RO129890B1 - Retroinjector for unstable liquids - Google Patents

Abstract

The invention relates to an injector for unstable liquids to be used as rocket engine fuels and to a process for manufacturing the same. According to the invention, the injector comprises a body () wherein a support () is mounted and axially provided with a circular orifice (), inside the support () there being a valve () which can slide between an upstream end position in which the valve () is in contact with a valve seat () confining an intake orifice () which is thereby tightly closed and a downstream end position in which the valve () tightly closes another orifice (), an annular groove which can be cut into the body () possibly accommodating an annular mini magnet (). The process, as claimed by the invention, consists in cutting a blind annular axial orifice () into a primary metal bar (), whereinto a hexagonal mandrel () is introduced and applying a quasi-uniform pressure onto an outer surface of the bar (), the value of the said pressure being higher than the value of the flowing pressure of the metal of which the bar () is made, the pressure being applied by normal squeezing between some squeezing jaws () up to the complete deformation of the material around the blind annular orifice () which gets the shape of the mandrel (), after which the bar () is released from the jaws () and the mandrel () is withdrawn, then the bar () is machined externally and internally by lathe turning in order to cut out the support () therefrom.

Description

The invention relates to a non-return injector for unstable liquids, used in the field of rocket propulsion systems, in more detail, to the injection systems of the liquid components of the propellant, in the combustion chamber / chambers of the compound, hybrid and combined type rocket engines, and / or from heat-generating gas-generating systems, used in space, civil or military propulsion.

In the case of reactive engines and gas-generators, the propellant is the substance or combination of substances that produces, by self-combustion, gases with high internal energy, so with high temperature and low molecular mass, which are accelerated in the engine effluent, to produce the propulsive force, or, in the case of gas generators, in the stator of some turbines, for their maintenance, or displace the propelling liquids from the tanks, to supply the combustion chamber / chambers.

The propellant is stored on board the vehicle, from where it is pumped to and consumed in the engine, and in the gas generators it is consumed to produce the mechanical work of displacement by means of the gas resulting from the combustion of the propeller at high pressure.

Chemical propellants are usually used in either solid or liquid form, but combined rocket engines suck in atmospheric air to save on-board oxidant, hybrid engines use non-self-igniting solid components, in combination with often unstable liquids, and compound engines use propellant. self-flammable solid, and liquid component also often unstable.

Injection of reactive and unstable liquids in compound engines and gas generators presents a higher risk of blow back than in other rocket propulsion systems, because the solid component of the propellant, located in the traction chamber, is self-igniting and produces gases under pressure. potential excess over the pressure of the injected liquid, being able to initiate reverse flows, with a detonating effect.

An efficient chemical oxidant for rocket engines is N ₂ O nitrogen oxide, a substance that is essentially unstable, due to the positive and large deformation enthalpy (ΔΗ \ = 1377 kJ / kg). This high enthalpy value is a thermochemical quality desired as favorable, but presents, on the other hand, a high risk of detonation, an accident that can be initiated by reverse flows, when hot combustion products would pass back through the injection system into the collectors. , to pipes and tanks, coming into contact with the nitrous oxide, and being able to initiate its detonation. in those closed spaces the effects become destructive.

The literature mentions a few such accidents with particularly serious consequences. At temperatures up to about 600 ° C, the nitrous oxide gas is stable, but above this temperature it becomes self-detonating in the gas phase. The risk of detonation at reverse flows is also present in concentrated oxygenated water H ₂ O ₂ , another oxidant widely used in rocket engines. This risk is especially planned on the combined engines and gas-generators, due to the self-igniting nature of the solid propellant in the room, with effect on any unstable liquid, and requires means to safely prevent the reverse flow of hot gases, objectively solved by the present invention. The risk of reverse flows also exists in hybrid engines, due to the reduction of the pressure of the liquid by cooling due to the self-relocation, being able to appear before the injectors the biphasic or gaseous state of the unstable liquid. In the gaseous state, such a reactive and unstable liquid may detonate in contact with reducing (if oxidizing) or oxidizing (if fuel) substances, in particular hot combustion gases. See the description of the disastrous accident recorded by Scaled Composites Company during cold handling of liquid nitrogen protoxide.

