Abstract:
A pulsed combustion apparatus includes a conduit having an outer wall and an inner wall. The inner wall has a number of apertures. An interior space is separated from the outer wall by the inner wall. An induction system is positioned to cyclicly admit charges to the interior space. An ignition system is positioned to ignite the charges. Flow directing surfaces are positioned to at least cyclicly direct cooling air through the apertures.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to pulse combustion, and more particularly to hybrid pulse combustion turbine engines. 
   In a conventional gas turbine engine, combustion occurs in a continuous, near constant pressure (Rankine cycle), mode. Such conventional gas turbine engine combustion is notoriously inefficient and has led to many efforts to improve efficiency. 
   It has been proposed to apply the more efficient combustion of near constant volume combustion pulse detonation engines (PDEs) to turbine engine combustors. 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, typically through an inlet valve as a mixture (e.g., of hydrocarbon fuel droplets or vapor in air). 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). 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. It has also been proposed to use an essentially deflagration combustion in a PDE. U.S. Patent Publication Nos. 20040123582A1 and 20040123583A1 and European Patent Convention publications EP1435447A1 and EP1435440A1 disclose various configurations of pulsed combustion gas turbine engines. 
   BRIEF SUMMARY OF THE INVENTION 
   One aspect of the invention involves a pulsed combustion apparatus. The apparatus includes a conduit and an inner wall. The inner wall has a number of apertures. An interior space is separated from the outer wall by the inner wall. An induction system is positioned to cyclicly admit charges to the interior space. An ignition system is positioned to ignite the charges. Flow directing surfaces are positioned to at least cyclicly direct cooling air through the apertures. 
   In various implementations, the inner wall may have an array of volumes (pockets). The apertures may include, for each of the pockets: a first aperture between the interior of such pocket and a space between the inner and outer walls; and a second aperture between the interior of the pocket and the interior space. An intermediate wall may be located between the outer wall and the inner wall and may have a number of apertures. The cooling air may be directed through the intermediate wall before reaching the inner wall. The inner wall may include an inner layer and an outer layer secured to the inner layer. The outer layer may have an array of three-dimensional excursion features (e.g., dome-like blisters) cooperating with the inner layer to form the pockets. The ignition system may be effective to induce detonation of the charges. 
   Another aspect of the invention involves a turbine engine including a case with an axis, a compressor, a turbine, and a circumferential array of combustion chamber conduits. The conduits are downstream of the compressor and upstream of the turbine. The array is supported for continuous rotation relative to the case in a first direction about the axis to cyclicly bring each conduit from a charging zone for receiving a charge from upstream to a discharging zone for downstream discharging of products of combustion of the charge. Each of the conduits includes an outer wall and an inner wall. An interior space is separated from the outer wall by the inner wall and has an array of pockets. Each pocket may have at least one exterior port and at least one interior port. 
   In various implementations, the inner wall may include a first layer and a second layer secured to an outer surface of the first layer. The second layer may have an array of outward blisters cooperating with the first layer to form the pockets. A third layer may be outboard of the second layer and may have an array of orifices. There may be a first airflow substantially through the compressor and turbine with a first portion of the first airflow passing through the combustor chamber conduits in the charges and a second portion of the first airflow bypassing combustion. A mass flow ratio of the first portion to the second portion may be between 1:1 and 1:3. The engine may be a turbofan engine. The first airflow may be a core airflow and a bypass airflow may bypass the compressor and turbine. A mass flow ratio of the bypass airflow to the core airflow may be between 3:1 and 9:1. The array may be on a free spool and the rotation may be driven by partially tangential direction of products of combustion. 
   Another aspect of the invention involves a gas turbine engine having a compressor, a turbine coaxial with the compressor along an axis, and a pulsed combustion combustor receiving air from the compressor and outputting combustion gases to the turbine. The combustor includes a number of combustion chamber conduits having first and second portions or chambers held for rotation about the axis through a number of positions, including: at least one charge receiving position for receiving a charge from upstream; at least one initiation position for initiating combustion of the charge; at least one discharge position for downstream discharging of products of combustion of said charge; and at least one cooling position cooling a wall separating the first and second chambers by directing cooling air from the second chamber to the first chamber through a plurality of apertures in the wall. 
