Patent Publication Number: US-2017370591-A1

Title: Turbine engine combustion assembly

Description:
GENERAL TECHNICAL FIELD 
     The invention relates to the field of combustion assemblies for turbine engines, and more particularly to devices for injecting fuel into the combustion chamber of these assemblies. 
     PRIOR ART 
     A turbine engine generally comprises, from upstream to downstream in the gas flow direction, a fan, one or more compressor stages, for example a high-pressure compressor and a low-pressure compressor, a combustion chamber, one or more turbine stages, for example a high-pressure turbine and a low-pressure turbine, and a gas exhaust nozzle. 
     The appended  FIG. 1  illustrates schematically a longitudinal section view of the combustion assembly  1  of an embodiment of a turbine engine according to the prior art. 
     The combustion assembly  1  is in communication upstream (to the left in  FIG. 1 ) with a compressor (not shown), which supplies it with air under pressure through a diffuser, and is connected downstream to a distributor which is itself connected to a high-pressure turbine (not shown in the figures). 
     The combustion assembly  1  is delimited by annular external casing  2  and internal casing  3 , one extending inside the other along a longitudinal axis X-X′. 
     The combustion assembly  1  comprises a “flame tube” or “combustion chamber”  4  which is the gas combustion site. 
     The flame tube  4  is positioned between the two casings, external  2  and internal  3 , and is provided with front  5  and rear  6  walls of revolution which extend generally one inside the other around the longitudinal axis X-X′. 
     The front  5  and rear  6  walls have a bent annular shape and are connected, upstream, to the inner casing  3 , on either side of a centrifugal injection wheel  7 , and downstream, to the outer casing  2  and to the inner casing  3  respectively. 
     This type of flame tube is called “annular” and extends around the longitudinal axis X-X′ of the combustion assembly  1 . 
     The front and rear walls  5  and  6  are generally positioned at a distance from the outer and inner casings  2  and  3 , so as to form an annular air supply duct  8  surrounding the flame tube  4 . 
     The flame tube  4  comprises several successive zones from upstream to downstream, namely a primary zone  9  wherein the injection wheel  7  leads and an intermediate zone  10  at the bend in the tube, wherein are located several dilution tubes  11 . 
     The air penetrates into the flame tube  4  through a plurality of air intake openings  12  provided through the front wall  5  and a plurality of air intake openings  13  provided through the rear wall  6 , this opposite a portion of the primary zone  9 . 
     The centrifugal injection tube  7  is mounted on an engine shaft  15 , and is driven in rotation thereby. The engine shaft  15  is coaxial with the longitudinal axis X-X′ of the combustion assembly  1 . 
     The combustion assembly is also equipped with a plurality of injectors  16  distributed regularly around the engine shaft  15 . These injectors  16  are positioned between the engine shaft  15  and the inner casing  3  which also constitutes the bottom (or “inner side”) of the flame tube  4  (with respect to the longitudinal axis X-X′). 
     Each injector  16  is positioned so as to project fuel axially (see arrow i), parallel to the longitudinal axis X-X′, onto the front face  17  of the injection wheel  7 , that is the upstream-oriented face of the combustion assembly  1 . 
     As the injection wheel  7  is driven in rotation, the film of fuel which comes into contact with the front face  17  is subjected to centrifugal force and is displaced radially toward the outside of the wheel (see arrow j). 
     The annular peripheral edge  18  of the wheel  7  is bored at regular intervals with several radially oriented holes  19 . 
     The fuel subjected to centrifugal force passes through the holes  19  and is projected radially relative to the engine shaft  15  into the flame tube  4  (arrow k) and is atomized into very fine droplets, which favors its mixing with the compressed air located there. 
     This type of combustion assembly with a centrifugal injection wheel has numerous advantages, particularly for small engines such as helicopter engines. These advantages are the following:
         it is not necessary to have a preferred type of injector,   these injectors are insensitive to the viscosity of the fuel, which is linked to the type of fuel and to the ambient temperature,   the casing of the turbine has a simple structure with low mass and consequently low cost,   it is possible to obtain a compromise between nitrogen monoxide (NOx) on the one hand, and emissions of carbon monoxide (CO) and unburned hydrocarbons (HC) on the other hand, which is such that the emissions are among the lowest of all aeronautical combustion systems.       