In known constructions of hybrid engines (compound engines are not yet in operation, or are not known to us), the only method to reduce the risk of detonation of the unstable oxidant is to ensure sufficient pressure of the liquid, so that it does not vaporize during injection. , which is an indirect method of protection,

EN 129890 Β1 depending on numerous non-stationary effects, such as instability of combustion in the engine, or local cavitation effects in liquid feed pipes. For this reason the literature mentions reverse flows as the main risk affecting the reliability of hybrid engines. The fatal accident occurred at Scaled Composites Company (SCC) in 2007, during the supply of nitrogen oxide to the main rocket engine of the Spaceship-two suborbital hybrid rocket engine, when the cold proton detonation, probably initiated by a small hydrocarbon residue, the explosion of the tank, the death of three workers due to the resulting skis, and the serious injury of three others, produced a justified international reaction in the field. The explosion occurred during cold maneuvers, without combustion, which is alarming. The serious accident shows how dangerous the chemical instability of the nitrous oxide is, under certain conditions, if uncontrolled vaporization of the liquid occurs. And in other incidents the reverse flows were the main cause of the explosion of the traction chambers or the oxidant tank of some hybrid engines.

at present the intimate causes of these detonations are not fully known. The press statements of the project manager of the SCC company Burt Rutan denote the ignorance of these risks, or their superficial knowledge, which explains the lack of adequate security measures, either in the design of the systems or in their manipulation. It is therefore necessary to find new methods of protection against local evaporation, especially those initiated by reverse flows.

It is noted that SCC is currently the only major user of hybrid rocket engines and, due to the successful image of its experiences with Space Ship suborbital rocket aircraft, has triggered worldwide unwarranted interest in hybrid rocket engines, otherwise inefficient engines. from a thermochemical point of view, unlike the other types of rocket engines. SCC uses the hybrid engine manufactured by Space-Dev in Denver, Colorado, currently purchased by Sierra Nevada Corporation, and transformed into the Space Propulsion, self-evaporating fuel engine. The only protection against reverse flow is the use of a one-way valve on the inner liquid supply pipe. Hot gas infiltration can occur up to this valve, which remains a considerable risk factor. The report of the state commission of inquiry shows very clearly that the SCC managers did not elaborate appropriate measures to protect the work of the personnel during the tests with nitrogen oxide.

US 4483139 discloses a construction of a non-return valve for a rocket engine consisting of a pre-combustion chamber in which solid fuel is burned, so that the generated gases present an oxygen deficiency when they pass through the central pipe body of the valve, towards a main combustion chamber, where full combustion takes place. The drainage in the valve body ends with a seat with a downstream valve forming an annular surface through which the fluid jet is controlled. The control is exerted by approaching or distancing the seat valve, with the help of a rod that slides in a central body, the rod being actuated by a screw / nut mechanism with fine pitch. The valve body also has pipes parallel to the shaft and valve axis, through which a secondary flow of gases B passes. However, this valve does not work as an injector.

JPH 10176606 A describes a flow passage through a ball valve, from the body of a liquid fuel pump, used in the overload circuit of an aircraft. In one embodiment, the centrifugal pump sends the fuel fluid through the main channel, to the non-return valve disposed in the valve body, into a pipeline in continuation of the main channel. In the sewer, upstream of a chair is a spherical valve that closes the flow, being pressed by a truncated spring, the valve being of the "normally closed" type. The opening is performed with the magnetic core rod, which pushes the ball and releases the seat, when the electromagnet coil is energized. However, this valve does not work as an injector either.

RO 129890 Β1

Besides the recommendation to use external pressurization systems and thus to maintain the permanent volatile liquid in the liquid phase, other recommendations or constructive solutions are not known. To our knowledge, there is no patent or published work with reference to injectors that can prevent, directly from the combustion chamber, the occurrence of reverse flows, which has, to date, left the risk of reverse flows unresolved.

