Abstract:
A pressurizing device and method, for pressurizing a first tank, the device including at least a second tank configured to contain a cryogenic fluid, a first pressurizing circuit for putting the second tank into communication with the first tank, the first pressurizing circuit including at least a first heat exchanger for heating a flow of the cryogenic fluid extracted from the second tank through the first pressurizing circuit, and a second pressurizing circuit with a compressor, branched off from the first pressurizing circuit and leading to the second tank. A feed system for feeding a reaction engine with at least a first liquid propellant includes at least a first tank configured to contain the first liquid propellant, and a device for pressurizing the first tank.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to the field of pressurizing devices, and in particular to a device for pressurizing a first tank with a cryogenic fluid contained in a second tank and introduced into the first tank via a pressurizing circuit after being heated in a heat exchanger of said pressurizing circuit. 
         [0002]    Pressurizing devices of this type are used in particular in the field of propulsion, and more particularly in systems for feeding propellants to reaction engines, and in particular to rocket engines. Thus, by way of example, one such pressurization device is used in the main cryogenic stage of Ariane 5 space launchers in order to pressurize the liquid oxygen tank for feeding the Vulcain main engine. 
         [0003]    A drawback of prior art pressurizing devices, and in particular that used in the main pressurizing stage, is that the second tank itself needs to be pressurized with a gas contained in other tanks under pressure. Thus, in the main cryogenic stage, the supercritical helium tank of the liquid helium subsystem used for pressurizing the liquid oxygen tank is itself pressurized with gaseous helium coming from a gaseous helium tank forming a high pressure reservoir. This high pressure reservoir contains supercritical helium at a pressure close to 400 bar and at ambient temperature. Three-quarters of the helium contained in the high pressure reservoir is used for pressurizing the supercritical helium tank of the liquid helium subsystem, with the remainder being supplied to the hydrogen and oxygen feed valves of the pogo corrector system, and to the engine flushing and engine control solenoid valve units. In order to bring the pressure that exists in the high pressure reservoir down to a utilization pressure of less than 100 bar, this reservoir also requires an inflation and expansion plate. The combined mass of the high pressure reservoir and of the inflation and expansion plate significantly penalizes the payload of the launcher. In addition, the inflation and expansion plate constitutes an element that is mechanically complex, and which can have a negative effect on the reliability of the launcher. 
       OBJECT AND SUMMARY OF THE INVENTION 
       [0004]    The invention seeks to propose a pressurizing device for pressurizing a first tank, the device comprising at least a second tank adapted to contain a cryogenic fluid, and a first pressurizing circuit for putting said second tank into communication with the first tank, wherein said first pressurizing circuit comprises at least a first heat exchanger for heating a flow of said cryogenic fluid extracted from the second tank through the first pressurizing circuit, and that enables the second tank to be pressurized without having recourse to a separate tank of gas under high pressure. 
         [0005]    In at least one embodiment, this object is achieved by the fact that the pressurizing device further comprises a second pressurizing circuit with a compressor branched off from the first pressurizing circuit and leading to the second tank. Thus, the second tank can be pressurized without having recourse to a tank of gas at high pressure, using the fluid that has been extracted from that second tank and then compressed prior to being reinjected into the second tank. 
         [0006]    The cryogenic fluid may in particular be contained in liquid or supercritical form in the second tank in order to be vaporized in the first heat exchanger. 
         [0007]    In a first embodiment, the second pressurizing circuit branches off from the first pressurizing circuit upstream from said first heat exchanger. This avoids reintroducing the cryogenic fluid into the second tank at a temperature that is too high. 
         [0008]    Nevertheless, in an alternative second embodiment, the second pressurizing circuit branches off from the first pressurizing circuit downstream from said first heat exchanger. This makes use of the increase in the enthalpy of the cryogenic fluid in said first heat exchanger in order to facilitate pressurizing the second tank. 
