Abstract:
The invention concerns a rocket engine wherein the combustion chamber includes at least one first monolithic component made of a thermostructural composite material comprising a porous wall through which the fuel is introduced in the core of the combustion chamber. A small part of the fuel is directed towards the neck for it to be cooled.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a rocket engine comprising a combustion chamber in which a fluid (liquid or gaseous) fuel, for example hydrogen, and a fluid (liquid or gaseous) oxidizer, for example oxygen, are burnt, said combustion chamber being connected to a divergent nozzle through which the gases resulting from the combustion escape. 
     BACKGROUND OF THE INVENTION 
     In known rocket engines of this type, because of the very high temperatures (of the order of 3300° C.) reached in said combustion chamber, the structure of the walls is particularly complex with networks of ducts for circulating a cooling fluid which, incidentally, may be said fuel itself. Examples of known walls are described, for example, in documents FR-A-2 773 850, FR-A-2 774 432, FR-A-2 791 589. In addition, the structure of said walls is not uniform but by contrast varies along the axis of the engine, according to the temperature at that point. Finally, particularly on account of the fact that the fuel is used as a cooling fluid and can circulate in the two opposite directions, these known engines require complex fuel supply manifolds. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome these disadvantages by allowing the production of a simple rocket engine, without a complex manifold, and having a very limited number of parts. 
     To this end, according to the invention, the rocket engine comprising a combustion chamber in the heart of which a fuel and an oxidizer are burnt and which is connected, by a throat, to a divergent nozzle through which the gases resulting from said combustion escape, said heart being supplied with oxidizer via its opposite end to said throat and being surrounded by a porous skin of thermostructural composite which receives fuel on its opposite outer side to said heart, some of this fuel being introduced into said heart through said porous skin, is notable in that said proportion of the fuel introduced into said heart through said porous skin constitutes the fuel supply to said engine and in that the proportion of said fuel not passing through said porous skin is directed toward said throat to cool it. 
     Thus, by virtue of the present invention, there is obtained a rocket engine that is simple, light in weight, can have just a few parts and can be produced with ease. 
     It will be noted that document WO-99/04156 describes a rocket engine comprising a combustion chamber in the heart of which a fuel and an oxidizer are burnt and which is connected, by a throat, to a divergent nozzle through which the gases resulting from said combustion escape, said heart being supplied with oxidizer via its opposite end to said throat and being surrounded by a porous skin of thermostructural composite which receives fuel on its opposite outer side to said heart, some of this fuel being introduced into said heart through said porous skin. 
     However, it must be pointed out that, in the rocket engine of document WO-99/04156, the proportion of fuel introduced into the heart through the porous skin is low and intended to cool the wall of said heart by seepage and that the proportion of fuel not passing through the porous skin is returned to fuel injectors. By contrast, in the rocket engine according to the present invention, the proportion of the fuel introduced into said heart through said porous skin is high and constitutes the fuel supply of said engine, whereas the proportion of said fuel not passing through said porous skin is directed toward said throat to cool it. 
     In addition, this earlier document anticipates the production of fuel circulation ducts in said porous skin, something that the present invention avoids through the novel structures proposed for the combustion chamber. 
     It will also be noted that, in the rocket engine of the invention, use is made of thermostructural composites—with a carbon matrix or ceramic matrix—not only because of their well-known mechanical and thermal resistance properties, but also for their intrinsic porosity which is generally rather considered to be a disadvantage (see patent U.S. Pat. No. 5,583,895). 
     Thanks to the excellent mechanical and thermal resistance properties of thermostructural composites, the rocket engine according to the present invention may have a very low mass with respect to known engines. Thanks to the porosity of these composites, a simple porous skin which nonetheless has good resistance to heat can be produced. Of course, the porosity of said skin may be adapted, in a known way, to any desired value when the matrix of the composite of which it is made is densified. 
     As a preference, said porous skin forms part of a first monolithic piece of thermostructural composite comprising two skins of composite spaced apart from one another leaving between them an intermediate space and joined together by a plurality of threadlike spacers of composite, passing across said intermediate space but not in any way impeding the free circulation of a fluid in said intermediate space. 