The technical problem solved by the present invention is the realization, in a single injector-valve device, of a superior injection and spraying of the propelling liquid, and stopping the reverse flows in the injector body, due to the reduced switching time of the valve.

This patent solves the proposed technical problem, and removes the disadvantages of existing solutions by constructing a new type of injector-bypass, for injection systems for rocket and gas-engine engines for such combined, compound and hybrid engines, a solution that quickly and completely reverses the flow, the construction being at the same time simple and cheap.

The invention has advantages in terms of very fast and complete blocking of the reverse flow of hot reactant gases, even at the exit of the combustion chamber, back through the injector system, towards the liquid tank, dangerous and common flows in hybrid rocket engines. also, much more present and very dangerous in the missile engines or combined gas generators, by the invention the gases are not allowed to advance at all inside the pipes, in contrast to the conventional one-way valves, which cannot be mounted directly on the combustion chamber wall, and thus expose a considerable mass of liquid unstable to contact with the flue gases.

The non-return injector for unstable liquids, according to the present invention, thus offers total protection against reverse flows, even at the interface with the engine chamber, isolating the volatile and explosive liquid from the hot gases even at the surface of the injector cylinder. It quickly stops the reverse flow, prevents the return of hot combustion products inside the injection manifolds and the piping of the feed system, both at the start of the compound, when the ignition of the solid propellant in the chamber first occurs, and after the liquid is stopped by the injector, when it is again possible for the combustion gases to return, due to their overpressure, in the supply system. The quick return of the valve to the seat is ensured by its reduced mass, and by the reduced mass of fluid entrained at closing the valve. It is offered to designers of rocket propulsion systems based on unstable liquids, such as nitrous oxide, the solution of eliminating the risk of reverse flows, and the correct functioning of the composite, hybrid or combined rocket aggregates.

The proposed invention thus eliminates the aforementioned shortcomings, by performing a safe injection, without reverse flow, through the small non-return injector, for safe spraying of chemically unstable and volatile liquids, with positive formation enthalpy, completely stopping the reverse flows. This type of absolute protection is also provided for compound, combined and hybrid gas generators. In addition, the non-return injector proposed by the invention has spray characteristics superior to the usual injectors, by the geometry of its nozzles, as described below.

In contrast to all known types of liquid injectors, in which the flow of liquid is possible in both directions, the direction depending only on the direction of the pressure difference on the injectors, the non-return injector allows only the flow of the liquid in one direction, regardless of the direction of the drop. pressure on the ends of the non-return injector, by combining in a single construction the classic axial or centrifugal injector with the one-way valve. Thus, a one-way micro-valve is made right on the surface from the combustion chamber, a

EN 129890 Β1 rocket engine cylinder, having simultaneously the role of liquid injector, valve that opposes the slightest tendency of reverse flow, from the chamber to the tanks, of the hot combustion gases, completely protecting the injection system against the destructive effects that would could be induced by hot gases.

In the normal case where the inlet pressure of the fluid in the nozzle injector is greater than the outlet pressure of the liquid in the combustion chamber, thus causing a positive pressure drop through the nozzle injector, the liquid is pushed through the converging hole in the body 1 of the valve non-return, pushes the ball valve 5, lifts it from the valve seat 6, moving it through the small cylindrical channel 4 to the valve seating limit on the opposite support 7, inside the support 2, seat that remains tightly sealed for as long as possible. the pressure drop is positive. The injected liquid can thus easily pass through the annular side channel 8 between the body 1 and the support 2 of the non-return valve, reaching the entrance to the multiple calibrated injection nozzles 9, and consuming, when passing through these nozzles, all the potential pressure energy, which thus converts into kinetic energy, greatly accelerating the liquid and spraying it into the wide hexagonal outlet 3.