         [0009]    In order to actuate said compressor, in certain embodiments the pressurizing device may also include a turbine for driving said compressor. Nevertheless, and alternatively, the pressurizing device may include some other type of motor, e.g. an electric motor for driving said compressor. 
         [0010]    The invention also provides a feed system for feeding a reaction engine with at least a first liquid propellant, the system comprising at least a first tank adapted to contain said first liquid propellant, and a pressurizing device for pressurizing the first tank, comprising at least a second tank adapted to contain a cryogenic fluid and a first pressurizing circuit for putting said second tank into communication with the first tank. Said first pressurizing circuit comprises at least a first heat exchanger for heating a flow of said cryogenic fluid from the second tank extracted via the first pressurizing circuit. The pressurizing device also further comprises a second pressurizing circuit with a compressor, and putting the first pressurizing circuit into communication with the second tank upstream from said first heat exchanger. In particular, said reaction engine may be a rocket engine. When said compressor is driven by a turbine, it may for example be actuated by the expansion of a propellant heated in a heat exchanger associated with a propulsion chamber and/or a nozzle of the reaction engine. 
         [0011]    In order to avoid chemical reaction with said first propellant, the cryogenic fluid of the second tank is inert, such as helium, for example. Other inert fluids, such as nitrogen for example, could nevertheless also be envisaged as alternatives. When the first cryogenic fluid is inert, it may also serve not only for pressurizing the first tank, but also by way of example for flushing various engine ducts and members in order to limit risks of explosion. 
         [0012]    In particular, the first liquid propellant may be an oxidizer and/or a cryogenic liquid having a condensation point that is higher than that of the cryogenic fluid of the second tank. More particularly, the first liquid propellant may be liquid oxygen. 
         [0013]    Furthermore, in certain embodiments, the feed system may also include at least one turbopump for pumping at least said first liquid propellant, and a hot gas generator for driving the at least one turbopump, said heat exchanger being configured to heat said flow of cryogenic fluid extracted from the second tank using heat generated by said hot gas generator, and in particular heat extracted from said hot gases, e.g. downstream from the turbopump. It is thus possible to make use of at least some of this remaining heat that would otherwise be lost for the purpose of heating the flow of cryogenic fluid extracted from the second tank. 
         [0014]    The invention also provides a method of pressurizing a first tank, wherein a flow of cryogenic fluid is extracted from a second tank through a first pressurizing circuit, and is heated in at least a first heat exchanger, a first portion of this heated flow then being introduced into the second tank in order to pressurize it. In at least one implementation of the invention, a second portion of this heated flow is taken from the first pressurizing circuit via a second pressurizing circuit, is compressed upstream from the heat exchanger by a compressor of said second pressurizing circuit, and is introduced into the second tank in order to pressurize the second tank. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention can be well understood and its advantages appear better on reading the following detailed description of an embodiment given by way of non-limiting example. The description refers to the accompanying drawings, in which: 
           [0016]      FIG. 1  is a diagrammatic illustration of a prior art system for feeding liquid propellants to a reaction engine; 
           [0017]      FIG. 2  is a diagrammatic illustration of a first embodiment of a system of the present invention for feeding liquid propellants to a reaction engine; 
           [0018]      FIG. 3  is a diagrammatic illustration of a second embodiment of a system of the present invention for feeding liquid propellants to a reaction engine; and 
           [0019]      FIG. 4  is a diagrammatic illustration of a detail of a variant of the first or second embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1  shows diagrammatically a prior art system  101  for feeding propellants to a reaction engine, and more specifically to a Vulcain type main engine propelling a main cryogenic stage of an Ariane  5  type launcher. This feed system  101  comprises a first tank  102  containing oxygen—or more generally an oxidizing propellant—in liquid form as a first propellant, a second tank  103  containing supercritical helium, in particular for pressurizing the first tank, a third Lank  104  containing gaseous helium at high pressure, in particular for pressurizing the second tank, and a fourth tank  105  containing hydrogen, or more generally a reducing propellant—in liquid form as the second propellant. The feed system  101  also has a feed circuit  111  for feeding the propulsion chamber  102  with oxygen, a feed circuit  112  for feeding the propulsion chamber  109  with hydrogen, and a gas generator  106  also connected to the pump outlet  107   b,    108   b  to be fed with hydrogen and oxygen. 
