Patent Publication Number: US-2018038278-A1

Title: Constant-volume combustion system for a turbine engine of an aircraft engine

Description:
TECHNICAL FIELD 
     The invention relates to a constant-volume combustion system, also designated by the acronym CVC, or by the term combustion according to the Humphrey cycle, this system being intended to equip a turbomachine of an aircraft engine. 
     STATE OF PRIOR ART 
     The combustion chamber of most of the current aircraft engines, of the turbojet engine type, operates according to the Brayton cycle which is a constant pressure continuous combustion cycle. 
     However, it is known that the replacement of a constant pressure combustion system by a constant-volume combustion system, that is implementing the Humphrey cycle, should bring about a specific consumption gain that can reach up to twenty percents. 
     Generally, the Humphrey cycle imposes to preserve the load in a physically closed volume for some part of the cycle, and it induces the implementation of a pulsed type operating region. 
     In practice, a constant-volume combustion aircraft engine includes a compressor, an exhaust pipe and a combustion chamber connected to the compressor and to the pipe, by respectively injection and ejection valves. 
     Each constant-volume combustion cycle includes a phase of intake and setting in the combustion chamber of a compressed air and fuel mixture, a phase of ignition by a controlled system and combustion of the mixture, and a phase of expansion and ejection of the combustion gas. 
     Valves are controlled in a synchronised manner to implement these three phases of the Humphrey cycle: they are in particular all closed during the combustion phase, after which the opening of the ejection valve(s) allows the expansion and ejection of the combustion gases. 
     In known constant-volume combustion systems, it has been attempted to date to reduce the general bulk of the system, in particular to integrate it in the thickness of the aircraft wing. 
     The object of the invention is on the contrary to provide a constant-volume combustion system architecture that can be simply integrated to a current turbomachine architecture, having a generally cylindrical shape and with a large diameter. 
     DISCLOSURE OF THE INVENTION 
     One object of the invention is a constant-volume combustion system for an aircraft turbomachine, this system comprising:
         several combustion chambers evenly distributed about a longitudinal axis;   a compressed air manifold extending about the longitudinal axis and comprising a radially oriented compressed air outlet for supplying compressed air from a compressor of the turbomachine, to each combustion chamber;   an exhaust pipe extending about the longitudinal axis and comprising a radially oriented inlet to receive the combustion gases from the combustion chambers as well as an axially oriented outlet, the combustion chambers being radially interposed between the outlet of the manifold and the inlet of the exhaust pipe;   timing means for timing the intake into each combustion chamber of compressed air from the outlet of the manifold and the ejection out of each combustion chamber of combustion gases to the exhaust pipe.       

     With this arrangement, the combustion system radially extends on a small length along the longitudinal axis, which facilitates its integration to a current turbomachine, where it can be installed in place of a continuous combustion chamber, namely between the compression stages and the turbine stages. 
     The invention also relates to a combustion system thus defined, comprising a combustion body carrying the combustion chambers, this combustion body including at each combustion chamber, a radially oriented compressed air intake aperture, and a radially oriented combustion gas exhaust aperture, and a rotary feeder with means for rotatably driving this rotary feeder, this rotary feeder including:
         an intake ring coaxial with the longitudinal axis and provided with intake ports, this intake crown being radially interposed between the outlet of the manifold and the combustion body;   an exhaust ring coaxial with the longitudinal axis and provided with exhaust ports, this exhaust ring being radially interposed between the inlet of the exhaust pipe and the combustion body.       

     The invention also relates to a combustion system thus defined, wherein the outlet of the manifold extends about the combustion chambers and wherein the combustion chambers are located about the inlet of the exhaust pipe. 
     The invention also relates to a combustion system thus defined, wherein the inlet of the exhaust pipe extends about the combustion chambers, and wherein the combustion chambers are located about the outlet of the manifold. 
     The invention also relates to a combustion system thus defined, wherein each combustion chamber includes an intake port and an exhaust port, and wherein each combustion chamber is rotatably mounted about an axis which is central to the same to be rotatable on itself, means for rotatably driving the combustion chambers, each intake port allowing intake of compressed air into the chamber when this port is facing the outlet of the compressed air manifold, each exhaust port allowing exhaust of combustion gases out of the combustion chamber when this exhaust port is facing the inlet of the exhaust pipe. 