     Thus, if in the rocket engine of the present invention, said divergent nozzle is arranged in the continuation of said combustion chamber, on the opposite side of said throat to said combustion chamber:
         said first monolithic piece maybe cylindrical and arranged coaxially with respect to the longitudinal axis of said engine so that one of said skins is an inner skin whereas the other is an outer skin;   said oxidizer maybe introduced into the cylindrical volume delimited by said inner skin on the opposite side to said nozzle, this volume forming the heart of said combustion chamber; and   said fuel maybe introduced into said intermediate space, which therefore has an annular cross section, also on the opposite side to said nozzle, so that said inner skin acts as a porous skin for the introduction of at least some of said fuel into the heart of said combustion chamber.       

     Said outer skin of said first monolithic piece may be completely sealed against liquids and against gases, for example by applying an appropriate coating. 
     It is advantageous for said first monolithic piece to have an inside diameter greater than that of said throat and for the annular orifice of said intermediate space, arranged on the same side as said nozzle, to lie facing the convergent part of said throat. 
     Thus, it is possible easily to use a small proportion of the fuel, introduced into said intermediate space of annular cross section but not passing through said inner skin toward the heart, to cool the region of the throat. 
     Said nozzle may comprise, beyond said throat, a sheath able to house said first monolithic piece. 
     Thus, the entity consisting of the nozzle, the throat and the sheath therefore forms a second monolithic piece, into which said first monolithic piece is inserted. This second monolithic piece may, for example, be made of metal. However, for the reasons mentioned hereinabove, it is advantageous for it, just like said first piece, also to be made of thermostructural composite. In this case, said second monolithic piece may advantageously constitute a continuation of said outer skin of said first monolithic piece, this continuation forming an integral part of said outer skin. The result of this then is that said first and second monolithic pieces form just one piece. 
     In an alternative form of embodiment of the rocket engine according to the present invention, said combustion chamber is arranged in said divergent nozzle near the vertex thereof. 
     In this case it is advantageous for:
         said combustion chamber to comprise:
           an inner first monolithic piece of composite, of cylindrical shape, arranged coaxially with respect to the axis of the engine and having an inner skin and an outer skin separated by an intermediate space, of annular cross section; and   an outer first monolithic piece of composite, of cylindrical shape, arranged coaxially with respect to said axis and having an inner skin and an outer skin separated by an intermediate space, of annular cross section, said outer first piece surrounding said inner first piece, so as to form between them an annular heart of combustion;   
           said inner and outer first pieces to form between them and the vertex of said divergent nozzle an annular passage for communication with said nozzle;   said oxidizer is introduced into said annular heart of combustion from the opposite side to said vertex of the nozzle; and   said fuel is introduced into said intermediate spaces, of annular cross section, of said inner and outer first pieces also from the opposite side to said vertex.       

     Thus, in this embodiment, the fuel is introduced into said annular combustion heart through the outer skin of said inner first piece and through the inner skin of said outer first piece. The combustion gases then pass from said annular combustion chamber to the divergent nozzle through said annular communication passage that forms a throat. The fuel passing through the outer skin of the outer first piece is able to cool the divergent nozzle near said annular communication passage. If need be, the inner skin of the inner first piece is sealed against liquids and against gases. 
     Advantageously, the vertex of said divergent nozzle is pierced with an orifice and the collection of said inner and outer first pieces is secured to said nozzle by a third monolithic piece of composite in the shape of a horn. 
     As a preference, said combustion chamber is supplied with fuel via a dome-shaped piece arranged on the opposite side of said combustion chamber to the vertex of the nozzle and the convex wall of which faces toward said nozzle and is made of thermostructural composite. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the attached drawing will make it easy to understand how the invention may be embodied. In these figures, identical references denote similar elements. 
         FIG. 1  depicts, schematically and in axial section, a first exemplary embodiment of the rocket engine according to the present invention. 