         [0021]    The oxidizing propellant feed circuit  111  has a first turbopump  107  connected to the gas generator  106  to receive hot gas for driving the turbine  107   a,  which turbine drives the pump  107   b  for feeding the propulsion chamber  109  with oxygen. The reducing propellant feed circuit  112  has a second turbopump  108  connected to the gas generator  106  also to receive hot gas from the gas generator  106  to drive the turbine  108   a,  which drives the pump  108   b  to feed the propulsion chamber  109  with reducing propellant. 
         [0022]    The feed system  101  also has a first pressurizing circuit  113  connecting the second tank  103  to the first tank  102  in order to pressurize the first tank  102 , and a second pressurizing circuit  114  connecting the third tank  104  to the second tank  103  for pressurizing the second tank  103 . The first pressurizing circuit  113  has a first heat exchanger  115  for heating and vaporizing the supercritical helium extracted from the second tank  103  using heat coming from the hot gas downstream from the turbine  107   a  of the first turbopump  107 . 
         [0023]    An engine tapping circuit  116  branches off from the first pressurizing circuit  113  downstream from the first heat exchanger  115 . This engine tapping circuit  116  serves to feed gaseous helium to a set of auxiliary subsystems that require gaseous helium, such as subsystems for flushing with helium. 
         [0024]    The second pressurizing circuit  114  includes an inflation and expansion plate  118  for controlling the passage of gaseous helium in both directions. This second pressurizing circuit  114  is connected to the second tank  103  via a hydrogen solenoid valve unit  119  that also serves to control a hydrogen feed valve  120  for controlling the hydrogen feed circuit  112 . In addition, between the plate  118  and the unit  119 , the second pressurizing circuit  114  presents branch connections for feeding various solenoid valve units. An oxygen solenoid valve unit  121  serves to control an oxygen feed valve  130  for controlling the oxygen feed circuit  111 . An engine flushing solenoid valve unit  122  serves to control purge and flushing valves. Finally, a chamber solenoid valve unit  123  serves to control a propulsion chamber oxygen valve  124  controlling the admission of oxygen into the chamber  109 , a propulsion chamber hydrogen valve  125  controlling the admission of hydrogen into the chamber  109 , a generator oxygen valve  126  controlling the admission of oxygen into the gas generator  106 , and a generator hydrogen valve  127  controlling the admission of hydrogen into the gas generator  106 . 
         [0025]    In the hydrogen feed circuit  112 , between the second turbopump  108  and the injection plate  110  of the propulsion chamber  109 , the feed system  101  also includes a second heat exchanger  128 , referred to as a “regenerative” heat exchanger, serving to cool the walls of the propulsion chamber  109 . In addition, in this feed system  101 , a third pressurizing circuit  129  connects this feed circuit  112 , downstream from the second heat exchanger  128 , to the fourth tank  105  in order to pressurize it with hydrogen that has been vaporized in the second heat exchanger  128  before being tapped off the hydrogen feed circuit  112 . 
         [0026]    In this prior art feed system  101 , the use of helium pressurized to high pressure (close to 400 bar), in the third tank  104  forming a high pressure reservoir of nearly 400 liters (L) for pressurizing the second tank  103  involves a large penalty in terms of total mass, thereby reducing the payload of the launcher. Thus, this third tank  104  presents a mass close to 100 kilograms (kg), to which there needs to be added the additional mass associated with the inflation and expansion plate  118  needed for dropping the pressure of the gaseous helium stored in the tank  104  to a utilization pressure of less than 100 bar. 