     The invention also relates to a combustion system thus defined, wherein the means for rotatably driving each combustion chamber comprise a toothed wheel rotatably driven about the longitudinal axis and for each combustion chamber, a pinion meshed with this toothed wheel by being radially spaced apart from the longitudinal axis, each pinion being rigidly coupled to a corresponding combustion chamber. 
     The invention also relates to a turbomachine comprising a constant-volume combustion system thus defined. 
     The invention also relates to a turbojet engine type aircraft engine comprising a turbomachine thus defined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side cross-section view of a first embodiment of the system according to the invention comprising a fixed combustion chamber and which is integrated to an engine with a centrifugal compressor; 
         FIG. 2  is a transverse cross-section view showing the arrangement of the combustion chambers for the first or the second embodiment of the invention; 
         FIG. 3  is a close-up view showing the arrangement of the intake and ejection ports in the first embodiment of the invention; 
         FIG. 4  is a partial schematic side cross-section view of a second embodiment of a system according to the invention also comprising a fixed combustion chamber and which is integrated to an engine with an axial compressor; 
         FIG. 5  is a partial schematic side cross-section view of a third embodiment of the system according to the invention comprising a rotary combustion chamber and which is integrated to an engine with a centrifugal compressor. 
     
    
    
     DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS 
     Generally, the invention is applicable to a turbomachine comprising a compressor that can be centrifugal or even axial, and a turbine that can be radial or even axial. 
     In  FIG. 1 , an engine  1  equipped with the constant-volume combustion system according to the invention has a general structure of a revolution about a main axis AX which corresponds to its longitudinal axis. 
     This engine includes upstream thereof a compressor  2  which is herein a centrifugal compressor, to supply a constant-volume combustion system generally designated by reference  3 , ejecting combustion gases at the inlet of an exhaust pipe  4  which is located downstream of this combustion system. 
     The compressor  2 , the combustion system  3  and the exhaust pipe  4  have themselves revolution structures while being located behind each other along the axis AX, being surrounded as a whole by a revolution case  6  represented symbolically. 
     The centrifugal compressor  2  is supplied with air from upstream of the engine and which is conveyed in parallel to the longitudinal axis. When this air has passed through the centrifugal compressor, it is radially ejected along a centrifugal direction, that is moving away from the axis AX, to be received at the inlet of a manifold  7  in which it first travels longitudinally to downstream of the engine. By continuing its travel in this manifold  7 , the air is then radially directed along a radial direction, that is to the axis AX, to exit from the manifold  7  in order to enter the combustion system  3  itself. 
     After they have been burned in the constant-volume combustion system  3 , the combustion gases are ejected from this system  3  radially along a radial direction by being taken in at the inlet of the exhaust pipe  4 . During their travel in this exhaust pipe, the gases are adjusted to be expanded in parallel to the axis AX. This expansion can, according to the architecture retained, be used to directly generate a thrust, or even drive a turbine not represented which is located downstream of the exhaust pipe  4 . 
     As visible in  FIG. 1 , the combustion system  3  itself has a general toric structure. This system is surrounded by the outlet of the manifold  7 , and it surrounds the inlet of the exhaust pipe  4 , while being located along the axis AX at the same level as the outlet of the manifold  7  and as the inlet of the exhaust pipe  4 . 
     This combustion system  3  includes a fixed combustion body  8  having here four combustion chambers  11 - 14  evenly spaced apart from each other about the axis AX. 
     Each combustion chamber  11 - 14  is a closed enclosure delimited by one or more walls, but including an intake aperture  11   a - 14   a  at its outer peripheral face, and an ejection aperture  11   e - 14   e  at its inner peripheral face. 
     The intake apertures  11   a - 14   a  enable the compressed air from the outlet of the manifold  7  to be taken in the chambers  11 - 14 , whereas the ejection apertures enable the combustion gases to be discharged to the inlet of the exhaust pipe. These intakes and ejections occur in an independent and coordinated manner for each of the chambers  11   a - 14   a  of the combustion body. 
     The gas intakes and ejections are insured and synchronised by a rotary feeder  16  which comprises an intake ring  17  surrounding the combustion body  8  by running along its outer face, and an ejection ring  18  running along the inner face of the combustion body  8  by being surrounded by the same. 
     The intake ring  17  and the ejection ring  18  each have a truncated cylinder shape, centred on the axis AX, and they join each other at a bottom  19  of the feeder  16 . This rotary feeder  16  thus has generally a U-shaped cross-section toric gutter shape which covers the upstream, inner and outer faces of the combustion body  8 . 
