Abstract:
The invention relates to the field of injectors, and in particular to an injector element ( 201 ) having at least one first helical channel ( 204 ) and at least one second helical channel ( 205 ), each of said helical channels ( 204, 205 ) following a respective helix ( 204   a,    205   a ) centered on a central axis (X) of the injector element ( 201 ). The helix ( 205   a ) of the at least one second helical channel ( 205 ) is situated inside the helix ( 204   a ) of the at least one first helical channel ( 204 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to the field of injectors, and in particular to elements for injecting a mixture of at least two propellants into a combustion chamber, such as for example a combustion chamber of a rocket engine. 
         [0002]    Patent document FR 2 712 030 A1 describes a two-propellant injector for injecting into a rocket engine combustion chamber, which injector has a feed structure in which the two propellants feed a plurality of injector elements arranged parallel to one another in an axisymmetric configuration over the surface of a circular injector plate structure that forms part of the injector. Such an injector plate may also be associated with quite a large number of injector elements, for example as many as one hundred or more, with their individual flow rates being combined in order to deliver the total flow rate for the engine. 
         [0003]    In that prior art injector, each injector element has a first channel for injecting the first propellant and a second channel for injecting the second propellant, the second channel being annular and coaxially adjacent around the outside of the first channel. 
         [0004]    In the present context, the term “annular channel” is used to mean a channel having a radial cross-section showing an annular flow section, whereas a “tubular” channel is used to mean a channel having an uninterrupted cross-section. Furthermore, the terms “upstream” and “downstream” are defined relative to the flow direction of the propellants. 
         [0005]    Thus, since the propellants are injected into the combustion chamber via the coaxial channels of the injector elements of the injector of FR 2 712 030 A1, the turbulence that arises in the boundary layers between said concentric and adjacent flows can serve to ensure uniform mixing of the two propellants by shear in their flow. 
         [0006]    Nevertheless, starting from that basic concept, difficulties are encountered in changing the geometrical parameters in order to increase the individual power of each injector element without degrading the quality of the injection and of the combustion. With greater flow rates, the mixing becomes less uniform and the quality of combustion degrades. 
         [0007]    One technique that has been proposed for improving the quality of mixing is that of imparting turning motion to at least one of the propellants. For that purpose, in the injector element disclosed for example in European patent application EP 0 344 463 A1, a twisted plate is used to generate such turning motion in one of the propellants. In another solution, disclosed in European patent application EP 1 873 390 A2, the injector element has helical channels for injecting one of the propellants. Nevertheless, it is desired to improve the uniformity of mixing above that provided by those devices of the prior art. 
       OBJECT AND SUMMARY OF THE INVENTION 
       [0008]    The present invention seeks to propose an injector element for injecting at least two propellants into a combustion chamber, the injection element comprising at least one first helical channel and at least one second helical channel, each of said helical channels having a center line following a respective helix centered on a central axis of the injector element, and making it possible to obtain more uniform mixing of the propellants. 
         [0009]    In at least one embodiment, this object is achieved by the fact that the helix of the at least one second channel is situated inside the helix of the at least one first channel. Thus, a point of intersection of the center line of at least one second helical channel with a plane perpendicular to said central axis is closer to the central axis than is a point of intersection of the center line of at least one first helical channel with the same plane. These helical channels following concentric helices encourage better mixing of the propellants. 
         [0010]    If the injector element has a plurality of such first helical channels and a plurality of such second helical channels, together they form concentric rings around the central axis. 
         [0011]    The helix of each helical channel may be a circular helix, i.e. a helix included in a circle, or alternatively it may be a conical helix. Such conical helices enable converging channels to be obtained, thereby encouraging better mixing of the propellants. Helices other than circular or conical helices could nevertheless also be envisaged, depending on requirements. 
         [0012]    Also for the purpose of improving mixing of propellants downstream from the injector element, at least one of said helical channels may present a non-circular section that is twisted around the helix. It is thus possible to obtain twisting of the flow lines in each helical channel twisted in this way, thereby facilitating mixing of the propellants downstream. 
         [0013]    In order to increase turbulence downstream from the injector element, and also in order to improve mixing of the propellants downstream from the injector element, the helices of the first and second helical channels may turn in opposite directions. This may be particularly effective if the first helical channel is connected to an inlet for a first propellant and the second helical channel is connected to an inlet for a second propellant, which inlet is separate from the inlet for the first propellant, with the turbulence between the two propellants thus being increased. 