   In various implementations, there may be at least one fuel injector for injecting fuel into air from the compressor to form the charges. The at least one cooling position may overlap a majority of the at least one charge receiving position. 
   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 partial longitudinal sectional view of a turbofan engine. 
       FIG. 2  is a partial isolated cut-away isometric view of a combustor of the engine of  FIG. 1 . 
       FIG. 3  is an enlarged cut-away view of an upstream end of the combustor of  FIG. 2 . 
       FIG. 4  is a longitudinal sectional view of the combustor of the engine of  FIG. 1  along a charging sector. 
       FIG. 5  is a longitudinal sectional view of the combustor of the engine of  FIG. 1  along a discharging sector. 
       FIG. 6  is a partial longitudinal sectional view of a combustion conduit of the engine of  FIG. 1 . 
       FIG. 7  is an enlarged sectional view of the conduit of  FIG. 6 . 
       FIG. 8  is a partial transverse sectional view of the conduit of  FIG. 6  taken along line  8 - 8 . 
       FIG. 9  is a partial transverse sectional view of the core conduit of  FIG. 6  taken along line  9 - 9 . 
       FIG. 10  is a partial interior view of an inner wall of the conduit of  FIG. 6 . 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   A new combustor tube configuration may be applied to a turbine engine. Exemplary turbine engines and combustors may be variations on those shown in U.S. Patent Publication Nos. 20040123582A1 and 20040123583A1 and European Patent Convention publications EP1435447A1 and EP1435440A1 (the disclosures of which are incorporated by reference herein as if set forth at length). 
     FIG. 1  shows a turbofan engine  20  having central longitudinal axis  500 , a duct  22  and a core  24 . The duct is supported relative to a case assembly  25  of the core by vanes  26 . Of inlet air entering the duct, a fan  28  drives a bypass portion along a first flow path  502  radially between the duct and the core and core portion along a second flowpath  504  through the core. In the core downstream of the fan, a compressor section  30  having alternating rings of rotor blades and stator vanes compresses the core air and delivers it further downstream to a combustor section  32  where it is mixed with fuel and combusted. A mixing duct  34  downstream of the combustor may mix a portion of air bypassing fueling and combustion with the portion that is fueled/combusted. Downstream of the mixing duct, a turbine section  36  is driven by the mixing duct output to, in turn, drive the compressor and fan. An augmentor (not shown) may be located downstream of the turbine. 
   The exemplary combustor includes a ring of combustion conduits  40  which may be operated as pulsed combustion conduits. Exemplary conduits are operated as pulsed detonation devices, although a similar structure may potentially be used with pulsed deflagration. The conduits are mounted in a carousel structure  42  ( FIG. 2 ) for rotation relative to the case assembly about the engine central longitudinal axis. In the illustrated embodiment and as discussed further below, the carousel forms a third free spool in addition to the high and low spools of the turbine/compressor combination. Other embodiments may have more or fewer spools and compressor and turbine section arrangements. 
   Each conduit includes a first volume (chamber)  44  and a second volume (chamber)  46  ( FIG. 3 ) that form respective first and second passageways. Each first volume  44  has a forward/upstream inlet end  47  and an aft/downstream outlet end  48  ( FIG. 4 ). Each second volume  46  has a forward/upstream inlet end  49  and an aft/downstream outlet end  50  ( FIG. 4 ). Along major portions of the lengths (e.g., about 50-70% or more) of the first and second volumes  44  and  46 , the first volume  44  is generally concentrically surrounded by the second volume  46 . Along these common lengths, a tube  52  (e.g., of annular section and straight) extends along a central longitudinal axis  506  from a tube inlet  53  to a tube outlet end  54  to separate the volumes  44  and  46 . As is discussed further below, downstream of the tube outlet end  54 , the cross-sectional shapes of the volumes  44  and  46  transition and may become circumferentially alternating or sandwiched. 