         FIGS. 2A  to  2 F schematically illustrate one embodiment of the combustion chamber of the engine of FIG.  1 . 
         FIGS. 3A  to  3 D schematically illustrate, on a larger scale, the steps in the method for moving on from the state of  FIG. 2E  to the state of  FIG. 2F ,  FIG. 3A  corresponding to the section line IIIA—IIIA of FIG.  2 E and  FIG. 3D  to the section line IIID—IIID of FIG.  2 F. In these  FIGS. 3A  to  3 D, the two portions of each stitch are depicted very far apart, for the purpose of clarity. 
         FIG. 4  schematically illustrates one embodiment of the engine of  FIG. 1 , comprising the combustion chamber of FIG.  2 F. 
         FIG. 5  depicts, schematically and in axial section, a second exemplary embodiment of the rocket engine according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The exemplary embodiment of the rocket engine I, according to the present invention and depicted schematically in  FIG. 1 , comprises a combustion chamber  1  and a divergent nozzle  2  connected to one another by a throat  3 . The longitudinal axis of the engine I bears the reference Z—Z. 
     The combustion chamber  1  comprises an outer wall  4 , of which the part  4 A, opposite the nozzle  2 , is roughly cylindrical, whereas the part  4 B of the outer wall  4 , arranged at the same end as said nozzle  2 , is convergent to connect with the throat  3 . Thus, the outer wall  4 , the throat  3  and the nozzle  2  are in continuity and able to constitute a single piece. 
     The combustion chamber  1  additionally comprises a porous inner wall  5 , the axis of which is coincident with the axis Z—Z and which is arranged inside the outer wall  4 , forming with the latter a cylindrical intermediate space of annular cross section  6 . The porous inner wall  5  is also roughly cylindrical, and its diameter D is greater than the diameter d of the throat  3 . Facing the convergent part  4 B of the outer wall  4 , the inner wall  5  has a convergent part  5 B which, with said convergent part  4 B, determines an annular passage  7  forming a restriction for the annular space  6 . 
     In the example depicted, said combustion chamber  1  consists, at least in part, of a first monolithic piece of thermostructural composite, in which said porous inner wall  5  consists of a skin made of composite. Likewise, said divergent nozzle  2  may constitute or form part of a second monolithic piece of thermostructural composite. Said first and second monolithic pieces, which may each comprise part of the throat  3  or alternatively just one of which comprises said throat  3 , are secured together or made as a single monolithic piece, to form the rocket engine I. 
     In the combustion chamber  1 , combustion takes place inside the cylindrical volume C delimited by the porous inner wall  5  and forming the heart of said combustion chamber. A stream of oxidizer, essentially oxygen, is introduced into the heart C through the end  5 A of said inner wall  5  which is the opposite end to the nozzle  2 , as illustrated by the arrows  8 . A stream of fuel, essentially hydrogen, is introduced into the annular intermediate space  6  through the opposite end  6 A thereof to the nozzle  2 , as is illustrated by the arrows  9 . Thanks to the appropriate porosity of the inner composite wall  5  and to the restriction formed by the passage  7 , most of the fuel introduced into the annular space  6  passes through said inner composite wall  5  and enters the inside of the heart C—as indicated by the arrows  10 —where it is burnt, thanks to the addition of the oxidizer (arrows  8 ). 
     The gases resulting from the combustion escape from said heart C through the end  5 B of the wall  5 , the opposite end to the end  5 A, and pass into the nozzle  2 , passing through the throat  3 , as illustrated by the arrows  11 . 
     Furthermore, a small portion of the fuel introduced into the annular intermediate space  6  (arrows  9 ) passes through the annular passage  7 , as illustrated by the arrows  12 , cooling the part  5 B of the inner wall  5 , the part  4 B of the outer wall  4  and the throat  3 . At this throat, fuel passing through the convergent annular passage  7  mixes with the combustion gases (arrows  11 ). 
       FIGS. 2A  to  2 F,  3 A to  3 D and  4  schematically illustrate one embodiment, in the form of composite, of the engine I of FIG.  1 . 
