Abstract:
According to the invention, the said engine (I), which comprises at least one flame tube ( 2 ) with a mobile transverse end wall ( 18 ), comprises an external envelope ( 3 ) around the said flame tube ( 2 ), which defines a peripheral annular space ( 4 ) in which fixed flow guides ( 11, 12, 13, 14 ) are positioned, these flow guides forming flow channels ( 10 ) for the air, and at least one mobile plug ( 25 ), connected to the said mobile end wall ( 18 ), to close off and open one of the flow channels ( 10 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a §371 national stage entry of International Application No. PCT/FR2009/000440, filed Apr. 16, 2009, which claims priority to French patent application Ser. No. 08/02210, filed Apr. 21, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a pulse detonation engine with a fuel-air detonating mixture. 
     BACKGROUND OF THE INVENTION 
     Such a type of engine is applicable, amongst others, although not exclusively, in the spatial and military aeronautical fields for the equipment of aircrafts, rockets, missiles, etc. 
     The operating cycle of such an engine could be reduced to the three following strokes:
         a first stroke relating to the engine supplying phase with a detonating mixture;   a second stroke relating to the detonating phase providing the compression and the release of the chemical energy generated by the mixture; and   a third stroke relating to the expansion phase of the detonating products.       

     The running of the different phases of the operating cycle of the engine is a potentially critical point and, in particular, the control of the supply and detonation phases being able to very strongly impact on the performance of such an engine. 
     It is already known from patent EP 1,482,162 a pulse detonation engine, the structure of which is defined by a flame tube closed at one end by a mobile transversal bottom (referred to as a thrust wall) where products generated by the detonation of the detonating mixture abut in order to generate the thrust. Such an engine requires the operation of both supply and detonation phases of the engine, through the mobility thereof, opening and closing the intake port, allowing to be dispensed with complex valve supply devices or the like. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to improve the above mentioned pulse detonation engine, minimizing, during the detonation phase, blocking the air flow from the air intake so as to limit the drag generated by the air intake. 
     To this end, according to the invention, the pulse detonation engine operating with a fuel-air detonating mixture and comprising:
         at least one flame tube with a transversal bottom being mobile with respect to the latter so as to be able to occupy two limit positions, a first position corresponding to the detonation phase of the detonating mixture in the combustion chamber and a second position corresponding to the supply phase of said chamber;   at least one intake port for the detonating mixture arranged in the side wall of said flame tube;       

     is remarkable in that:
         said engine comprises an external shell around said flame tube defining a peripheral ring space along the side wall of said flame tube, enabling the air flow from the air intake of said engine;   fixed flow guides are arranged in the peripheral ring space in order to define air flow channels in such a space, and   at least one mobile block arranged in the ring space and connected to said mobile bottom, is provided for moving along the side wall of said flame tube, said mobile block being able to obstruct, when said mobile bottom occupies the second position, one of said flowing channels so as to orient part of the air flow towards said intake port and release said flowing channel when said bottom is in the first position.       

     Thus, through the invention, blocking the air flow coming from the air intake is minimized during the detonation phase since the air flow can circulate in the flowing channels of the ring space, bypassing the mobile blocks when the intake port(s) is/are obstructed, resulting in the drag generated by the air intake being limited. 
     Moreover, the engine can be dispensed with complex controlling devices of the mobile block(s), since it is the transversal bottom that requires the mobile blocks to be moved as a result of its mobility. 
     The structure of the engine also allows a cylindrical nozzle, for example, of the ejecting type, being concentric with the combustion chamber to be supplied and thereby benefit from the advantages of a double flow engine. 
     Advantageously, said fixed guides could be arranged parallel to each other in a concentric way around the side wall of said flame tube. Thereby, the flowing channels of the ring space are parallel to each other, facilitating the air flow, upon the detonation phase, along the side wall of the flame tube. 
     For example, the shift of said mobile block could be a side sliding along the side wall of said flame tube. 
     Moreover, said mobile block could advantageously join the external face of the ends opposite the two adjacent fixed guides so as to obstruct the flowing channel partially formed by those two fixed guides, when said mobile bottom occupies the second position. 
     In addition, said mobile bottom, sliding between the first and the second position, could advantageously have the shape of a piston with its transversal wall facing said chamber and with a side skirt cooperating with the wall of said flame tube, and a crown, comprising at least one detonating mixture supply opening, could then be integral with the transversal wall of said piston and cooperate with the side wall of said flame tube for obstructing at least partially said intake port in the second position of said mobile bottom. 