     However, this type of combustion assembly also has disadvantages connected with the position of the injectors, which are placed below the flame tube in proximity with the engine shaft and therefore toward the interior of the combustion assembly. Now turbine engines are employed with increasingly higher temperature rise cycles to reduce their specific fuel consumption, which causes coking (that is solidification) of the fuel. It is therefore necessary to clean more and more frequently the injection system and the numerous labyrinth seals positioned around it so as to avoid failures (such as blocking of the shaft by solidified fuel (“coke”), premature wear of the hot parts due to poor fuel distribution, or failure of the engine to start due to blockage of fuel intake). 
     It is then necessary to disassemble a large portion of the turbine engine (and thus to remove the helicopter engine) to be able to have access to the injectors situated in a central location, clean and/or replace them and gain access to the labyrinth seals positioned in proximity to the injection wheel. It is in fact not possible to change the injector when the engine is in place, which leads to additional handling and costs and increases the down-time of the helicopter. 
     In addition, in a combustion assembly like that shown in  FIG. 1 , the diameter of the injection wheel is considerable, because it is necessary to leave sufficient space between the engine shaft  15  and the edge of the wheel  7  to place the injectors  16 . The result is that this injection wheel has considerable mass and is subjected to considerable forces due to the speed of rotation. 
     Document U.S. Pat. No. 4,040,251 describes a combustion assembly of the aforementioned type, wherein the injector and its feed tube are positioned within the thickness of the inner casing and of the bottom of the flame tube. The spraying opening of the injector leads into the opening provided in the bottom for passage of the injection wheel. 
     As with the combustion assembly described previously, access to the injector is difficult and its maintenance is therefore complex and costly. 
     PRESENTATION OF THE INVENTION 
     The invention has as its purpose to provide a combustion assembly of the aforementioned type, but which resolves the disadvantages mentioned above. 
     In particular, the invention has as its purpose to propose a combustion assembly wherein the injector(s) of the flame tube is/are easily disassembled without it being necessary to disassemble the entire turbine engine and remove it from the airframe of the helicopter. 
     To this end, the invention relates to a turbine engine combustion assembly comprising:
         an annular flame tube, comprising a front wall equipped with an upstream zone oriented upstream of the combustion assembly, a rear wall provided with an upstream zone oriented upstream of the combustion assembly and a bottom positioned opposite an engine shaft,   an injection wheel driven in rotation by said engine shaft coaxial with the longitudinal axis X-X′ of the combustion assembly, said injection wheel protruding partially into the flame tube through its bottom and being configured to centrifugally atomize fuel into the flame tube,   at least one injector capable of depositing a film of fuel onto said injection wheel.       

     In conformity with the invention, said injector is positioned through said upstream zone of the front wall or through said upstream wall of the rear wall of the flame tube and in such a manner that its injection opening leads inside this tube opposite to the portion of said injection wheel which is located in said flame tube. 
     Thanks to these features of the invention, it is much easier to disassemble the injectors because it is no longer necessary to have access to an area located between the bottom of the flame tube and the drive shaft of the injection wheel. This disassembly can be carried out on the site where the machine (the helicopter for example) equipped with this combustion assembly is located. 
     Advantageously and according to a first variant embodiment, said injector is positioned through the upstream zone of the front wall of the flame tube, said injection wheel is curved at its perimeter upstream of the combustion assembly, so as to have an annular edge, this annular edge being bored with several radial injection holes and said injector leads into the flame tube opposite the front face of the annular peripheral portion of said injection wheel which is located in the flame tube. 
     Advantageously and according to another variant embodiment, said injector is positioned through the upstream zone of the rear wall of the flame tube, while the injection wheel is curved at its perimeter downstream of the combustion assembly, so as to have an annular edge, this annular edge being bored with several radial injection holes and said injector leads into the flame tube opposite the rear face of the annular peripheral portion of said injection wheel which is located in the flame tube. 
     Advantageously and according to yet another variant embodiment, said injection wheel is solid and has an annular fuel receiving radial face which protrudes into the flame tube and the injector leads into the flame tube opposite this annular fuel receiving face. 
     In the preferred case, the injector is oriented so as to project fuel tangentially onto said fuel receiving face of the injection wheel. 