         [0014]    Nevertheless, it is also possible to envisage that said first and second helical channels are connected to the same propellant inlet. In particular, although not only in this situation, the injector element may have at least one third channel, that may also be helical, following a helix centered likewise on the central axis of the injector element, but possibly presenting as an alternative some other shape, such as for example an annular shape or a straight tubular shape. This third channel may be arranged outside the helix of the first helical channel, inside the helix of the second helical channel, or between the helices of the first and second helical channels. 
         [0015]    At least one of the first and second channels may be formed inside a single-piece part. By means of these provisions, it is possible to optimize the section of the helical channel in order to obtain better mixing with reduced head loss. In addition, the injector element may thus be made more robust. Said single-piece part may in particular be produced by additive fabrication. 
         [0016]    In order to facilitate mixing, while separating the flow lines of the second propellant, the injector element may have a plurality of helical channels for injecting the second propellant, each following a respective helix centered on the central axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention can be well understood and its advantages appear better on reading the following detailed description of embodiments given as non-limiting registrations. The description refers to the accompanying drawings, in which: 
           [0018]      FIG. 1  is a diagrammatic view of a liquid propellant rocket engine; 
           [0019]      FIG. 2A  is a cutaway side view of an injector element in a first embodiment; 
           [0020]      FIG. 2B  is a diagrammatic view of the helical channels of the  FIG. 2A  injector element; 
           [0021]      FIG. 3A  is a cutaway side view of an injector element in a second embodiment; 
           [0022]      FIG. 3B  is a diagrammatic view of the helical channels of the  FIG. 3A  injector element; 
           [0023]      FIG. 4A  is a cutaway side view of an injector element in a third embodiment; 
           [0024]      FIG. 4B  is a cross-section view of the  FIG. 4A  injector element on line IVB-IVB; 
           [0025]      FIG. 5  is a cross-section view of an injector element in a fourth embodiment; 
           [0026]      FIG. 6A  is a diagrammatic view of three helical channels of an injector element in a fifth embodiment; 
           [0027]      FIG. 6B  is a cross-section view of the  FIG. 6A  injector element; 
           [0028]      FIG. 7A  is a diagrammatic side view of a helical channel in a variant of the invention; and 
           [0029]      FIG. 7B  is a cross-section view of the  FIG. 7A  channel on plane VIC. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]      FIG. 1  is a diagram showing a rocket engine  1  having liquid propellants, and in particular cryogenic liquid propellants. The rocket engine  1  has a tank  2  for the first propellant, a tank  3  for the second propellant, a gas generator  4  fed by the first and second propellants, a turbopump  5  actuated by combustion gas coming from the gas generator  4 , a main combustion chamber  6  fed with propellants by the turbopump  5 , and a converging-diverging nozzle  7  for thrust ejection of the combustion gas generated in the main combustion chamber  6 . 
         [0031]    In order to obtain efficient combustion both in the gas generator  4  and in the main combustion chamber  6 , these components have injector members for injecting propellants that make it possible to obtain a uniform mixture and distribution of the propellants. Typically, these injector members are in the form of injectors comprising an injector plate having a plurality of injector elements for the two propellants arranged therein. 
         [0032]      FIGS. 2A and 2B  show an injector element  201  for injecting and mixing two propellants E 1  and E 2 . The injector element  201  presents a central axis X, which is also the main flow axis of the propellants E 1  and E 2 . 
         [0033]    The injector element  201  comprises a set of first helical channels  204  for injecting the first propellant E 1  arranged around a set of second helical channels  205  for injecting the second propellant E 2 . In this first embodiment, the helices  204   a  forming the center lines of the first channel  204  are circular helices turning in a first direction and the helices  205   a  forming the center lines of the second channel  205  are helices that are likewise circular but turning in a second direction opposite to the first direction, about the same central axis X. 
         [0034]    The injector element  201  is formed as a one single-piece part with the helical channels  204  and  205  being formed in the mass of this single-piece part. 
         [0035]    The first helical channels  204  are connected to an inlet for the first propellant E 1  and they are configured to inject this first propellant E 1 , while the second helical channels  205 , situated inside the helices  204   a  of the first helical channel  204 , are connected to an inlet for the second propellant E 2  and they are configured to inject this second propellant E 2 . While the injector element  201  is in operation, the helical channels  204  and  205  separate the flow lines of each of the propellants E 1  and E 2 , imparting rotary motion in opposite directions to each of the propellants. The angle of inclination of the flow of the second propellant E 2  relative to that of the first propellant E 1  leads to shear between them, producing turbulence that serves to obtain uniform mixing of the two propellants E 1  and E 2  downstream from the injector element  201 . 