     Preferably, at least one first intake port, having a flowing hole with a fixed section, is obstructed in the first position of said mobile bottom and released in the second position of said bottom and at least one second intake port, able to receive a mobile projection, has a flowing hole with a variable section, said hole having a section being reduced in the first position of said mobile bottom and a section being enlarged in the second position of said bottom. 
     Said pulse detonation engine could advantageously comprise at least one predetonation tube arranged laterally with respect to said combustion chamber, at least approximately along the latter, making easier the air and fuel supply of the pre-detonation tube(s). 
     Moreover, a mobile projection could be engaged into said second opening and join the internal face of the ends of one of said fixed guides, when said mobile bottom occupies the first position, so as to form a transversal passage putting in a fluid communication said pre-detonation tube and said combustion chamber for allowing, more particularly, the transfer of the explosion waves, and one of the ends of said transversal passage then corresponds to said flowing hole of said second intake port having a reduced section, when said mobile bottom occupies the first position, and the other end corresponds to the upstream hole, oriented to the air intake, of said pre-detonation tube. 
     In an advantageous embodiment of the present invention, the pulse detonation engine comprises a plurality, at least two, of pre-detonation tubes in diametrically opposed side positions with respect to said combustion chamber. Thus, the engine is far more robust than a single pre-detonation tube engine, more particularly substantially improving the propagation of the detonation in the chamber. 
     According to another advantageous feature, at least one of said fixed guides could have the shape of a fork with teeth oriented to the air intake so as, upon the supply phase, to orient the air flow towards one or more released intake ports. 
     Moreover, return resilient means are provided in said flame tube for bringing back said mobile bottom from the first position to the second position. Such return resilient means comprise, for example, at least one spring acting on the transversal wall of said bottom. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the appended drawing will better explain how this invention can be implemented. In these figures, like reference numerals relate to like components 
         FIG. 1  is a close-up schematic view in a longitudinal section of an exemplary embodiment of the pulse detonation engine according to this invention, showing the mobile bottom in the first position. For clarity reasons, the mobile blocks, the mobile projection, the guiding openings and the intake port, concealed behind the piston crown, are shown in a close-up detailed view in broken lines. The fixed guides and the pre-detonation tube, concealed by the side wall of the flame tube are, as far as they are concerned, shown in phantom lines. 
         FIG. 2  is a view like  FIG. 1  showing the mobile bottom in the second position. 
         FIGS. 3 and 4  schematically show a detailed view of the external side surface of the flame tube, respectively in the first and second positions of the mobile bottom. 
     
    
    
     DETAILED DESCRIPTION 
     According to a preferred embodiment of this invention, the pulse detonation engine, schematically and partially shown on  FIGS. 1 and 2 , comprises a cylindrical flame tube  2  with a longitudinal axis A and an external shell  3  covering the flame tube  2  and defining a peripheral ring space  4  along the side wall  5  of said tube  2 . 
     Moreover, the engine I comprises, in such a preferred embodiment, two pre-detonation tubes  6 , but the number thereof could be different, arranged laterally with respect to the combustion chamber  7  of the flame tube  2 , in diametrically opposed positions with respect to the latter. In such an embodiment, the front end  8 , oriented to the air intake, of the pre-detonation tubes  6  (on the left on  FIGS. 1 and 2 ) opens into the peripheral ring space  4  through a hole  9 , whereas the downstream end of said tubes  6  (not shown on the figures) opens into the outside. Each pre-detonation tube  6  could comprise a central priming device (not shown on the figures) allowing the pressure to be maintained for a sufficiently long period at the level of the front end  8  of the tube  6  after an explosion. 
     Moreover, according to the invention and as shown on  FIGS. 3 and 4 , flowing guides  11 ,  12 ,  13  and  14  are fastened, preferably in a concentric manner, to the side wall  5  of the flame tube  2  in the ring space  4  so as to form, in such a space, parallel flowing channels  10  along the flame tube  2 . Each flowing channel  10  is for example bounded by two guide pairs, one guide pair comprising a downstream guide  13  or  14  (on the right on  FIGS. 3 and 4 ) and an associated upstream guide  19  or  12  (on the left on the same figures). According to such a preferred embodiment, some downstream guides  13 , referred to as first guides, could have the shape of a fork  16  with two teeth  15  facing the associated upstream guide  11 , referred to as the third guide. Other downstream guides  14 , referred to as second guides, more particularly intended for being arranged before the upstream hole  9  of the pre-detonation tubes  6 , could comprise two parallel independent branches  17  having their projecting ends being oriented towards the associated upstream guide  12  referred to as the fourth guide. 