     To produce it, the starting point is to produce, for example out of a synthetic foam material through which a needle can pass, a former  20  (see  FIG. 2A ) exhibiting the interior shape of the inner porous wall  5 , including the convergent part  5 B. Then, any known method (winding, weaving, etc.) is used to apply to this former  20  a structure  21  of high-strength fibers such as fibers based on carbon or on silicon carbide, which structure is intended to form a fibrous framework for said inner wall  5  (see FIG.  2 B). Next, an annular core  22 , for example made of a polystyrene foam not impregnable by the resins intended to form the composite matrices and representative of the annular intermediate space  6 , including the passage  7 , is applied to the fibrous structure  21  (see FIG.  2 C). The material of the core  22  can be pierced by a needle and removed thermally. 
     A structure  23  of high-strength fibers (C, SiC, etc.) is applied to the annular core  22 , this structure being intended to constitute a fibrous framework for at least part of said outer wall  4  (see FIG.  2 D). 
     As shown in  FIG. 2E and , on a larger scale, in  FIG. 3A , the fibrous structure  21 , the annular core  22  and the fibrous structure  23  are joined together by stitching without knotting of a continuous filament  24 , itself consisting of a plurality of high-strength fibers (C, SiC, etc.). The continuous filament  24  forms portions  25 ,  26  passing through the elements  21 ,  22 ,  23  and connected alternately to one another by bridges  27  applied to the fibrous structure  23  and by loops  28  penetrating the former  20 . 
     After this stitching operation, the former  20  is removed and the loops  28  are knocked over and pressed against the fibrous structure  21  to form masses  29  (see FIG.  3 B), then the collection of fibrous structures  21  and  23  is impregnated with a curable resin that is relatively low in viscosity and possibly diluted, for example with alcohol. Impregnation is preferably performed under vacuum, so that said resin not only penetrates the fibrous structures  21  and  23  but also runs along and into the portions of penetrating filament  25 ,  26 . During this impregnation, the core  22  is not impregnated with resin because it is impermeable thereto. 
     The impregnated resin is then cured, for example by raising its temperature, for long enough for the fibrous structures  21  and  23  to become rigid skins  30  and  31  respectively, and for the portions of penetrating filament  25  and  26  to become rigid threadlike spacers  32 . (see FIG.  3 C). These spacers  32  are firmly anchored at their ends in the rigid skins  30  and  31  by rigid anchors  33  and  34  formed, respectively, from the masses  29  and the bridges  27 . 
     To form the matrix of all the rigid skins  30  and  31  and spacers  32 , said assembly is subjected to pyrolysis at high temperature, for example of the order of 900° C., something which stabilizes the geometry of said assembly and eliminates the core  22 . This assembly may possibly be densified and treated in a known way so that its matrix turns into one of the ceramic type. This then yields the monolithic piece  40  (see  FIGS. 2F and 3D ) intended at least in part to form the combustion chamber  1  and comprising:
         an outer skin  41  of composite, originating from the skin  31  and intended at least in part to form the outer wall  4 ,  4 A,  4 B of the combustion chamber  1 ;   an inner skin  42  of composite, originating from the skin  30  and intended to form the inner wall  5 ,  5 A,  5 B of the combustion chamber  1 ; and   a plurality of threadlike spacers  43  of composite, originating from the spacers  32 .       

     In this monolithic piece  40 , the skins  41  and  42  are spaced apart, delimiting an annular space  44  crossed by the spacers  43  without being plugged and intended to form the annular space  6  of the combustion chamber  1 . 
     It is known that, through its nature, a composite is porous and that this porosity depends on the conditions under which the matrix is formed. It can therefore be readily appreciated that the porosity of the inner skin  42  can be tailored to impart thereto the required porosity for the inner wall  5 ,  5 A,  5 B. In so doing, the outer skin  41  is given a porosity identical to that desired for the inner skin  42 . Now, since the outer wall  4  needs to be impervious, it may be advantageous for the outer skin  41  to be externally coated with a sealing coating  45 , as is depicted in FIG.  2 F. 