     It is also possible for the fuel receiving face of the injection wheel to form an angle α with the axis of the injection opening of the injector, this angle α being comprised between 90° and 180°. 
     According to a first variant, in the combustion assembly according to the invention, the axis of the injection opening of the injector extends in a plane which includes the axis of the injection wheel and which is perpendicular to the median plane of the wheel perpendicular to the axis of the injection wheel. 
     According to a second variant, in the combustion assembly according to the invention, the axis of the injection opening of the injector is not perpendicular to the median plane of the wheel perpendicular to the axis of the injection wheel. 
     The invention also relates to a turbine engine comprising a combustion assembly as aforementioned. 
    
    
     
       PRESENTATION OF THE FIGURES 
       Other features and advantages of the invention will appear from the description that will now be made of it, with reference to the appended drawings which represent, indicatively but without limitation, different possible embodiments of it. 
       In these drawings: 
         FIG. 1  is a longitudinal section view of a combustion assembly according to one embodiment of the prior art, 
         FIGS. 2 and 3  are schematic views, in longitudinal section, of two embodiments of a turbine engine combustion assembly conforming to the invention, 
         FIG. 4  is a schematic view of the combustion assembly, taken along a section plane embodied in line IV-IV of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment of the invention will now be described in connection with  FIG. 2 . 
     This  FIG. 2  is a schematic of a combustion assembly  20  which is simplified with relation to that of  FIG. 1  because it shows only the flame tube and the injection assembly. 
     The flame tube  21  comprises a bottom  22  (or inner side of the flame tube), a front wall  23  and a rear wall  24 . The bottom  22  connects the front wall  23  and the rear wall  24 . 
     As for the previous combustion assembly  1 , the flame tube  21  is annular and extends around the longitudinal axis X-X′ of the combustion assembly  20 . 
     The bottom  22  is bored with an opening  25  allowing passage of a portion of the injection wheel  26  into the interior of the flame tube  21 . In other words, the injection wheel  26  protrudes partially into the bottom of the flame tube  21 . 
     The front wall  23  has an upstream zone  230 , oriented upstream of the combustion assembly and of the turbine engine (to the left in  FIG. 2 ), bored with a plurality of air intake openings  27 , opposite the primary combustion zone  28  of the flame tube. 
     Likewise, the rear wall  24  has an upstream zone  240 , oriented upstream of the combustion assembly and the turbine engine, bored with a plurality of air intake openings  29  opposite the primary combustion zone  28  of the flame tube. 
     The injection wheel  26  is driven in rotation by the engine shaft  30 , coaxial with the longitudinal axis X-X′. It has a front face  31 , oriented upstream of the combustion assembly and an opposite rear face  32  oriented downstream. 
     This injection wheel  26  is curved at its perimeter so as to define a peripheral annular edge  33  bored, preferably at regular intervals, with holes  34  oriented radially with respect to the longitudinal axis X-X′ of the combustion assembly  20 . These holes  34  can be orifices or slots. 
     In comparison with the injection wheel  7  of the prior art (see  FIG. 1 ), it will be noted that here the injection wheel  26  penetrates further inside the flame tube  21  because not only is its annular peripheral edge  33  complete inside, but also an annular peripheral portion  260  of the disk that constitutes the wheel  26 . This annular portion  260  is located in the extension of the edge  33 . 
     The inner face of the annular edge  33  is thus located at a distance D 1  from the bottom  22  of the flame tube  21  which is, for its part, opposite the engine shaft  30 . 
     The combustion assembly also comprises one or more injectors  35 , of which only one is visible in  FIG. 2 . 
     This injector  35  is connected to a fuel feed tube  36 , itself connected to a fuel source not shown in the figure. 
     The injector  35  has an injection opening  37 . 
     Unlike the prior art, the injector  35  is positioned so as to pass through the front wall  23  of the flame tube  21 , preferably its upstream zone  230 , through which the air intake openings  27  are provided. In addition, this injector  35  is positioned so that its injection opening  37  leads to the interior of the flame tube  21 . 
     To this end, it will be noted that the distance Dl is sufficient to allow passage of the fuel jet leaving the injection end  37  of the injector  35 . 