   The exemplary carousel comprises a circumferentially extending outboard wall  60  spaced apart from a circumferentially extending inboard wall  62 . A circumferential array of radial/longitudinal walls  64  span between the outboard and inboard walls  60  and  62  to generally surround the individual second volumes  46 . Thus, the exemplary radial walls are each shared by a pair of adjacent volumes  46 , the two radial walls and intervening portions of the outboard and inboard walls  60  and  62  forming the outer “wall” of such volume  46 . 
   At an upstream end of the carousel, the first volume  44  is essentially an outboard annular sector and the associated volume  46  is essentially an annular sector immediately inboard thereof and separated therefrom by a wall of a duct portion  66 . From adjacent the upstream/inlet end  47  at the car, the first volume  44  cross-section may transition from the annular sector to another shape such as a circle at the upstream end/inlet  53  of the tube  52 . 
   The first and second volume upstream ends  47  and  49  are proximate an aft, downstream portion of a fixed manifold  80  ( FIG. 4 ). In the exemplary embodiment, along a charging sector of the manifold, the manifold  80  splits the core flow into two portions: an inboard portion along an inboard passageway  81  and an outboard portion along an outboard passageway  82 . The passageways  81  and  83  are separated by a circumferential wall  83  having an upstream rim  84  just downstream of the last compressor stage and having a downstream rim  86 . The downstream rim  86  is in close aligned proximity to an upstream rim  90  ( FIG. 3 ) of the duct  66  radially between respective upstream rims  92  and  94  of the outboard and inboard walls  62  and  64  of the carousel. Along this charging sector, the manifold has a circumferential array of fuel injectors  100  mounted in a wall  102  of the core. The injectors have outlets  104  positioned sufficiently downstream of the rim  84  so as to introduce fuel only to the outboard portion of the core flow along the manifold outboard passageway  82 . This combined fuel/air flow, in turn, passes into the first volumes  44  of a transiently aligned group of the combustion conduits  40 . A sealing system (not shown) may be formed between the manifold and carousel. An unfueled portion of the core air passes though the manifold inboard passageway  81  inboard of the wall  83  and enters the second volumes  46  of the transiently aligned conduits  40 . 
   Outside of the charging sector, in ignition/discharging sector, the manifold has a blocking element  120  ( FIG. 5 ) that seals the inlet ends  47  of the transiently aligned first volumes  44 . In the exemplary embodiment, however, the blocking element  120  effectively blocks only the outboard (fueled in the charging sector) portion of the core flow path, still permitting flow through the inboard portion, in turn, into the second volumes  46 . Although the outboard portion of the core flow may be entirely blocked, in the exemplary embodiment it is merely diverted to bypass the combustor, passing outboard of the combustor through a passageway  124  formed by a local radial elevation and longitudinal extension  126  of the wall  102 . This bypass diverts unfueled relatively cool air to mix with and further cool/quench the combustion products in the discharge sector. The mixing duct  34  may thus provide for a transition to circumferentially homogenize the flow entering the turbine section. 