Because the holes of the nozzles 9 are practiced inclined 45 ° to the axis of symmetry of the support, their axes are mutually perpendicular and produce the intersection of the individual jets of liquid coming out through each nozzle. This collision of the liquid jets is a known method of increasing the degree of spraying of the axial injectors and, in this case, is used in the non-return injector, to amplify the turbulence and the strong atomization of the liquid displaced by the anti-return injector, as opposed to the known cases. .

At the slightest tendency to reverse the pressure drop on the non-return injector, for example, when the gas flow produced by the solid propellant in the chamber increases temporarily, or the liquid supply pressure temporarily decreases, the valve 5 with very low mass, under a grams, it will be strongly driven by the gases in the room, which tend to flow backwards through the injector, due to the larger opening of the central hole 7 in the support 2 under the valve, than the openings of the side nozzles 9 (at least 5 times larger), and pushed with very high acceleration towards the seat 6. The opening 5 times smaller of the nozzles causes that, at the same pressure drop, Δρ · = pj - p _c , the eventual reverse flow of the fluid through the nozzles is always so much less than the flow driven through the central hole, at its maximum opening, because the flow D _ox is proportional to the flow area of the fluid through injectors Α _{) Σ} and with the flow coefficient of the injector of them c _D , both obviously constant:

^D O _X = ^C D ^A p yfcPjiPj - Pc) = ^C D ^A p yfcPj ^ Pj

Bypassing the valve by the gas is also prevented by the mass of liquid that is still present in the injector, and acts as an incompressible piston. The wider opening of the hole under the valve 7, for example, with a diameter of 4 mm, compared to the opening of the nozzles 9, further diminishes the tendency of the gases to bypass the valve on the lateral path 8, and will rapidly raise the valve on the seat 6. At an overpressure the inverse of 70 bar, the acceleration of the closing of the valve can reach 40,000 g, the closing time of the valve, that is the travel time of the 2 mm of return path on the seat being only 20 ps. In these conditions, at a distance of only 2 mm, the valve reaches a velocity of 21 m / s, equivalent to the speed of a free fall from the height of 20 m. The effect of the elastic collision at the return of the valve on seat 6 is felt as a pressure of 500 bar. on the seat, which will be taken into account when choosing the construction material for the valve seat. at the same time the hot gases do not penetrate into the side channel 8 of the injector by more than 5 mm, so that the valve closes before

RO 129890 Β1 reaching the gazelle above it. The efficiency of closing the non-return valve is thus far superior to that of the one-way valves which, besides the high mass and time constant, can only be located at a certain distance from the direct room-injector interface, leaving room for the interaction between the detonating liquid and the gases. hot. This shortcoming is removed by the present invention, which completely blocks the reverse flow.

In another embodiment, the seating force of the valve is further increased by the field created by the magnetic mass of the body of the non-return valve, made of stainless, hypermagnetic, coercive alloy, corresponding to the concrete application, for example, ALNICO or ALNIFE. The additional force provided by the magnetic path can reach the equivalent of a pressure difference of 4 bar in the injector itself, exceeded by the normal injection pressure of at least 10 bar, necessary to maintain the volatile liquid of type N ₂ O in the exclusively liquid phase, thus avoiding local cavitation.

The non-return injector, due to its unique ability to stop reverse fluid flows, is intended for engines and gas generators with solid-liquid compound propellant, particularly exposed to the risk of reverse flows, but also to hybrid engines in general, which are nowadays trendy worldwide. aerospace, being used on an industrial scale. The non-return injector therefore has a larger industrial use than the current hybrid rocket engines, for all applications where hybrid and compound rocket engines are suitable, civil or military.

Because hybrid engines have very low propulsion efficiency, they cannot serve as the main propulsion means in orbital launch systems, where extremely high flight speeds are required, but compound engines can successfully serve the construction of efficient orbital launchers. The non-return injector is an essential utility in such engines. Once the main risk of detonation has been eliminated by reverse flow, all other improvements to these engines become feasible.

