Abstract:
In a combustion chamber of a liquid propellant engine, a combustible liquid and an oxidising mixture are fed by means of two different independent and mechanically separate feed pumps and driven by respective turbines which are also independent and mechanically separate from each other; the oxidising mixture generated by a combustible liquid pre-burner passing through one of the turbines; and the heated combustible liquid passing through the other turbine before it is supplied to the combustion chamber; the oxidising mixture, after having passed through the respective turbine, flows into the combustion chamber via an injection plate.

Description:
[0001]    The present invention relates to a liquid propellant engine and, in particular, to a liquid propellant engine for aerospace use. 
         [0002]    A liquid propellant engine for aerospace use must satisfy a robustness requirement for its possible reuse. 
       BACKGROUND OF THE INVENTION 
       [0003]    As is known, a liquid propellant engine is subject to high thermo-mechanical loads which increase with increasing engine performance. High performance can be obtained by increasing the power parameters of the engine, such as the pressure in the combustion chamber. 
         [0004]    Practically, it is observed however that with the increase in these parameters a progressive decrease of the functional reliability of the engine occurs. 
         [0005]    The document RU23528043 C1 describes a liquid propellant engine comprising a combustor having a combustion chamber and an expansion nozzle located downstream of the combustion chamber cooled by a flow of liquid propellant. The engine also comprises a fuel pump and an oxidant pump connected angularly to each other by means of a common torsion shaft to rotate at the same angular speed. The two pumps are thus both driven by a turbine which drives the common shaft and, in turn, driven by a pre-burner receiving in input a flow of fuel and oxidant and forming an output oxidising mixture which, having passed through the turbine, is supplied to the combustion chamber. 
         [0006]    The turbine previously described is associated to a supplementary turbine, which is also angularly coupled to the common shaft to rotate in unison with the two pumps and the other turbine. The supplementary turbine has an inlet connecting with the outlet of a cooling circuit of the combustor and, in this specific case, also heating the combustible liquid, and an outlet connected to the combustion chamber. 
         [0007]    Liquid propellant engines of the type described above have some problematic aspects. 
         [0008]    First, since the two pumps are connected to each other by a rotating shaft, a possible leakage of fuel and oxidant drawn through by the pumps would inevitably mix causing damage to the engine with catastrophic consequences. 
         [0009]    In order to avoid such mixing, dynamic seal devices associated with the common shaft are normally present in known engines. Such seal systems are relatively complex and expensive and in any case not completely reliable. 
         [0010]    In addition, since the rotation speeds of the oxidant pump and the combustible liquid pump are equal, it is particularly difficult to determine a speed value which corresponds to a high degree of overall engine efficiency. In all cases, the value determined will, however, always be a compromise value, for which at least one of the pumps or turbines will operate in a condition other than that of maximum efficiency, with an immediate impact on the overall engine efficiency. 
         [0011]    In addition, known liquid propellant engines of the type described above have a theoretical limit to the increase in engine thrust. As is known, in fact, the thrust increases linearly with the increase in the fuel flow rate. Increasing the flow rate and needing to comply with a set value of the combustion chamber pressure, it is necessary to increase the throat section of the combustion chamber and consequently the size of the expansion nozzle. The aforesaid increases in cross-sections mean an increase in the radial dimensions of the engine. Although the increase in the radial dimensions involves an increase in the surface area of the combustion chamber side wall and, in essence, in an increase in the useful heat exchange surface area, this increase in surface area is still not sufficient to achieve thermal balance in conditions of high fuel flow rates. Indeed, while the thrust increases directly in proportion to the flow rate, the increase in the surface area of the side wall depends, however, on the square root of the flow rate. It follows that in order to maintain an adequate extraction of heat for the fuel flow rate and hence the level of thrust, the increase in the surface area of the side wall is not sufficient to remove the heat generated. For this reason, it is necessary to increase the length of the combustion chamber, which inevitably leads to an increase in the axial size of the engine and, proportionally, of its weight. 
         [0012]    U.S. Pat. No. 8,250,853 B1 corresponds to the preamble of claim  1  and shows an engine in which the combustion chamber is supplied with liquid oxygen directly from the outlet of the oxidant pump. At the same time, this document shows a gas generator having an output gas which, after passing through the corresponding turbine, is discharged into the atmosphere or into a nozzle separate from the combustion chamber. 
         [0013]    The performance of this engine is penalised by the fact that part of the propellants is not introduced into the combustion chamber and is discharged without producing engine thrust. 
       SUMMARY OF THE INVENTION 
       [0014]    The objective of the present invention is to provide a liquid propellant engine which makes it possible to resolve the above problems simply and economically. 
         [0015]    The above objective is achieved by a liquid propellant engine as claimed in claim  1 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For a better understanding of the present invention a preferred embodiment is now described, as a non-limiting example, with reference to the accompanying drawings, wherein: 
           [0017]      FIG. 1  shows, schematically and substantially in block form, a preferred embodiment of the liquid propellant engine according to the invention; and 
           [0018]      FIG. 2  is a figure similar to  FIG. 1  and illustrates an alternative embodiment of the liquid propellant engine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Number  1  in  FIG. 1  indicates, as a whole, a liquid propellant engine with a double supply turbopump. In particular, the engine  1  comprises a combustor  2 , known per se, an assembly  3  for feeding a combustible liquid and an assembly  4  for feeding and supplying the combustion chamber  2  with an oxidising mixture with a high oxidant content. 
         [0020]    The combustor  2  comprises a combustion chamber  5 , an injection plate  6 , a diffuser nozzle  7  and a regenerative cooling circuit  8  for the combustion chamber  5  and for the diffuser nozzle  7 , all known per se and not described in detail. 
