HOT-GAS-GENERATING APPARATUS WITH IONIC MONOPROPELLANT AND LOW VOLTAGE IGNITION

Abstract

A hot-gas-generating apparatus for reacting a propellant comprises a combustion chamber, at least one injector that is arranged upstream of the combustion chamber and can be closed, on the combustion chamber side, to the propellant, electrodes being integrated in said injector, and at least one supply line for the propellant. In this context, the propellant is a monopropellant and a substantially water-free ionic solution having low vapor pressure, preferably with a residual water content of less than five percent by mass, which is capable of self-sustaining combustion at a given combustion chamber pressure, and the electrodes have at least two electrodes of opposite polarity which are suitable for electrically igniting the propellant by means of a flow of current through the propellant when this propellant flows between the opposite-polarity electrodes.

Claims

1. A hot-gas-generating apparatus for reacting a propellant comprising a combustion chamber (2); at least one injector arranged in front of the combustion chamber (2), the injector being able to block the propellant supply towards the combustion chamber (2), and the injector incorporating electrodes (5, 6); at least one supply line (1) for the propellant, whereby the propellant is a monergolic propellant and a substantially anhydrous ionic solution of very low vapor pressure, with a residual water content of less than five percent by mass, and the capability of self-sustained combustion at a given combustion chamber pressure; the electrodes (5, 6) comprise at least two electrodes of opposite polarity capable of electrically igniting the propellant by an electric current passing through the propellant when the propellant passes between the electrodes of opposite polarity; and for blocking the propellant supply towards the combustion chamber (2), an automatically sealing injector head (5) is situated between the combustion chamber (2) and the injector, said injector head (5) allowing the propellant to pass only if the inlet pressure of the injector is greater than the crack-pressure and represents an overpressure relative to the combustion chamber pressure, and thus a sealing effect is achieved if the combustion chamber pressure exceeds the inlet pressure of the injector minus the crack pressure.

2. The hot-gas-generating apparatus according to claim 1, wherein the at least one injector head (5) incorporates at least one of the electrodes; and with the injector closed, the electrodes (5, 6) of opposite polarity are in electrical contact and in sealing contact.

3. The hot-gas-generating apparatus according to claim 2, wherein the propellant is present as an ionic solution as it passes between the electrodes of different polarity; the electrical ignition of the flowing ionic solution takes place in the region of an outlet of the injector; and a decomposition temperature of the propellant is locally exceeded.

4. The hot-gas-generating apparatus according to claim 3, further comprising an actuator for opening and closing the injector, wherein the injector is able to block the propellant supply towards the combustion chamber (2).

5. The hot-gas-generating apparatus according to claim 4, further comprising heat pipes for passive cooling of the propellant, wherein the heat pipes are arranged upstream of the combustion chamber (2).

6. The hot-gas-generating apparatus according to claim 5, wherein the electrodes (5, 6) have a catalytically active surface.

7. The hot-gas-generating apparatus of claim 6, wherein the catalytically active surface is coated with at least one noble metal.

8. The hot-gas-generating apparatus of claim 7, wherein the at least one noble metal comprises at least one metal selected from the list consisting of: copper, silver, platinum, palladium, iridium, rhodium, osmium, ruthenium and rhenium.

9. The hot-gas-generating apparatus according to claim 6, wherein an electric potential between the electrodes of 3 to 1000 volts is applied to ignite the propellant.

10. The hot-gas generating apparatus of claim 9 wherein the electric potential between the electrodes is between 10 to 120 volts.

11. The hot-gas-generating apparatus according to claim 9, further comprising an electrically operated pump for delivering the propellant from a propellant tank to the injector.

12. The hot-gas generating apparatus of claim 11 wherein the propellant tank comprises a textile construction.

13. A monergolic propellant with at least one soluble catalyst and very low vapor pressure, comprising a substantially anhydrous ionic solution, with a residual water content of less than five percent by mass, which is capable of self-sustaining combustion at a given pressure, characterized in that the anhydrous ionic solution is based on at least one (substituted) ammonium cation.

14. The monergolic propellant of claim 13 wherein the at least one substituted ammonium cation is selected from a list consisting of: (mono-, di-, tri-, tetra-)methylammonium-, (mono-, di-, tri-)ethylammonium-, n-propylammonium-, allylammonium-, propargylammonium-, ethylenediammonium-, propylenediammonium-, hydrazinium-, guanidinium-, aminoguanidinium-, and 5-aminotetrazolate cations.