     The engine I also comprises a transversal bottom  18  fittingly housed inside the flame tube  2 . Such a transversal bottom  18  bounds, with the side wall  5  of the flame tube  2 , the combustion chamber  7  able to cyclically receive a fuel load, symbolized by the arrow  19  on  FIG. 2 , coming out of a supply device, present in the ring space but not shown on the figures, supplying the fuel-air detonating mixture. The transversal bottom  18  defines a thrust wall against which the detonation products of the detonating mixture apply for generating the thrust. 
     According to the preferred embodiment, the transversal bottom  18  is mounted being mobile, but not exclusively, with respect to the flame tube  2  of the engine I and could move between two distinct limit positions, a first position ( FIGS. 1 and 3 ) isolating the combustion chamber  7  from the peripheral ring space  4 , corresponding to the detonation phase of the detonating mixture, and a second position ( FIGS. 2 and 4 ) putting in fluid communication the combustion chamber  7  and the peripheral ring space  4 , corresponding to the supply phase of the chamber with detonating mixture. 
     To this end, first ports  20 A for the intake of the detonating mixture in the chamber  7 , having a flowing hole with a fixed section, are arranged in the side wall  5  of the flame tube  2 , advantageously between the teeth  15  of the first guides  13 , said first intake ports  20 A being fully obstructed when the mobile transversal bottom  18  is in its first position, and released when it occupies its second position. 
     Second intake ports  20 B are also provided in the side wall  5  of the flame tube  2  between the branches  17  of the second guides  14 . Such second intake ports  20 B have the feature of having a fluid flowing hole  35  with a variable section, said flowing hole  35  having a reduced section in the first position of the mobile bottom  18 , allowing the transfer of the explosion waves from the pre-detonation tubes  6  to the combustion chamber  7  through a transversal passage (to be further described subsequently) and an enlarged section in the second position of the mobile bottom  18 , for allowing for the supply with detonating mixture of the combustion chamber  7  and the pre-detonation tubes  6 . 
     As shown on  FIGS. 1 and 2 , moving the mobile bottom  18  between its two positions is, in such a preferred embodiment, of the sliding type according to the longitudinal axis A, but it could be different (for example of the helical type). 
     In the shown embodiment, the mobile bottom  18  has structurally the shape of a piston  21  comprising a transversal wall  22  facing the combustion chamber  7  with a side skirt  23  fittingly cooperating with the side wall  5  of the flame tube  2 . The mobile bottom  18  further comprises a crown  23 A being integral with the transversal wall  22  of the piston  21  and fittingly cooperating with the side wall  5  of the flame tube  2  for fully obstructing the first intake ports  20 A and partially the second intake ports  20 B having a flowing hole  35  with a reduced section, when the mobile bottom  18  occupies the second position. 
     Side supply openings  24  are provided in the side wall of the crown  23 A of the piston  21 . Such supply openings  24  communicate with the first  20 A and second  20 B intake ports, when the mobile bottom  18  occupies the second position, for putting in fluid communication the ring space  4  and the combustion chamber  7  upon the supply phase. 
     Moreover, according to the invention, mobile blocks  25  are arranged inside the flowing channels  10  between the first  13  and second  14  guides and are fastened, preferably in a concentric manner, to the crown  23 A of the piston  21 . Such mobile blocks are provided, according to the invention, for laterally sliding in guiding openings  26  provided in the side wall  5  of the flame tube  2 , but other types of shift of the blocks  25  could be contemplated. Thereby, as shown on  FIG. 3 , each mobile block  25  is offset, to the right on  FIG. 3 , with respect to the ends of the teeth  15  of the first guides  13  and of the branches  17  of the second guides  14 , when the mobile bottom  18  occupies the first position, so that the air flow of the air intake, symbolized by the arrow  27 , is able to circulate freely in the flowing channels  10  along the wall of the flame tube  2 , bypassing the mobile blocks  25 . 
     As illustrated on  FIG. 4 , the mobile blocks  25  fittingly join the external face of the ends opposite the teeth  15  and the branches  17 , when the mobile bottom  18  occupies the second position, so as to obtain the flowing channels  10  and orient the air flow of the air intake, symbolized by the arrow  28  on  FIGS. 2 and 4 , in the direction of the first released intake ports  20 A and of the enlarged section flow hole  35  of the second intake ports  20 B. 