         [0027]      FIG. 2  shows a feed system  1  in a first embodiment of the present invention that requires smaller mass and less complexity compared with the prior art. The feed system  1  has a first tank  2  containing liquid oxygen as a first propellant, a second tank  3  containing supercritical helium, in particular for pressurizing the first tank, a third tank  4  containing gaseous helium, and a fourth tank  5  containing liquid hydrogen as the second propellant. The feed system  1  also has a circuit  11  for feeding the propulsion chamber  9  with oxygen, and a circuit  12  for feeding the propulsion chamber  9  with hydrogen, together with a gas generator  6  connected to the outlets from the pumps  7   b  and  8   b  to be fed with hydrogen and oxygen. 
         [0028]    The oxygen feed circuit  11  has a first turbopump  7  connected to the gas generator  6  to receive hot gas for actuating the turbine  7   a,  which drives the pump  7   b  to feed the propulsion chamber  9  with oxygen. The hydrogen feed circuit  12  has a second turbopump  8  connected to the gas generator  6  also to receive hot gas from the gas generator  6  for actuating the turbine  8   a,  which drives the pump  8   b  for feeding the propulsion chamber  9  with hydrogen. 
         [0029]    The feed system  1  also has a first pressurizing circuit  13  connecting the second tank  3  to the first tent  2  for pressurizing the first tank  2 . This first pressurizing circuit  13  has a first heat exchanger  15  for heating and vaporizing the supercritical helium extracted from the second tank  3  using the heat coming from the has gas downstream from the turbine  7   a  of the first turbopump  7 . A second pressurizing circuit  14 , branched off from the first feed circuit  13  upstream from the first heat exchanger  15 , returns to the second tank  3  and serves to pressurize it. For this purpose, this pressurizing circuit  14  includes a turbocompressor  31  in which the compressor  31   b  serves to compress the flow of supercritical helium taken from the first pressurizing circuit  13  in order to reinject it at higher pressure and higher temperature into the second tank  3 . An engine tapping circuit  16  is branched off from the first pressurizing circuit  13  downstream from the first heat exchanger  15 . This engine tapping circuit  16  serves to feed gaseous to a set of auxiliary subsystems that require gaseous helium, such as subsystems for flushing with helium. 
         [0030]    In the hydrogen feed circuit  12 , between the second turbopump  8  and the injection plate  10  of the propulsion chamber  9 , the feed system  1  also includes a second heat exchanger  28  referred to as a “regenerative” heat exchanger, serving to cool the walls of the propulsion chamber  9 . In addition, in this feed system  1 , a third pressurizing circuit  29  connects this feed circuit  12  downstream from the second heat exchanger  28  to the fourth tank  5  in order to pressurize it with hydrogen vaporized in the second heat exchanger  28  before being tapped off the hydrogen feed circuit  12 . The hydrogen feed circuit  29  passes through the turbine  31   a  of the turbocompressor  31  downstream from the second heat exchanger  28  so that partial expansion of the vaporized hydrogen in the second heat exchanger  28  actuates this turbine  31   a  in order to drive the compressor  31   b  to which it is coupled. 
         [0031]    The third tank  4  is also connected to a hydrogen solenoid valve unit  19 , to an oxygen solenoid valve unit  21 , and to an engine flushing solenoid valve unit  22  so as to feed them with gaseous helium under pressure. As in the prior art, the hydrogen solenoid valve unit  19  serves to control a hydrogen feed valve  20  for controlling the hydrogen feed circuit  12 , and the oxygen solenoid valve unit  21  serves to control an oxygen feed valve  22  for controlling the oxygen feed circuit  11 . The engine flushing solenoid valve unit  22  serves to control purge and flushing valves. Finally, the propulsion chamber oxygen valve  24  controlling the admission of oxygen into the chamber  9 , the propulsion chamber hydrogen valve  25  controlling the admission of hydrogen into the chamber  9 , the oxygen generator valve  26  controlling the admission of oxygen into the gas generator  6 , and the hydrogen generator valve  27  controlling the admission of hydrogen into the gas generator  6  are all under direct electrical control, thereby making it possible to eliminate the prior art control solenoid valve unit, thus further reducing the reliance on pressurized helium and thus further reducing the volume needed for the third tank  4 . 
