° and 160° (more narrowly, 90° and 120°). 
   In the exemplary combustor, there is a brief interval shown for the conduits  30 D,  30 E, and  30 F wherein both its inlet and outlet are blocked after the outlet been exposed to the ignitor. Alternative configurations may lack this interval. Shortly thereafter (e.g., as shown for the conduit  30 G) the conduit outlet clears the surface  58  at a second end  82  of the open area  47  and is thus opened. A blow down flow  84  of high pressure combustion gases then exits the conduit outlet. This blow down interval may continue (e.g., for the conduits shown as  30 G,  30 H,  30 I,  30 J, and  30 K). 
   After the blow down interval, there may be a buffer filling interval wherein an inlet buffer flow  90  generates the buffer slug  52  upstream of the combustion gases  70 . The exemplary flow  90  may be of unfueled air. In the exemplary combustor, this flow  90  is isolated from the flow  56  by a narrow segment  92  of the upstream member  44  (thereby defining a port through which the flow  90  passes). Alternative configurations could lack such a segment  92  and rely on injector positioning to keep the flow  90  relatively unfueled. Thereafter, through several further stages (e.g., for conduits  30 M,  30 N,  300 ,  30 P,  30 Q,  30 R, and finally returning to  30 A,  30 B, and  30 C) the conduit may be recharged with propellant. 
   Further details of the downstream member  45  can be seen in  FIGS. 3-5 . In the exemplary somewhat schematic illustration, the downstream member has a downstream face  100  generally radially extending. From the upstream face  58  to the downstream face  100 , the open area  47  defines a convergent-divergent nozzle ( FIG. 4 ) characterized by a convergent (flow contraction) portion  102 , a throat portion  104 , and a divergent (flow expansion) portion  106 . The exemplary convergent portion  102  is characterized by inboard and outboard surface portions  107  and  108  of a circumferentially elongate upstream channel. Viewed in central longitudinal section, the exemplary portions  107  and  108  are straight and downstream convergent toward each other. Similarly, the exemplary divergent portion  106  is characterized by inboard and outboard surface portions  110  and  112  of a circumferentially elongate downstream channel. Viewed in central longitudinal section, the exemplary portions  110  and  112  are straight and downstream divergent away from each other. Sectionally convex throat transitions join the surface portion  107  to the surface portion  110  and the surface portion  108  to the surface portion  112 . Other nozzle shapes (e.g., curved or otherwise contoured surface portions) are possible. 
   According to the present invention, the effective nozzle properties may vary circumferentially. In the exemplary embodiment, the effective throat area may be varied by varying the throat radial span ART. The effective exit area may be varied by varying the exit radial span ΔR E . The effective exit angle may be varied by varying longitudinal/radial angle θ E  between the surface portions  110  and  112 . There may be similar control of the properties of the convergent portion  102 . Other parameters may be varied. In the exemplary nozzle, the radial span ART generally decreases in the direction of rotation  506  (e.g., from near the second end  82  to near the first end  47 ). The change may be stepwise or smoothly continuous. The change occurs over a greater circumferential span than the technical incidental and transient change from a conduit passing from a blocked area to a nozzle area that remains constant for the rest of the discharge cycle. The change may take place over a major portion of the cycle (e.g., at least 180° of a single cycle per revolution configuration). More broadly, the change may take place over an area between a third of a cycle and a full cycle.  FIG. 7  shows a full cycle change in a nozzle  200  effectively eliminating the blocking of the conduit outlets. A divider wall  202  in the nozzle divergent section  204  helps block any backflow of high pressure exhaust products into the adjacent tube purging at a lower pressure. 
   In steady-state operation, the rotation may be driven by aerodynamic factors (e.g., from a slight tangential orientation of the conduits). At start-up, engine spool rotation may be commenced by conventional drive (e.g., pneumatic, electric, or starter cartridge). Operation of the exemplary combustor may tend to be self-timing. However, additional timing control may be provided. For example, means may be provided to change the relative phases of the downstream and upstream members  44  and  45  (e.g., by shifting their orientational phase about the axis  500 ). Alternatively, means may be provided for varying the attributes of either of these members individually. For example, there may be multiple open areas in the downstream member  45  or a single passageway may have multiple outlets or inlets which may be selectively opened or closed individually or in combinations. Similarly, the circumferential extent of blocking provided by the upstream member  82  might be made adjustable as might be the circumferential extents and positions of the respective fueled and unfueled flows  56  and  90 . 
   In alternative embodiments, the conduit array may be fixed and at least the downstream member may be rotating. An upstream member rotating synchronously with the downstream member will provide a similar operation as discussed above for  FIG. 6 . However, the valving interaction of the upstream member with the conduits could easily be replaced with discrete valves at the inlet ends of each conduit. Such discrete valves would provide greater flexibility in timing control of the combustion process. 
   One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, even with the basic construction illustrated, many parameters may be utilized to influence performance. Accordingly, other embodiments are within the scope of the following claims.