     The injection operation is as follows. The fuel leaving the injector  35  leaves through the injection opening  37  and is projected against the front face  31  of the portion  260  of the injection wheel  26 , where it forms a fuel film F. 
     Under the influence of centrifugal force due to the rotation of the injection wheel  26 , the fuel film is displaced toward the perimeter of the wheel and passes through the holes  34 , which has the effect, in contact with the air surrounding the wheel, of pulverizing or atomizing the fuel into very fine droplets G, distributed in the interior of the flame tube  21 . 
     The fact that the injector  31  is positioned through the front wall  23  of the flame tube facilitates its disassembly. Preferably, its configuration will be adapted so as to provide for its extraction through this front wall  23 . 
     Also advantageously, it will be noted that the injection wheel  26  has a smaller diameter than that of the prior art shown in  FIG. 1 , because the bottom  22  of the flame tube  21  can be positioned nearer the engine shaft  30 . It will be noted in this regard that  FIGS. 1 and 2  are not shown at the same scale. 
     The injection wheel  26  having a smaller diameter, its mass is smaller than that of a wheel of the prior art and its mechanical strength is also improved as a result. 
     Another embodiment of the invention will now be described in connection with  FIG. 3 . The same elements bear the same numerical references and will therefore not be described in detail again. 
     The injection wheel bears the reference number  41 . It is driven in rotation by the engine shaft  30 . 
     It differs from the injection wheel  26  in that it is solid, that is it is not bored with injection holes  34 . Its peripheral edge  42  is flared so as to define a circular radial face  43 , preferably flat, for receiving the fuel film F. 
     The injector  35  is positioned so that its injection opening  37  is opposite this face  43 . 
     The axis of the injection opening  37  forms an angle α (alpha) with the fuel receiving face  43 . This angle α is advantageously comprised between 90° and 180°. When it is 180°, fuel injection occurs tangentially to the face  43 . 
     It will also be noted that, in this case, considering the median plane P of the wheel ( 41 ) to be perpendicular to the axis of the engine shaft  30  driving this wheel, then the axis of the injection opening  37  of an injector  35  extends in a plane P 1  which is both perpendicular to P and including the axis of the engine shaft  30 . In  FIG. 3 , the plane P 1  corresponds to the plane of the paper of the figure and in  FIG. 4 , the plane P 1  is shown by a dotted straight line. 
     However, it is also possible to orient the axis of the injection opening  37  so that it is not perpendicular to P. In other words, this axis then protrudes or separates from the plane P 1  corresponding to the plane of  FIG. 3 . In  FIG. 4 , this axis is referred to as X 1 -X′ 1 . 
     In this embodiment, it will be noted that the injector  35  is advantageously inserted less deeply into the flame tube  21  than in the embodiment of  FIG. 2 , because it is not necessary for its injection opening to reach the zone located below the annular edge  33  of the injection wheel. It is sufficient that the injector allows the projection of fuel onto the face  43 . The disassembly of the injection  35  is thereby facilitated. 
     As before, the fuel film F is subjected to the centrifugal force generated by the wheel  41  and is atomized in the form of fuel droplets G. 
     This embodiment of the invention makes it possible to have an injection wheel  41  which has a structure with great simplicity and good mechanical endurance because it is not bored with through holes. Its diameter is also smaller than in the prior art because the bottom  22  of the flame tube  21  can be brought closer to the engine shaft  30 . Finally, combustion occurs substantially on only one side of the injection wheel  41 , to the left in  FIG. 3  here. 
     Moreover, it will be noted that variant embodiments of the invention are possible. In particular, the injector  35  can be positioned through the rear wall  24  of the flame tube  21 , preferably through its upstream zone  240 . 
     In this case, and when the injection wheel  26  is made according to the embodiment of  FIG. 2 , its annular edge  33  is turned downstream of the combustion assembly  20  and fuel injection occurs on the rear face  32  of the wheel. 
     When the injector is positioned through the rear wall  24  and the injection wheel  41  conforms to the embodiment of  FIG. 3 , then its receiving face  43  is oriented toward the rear wall  24 . 
     The different possible inclinations of the axis of the injection opening  37  and the different values of the angle α previously described also apply to this variant embodiment. 
     Finally, according to another variant embodiment, it is possible to provide that the flame tube  21  is made in several portions, assembled using a flange  50  which facilitates disassembly.