         [0036]    Although the helical channels  204  and  205  in this first embodiment follow circular helices, it is possible to envisage other alternative shapes. Thus, in the embodiment shown in  FIGS. 3A and 3B , where each element receives the same reference number as the equivalent element in the first embodiment, the helical channels  204  and  205  follow center lines in the form of conical helices  205   a  converging on the central axis X in the downstream direction. Thus, during operation of this injector element  201 , the flows that are obtained of the propellants E 1  and E 2  are not only rotating, but also converging. This convergence thus encourages mixing of the two propellants E 1  and E 2  downstream from the injector element  201 . It is possible to envisage other helical shapes for other embodiments. It should thus be understood that in the present context, the term “helix” is used broadly, possibly even covering a line presenting a variable angle relative to the central axis X and thus presenting a variable pitch between spires. 
         [0037]    In yet another embodiment, shown in  FIGS. 4A and 4B , the concentric first and second helical channels  204  and  205  are all connected to the inlet of the second propellant E 2 . It is thus possible to inject the second propellant E 2  via a plurality of concentric rings  210  of helical channels  204 ,  205 , thereby obtaining a better match to a desired flow rate for the second propellant E 2 . A third channel  206  of annular section and connected to the inlet for the first propellant E 1  serves to inject the first propellant E 1 . This third channel  206  is situated outside the helices  204   a,    205   a  of the first and second helical channels  204 ,  205 . The remaining elements of the injector element  201  shown in  FIGS. 4A and 4B  are given the same reference numbers as the corresponding elements in the preceding figures. 
         [0038]    Nevertheless, as an alternative, the third channel  206  may be situated inside the concentric rings  210  of the first and second helical channels  204  and  205 , as in the embodiment shown in  FIG. 5 . In this embodiment, the third channel  206  is a straight tubular channel. As in the above-described embodiment, the concentric first and second helical channels  204  and  205  are all connected to the inlet for the second propellant E 2 , while the third channel  206  is connected to the inlet for the first propellant E 1 . The remaining elements of the injector element  201  shown in  FIGS. 5A and 5B  are given the same reference numbers as the corresponding elements in the preceding figures. 
         [0039]    At least one third channel  206  may also be helical, as in the embodiment shown in  FIGS. 6A and 6B . In this embodiment, the injector element  201  has a plurality of third helical channels  206  arranged between the first helical channels  204  and the second helical channels  205 . As can be seen in  FIG. 6A , which is a diagram of one of the channels  204 , one of the channels  205 , and one of the channels  206 , in order to optimize mixing of the propellants E 1  and E 2  downstream, the third helical channels  206  turn in the opposite direction to the first and second helical channels  204  and  205  about the central axis X. As in the above-described embodiment, the concentric first and second helical channels  204  and  205  are all connected to the inlet for the second propellant E 2 , while the third channel  206  is connected to the inlet for the first propellant E 1 . 
         [0040]    In each of the above-described embodiments, the helical channels are formed in a single-piece part, thereby making it possible in particular for them to be given a particular section. For example, as shown in  FIGS. 7A and 7B , each helical channel  205  may present a non-circular section transversely relative to the helix  205   a,  this non-circular section being twisted around the helix  205   a  in order to cause flow lines to turn around the helix  205   a.  In operation, this provides even more effective mixing of the propellants downstream from the injector element. 
         [0041]    Several methods may be used for fabricating single-piece parts of shapes that are this complex. In particular, so-called additive fabrication methods may be used for fabricating such a part. In this context, the term “additive fabrication” is used to mean fabrication methods in which a material is assembled, typically layer by layer, so as to build up a part from data defining a three-dimensional (3D) model. Among additive fabrication methods that are suitable for use in fabricating such a single-piece part, there are in particular selective laser melting and selective laser sintering, both of which methods make it possible to use additive fabrication to make parts out of metallic or ceramic material. Nevertheless, other fabrication methods may be envisaged, such as casting (in particular lost model casting), machining (in particular electric discharge machining), etc. Alternatively, the injector elements may also be produced by assembling a plurality of parts. 
         [0042]    Even though the present detailed description refers to a rocket engine having a turbopump actuated by the combustion gases from a gas generator, injectors of the same type could naturally be used in other types of fluid propellant rocket engine, such as for example rocket engines of the so-called “expander” cycle type or rocket engines having pressurized propellants. 
         [0043]    Although the present invention is described with reference to a specific embodiment, it is clear that various modifications and changes can be made to these embodiments without going beyond the general scope of the invention as defined by the claims. In addition, individual characteristics of the various embodiments described may be combined in additional embodiments. Consequently, the description and the drawings should be considered in a sense that is illustrative rather than restrictive.