Injector for a rocket engine

Abstract

The invention relates to an injector for a rocket engine, comprising a main part (10, 12) in which a fuel feed and an oxidator feed are provided and comprising an adjusting element (20) which, in cooperation with the main part (10, 12), defines a throttle point in the fuel feed as well as a throttle point in the oxidator feed, wherein the adjusting element (20) can be adjusted relative to the main part (10, 12), and the throttle points are designed such that during operation, the fuel and the oxidator flow through the narrowest cross-section of the throttle points at a respective sound velocity.

Description

[0001] Injector for a rocket engine

[0002] The invention relates to an injector for a rocket engine.

[0003] Thrust control in rocket engines is a complex process due to the nonlinearity and the coupling of fluid-mechanical and thermodynamic processes during injection and combustion. For optimal thrust control in the engine, four parameters must be controlled: fuel mass flow, oxidizer mass flow, fuel injection rate, and oxidizer injection rate. While the total mass flow must be varied for thrust control, both the mixture ratio and the injection rates must be kept as constant as possible for optimal performance. This problem is further complicated by the fact that all four parameters are coupled via the combustion chamber pressure. This sometimes leads to feedback and oscillations, which complicate control and, in the worst case, can lead to engine destruction.

[0004] In most existing systems, mass flow control is achieved via two separate control valves. These throttle the mass flow to the desired value. With a constant injection geometry, this means changing the injection speeds. Such systems have a limited control range and accept the resulting power loss. The control valves usually operate according to the throttling principle; the flow rate depends on the pressure difference. Systems that partially rely on the cavitation principle are also known; these are therefore partially pressure-decoupled. In the current state of the art, the control valves are designed as separate components.

[0005] One approach to continuously controlling the injection rate is the “variable area injector.” Here, the size of the injection openings is continuously changed. In previous designs, this approach has been limited to injectors with individual elements (particularly pintle injectors, occasionally continuous impingement injectors). The cross-sectional change is usually achieved by the axial displacement of two concentric conical surfaces. This concept is used, for example, in the Merlin engine from SpaceX or the LMDE engine of the Apollo program (Lunar Module Descent Engine). With variable pintle injectors, due to existing proportionalities, both injection openings are adjusted via a single control parameter and are therefore no longer independent. In addition, the injector geometry can be used as a shut-off valve (face shutoff). This is usually achieved using metallic sealing surfaces.

[0006] US Pat. No. 4,782,660 discloses an injector in which there are coupled constrictions for throttling the fluids for the oxidizer and the fuel, and coupled injection ports. The throttles are not operated in the cavitation range, so the mass flow depends on the combustion chamber pressure. Changes in the combustion chamber pressure therefore have an undesirable effect on the mass flow.

[0007] A non-adjustable injector is known from CN 114562389. In this case, injection occurs directly from a recovery diffuser.

[0008] US 2021 / 363939 A1 discloses an injector that has two slide valves that are not rigidly coupled to each other, which are used to control the supply of oxidizer and fuel during engine start-up. Thrust control is not possible with the disclosed design. Furthermore, it uses a geometry that is unsuitable for cavitation operation.

[0009] The object of the invention is to provide an injector for a rocket engine which has a simple structure and can be reliably controlled over almost its entire operating range.

[0010] To achieve this object, the invention provides an injector for a rocket engine, comprising a base body in which a fuel supply and an oxidizer supply are provided, and an actuating element which, in cooperation with the base body, defines both a throttle point in the fuel supply and a throttle point in the oxidizer supply, wherein the actuating element is adjustable relative to the base body and wherein the throttle points are designed such that, during operation, the fuel and the oxidizer each flow through the narrowest cross section of the throttle points at the speed of sound.

[0011] The basic concept of the injector according to the invention is based on the principle of the "variable area injector," which operates in a so-called "choked flow" state, i.e., in a state in which the flow in the narrowest cross-section of the throttle point is at the speed of sound. This principle can be used for both pressure-liquefied fluids and normal fluids.