The invention, by its construction and operation, presents the following unique advantages:

- creating an isolation interface at the immediate interface of the combustion chamber, on the cylinder wall from the room, by placing the one-way valve even in the injectors;

- the complete elimination of the possibility of penetration of the free volume of the injection system by the flue gases, by reverse flow, is the key to ensuring an equal reliability of the composite and hybrid engines, with the other rocket engines with chemical propellants, of the type found in current operation;

- positioning the one-way valve even in the injectors, in the unique construction described, reduces the mass of fluid operated in the opposite direction to the overpressures in the engine, which contributes to the reduction of the valve closing time constant;

- the very low mass of the mobile valve, below one gram, reduces again the valve closing time constant;

- The intersecting side joints reduce the spraying and vaporization time of the liquid. The liquid jets that travel through the injector intersect at an angle of 90 °, unlike the current constructions, where the simple axial jets of the different liquids are intersected, as in the usual two-component liquid rocket engines, with delayed atomization effect;

- spraying at the outlet of the injector nozzles, in the hexagonal cavity of its support, produces a cushioning effect of combustion pressure instability in the combustion chamber, and acoustic vibration damper, as a small combustion chamber, which reduces the impact on the environment, and increases the durability of the engine injection system, allowing its construction with less material and, therefore, easier, a decisive element in achieving superior flight characteristics of the missile aircraft in general.

Brief presentation of the drawings:

FIG. 1 shows a 3-D semi-section, in a first embodiment of the non-return injector, according to the invention;

RO 129890 Β1

FIG. 2 shows the support of the non-return injector, in the same embodiment, but in 1 position allowing the view of the injection nozzles 9 and the mounting hexagon 3;

FIG. 3 illustrates embodiment 2, wherein the body of the non-return valve is provided 3 with a hypermagnetic ring 16, with permanent magnetism;

FIG. 4 shows the diagram of the magnetostatic force. 5

Example 1

Example 1 of embodiment (in connection with FIGS. 1 ... 3) is shown in FIG. 1, in semi-7 axonometric section. The non-return injector, according to the invention, has the body 1 made of stainless steel or, possibly, of stainless magnetic material. It will be taken into account that in position 9 in the figure the combustion chamber of the motor on which the anti-return injector is located is on the left side of the drawing, called downstream, and the collector, which brings the liquid under pressure to the 11 anti-return valve, is on the right side of the drawing, called upstream. The bracket 2 is made of austenitic, paramagnetic stainless steel, for example, of the type AISI316L or equivalent, and 13 is fixed in the body of the non-return injector by screwing with a fine thread, the screw torque being applied with a hexagonal wrench inserted into the hexagon 3 of the support. The support supports the valve 5 on the downstream port 7 of the support, when the non-return injector is opened by the simple overpressure of liquid entered through the opposite opening 17, upstream. At the gradual reduction of the pressure 17 of access of the liquid through the hole 17 upstream, at the shutdown of the supply system, or in all the fortuitous cases, the eventual high back pressure of the gases in the combustion chamber constitutes the only factor acting on the valve 5 through the downstream port. 7, and countercurrently pushes the valve to the closing seat 6, a stage in which the support ensures the proper driving of the valve 21 through the cylindrical sliding channel 4, until near the seat 6, but leaving a small unpaved road near the seat 6, sufficient. to avoid asymmetrical positioning of the valve 23 on the seat, and to compromise the watertight closing. The correctly centered driving role of the valve from the downstream port 7 to the seat 6 is ensured by the 25 coaxial tolerances imposed on the support and the body on the small, cylindrical common centering surface 19, specifically provided for this purpose. closing the non-return valve in the presence of accidental or stopping backpressures 27 is firm even without the use of an elastic spring, which greatly simplifies the construction of the non-return valve, and increases its reliability. The entire 29 non-return valve assembly is fixed to the engine cylinder by means of a screw, using the outer thread 14 of the body, the torque being made with a screwdriver that enters the transverse groove 18, with 31 standardized dimensions, provided for mounting on the body head. The sealing of the non-return valve body on the mounting holes in the cylinder head is performed on the conical surface 15, below 33 the body head, with precisely controlled geometry.