     The intake ring  17  surrounds the combustion body  8  by being interposed between this combustion body  8  and the outlet of the manifold  7 . In an analogous way, the ejection ring  18  is surrounded by the combustion body  8  by being interposed between this body and the inlet of the exhaust pipe  4 . 
     As visible in  FIG. 3 , the intake wall  17  includes a series of four intake apertures or ports referred to as  17   a , evenly distributed along this intake wall, that is evenly distributed about the axis AX. 
     In the same manner, the ejection wall  18  includes four ejection apertures or ports  18   e  evenly distributed along this wall, that is about the axis of revolution AX. 
     In use, the feeder  16  is rotatably driven about the axis AX, to sequence gas intakes and ejections for the different chambers. 
     More particularly, when a port  17   a  of the feeder  16  is at least partially facing the intake aperture  11   a  of the window  11 , compressed air from the compressor is taken in the chamber  11  via the outlet of the manifold  7 . 
     Since the feeder  16  continues rotating, the port  17   a  spaces apart from the intake aperture  11   a  until the latter is closed. Under this situation, the ejection aperture  11   e  is also closed by the ejection wall  18 , such that fuel can be injected into the chamber  11  via an injector  21  visible in  FIG. 1 . After the fuel is injected, the combustion in the closed chamber is triggered by a plug  22 , or any other controlled ignition system. 
     Since the feeder  16  continues rotating, about the axis AX, an ejection port  18   e  comes to face the ejection aperture  11   e  of the chamber  11 , which enables the combustion gases to be ejected into the exhaust pipe  4  via its inlet, to produce a thrust or supply a turbine. 
     Since the feeder  16  continues rotating, a new window  17   a  comes in registry with the intake aperture  11   a , which enables a new compressed air intake to be started. 
     It is to be noted that during the start of the compressed air intake, the gas ejection is still open because there is an overlapping portion during which the intake and the ejection ports are simultaneously open. This overlapping enables the combustion gases to be flushed. 
     On the other hand, the cycle just described for the combustion chamber  11  happens in the same way for the other chambers, that is chambers  12 - 14 . 
     As visible in  FIG. 1 , the manifold  7  is delimited by two revolution walls, namely an inner wall  23  and an outer wall  24 , the inner space of this manifold thus having a generally toric-shape centred on the axis AX. The inner wall  23  can be fixed, or be rigidly integral with the rotary feeder  16  to rotate with the same, as is the case in the example of  FIG. 1 . 
     The outer wall  24  is here fixed by being for example rigidly fastened to the case  6 . It includes an inner peripheral edge, located facing the ring for supplying the feeder  16  which is on the contrary rotating. A circular sealing means  27  is interposed between the inner edge of the outer wall  24  and the outer face of the supply wall  17  in order to insure a satisfactory sealing at this junction, when the feeder  16  rotates relative to the inner edge of the outer wall  24 , that is when the engine is in use. 
     The exhaust pipe  4  is itself delimited by an outer revolution wall  28  and an inner revolution wall  29 , this pipe  4  having itself a toric architecture about the longitudinal axis AX. 
     The inner wall  29  is here fixed. It includes an outer peripheral edge which is located facing the ejection ring  18  along which it runs. A sealing means  31  is interposed between this outer edge and the inner face of the ejection ring  18  to insure a satisfactory sealing of the junction of these two elements when the rotary feeder rotates, that is when the engine is in use. 
     The outer wall  28  which is also fixed includes an outer peripheral edge which is rigidly fastened to an internal portion of the combustion body  8  which is also fixed. 
     The sealing of the rotary feeder with the combustion body is also optimised by four circular sealing means. 
     Two circular sealing means  32  are interposed between the inner face of the intake ring  17  which is rotary and the outer face of the combustion body  8  which is fixed, by being disposed on either side of the intake ports  17   a  and the intake apertures  11   a - 14   a  along the longitudinal axis AX. Both these means aim at limiting, or even cancelling, the amount of air taken in by an intake port  17   a  which leaks before reaching the corresponded intake aperture. 
     Analogously, two other circular sealing means  33  are also interposed between the outer face of the ejection ring  18  which is rotary and the inner face of the combustion body  8  which is fixed, by being disposed on either side of the ejection ports  18   e  and the ejection apertures  11   e - 14   e  along the longitudinal axis AX. 