[0012] If compressible fluids (gases, gas-liquid two-phase mixtures) are allowed to flow through an orifice and the pressure difference is increased by lowering the downstream pressure (i.e., the pressure behind the cross-section in question), the flow velocity and thus the mass flow rate continue to rise until the fluid reaches the speed of sound (critical pressure ratio). A further increase in velocity in the narrowest flow cross-section is not possible by further lowering the downstream pressure. The amount of gas flowing out depends only on the narrowest flow cross-section, the upstream pressure, and the thermodynamic properties of the gas upstream of the nozzle. As long as the critical pressure ratio is not exceeded, the mass flows are not influenced by the downstream pressure. This condition is called "choked flow." A hypothetical injector with this form of injection would not exhibit any coupling of the mass flows with the combustion chamber pressure.This means that the mass flows are no longer related to the condition in the combustion chamber and are completely decoupled from a control point of view.

[0013] In principle, choked-flow operation is also conceivable for gaseous propellants. However, due to their low density, gaseous propellants are not suitable for rocket engines. Furthermore, injection at supersonic speed makes stable combustion more difficult. Liquid propellants, on the other hand, are much more suitable because they do not have the disadvantages of gaseous propellants. While in normal subsonic flows, pressure and velocity cannot change suddenly with location, this is possible in flows at the speed of sound and above (compare compression / thinning shock). However, liquids can be evaporated by sufficiently reducing the pressure. The vaporization pressure depends on the condition and type of fluid and occurs almost instantaneously when the pressure is reduced. The gas content increases continuously with further reductions in pressure, as does the flow velocity.Two-phase mixtures of gas and liquid have a significantly lower speed of sound than the corresponding single-phase flows, which means that choked flow can also be achieved if the pressure is sufficiently reduced. Analogous to the choked flow in single-phase flows, this is referred to as "two-phase choked flow." The resulting mass flow, identical to pure gas, is decoupled from the pressure after the opening. The influence of the upstream pressure is significantly lower than with a purely gaseous medium. This effect is particularly useful for injectors in rocket engines.

[0014] The particular advantage of the injector according to the invention is that it is particularly easy to control. Considering the four control parameters of total mass flow, mixture ratio, fuel injection rate, and oxidizer injection rate, only the total mass flow is varied during operation, while the remaining parameters are fixed by design specifications. If the injector is operated in such a way that cavitation occurs in the narrowest cross-section during "two-phase choked flow," and the input conditions are kept constant, all parameters are, to a first approximation, only linear functions of the geometry, in particular the flow cross-sections. While there are certain nonlinearities due to friction and swirl effects, these have only a minor impact.

[0015] The design of the injectors according to the invention, which can be operated in the cavitation state due to their design, represents a significant difference to the state of the art.

[0016] The term "rocket engine" is not limited here to a propulsion system for an actual rocket, i.e., for the purpose of escaping the Earth's gravitational field. It refers to any propulsion system that operates by expelling combustion gases, even in a vacuum, for example, for the purpose of satellite attitude control. According to one embodiment of the invention, the throttle point coincides with the injection port. This is advantageous when the vapor pressure of the liquids used as propellant and oxidizer is higher than the combustion chamber pressure. Examples of such liquids are nitrous oxide, ethane, propane, propylene, or ethylene.

[0017] The fluids are injected directly from the narrowest cross-section at their critical speed of sound. Since this speed is significantly lower than that of pure gas due to the properties of two-phase flow, stable combustion results.

[0018] In principle, it is conceivable to provide separate injection ports to reduce the velocity. However, due to the compressibility of the gas component, the velocities would again be dependent on the combustion chamber pressure, so separate injection ports are preferably avoided.

[0019] Preferably, the control element or the base body is designed with slots in the area of ​​the throttle points, whereby the position of the control element relative to the base body determines the flow cross-section at the throttle points. By overlapping the slots in the control element or the base body with the structure of the base body or the control element, the overall flow cross-section can be adjusted very precisely.

[0020] According to one embodiment, the control element is designed as a hollow cylinder at its injection-side end, which is provided with paired slots on the fuel supply side and the oxidizer supply side. This results in advantageous geometric relationships,

[0021] The hollow cylinder can be guided in the combustion chamber end of the base body, preferably by means of a seal. This ensures that the flow cross-sections are maintained with great precision. In particular, it ensures that the fuel-to-oxidizer mixture ratio is always constant and does not vary due to radial positional tolerances.