Fig. 2 separately shows the support of the non-return injector, from the downstream perspective, in the same 35 example of achieving the geometry of the non-return injector, but in the position that allows to highlight the multiple injection nozzles 9, in the present example in number 3, practiced 37 evenly, in the middle of the flat surfaces of the hexagonal prism 3 of mounting. The diameter of the nozzles is dictated by the flow rate of the non-return valve, and the diameter of the outlet 7 of the discharge pressure 39 downstream is set four times larger than of the individual nozzle, so that its cross-sectional area is more than 5 times greater than the cumulative area of the the nozzles, ensuring a fast and safe closure of the valve 41 under the action of the back pressure in the downstream combustion chamber, before the penetration of the gas through the nozzles. 43

Example 2

Fig. 3 reproduces the example of embodiment 2, wherein the body of the non-return valve is provided 45 with a hypermagnetic ring 16 with permanent magnetism, made of suitable alloy ALNICO, ALNIFE or equivalent, fixed by friction in the head of the anti-return valve, where a circular groove has been previously provided 47 with rectangular section and suitable geometric tolerances. By installing

EN 129890 Β1 of this annular minimagnet, the body of the non-return valve becomes capable of securing the closure of the non-return valve by attracting the valve to the seat in the absence of upstream downstream gas pressure. The magnetic holding force on the seat, with a possible value of 6 N, is impressive, equivalent to a 4 bar gas pressure, but at the gradual opening of the non-return valve the force decreases quasi-hyperbolically, the force-displacement diagram being represented in fig. 4. The displacement of the valve is measured axially, starting with the value 0 from the fully closed position, being rendered in mm.

The magnetic action of the body on the valve plays a dual role. In the normal-closed position of the non-return valve, the magnetostatic force ensures that the non-return valve remains in the closed position, even in the presence of vibrations or inertial shocks of any kind, which may occur during the installation of the injection system on the test stand or on the launch system. In the open position, the magnetostatic force ensures the return of the non-return valve to the closed position, even in the absence of gas-dynamic backpressures, a useful effect for the normal shutdown of the injection system, during which the liquid supply pressure is gradually reduced to the ambient pressure value.

Claims (4)

claims 1. Non-return injector for unstable liquids, composed of a body (1) fitted with a spherical valve (5) and a valve seat (6), characterized in that the body (1) is tubular, has an external thread and inside, where it is screwed, with the coaxiality, a support (2) provided with an inner cylindrical surface (4), in which the ball (5) spherically slides without friction, between a limit position upstream, where the valve (5) spherical sits on the truncated seat (6) of the tubular body (1), provided with a suction port (17), which it seals, and a downstream limit position, when the spherical valve (5) is rested on the edge of an orifice (7) of mounting from the support (2), which it also closes tightly, and the support (2) is provided inside with a conical median surface, having an odd number of injection nozzles (9), equidistant, whose axes are inclined 45 ° to the axis of symmetry of the support ui (2), the axis of the nozzles being mutually perpendicular, the ratio between the diameter of the injection nozzle (9) and the diameter of the hole (7) being 1: 4. 2. Non-return injector, according to claim 1, characterized in that a transverse groove (18) is provided on the front of the head of the body (1), for the screwdriver, and the axial outlet port in the support (2) has a cavity (3). inner hexagon, for assembly, which is executed by screwing into the body (1) through the fine thread (20) conjugated. 3. Non-return injector, according to claims 1 and 2, characterized in that an annular groove is formed in the head of the body (1) in which an annular minimagnet (16), made of hypermagnetic alloy, is installed by fretting to attract the valve ( 5) spherical on the trunk seat (6) with a force equivalent to a 6 bar gas pressure. 4. Non-return injector, according to claims 1 and 2, characterized in that said body (1) is made of fully magnetized stainless steel material to attract the ball (5) spherically to the thrust seat (6) with a force equivalent to a pressure. 4 bar gas turbines.