     According to the invention, the compressed air and combustion gas stream passing through the combustion chambers is moving radially, that is perpendicularly to the axis AX. 
     In the example of  FIG. 1 , this stream is radial, that is it is directed to the axis, which is appropriate for an architecture with a centrifugal compressor, that is delivering a compressed air radial stream remotely from the axis, this stream being also possibly deviated to be redirected to the axis for the combustion thereof. 
     The invention is also applicable to an axial compressor engine architecture, as in the example of  FIG. 4 , wherein the stream passes through the combustion chambers by being oriented in a centrifugal manner, unlike the case of  FIG. 1 . 
     In the example of  FIG. 4 , the engine, referred to as  41  includes an axial compressor, not represented, which delivers compressed air in an axial manifold  42  delimited by an cylindrical inner wall  43  and an outer revolution wall  44  both of which are fixed. 
     The compressed air first travels longitudinally in this manifold  42  to be then radially deviated therein in order to exit from this manifold by following a centrifugal radial direction, so as to enter the constant-volume combustion system  46  which surrounds the outlet of this manifold  42 . 
     The combustion gases are then radially ejected from the system  46  along a radial direction to come to the inlet of an exhaust pipe  47  which is also delimited by an inner revolution wall  48  and an outer revolution wall  49 . This exhaust pipe has a toric shape the inlet of which surrounds the combustion system  46 , and its inner wall as well as its outer wall are both fixed. 
     The trajectory of the combustion gases which are taken radially in this exhaust pipe  47  is adjusted in order that they travel longitudinally, so that these gases are expanded along the direction AX so as to be able to supply a turbine not represented or to generate directly a longitudinally oriented thrust. 
     The constant-volume combustion system  46  is quite analogous to the combustion system  3  of the example of  FIGS. 1 and 3 . It includes a combustion body  51  which is identical to the combustion body  8 , and which comprises several combustion chambers evenly distributed about the axis AX. 
     The gas intake and ejection is once again synchronised by a rotary feeder  52  which is analogous to the feeder  16  of the example of  FIG. 1 , this feeder having also a U-shaped cross-section toric gutter shape which partially covers the combustion body. 
     But, the feeder  52  is herein oriented upstream, in opposition to that of  FIG. 1 , that is it covers the downstream face of the combustion body, as well as the outer and inner peripheral faces of this body. 
     This rotary feeder  52  includes also an outer ring, referred to as  53  as well as an inner ring referred to as  54  which it is also cylindrical. Thus, the general structure of the feeder  52  is identical to that of the feeder  16 , but it is its inner ring  54  which is equipped with intake ports to make up the intake ring, and it is its outer ring  53  which is provided with ejection ports to make up the exhaust ring. 
     Analogously, the intake apertures are located at the inner cylindrical wall of the combustion body  51 , and the ejection apertures are formed at the outer wall of this combustion body  51 . 
     The operation of this other engine  41  is analogous to that of the engine  1 : the intakes and exhausts being synchronised here again by a circular rotary feeder which surrounds the combustion body, but the gases taken in and ejected follow here a trajectory which is centrifugal instead of being radial. 
     The sealing of the rotary feeder  52  with le combustion body  51  is here again optimised by four circular sealing means. 
     Two circular sealing means are interposed between the outer face of the rotary intake ring and the inner face of the fixed combustion body, by being disposed on either side of the intake ports and apertures along the axis AX. Both means aim at limiting, or even cancelling, the amount of air taken in by an intake port which leaks before reaching the corresponding intake aperture. 
     Analogously, two other circular sealing means are interposed between the inner face of the rotary ejection ring and the outer face of the fixed combustion body, by being disposed along the axis AX on either side of the ejection ports and apertures. 
     In a complementary fashion, a circular sealing means is interposed between the outer edge of the inner wall  43  of the manifold  42  and the inner face of the supply ring in order to ensure a satisfactory sealing for this junction, when the feeder rotates. 
     Another circular sealing means is interposed between the inner edge of the inner wall  48  of the exhaust pipe  47  and the outer face of the ejection ring to ensure a sealing of the junction of both these elements when the rotary feeder rotates. 
     In the embodiment of  FIGS. 1 to 4 , the combustion body is fixed, and it is a rotary feeder which synchronises the intakes and exhausts for each combustion chamber, these intakes and exhausts occurring along radially oriented trajectories. 