   Ignition and discharge may occur when each first volume  44  is so sealed. The engine includes means for initiating the combustion of the fuel/air charges in the combustion chambers. Exemplary means initiate this as soon as the first volume  44  is closed off at the beginning of the ignition/discharging sector.  FIG. 5  shows means in the form of a single low profile spark plug  130  for each conduit  40 . When a single such plug is used, it is advantageously located proximate the upstream end of the first volume  44 . In the exemplary embodiment, the plug is mounted in the outboard wall  60  just downstream of its forward rim  92 . This exemplary spark plug rotates with the carousel and is powered/controlled by an appropriate distributor mechanism or the like providing electrical communication between rotating and non-rotating portions of the engine. An alternative embodiment would mount the plug  130  in the blocking member  120 . Such a mounting may reduce complexity of electrical communication between rotating and non-rotating parts of the engine. Yet alternate initiation systems include multi-point, continuous (e.g., laser or other energy beam), or multi-continuous systems. Examples of such systems are found in U.S. Patent Publication No. 20040123583A1. The first volume  44  has an overall length and a characteristic transverse dimension identified as a diameter. When triggered, the igniter produces a detonation pulse which propagates a flame front radially outward from an associated ignition point at the plug at a supersonic speed (e.g., over about 3,000 feet per second (fps) and typically in the range of 4,000-6,000 fps). Near total combustion will be achieved in the time required for the flame front to travel from the plug to the tube outlet ends  54  or the second volume outlet  48 . With the plug proximate the upstream end of the first volume  44  and the diameter substantially smaller than the length, this travel distance is essentially equal to the length. An exemplary operating pressure ratio (OPR) for such detonation combustion is between 2:1 and 6:1. 
   Combustion gases discharged from the tube outlet ends  54  encounter turning vanes  140  which may be unitarily formed with the carousel disk. In the exemplary embodiment, an equal number of turning vanes  140  are alternatingly interspersed with the tubes  52  and may comprise extensions of the walls of the tubes interspersed with the walls  64  diverting flow through the second passageways. Adjacent vanes divert the discharge flows by an angle relative to the tube axis  506  and local longitudinal centerplane of the engine. In the exemplary embodiment, this diversion applies sufficient torque to the carousel to rotate the carousel at a desired rotational speed. In an exemplary engine, an exemplary steady state rotational speed of the carousel is 2,000-18,000 RPM. The specific operating range will be influenced by engine dimensional considerations in view of carousel structural integrity and the number of charge/discharge cycles per rotation. A narrower range of 6,000-12,000 target RPM is likely with the lower third of this range more likely for a two cycle/rotation engine and the upper third for a one cycle/rotation engine. In operation, these speeds will likely be substantially lower than the high spool speed and approximately the same or moderately lower than the low spool speed. An initial rotation may be provided by the engine starter motor or by a dedicated starter motor for the combustor. 
   Various inventive aspects relate to cooling of the combustion conduits.  FIG. 6  shows respective downstream flows  150  and  152  in the volumes  44  and  46 . The nature of the respective flows may depend upon the specific cycle stage and the location along the length of the volumes. For example, the flow  150  may be a charging flow, a discharging flow, or a purging flow. As is discussed in further detail below, the flow  152  may principally be a cooling flow which may be influenced by the flow  150 . The exemplary tube  52  is foraminate, permitting fluid communication between the flows as well as a conductive thermal communication.  FIG. 7  shows details of the exemplary wall of the tube  52 . This wall includes an inner first wall structure  160  and an outer second wall structure  162  (intermediate when viewed relative to the wall structure  160  on the one hand and the adjacent outer conduit wall portion  60 ,  62 , or  64  on the other hand). The exemplary second wall structure  162  is a single tubular layer having a circumferential and longitudinal array of metering apertures  164 . The exemplary first wall structure  160  is double layered, having a generally tubular inner layer  166  with a blistered outer layer  168  secured thereto. For example, the inner surface of unblistered portions of the outer layer  168  may contact and be secured (e.g., via bonding, welding, or the like) to adjacent portions of the outer surface of the inner layer  166 . The blisters  170  on the outer layer  168  cooperate with adjacent portions of the inner layer  166  to define blister internal volumes  172 . Each blister has associated therewith one or more apertures  174  in the outer layer  168  and  176  in the inner layer  166 . 