[0022] According to one embodiment, the actuator is provided with seals that can interact axially with a contact surface in the base body to shut off the fuel and oxidizer feeds. The axial sealing effect can be used to reliably shut off the fuel and oxidizer feeds, so that no fuel or oxidizer is wasted when the engine is shut down, and a stable injection state is immediately achieved upon restart, since the injector is already filled with fuel and oxidizer.

[0023] According to one embodiment, a pressure recovery section is provided in the fuel and / or oxidizer supply downstream of the throttle point, and the injection opening is arranged downstream of the pressure recovery section. This embodiment is used for liquids whose vapor pressure is below the combustion chamber pressure (e.g., liquid oxygen, hydrogen peroxide, methane, liquid hydrogen, ethanol, etc.). The choked flow must be generated in a cavitation venturi. Similar to a venturi tube, the liquid is accelerated by narrowing its cross-section. This causes the pressure to drop below the vapor pressure. Cavitation and choked flow occur in the narrowest cross-section. The fluid then flows through the pressure recovery section, where the flow cross-section continuously increases.This slows down the fluid again, and the pressure rises back to the combustion chamber level. Finally, the fluid is injected into the combustion chamber via separate injection ports. The cavitation venturis and the injection ports for oxidizer and fuel are geometrically coupled and can all be varied with a single control parameter.

[0024] In this design variant, too, the injection velocity can be controlled solely by the size of the injection port due to the incompressibility of the fluid and the upstream cavitation venturi. The resulting pressure and velocity curves are not consistent with those upstream of the venturi.

[0025] The injector can be designed as a needle injector ("pintle injector"), so that the geometry of the nozzle needle can influence the way the fuel and oxidizer are mixed. The pressures in the fuel and oxidizer systems exert forces on the actuator. These forces can be balanced by adequately dimensioning the effective cross-sections in the axial direction. The injector area is exposed to the combustion chamber pressure and, due to the variable combustion chamber pressure, cannot be compensated by the pressure in the fluid system. However, the combustion chamber pressure is almost linearly related to the position of the actuator. To compensate for the pressure forces, a linear compression spring is used. This spring is compressed when the actuator opens and applies a counterforce to the actuator that is directly proportional to the combustion chamber pressure.The actuator is therefore, to a first approximation, force-free and only has to overcome deviations from the ideal state and friction in the sealing points.

[0026] The above-mentioned object is also achieved by an injector of the type described above in combination with a combustion chamber. Regarding the resulting advantages, reference is made to the above explanations.

[0027] A portion of the fuel and / or oxidizer injected into the combustion chamber can impinge on the combustion chamber wall, cooling it. This allows the mechanical stresses on the combustion chamber wall to be well controlled.

[0028] The invention is described below with reference to various embodiments illustrated in the accompanying drawings, in which:

[0029] Figure 1 shows a schematic view of a rocket engine with an injector according to the invention;

[0030] Figure 2 shows a perspective view of the injector according to a first embodiment;

[0031] Figure 3 shows the injector of Figure 2 in a side view;

[0032] Figure 4 shows the injector of Figure 2 in a view from the combustion chamber;

[0033] Figure 5 shows a section along the plane VV of Figure 4, with the injector in a closed state; Figure 6 shows the injector of Figure 5, with it in an open state;

[0034] Figure 7 shows, on an enlarged scale, detail VII of Figure 6;

[0035] Figure 8 shows a conceptual representation of the interaction of the actuating element with the base body;

[0036] Figure 9 shows a schematic representation of the flow conditions resulting during injection; Figures 10a to 10f show various injection configurations that can be used with the injector of Figures 2 to 7;

[0037] Figure 11 shows schematically an embodiment variant of the injector of Figures 2 to 7;

[0038] Figure 12 schematically shows an injector according to a second embodiment; Figures 13a to 13c show an injector of the second embodiment in a cross-section, the pintle of the injector in a side view, and a section through the pintle;

[0039] Figure 14 shows a section through an injector according to a further embodiment, the injector being shown in the closed state;

[0040] Figure 15 shows the injector of Figure 14 in the open state;

[0041] Figure 16 shows the injector of Figure 14 in a perspective view; and

[0042] Figure 17 shows the flow conditions resulting from the operation of the injector of Figures 14 to 16.

[0043] Figure 1 schematically shows a rocket engine 1. It has an injector 2, with which a propellant and an oxidizer can be injected into a combustion chamber 4. The combustion gases exit the rocket engine 1 through a nozzle 5.