         [0032]    In a particular example of this embodiment of the invention, it is thus possible to use a turbocompressor  31  of size and thus mass that are limited, in order to replace the high pressure reservoir that was formed in the prior art feed system by a tank  104  of gaseous helium under high pressure and at ambient temperature, and leading to the prior art requiring an inflation and expansion plate  118  in order to drop the pressure of the gaseous helium to an acceptable utilization pressure. For example, the tank  104  in the comparative example shown in  FIG. 1 , having a capacity of nearly 400 L at pressure of nearly 400 bar, with a mass close to 100 kg, can be replaced together with the inflation and expansion plate  118  by means of a turbocompressor  31  of mass less than 20 kg. 
         [0033]    In this particular embodiment, the turbocompressor  31  is actuated by expanding a small flow of gaseous hydrogen reaching the turbine  31   a,  this hydrogen flow itself being taken from the “regenerative” heat exchanger  28  used for cooling the walls of the propulsion chamber  9 . The compressor  31   b  compresses a small flow of supercritical helium, less than 50 grams per second (g/s coming from the second tank  3  and taken from the first pressurizing circuit  13  via the second pressurizing circuit  14 . At the outlet from the compressor  31   b,  this supercritical flow of helium reaches a thermodynamic state that is sufficient, with pressure greater than 30 bar and temperature greater than 20 kelvins (K), to enable the second tank  3  to be pressurized and to maintain this pressure therein in spite of a greater mass flow rate of supercritical helium being extracted from the second tank  3  for pressurizing the first tank  2  and the engine tapping. 
         [0034]    In this particular embodiment, a third tank  4  containing a smaller quantity of helium suffices (e.g. a reservoir of less than 100 L) at a pressure that is reduced (e.g. at a pressure of less than 100 bar), and at ambient temperature in order to feed the oxygen solenoid valve unit  21 , and an engine flushing solenoid valve unit  22 . The mass of this third tank  4  forming a low pressure reservoir is thus much less than the mass of the high pressure reservoir that has been used in the prior art. Eliminating the hydrogen and control solenoid valve units also contributes to reducing the overall mass by about 100 kg in this particular embodiment compared with the comparative example shown in  FIG. 1 . 
         [0035]    In a variant of this first embodiment, in order to optimize pressurizing the second tank  3 , the second pressurizing circuit  14  may pass through a heat exchanger downstream from the compressor  31   b  in order to further raise the temperature of the cryogenic fluid before reinjecting it into the second tank  3 . 
         [0036]    In a second embodiment, shown in  FIG. 3 , in which each element is given the same reference number as an equivalent element in  FIG. 2 , the second pressurizing circuit  14  is branched off from the first pressurizing circuit  13  downstream from the first heat exchanger  15  in such a manner that the flow rate of helium for reinjecting into the second tank  3  is preheated in the first heat exchanger  15  before being taken to the second pressurizing circuit  14  and compressed by the compressor  31   b.  The remaining elements in this feed system  1  of the second embodiment are arranged in equivalent manner to the first embodiment. 
         [0037]    Although the compressor  31   b  in both of the embodiments shown in  FIGS. 2 and 3  is coupled to the turbine  31   a  with which it forms a turbocompressor  31 , in a variant shown in  FIG. 4  and applicable to both embodiments, the compressor  31   b  is actuated instead by an electric motor M. This produces even greater flexibility in the control of this compressor  31   b.    
         [0038]    Although the present invention is described with reference to specific embodiments, it is clear that various modifications and changes may be made to these embodiments without going beyond the general scope of the invention as defined by the claims. Consequently, the description and the drawings should be considered in a sense that is illustrative rather than restrictive.