15. The monergolic propellant of claim 13, wherein the at least one soluble catalyst comprises a salt of a transition metal.

16. The monergolic propellant of claim 13, wherein the at least one soluble catalyst comprises a complex of at least one transition metal.

17. The monergolic propellant according to claim 13, wherein the substantially anhydrous ionic solution comprises a non-volatile, non-ionic additive with a boiling point of more than 150° C. at 1 bar in concentrations of up to a maximum of 15 mass percent, which serves to lower the melting point.

18. The monergolic propellant of claim 17 wherein the additive is selected from a compound class selected from a list consisting of: ureas, guanidines, formamides, imidazoles, triazoles or tetrazoles.

19. Monergolic propellant according to claim 17, wherein the anhydrous ionic solution further comprises suspended powdered fuels with average particle sizes of less than 100 .Math.m.

20. The monergolic propellant of claim 19, wherein the powdered fuel comprises at least one material selected from the list consisting of: aluminum, aluminum alloys, magnesium, magnesium alloys, boron and zinc.

21. The monergolic propellant of claim 13, wherein the anhydrous ionic solution comprises at least one anion selected from a list consisting of: nitrate, perchlorate, dinitramide and nitroformate anions.

22. A method for igniting the monergolic propellant of claim 13, using the hot-gas-generating apparatus of claim 1, the method comprising: passing a mass flow of the monergolic propellant between said at least two electrodes of opposite polarity; and decomposing the propellant of said mass flow in the electric field of said electrodes of opposite polarity during the ignition.

23. The method according to claim 22, wherein up to 50% of a maximum propellant mass flow of said hot-gas-generating apparatus is passed between said electrodes of opposite polarity.

24. The method of claim 23, further comprising heating the monergolic propellant to at least 20° C. before ignition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Two possible embodiments of the hot-gas-generating apparatus according to the invention are presented below, although the given claims also explicitly provide for the realization of other embodiments. The first embodiment is based on a single conical injector and is shown in FIGS. 1 - 5. The second embodiment combines two opposing injectors of polygonal geometry and is shown in FIGS. 6 - 9. The individual figures thereby show:

[0024] FIG. 1: a perspective view of the hot-gas-generating apparatus with single injector and expansion nozzle with a schematic representation of the power supply.

[0025] FIG. 2: a top view of the hot-gas-generating apparatus with single injector and expansion nozzle, and illustration of plane A-A of the sectional drawing.

[0026] FIG. 3: Sectional drawing representing plane A-A of FIG. 2.

[0027] FIG. 4: a detailed view of the injector unit from the sectional drawing shown in FIG. 3 with the injector closed.

[0028] FIG. 5: a detailed view of the injector unit from the sectional drawing shown in FIG. 3 with the injector open, where the arrows indicate the direction of the propellant flow.

[0029] FIG. 6: a perspective view of the hot-gas-generating apparatus with double injector and expansion nozzle.

[0030] FIG. 7: a top view of the hot-gas-generating apparatus with double injector and expansion nozzle, and illustration of plane A-A of the sectional drawing.

[0031] FIG. 8: a sectional drawing representing plane A-A of FIG. 7 and a schematic representation of the power supply.

[0032] FIG. 9: a detailed view of the injector unit from the sectional drawing shown in FIG. 8 with one closed and one open injector. In this example, the converse opening state only serves to illustrate possible injector states and does not describe any real mode of operation. The arrows indicate the flow direction of the propellant in the open injector.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0033] In both embodiments of the invention, a substantially anhydrous ionic monopropellant is provided axially through a central propellant supply line 1. The propellant supply line 1 is in communication with the injector housing 4, from which the described monopropellant is injected into the combustion chamber 2. In the embodiment examples, the injector housing 4 and the combustion chamber 2 are connected by a flange which accommodates a temperature-resistant combustion chamber seal 11, made of e.g. flexible graphite. At low loads, the combustion chamber 2 can be made of a nickel-base alloy. At higher loads, the use of ceramic composites, ablative materials such as carbon fiber reinforced phenolic composites, or noble metal alloys such as Ir-Re is advisable. In both embodiments, the gases produced during combustion exit the combustion chamber 2 at supersonic velocity through a de Laval nozzle. The resulting thrust can be used to accelerate aircraft and spacecraft. Apart from being used for thrust generation, the combustion gases can also be used without necessity of a de Laval nozzle in order to drive turbomachinery and piston machines or for ignition purposes.