[0044] The injector 2 is shown in detail in Figures 2 to 7. The injector has a two-part base body 10, 12. Part 10 of the base body serves for attachment to the combustion chamber and has an oxidizer supply 14. Part 12 of the base body serves for connecting an actuator 3 and has a fuel supply 16.

[0045] The injector according to the first embodiment is designed for pressure-liquefied liquids whose vapor pressure is above the combustion chamber pressure. Examples include nitrous oxide, ethane, propane, propylene, and ethylene.

[0046] Part 12 of the base body of the injector 2 is provided with a guide 18 arranged concentrically with a central axis M of the injector 2. Generally speaking, the guide 18 defines a radially inner valve seat, while part 10 of the base body 10, 12 defines a radially outer valve seat. An actuating element 20 cooperates with these two valve seats and is axially displaceable within the base body 10, 12. In a closed position of the actuating element, the injection cross-section for the fuel and the oxidizer is closed, and in open positions of the actuating element, the injection cross-section for the fuel and the oxidizer is more or less exposed depending on the axial position.

[0047] The guide 18 comprises a combustion chamber-side guide ring 22 and a spacer 24 adjoining it, which are secured in part 12 of the base body 10, 12 by means of a screw bolt 26. The outer surface of the guide ring 22 and the adjoining area of ​​the spacer 24 together form a radially inner guide surface 25 (see Figure 7).

[0048] An annular seal 28 is arranged between the guide ring 22 and the spacer 24.

[0049] Approximately at the level of the guide ring 22, the part 10 of the base body 10, 12 is provided with a guide surface 30 arranged concentrically to the central axis M of the injector 2. An annular seal 32 is arranged in the guide surface 30.

[0050] The actuator 20 is designed at its combustion chamber end with a hollow cylindrical section 34, which is guided on the outside by the guide surface 30 and on the inside by the guide surface 25. The seals 28, 32 ensure that the guiding effect is maintained even if extremely tight tolerances are not maintained between the interacting components.

[0051] On the side facing away from the combustion chamber, the hollow cylindrical section 34 of the actuating element 20 is adjoined by a radially outer shoulder 36 and a radially inner shoulder 38. These each form a seat for an annular seal 40 and 42, respectively.

[0052] When the actuating element 20 is in the closed position, the seal 40 rests against a conical contact surface 44 of the part 10 of the base body 10, 12. When the actuating element 20 is in the closed position, the seal 42 rests against a conical surface 46 formed on the spacer 24.

[0053] Teflon or a metallic material can be used as the material for seals 28, 32, 40, 42.

[0054] As can be seen in particular in Figure 4 in combination with Figure 5, the hollow cylindrical section 34 of the actuating element 20 is provided on the combustion chamber side with slots arranged in pairs, namely with radially outer slots 48 and with radially inner slots 50.

[0055] The slots 48, 50 have their maximum depth at the combustion chamber end of section 34 of the actuating element 20, measured in the radial direction, so that they meet there at a tip 52. With increasing axial distance from this tip 52, the depth of the slots 48, 50 decreases until they both finally end at the same level. In the closed state of the actuating element 20, the slots 48, 50 end within the guide section, which is formed by the guide surface 30 in part 10 of the injector base body and the guide surface 25 of the guide 18.

[0056] The axial position of the actuating element 20 is adjusted by means of the electromechanical actuator 3. In the illustrated embodiment, the rotary movement of a spindle 60 is translated into an actuating movement of a plate 62, which in turn is coupled to the actuating element 20. When the actuating element 20 is in the closed position (see Figure 5), the seals 40, 42 resting on the conical contact surfaces 44, 46 ensure that neither fuel nor oxidizer can enter the combustion chamber ("face shutoff").

[0057] When the actuating element is moved from the closed position to an open position, as shown, for example, in Figure 6, the seals 40, 42 initially lift off the contact surfaces 44, 46. At this point in time, however, the slots 48, 50 continue to lie completely within the guide surfaces 25, 30, so that (assuming correspondingly tight tolerances) neither fuel nor oxidizer enters the combustion chamber. Only when the actuating element 20 is retracted far enough that the beginning of the slots 48, 50 lies above the transition of the guide surfaces 25, 30 into the conical contact surfaces 46, 44 is a flow cross-section for the fuel and oxidizer released in the region of the slots. These then flow through the slots 48, 50 into the combustion chamber according to the specified geometry.