     A second monolithic composite piece  50  intended to form at least said nozzle  2  is produced. Such a second composite piece  50  is easy to produce by winding or weaving strong fibers (C, Si, etc.) onto an appropriate former, then by impregnating with resin and pyrolyzing the matrix thus formed. Next, to obtain the engine I, the composite monolithic piece  40  is assembled with the composite monolithic piece  50 . This can be done in any known way, for example mechanically or by bonding. In addition, in a preferred embodiment illustrated schematically in  FIG. 4 , there is provided on the monolithic composite piece  50  not only a part  51  able to form the throat  3  but also a part  52  able to act as a housing for said composite monolithic piece  40 . In this case, the outer wall  4  of the engine I is then formed by the superposition and assembly of the skin  41 , possibly of the coating  45 , and of the part  52 . 
     As an alternative, it will be readily appreciated from that which has been described that the second composite piece  50  may be the continuation of the outer skin  41  and form a monolithic piece therewith, as illustrated schematically in FIG.  1 . 
     In the alternative form of embodiment II of the rocket engine, according to the present invention and depicted in  FIG. 5 , the combustion chamber  60  is arranged inside the divergent nozzle  61 , near the vertex  62  thereof. This divergent nozzle  61  consists, for example, of a composite monolithic piece obtained in a similar way to the nozzle  2  as described hereinabove. In addition, provision is made for the vertex  62  of the divergent nozzle  61  to be pierced with an orifice  63 . 
     The combustion chamber  60  comprises:
         an inner composite monolithic piece  64 , of cylindrical shape, arranged coaxially with respect to the axis Z—Z of the engine and having an inner composite skin  65  and an outer composite skin  66 . This composite piece  64  may be obtained in the way described hereinabove with respect to the composite piece  40 ; and   an outer composite monolithic piece  67 , of cylindrical shape, arranged coaxially with respect to the axis Z—Z and having an inner composite skin  68  and an outer composite skin  69 . The composite piece  67  may also be obtained in a similar way to the piece  40 .       

     The outer composite piece  67  surrounds the inner composite piece  64  delimiting between them an annular heart C for said combustion chamber  60 . 
     The composite pieces  64  and  67  are secured, on the same side as the nozzle  61 , to a manifold  70  able to supply them with gaseous fuel and, on the opposite side, to a third composite monolithic piece  71 , in the form of a horn, connecting them to the divergent nozzle  61  along the edge of the orifice  63 . The combustion chamber  60  forms, between itself and the vertex of the nozzle  61 , an annular passage  72  forming a throat and providing communication with said nozzle. 
     Just like the wall  41  of the piece  40 , the inner skin  65  of the inner piece  64  is advantageously sealed against gas. 
     Through the piece  71 , the gaseous oxidizer is introduced into the annular heart C, from the opposite side to the vertex  62 , by injectors  73 . Through the piece  71  and the manifold  70 , the fuel is introduced, from the opposite side to the vertex  62 , into the annular intermediate spaces  74  and  75  (analogous to the intermediate space  44  of the piece  40 ) of the composite pieces  64  and  67 . Through the outer skin  66  of the piece  64  and through the inner skin  68  of the piece  67 , said fuel passes into the annular heart C, where it burns with the oxidizer. The combustion gases escape from the combustion chamber  60  from the same side as the vertex  62  and pass into the nozzle  61  through the throat  72 . The fuel gas escaping through the outer skin  69  cools the nozzle  61  near the combustion chamber  60 . The paths of the gases are indicated by arrows in FIG.  5 . 
     In the embodiment depicted in  FIG. 5 , the fuel supply device comprises a hollow dome  76  supplied with fuel by a duct  77  passing through said piece  71  and itself supplying the manifold  70 . The convex side of the dome  76  faces the same direction as the nozzle  61 , away from the combustion chamber  60 . As a preference, at least the convex wall  78  of said dome  76  is made of thermostructural—and therefore porous—composite, so that this dome is cooled by seepage of said fuel through said convex wall  78 .