         [0021]    The cooling circuit  8  surrounds the combustion chamber  5  and the nozzle  7  and conveys a cooling fluid, in this case a combustible liquid, which enters from an inlet  10  of the cooling circuit  8  and exits via an outlet  11  of the circuit  8  at a higher temperature, having extracted heat from the side walls of the combustor  2 . 
         [0022]    The assembly  3  comprises a turbopump  9 , in turn comprising a pump  12  having a respective drive shaft  13 , an inlet  14  connected to a tank which is known and not illustrated and an outlet mouth  15  connected to the inlet of the circuit by means of a duct  39 . 
         [0023]    The assembly  3  further comprises a driving turbine  16  for the pump  12 . The turbine  16  is angularly connected to shaft  13  in a manner known per se and has an inlet mouth  18  connected to the outlet  11  by means of a pipe  20  and an outlet mouth  19  connected to the injection plate  6  by means of a pipe  21 . The combustible liquid is thus taken from the mouth  11  following a closed path, passes through the turbine  16  and enters the combustion chamber  5  through the injection plate  6 . 
         [0024]    Still with reference to  FIG. 1 , the assembly  4  comprises a burner  22 , known per se and not described in detail comprising two inlets  23  and  24  and an outlet  25 . The assembly  4  further comprises a turbopump  26 , in turn comprising a pump  27  having a drive shaft  28 , an oxidising fluid inlet mouth  29  and an outlet mouth  30  connected to the inlet  23  of the burner  22  through a duct  31 . 
         [0025]    The assembly  4  also comprises a driving turbine  32  for the pump  27 . The turbine  32  is angularly integral with the shaft  28  in a manner known per se, and has an inlet mouth  34  connected to the outlet  25  of the burner  22  by means of a pipe  36  and an outlet mouth  35  connected to the injection plate  6  by means of a pipe  37 . 
         [0026]    Still with reference to  FIG. 1 , the inlet  24  of the burner  22  is connected to the outlet port  15  of the pump  12  by means of a pipe  38 . 
         [0027]    In steady state conditions, the pump  12  sends the combustible liquid to the inlets  10  and  24  while the pump  27  sends the oxidising fluid to the inlet  23  of the burner  22 . 
         [0028]    The burner  22  burns the oxidising fluid and the combustible liquid and generates an oxidising mixture which passes through the turbine  32  before flowing through to the combustor  2 . Simultaneously, the combustible liquid supplied by the pump  12  into the inlet  10  of the same combustor  2  passes through the circuit  8 , heats up and gasifies and exits from the circuit  8  through the outlet  11  and passes through the turbine  16  before entering the combustion chamber  2  through the injection plate  6  and burns with the oxidising mixture inside the chamber  5 . 
         [0029]    The embodiment illustrated in  FIG. 2  relates to an engine  50 , which differs from the engine  1  in some constructional details and for which the constituent parts are indicated where possible using the same reference numbers as for the corresponding parts of the engine  1 . 
         [0030]    The engine  50  comprises two combustors  2  constructively and dimensionally identical or different to each other. The combustors  2  are connected to the assemblies  3  and  4  in parallel. In the example described, the injection plates  6  are fluidly connected to the pipes  37  and  21  for supplying the two injection plates  6 . 
         [0031]    Still with reference to  FIG. 2 , the combustible liquid fed by the pump  12  is divided between the inlets  10  of the combustors, one inlet of which is connected to the pipe  39  and the outlets of which are connected to the inlets  10  via two pipe portions indicated by  43  and  44 . Similarly, the outlets  11  of the same combustion chambers  2  are connected to the pipe  20  via the pipes  45  and  46 . 
         [0032]    From the foregoing it is clear, firstly, how the use of a pair of distinct and independent turbopumps, i.e. devoid of mechanical rotational constraints makes it possible to increase considerably the safety and increase the overall efficiency of the engine. 
         [0033]    As regards safety, the engines  1  and  50  described make it always possible, even in the presence of leakage, to keep the combustible liquid and the oxidising mixture separate using traditional static sealing systems rather than the complex and expensive dynamic sealing systems necessary in the known solutions. 
         [0034]    As regards engine efficiency it is clear on the other hand that the absence of mechanical constraints between the pumps and therefore between the two turbopumps, makes it possible to control the fuel flow the flow of oxidising mixture in a precise manner. There are actually no obstacles to controlling the turbopumps independently from each another. The foregoing arises from the fact that the pumps  12  and  27  are mutually mechanically separated and therefore their rotation speeds can be set without restriction through adjustment of the respective, also mutually independent, turbines  16  and  32  and therefore controllable without mechanical constraints. In other words, unlike known engines, the engines  1  and  50  described comprise two turbine pumps  9 ,  26  which in practice are two distinct units, fluidly separate and independent from one another. 
         [0035]    This makes it possible to control the pumps  12  and  27  in such a way that these, and ultimately the two turbopumps, work in conditions of maximum efficiency. 
         [0036]    In addition, the oxidising mixture produced by the burner  22  is not only used to feed the turbine  32 , but also subsequently for feeding the combustion chamber  5 . In other words, the whole flow of oxidising mixture downstream of the turbine  32  is used for combustion in the combustion chamber  5 , together with the fuel coming from the pipe  21 . 
         [0037]    Finally, the use of two combustion chambers  2  arranged in parallel makes it possible to increase the engine thrust by increasing the fuel flow rate while, at the same time, limiting the dimensions and therefore the bulkiness of the engine.