[0058] The resulting narrowest flow cross-section for the fuel and the oxidizer is marked by arrows in Figure 7.

[0059] The geometric conditions are tuned so that cavitation occurs during injector operation and sonic speed is reached at the narrowest flow cross-section. Thus, the injection velocity is constant, and the mass flow depends (to a first approximation) directly on the cross-section of the cavitation venturi and the injection port. This allows the entire injector to be controlled using a single parameter, namely the position of the control element 20 and thus the flow cross-section at the narrowest point.

[0060] The mixing ratio is determined exclusively and invariably by the ratio of the cross-sections for the injection of the fuel and the oxidizer, i.e., by the cross-sections of the slots 48, 50 relative to one another. The injection velocity is determined by the speed of sound in the narrowest cross-section, whereby the speed of sound is comparatively low because a mixture of liquid and gas is present in the narrowest cross-section, a so-called "two-phase choked flow." Figure 8 schematically shows the interaction of the hollow cylindrical section 34 of the actuating element 20 with the inner guide surface 25 and the outer guide surface 30. On the left-hand side, the narrowest flow cross-section for the fuel T and the oxidizer O is again marked with thick arrows.For clarity, the cut is placed here in such a way that it runs through a pair of slots 48, 50 on both the right and left sides of the hollow cylindrical section 34.

[0061] The flow pattern resulting during operation is shown schematically in Figure 9.

[0062] Figure 9 shows schematically the injection geometry of the injector of Figures 2 to 7.

[0063] The combination of the injection jets from the injected fuel T and the injected oxidizer O results in main injection jets, designated here by reference symbol H. The external slots 50, through which the oxidizer flows, create secondary jets on the outside, designated here by reference symbol No. These secondary jets lead to a limited film cooling effect that cools the transition region between the injector and the combustion chamber. This is particularly important in radiation-cooled combustion chambers.

[0064] In the same way, secondary jets NT are formed at the slots 48 for the fuel T, which form a fuel-rich zone with a comparatively low temperature along the guide 18, so that the guide is protected from overheating.

[0065] Different injection patterns can be realized by arranging the slots 48, 50. It should be emphasized that different injection patterns are possible simply by replacing the actuator 20 while the injector remains otherwise unchanged. This is explained below using Figure 10.

[0066] Figure 10a shows two pairs of diametrically opposed slots 48, 50. Figure 10b shows the slot pattern of the injector shown in Figures 2 to 7.

[0067] In Figure 10c, four pairs of slots 48, 50 are used, which are arranged at an angle of 90° to each other.

[0068] Figure 10d shows pairs of slots 48, 50 which are not radially aligned but have a tangential component so that swirling effects around the central axis M are possible.

[0069] It is also possible to arrange the slots not in pairs, or not exclusively in pairs, but in a different number. As shown in Figure 10e, a total of six slots 50 are provided for the propellant, while only three slots 48 are provided for the oxidizer.

[0070] In Figure 10f, three slots are used for the fuel and six slots for the oxidizer.

[0071] Figure 11 shows an alternative design of the injector according to the first embodiment. The same reference numerals are used for the components known from the first embodiment, and reference is made to the above explanations.

[0072] The injector of Figure 11 corresponds to the embodiment of Figures 2 to 7 in that here too the fuel is injected directly into the combustion chamber from the narrowest cross section of the injector.

[0073] The main difference from the injector of Figures 2 to 5, which has several discrete injection openings formed by the slots, is that the injector of Figure 11 features a continuous annular gap for both the fuel and the oxidizer. This annular gap is formed by the combustion chamber-side end of a hollow cylindrical section 34 of the actuating element 20, which, together with the associated valve seat surfaces in part 10 of the base body and the guide 18, defines the respective injection cross-section.

[0074] The injector shown in Figure 11 also exhibits a two-phase choked flow at the narrowest flow cross-section, i.e., where the fuel and oxidizer exit the combustion chamber. The narrowest cross-section, which coincides with the injection port, is marked E.

[0075] Figure 12 shows an injector according to a second embodiment. The same reference numerals are used for the components known from the first embodiment, and reference is made to the above explanations.