   In an exemplary embodiment, in at least a portion of the charging and purge portions of the cycle, a flow  180  (represented in  FIG. 7  by a single streamline although overall potentially representing a much more complex net flow) diverts from the flow  152  in the outer volume/passageway  46  to the inner volume/passageway  44 . This flow  180  passes through a volume  182  between the wall structures  160  and  162 . In the exemplary embodiment, the apertures  164  are positioned near downstream extremities of adjacent blisters.  FIG. 8  shows apertures  164  at an exemplary circumferential pitch of half that of the blisters, with one group of the apertures aligned with the blisters and one group aligned out of phase with the blisters. Some portion of the flow  180  (e.g., schematically represented as  184 ) will flow around/over the blisters. Another portion (e.g., shown schematically as  186 ) will flow into the blisters through the apertures  174 .  FIG. 9  shows the apertures  174  as small circular apertures along leading sides of the blisters. The flow  186  may then pass out of the blister to merge with the flow  150  in the volume/passageway  44  through the apertures  176 . Exemplary apertures  176  are relatively large and located relatively downstream along the associated blister. At the downstream end  54  of the tube the flow  184  may be blocked or may be diverted to join one or both of the flows  150  or  152 . For example, it may rejoin the flow  152 , with the flows  150  and  152  later rejoining at the outlet ends  50  and  48  before encountering the turbine. 
   The enhanced surface area provided by the wall structure  160  draws substantial cooling from the flows  184  and  186 . These cooling flows may be driven by a pressure differential between the volumes  46  and  44 . Such a pressure differential may be achieved via appropriate positioning of the duct rim  90  to provide an appropriate initial balance of flows into the volumes. Additionally, the compressor blade immediately ahead of the forward/upstream inlet end  49  may be warped such that a higher pressure flow is directed into the inboard annulus that feeds volume  46  surrounding the combustor tube volume  44 . Thus a positive pressure differential across the wall of combustor tube  52  assures cooling airflow into the volume  44  during the refresh cycle. The tube wall geometry promotes cooling in two ways: air entering the blisters  170  through the apertures  174  impinges on the outer surface (backside) of the inner layer  166  and then exits through the apertures  176  to form an unfueled laminar film on the combustion side of inner layer  166 . 
   Especially during ignition and discharge, the pressure increase within the first volume/passageway  44  may cause a reverse flow outward through the wall structure  160 . The flow reversal may be minimized by bell-mouthing the edges of apertures  174  and  176  to create a preferential inflow coefficient of discharge (CD). The bell-mouthed apertures would restrict reverse flow when the combustion event causes a pressure rise in volume  44 . Additionally, the refresh cycle is substantially longer than the period of time associated with the combustion and blow-down (discharge) event. Thus, the flow time history of the air adjacent to the combustion tube wall  52  will be inboard from volume  46  to volume  44  for the majority of the time and the reverse flow during the brief elevated pressure period of the combustion event will be severely restricted by the bell mouth shaping of apertures  174  and  176 . The net effect is a strong cooling action on the inner layer  166  of the combustion tube  52 . 
   In exemplary embodiments, there may be between four and sixty combustion conduits, more narrowly, twenty and forty. Exemplary conduit lengths are between six inches (15 cm) and forty inches (102 cm), more narrowly, twelve inches (30 cm) and thirty inches (76 cm). The exemplary first passageway  44  cross-sectional areas are between 1.0 inch 2  (6.5 cm 2 ) and twenty inch 2  (129 cm 2 ), more narrowly, 2.0 inch 2  (12.9 cm 2 ) and eight inch 2  (51.6 cm 2 ). An exemplary discharging sector is between 5° and 120°, more narrowly, 10° and 100°. However, the key limitation regarding the charging sector is the time required to charge the combustion conduits at a given radius from the engine centerline and rotational speed. This gives rise to the possibility of multiple charge/discharge cycles during one 360° rotation of the carousel. In such a situation there could be multiple charging and discharging sectors. 
   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, the details of any particular application will influence the configuration of the combustor. Various features of the combustor may be fully or partially integrated with features of the turbine or the compressor. If applied in a redesign of an existing combustor or turbine engine, details of the existing combustor or engine may implement details of the implementation. The principles may be applied to a variety of existing or yet-developed pulsed combustion devices. The principles may be applied in applications beyond turbine engines. Accordingly, other embodiments are within the scope of the following claims.