     Furthermore, the mobile projections  29 , being indented on their downstream side face  30 , are fastened to the crown  23 A of the piston  21  and can slide, preferably parallel to the mobile block  25 , in the second intake ports  20 B adjacent to the pre-detonation tubes  6 . As illustrated on  FIG. 3 , the mobile projections  29  fittingly join the internal face of the ends of the opposite branches  17 , in the first position of the mobile bottom  18 , and thereby define a transversal passage allowing the transfer of the explosion wave from the pre-detonation tubes  6  to the combustion chamber  7 , one of the ends of the transversal passage corresponding to the reduced section flowing hole  35  and the other end to the upstream hole  9  of the pre-detonation tubes  6 . 
     A housing  31  is provided on the downstream side face of the fourth guides  12 , being arranged opposite the pre-detonation tubes  6 , for receiving the mobile projections  29 , when the mobile bottom  18  is in the second position. 
     In addition, return resilient means are provided between the transversal mobile bottom  18  and the flame tube  2 , for spontaneously bringing said bottom  18  from its second position ( FIG. 2 ) back to its first position ( FIG. 1 ). For example, such means are merely defined by a compression spring  32  arranged between the upstream face of the transversal wall  22  of the piston  21  opposite the combustion chamber  7 , and a transversal abutment  33  provided in the flame tube  2 . Usually, a guiding rod  34  of the spring  32  fastened to the upstream face of the transversal wall of the piston  21  could be associated with said spring  32 . 
     The operating cycle of such a pulse detonation engine I as described above is as follows. 
     First of all, it is assumed that the engine I is in the configuration, as illustrated on  FIGS. 1 and 3 , for which the mobile transversal bottom  18  is in its first position, that is:
         the mobile blocs  25  are offset to the right on  FIG. 3  so as to allow the air flow to circulate along the side wall  5  of the flame tube  2 ;   the mobile projections  29  join the internal face of the ends of the branches  17  opposite the second guides  14  so as to form the transversal passages allowing the fluid communication between the pre-detonation tubes  6  and the combustion chamber  7 . The pre-detonation tubes  6  are thereby separated from the detonating mixture input; and   the first intake ports  20 A are fully obstructed by the side wall of the crown  23 A so that the combustion chamber  7  is isolated from the detonating mixture input.       

     Under the impulsion of the explosion waves generated in the pre-detonation tubes  6  and of the transmission thereof via the transversal passages, the detonation of the compressed reactive mixture occurs in the chamber  7 . As the pressure strongly increases in the chamber  7 , the mobile bottom  18  starts to move to the back (to the left on  FIG. 1 ) simultaneously resulting in the first intake ports  20 A opening, the section of the hole  35  of the second intake ports  20 B enlarging and the mobile blocks  25  sliding, to the ends of the teeth  15  and branches  17 , and the mobile projections  29 , to the housings  31  of the fourth guides  12 . 
     The pressure in the combustion chamber  7  is temporarily dropped under the effect of the rear expansion of the detonation products, but under the effect of the inertia thereof and the acquired velocity, the piston  21  goes on moving back against the spring  32  until the mobile bottom  18  reaches its second position. 
     When the mobile bottom  18  occupies the second position, the first released intake ports  20 A and the second intake ports  20 B, having its hole  35  with an enlarged section, communicate with the supply openings  24  of the crown  23 A. Moreover, the mobile blocks  25  obstruct the flowing channels  10  joining the external face of the ends of the opposite teeth  15  and branches  17  and the mobile projections  29  are in abutment in their respective housing  31 , 
     Afterwards, a self-sucking phenomenon, resulting from the depression caused by the overexpansion of the detonation products, allows the autonomous filling of the combustion chamber  7  and the pre-detonation tubes  6  with a detonating fuel-air mixture. 
     Then, under the action of the compression spring  32 , the mobile bottom  18  is sent back to the combustion chamber  7 , the crown  23 A of the piston  21  fully obstructing the first intake ports  20 A and partially the second intake ports  20 B, the hole  35  thereof having a reduced section, whereas the mobile blocks  25  are in abutment with the guiding openings  26  and the mobile projections  29  join the internal face of the ends of the opposite branches  17 . 
     A new operating cycle of the engine I can then start.