[0076] The main difference between the injector of the first embodiment and that of the second embodiment is that the injector of the second embodiment is designed for liquids whose vapor pressure is below the combustion chamber pressure. Examples include liquid oxygen, hydrogen peroxide, methane, liquid hydrogen, and ethanol.

[0077] Since the vapor pressure of these liquids is below the combustion chamber pressure, direct injection from the cavitation venturis 70, 103 is not possible. Therefore, a pressure recovery section 72 for the fuel and a pressure recovery section 74 for the oxidizer are provided adjacent to the cavitation venturi, designated by reference numeral 70 in Figure 12. In the pressure recovery sections 72, 74, the fluid is decelerated again by continuously increasing the flow section, so that the pressure rises back to combustion chamber level.

[0078] The fuel and oxidizer can then be injected downstream of the pressure recovery section 74. The injection ports, which do not coincide with the narrowest cross-section here, are designated 102 and 103.

[0079] The injector here is designed as a "pintle injector." The injection pattern can be adjusted and influenced using generally known features, such as grooves in the nozzle plate.

[0080] Figures 13a to 13c show the injector of Figure 12, wherein instead of the pressure recovery section 72, 74 shown very schematically in Figure 12, a concrete, flow-optimized geometry is shown here.

[0081] Here, too, the injector is controlled solely by the axial adjustment of the control element 20 by means of the actuator 3 (shown schematically in Figure 13). The only control parameter is the mass flow, which depends solely on the flow cross-section in the cavitation venturi 70.

[0082] For the sake of completeness, the requirements that must be met without exception in order for a cavitation state to occur in an injector geometry for fluids whose vapor pressure is lower than the combustion chamber pressure are summarized below:

[0083] There must be a narrowest point which

[0084] has a flow cross-section that is smaller than the injection opening.

[0085] A pressure recovery section / diffuser must exist behind the narrowest point. The pressure recovery must be sufficiently efficient for successful cavitation operation.

[0086] Without correctly dimensioned pressure recovery, cavitation operation cannot occur

[0087] The flow cross-section at the narrowest point must be sufficiently small so that, for a given pressure drop and injection port size, and the required injection velocity or mass flow, the static pressure at the narrowest point falls below the vapor pressure. If the cross-sectional area is too large or the pressure difference is too small, normal flow without cavitation occurs.

[0088] The pressure ratio between the combustion chamber and the supply line must exceed a critical ratio. This critical ratio is determined by the ratio of the cross-sections of the injection port and the cavitation port, as well as by friction and turbulence losses generated in the injector (particularly in the pressure recovery section). If pressure losses are too high, the required pressure ratio rises to unrealistically high values. Effective pressure recovery and flow-dynamic optimization are therefore prerequisites for a functional design. If the pressure drop is too high, normal flow will occur instead of cavitation. The narrowest point must be sufficiently long, as evaporation of the fluid only occurs after a certain delay (boiling delay). This can be accelerated to a certain extent by reducing the pressure to a value below the vapor pressure.This also applies to cavitating injected fluids with a vapor pressure that is greater than the combustion chamber pressure.

[0089] Figures 14 to 16 show an injector according to a further embodiment. The injector corresponds in basic design to the injector shown in Figures 1 to 7. Reference numerals familiar from the injector shown in Figures 1 to 7 are used, and reference is made to the above explanations in this regard.

[0090] A difference between the embodiment of Figures 1 to 7 and the embodiment of Figures 14 to 16 is that the guide 18 ("pintle") is constructed in one piece and is screwed into part 12 of the base body 10, 12. The outer surface of the guide 18 forms a radially inner guide surface 25.

[0091] The pintle 18 is screwed into part 12 of the base body 10, 12. The outer surface of the pintle 18 forms a radially inner guide surface 25.

[0092] An outer conical sealing surface 44 and an inner conical sealing surface 46 adjoin the hollow cylindrical section 34 of the actuating element 20 on the side facing away from the combustion chamber. Opposite these sealing surfaces, there is a groove (36 and 38) in the base body 10 and pintle 18 for the sealing rings 40 and 42. When the actuating element 20 is in the closed position, the seal 40 rests against a conical contact surface 44 of the part 20. When the actuating element 20 is in the closed position, the seal 42 rests against a conical surface 46 formed on the actuating element 20.