     But the invention also relates to an architecture in which each combustion chamber is provided rotary and rotatably driven to synchronise the air intakes and combustion gas exhausts. 
     It is the case in the example of  FIG. 5  where this solution is applied to an engine  61  provided with a compressor which is centrifugal, this engine  61  thus having a general structure identical to that of the engine of  FIG. 1 . 
     This engine which appears in  FIG. 5  comprises much like that of  FIG. 1 , a centrifugal compressor  2  upstream thereof to supply a constant-volume combustion system  62  which ejects combustion gases at the inlet of the downstream exhaust pipe  4 . 
     The compressor  2 , the combustion system  62  and the exhaust pipe  4  have themselves revolution structures while being distributed behind each other along the axis AX, being surrounded as a whole by a case  6 . 
     The compressor  2  delivers air it radially ejects along a centrifugal direction, this being received at the inlet of the manifold  7  in which it first travels longitudinally to downstream before being radially adjusted along a radial direction at the outlet of the manifold  7  to enter the system  62 . 
     After being burned in the system  62 , the gases are radially ejected along a radial direction to be taken in at the inlet of the exhaust pipe  4  in which they are then adjusted to be expanded in parallel to the axis AX. 
     The combustion system  62  houses in a general toric structure which is surrounded by the outlet of the manifold  7  and which surrounds the inlet of the exhaust pipe  4 , while being located along the axis AX at the same level as the outlet of the manifold  7  and as the inlet, the pipe  4 . 
     The constant-volume combustion system includes here again several distinct combustion chambers, for example four in number, which are evenly distributed about the axis AX, one of these chambers appearing in the Fig. by being referred to as  63 . 
     This combustion chamber  63  is surrounded by a fixed outer jacket  64  in which there are rotatably mounted so as to be able to pivot about a longitudinal axis of rotation AR which is radially spaced from the axis AX. 
     The engine is still equipped with means for rotatably driving each inner shroud of the combustion chamber. These driven means are here a gear train  66  comprising for example a main wheel  67  with a large diameter centred on the axis AX, and for each combustion chamber, a pinion  68  driven by this main wheel and itself driving the combustion chamber to which it is mated by being for example rigidly fastened thereto. 
     The fixed jacket  64  includes an intake aperture  69  which is located at the region of this jacket which is the farthest from the axis of revolution AX, this aperture being thus facing the outlet of the manifold  7 . Analogously, this fixed jacket  64  also includes an ejection aperture  71  which is on the contrary located at the closest region thereof to the axis AX, to directly open into the inlet of the exhaust pipe  4 . The intake and exhaust apertures are advantageously spaced apart from each other along the axis AX. 
     In a complementary fashion, the rotary combustion chamber  63  includes an intake port and an exhaust port, respectively located along the axis AX, at the intake aperture  69 , and at the ejection aperture  71 . These ports can be spaced apart from each other about the axis AR so as to optimise timing of the compressed air intakes and combustion gas ejection. 
     Thus, during the rotation of the combustion chamber  63  about its axis AR, when the intake port is facing the aperture  69 , compressed air is taken in the chamber, from the outlet of the manifold  7 . When the intake port is no longer facing the aperture  69 , the chamber  63  is completely closed, which enables fuel to be injected and combustion to be caused by a controlled ignition, implementing for example a plug. 
     Then, the rotational movement of the chamber  63  results in a situation in which the ejection port is located facing the exhaust aperture  71 , which enables the combustion gases to be ejected into the inlet of the exhaust pipe  4  to be expanded in order to drive a turbine or to generate a thrust. 
     The intake and exhaust ports can be located at the same level about the axis AR by being spaced apart from each other along this axis, such that when the intake port is facing the aperture  69 , the exhaust port is sealed by the rest of the jacket. In the same manner, when the exhaust port is facing the aperture  71 , the intake port is sealed by the rest of the jacket in this region. In this case, the intake and exhaust apertures are then also spaced apart from each other along the axis AX by an appropriate value. 
     As will be understood, the other combustion chambers have the same operation as the chamber  63 , which enables these different chambers to deliver combustion gases at the inlet of the exhaust pipe  4 . 
     In the example that has been described, the invention is applied to a turbomachine of an aircraft engine, but the invention is applicable as well to a turbomachine being part of a different equipment, such as in particular a terrestrial electrical power generation equipment or else.