[0093] The radial sealing rings 107 and 108 seal the movable actuator 20 and the base bodies 10, 12 against the environment. Alternatively, the sealing rings 107 and 108 can be replaced with metallic bellows seals.

[0094] In summary, the described injectors are characterized by the following properties: If one considers the four control parameters total mass flow, mixture ratio, fuel injection speed and oxidizer injection speed, only the total mass flow is varied during operation, while the remaining parameters can be fixed by suitable measures.

[0095] If the injector is operating in cavitation mode (2-phase choked flow) and the input conditions are kept constant, all parameters are, to a first approximation, only linear functions of the geometry (flow cross-sections). Nonlinearities due to friction and turbulence effects are present, but these have only a minor impact.

[0096] The relationship between mass flow and injection velocity (and thus the cross-section of the cavitation venturi and the injection port) is, to a first approximation, directly proportional. If the mass flow is halved, the injection cross-section must also be halved to maintain a constant injection velocity. This allows both parameters to be controlled by a single coupled parameter.

[0097] The injection speeds of fuel and oxidizer can be controlled via a coupled parameter, as is usual with variable area injectors.

[0098] This allows the entire control system to be summarized in a single control parameter for mass flow control. Injection speeds and mixture ratios are determined by the geometry.

[0099] By correctly selecting the geometries, a linear relationship between thrust and manipulated variable can be constructed. This, combined with the pressure decoupling caused by cavitation, represents a significant simplification of the control loop.

[0100] The injector is well suited for miniaturization (e.g. satellite engines) due to the lower requirements on the size of the flow opening.

[0101] In the first design, the actuator runs on both the inside and outside of a sealed guide; the fuel and oxidizer are located on the inside and outside, respectively. If the actuator is moved far enough that the slots extend beyond the guide, the fuel can enter the combustion chamber through the opening that forms. The two components then collide (similar to the classic impingement design) and are atomized. The injection openings increase in size proportionally to the travel of the actuator. The mixing ratio is determined by the slot widths. Scaling is easily achieved during production by adding or removing pairs of slots.

[0102] A face shutoff is possible by integrating valves directly into the injector geometry.

[0103] To improve face shutoff characteristics, soft sealing packings are installed close to the injection ports. This improves leak tightness over longer periods. This is particularly relevant for satellite engine applications.

Claims

Patent claims 1. Injector for a rocket engine, with a base body (10, 12) in which a propellant supply and an oxidizer supply are provided, and an adjusting element (20) which, in cooperation with the base body (10, 12), defines both a throttle point in the propellant supply and a throttle point in the oxidizer supply, wherein the adjusting element (20) is adjustable relative to the base body (10, 12) and wherein the throttle points are designed such that, during operation, the propellant and the oxidizer flow through the narrowest cross section of the throttle points at the speed of sound.

2. Injector according to claim 1, characterized in that the throttle point coincides with the injection opening.

3. Injector according to claim 2, characterized in that the adjusting element (20) or the base body (10, 12) is designed to be slotted in the region of the throttle points and the position of the adjusting element (20) relative to the base body (10, 12) determines the flow cross-section at the throttle points.

4. Injector according to claim 3, characterized in that the adjusting element (20) is designed at its injection-side end with a hollow cylindrical section (34) which is provided with slots (48, 50) arranged in pairs on the side of the fuel supply and on the side of the oxidizer supply.

5. Injector according to claim 4, characterized in that the hollow cylinder (34) is guided in the combustion chamber-side end of the base body (10, 12), preferably by means of a seal (28, 32).

6. Injector according to one of the preceding claims, characterized in that the actuating element (20) is provided with seals (40, 42) which can interact in the axial direction with a contact surface (44, 46) in the base body (10, 12) in such a way that the fuel supply and the oxidizer supply are blocked.

7. Injector according to claim 1, characterized in that downstream of the throttle point a pressure recovery section (72, 74) in the supply of the fuel and / or the oxidizer and the injection opening (E) is arranged downstream of the pressure recovery section.

8. Injector according to claim 7, characterized in that it is designed as a needle injector.

9. Combination of an injector (2) according to one of the preceding Claims and a combustion chamber (4).

10. Combination according to claim 9, characterized in that part of the fuel and / or oxidizer injected into the combustion chamber (4) impinges on the combustion chamber wall in such a way that it is cooled.

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