[0034] Thus, the hot-gas-generating apparatus of FIG. 1 can be used as a hot gas source for a reaction engine, as an igniter of a reaction engine, as an igniter for turbomachinery or as an igniter of a piston machine, or to provide the working gas for turbomachinery or for a piston machine.

[0035] In both embodiments, combustion chamber 2 and injector housing 4 are in electrical contact with each other and one pole of a power supply 14. The opposite pole is in electrical continuity with the electrical contact 3, which has a continuing electrical connection to the injector socket 12 (only shown in the embodiment featuring the single injector), the injector screw 9 and the injector electrode 5. Sources of constant polarity current, such as batteries, fuel cells and photovoltaic systems, can be used as power source 14. Likewise, the supply of alternating voltage from e.g. rotating or linear alternators is also possible. The power supply can be disconnected from the electrodes by an electrical switch 15.

[0036] In the closed state, the injector electrodes 5 are in contact with and sealed against the corresponding counter electrode 6 and thus prevent the backflow of hot gas from the combustion chamber 2 upstream in the direction of the propellant supply 1. In the open state (FIG. 5 and FIG. 9), the presence of propellant in the electrode gap between the counter electrodes 6 and injector electrodes 5 results in the formation of an electrochemical cell.

[0037] When current is applied, the propellant in the electrode gap can be heated and ignited. Injector electrodes 5 and counter electrodes 6 can form an electrode gap with an annular (cf. FIGS. 1 - 5), rectangular (cf. FIGS. 6 - 9) or polygonal cross section. In addition to single injectors (in FIGS. 1 - 5 so-called pintle-type injector) and double injectors (in FIGS. 6 - 9 so-called sheet impingement), other types of impingement injectors or a plurality of injector elements can also be combined in a combustion chamber 2. The selection of materials for injector electrode 5 and counter electrode 6 depends on the respective monopropellant and noble metals such as copper, silver, platinum, palladium, iridium, rhodium, osmium, ruthenium, rhenium, or a combination thereof can be used as a compact base material or coating to improve corrosion resistance and catalytic activity towards the propellant.

[0038] In the open state, the injector electrodes 5 are electrically separated from the injector housing 4 upstream of the electrode gap by insulators 7. The insulators 7 can be made of an electrically non-conductive material of moderate temperature resistance, including for example, high-performance polymer classes such as perfluorinated hydrocarbons (PTFE, PCTFE), polyamide-imides (PAI), or polyaryletherketones (PEEK). Polymeric materials might be fiber-reinforced. Another conceivable option are thermally conductive insulators 7 with increased temperature resistance, which can be made of ceramic materials or polymer-coated metallic materials. Reducing the level of thermal requirements concerning the insulators can only be achieved by cooling the injector housing 4. Regarding low load and short duration applications, the injector housing 4 may rely on heat sink cooling and therefore comprise materials of high thermal conductivity such as copper, silver, aluminum, or a combination thereof as illustrated in the embodiments shown herein. In case of high loads, additional radial heat pipes can be integrated into the injector housing 4. Starting from the injector housing 4, the heat can be dissipated either to the surrounding air, a coolant circuit or emitted by radiative transfer to the environment. Owing to the good thermal stability of the propellant, the coolant circuit might also be thermally connected to the propellant reservoir.

[0039] As shown in the embodiments for example, the closure of injector electrodes 5 and counter electrodes 6 in the event of insufficient propellant overpressure relative to the combustion chamber 2 is supported by compression springs 8. The stroke of the compression springs 8 can be limited by the injector screw 9 and the injector socket 12 or directly by the injector electrode 5 and an injector nut 13, which is secured against rotation. As an alternative or complementary to the compression springs 8, actuators can be installed, which allow for controlled opening and / or closing of the injectors. In this case, automatic closure in the event of insufficient propellant overpressure can also be ensured by a fast control circuit relying on sensors in the propellant supply and combustion chamber.

[0040] The injector housing 4 and all parts in contact with the propellant are sealed against the environment by injector seals 10. O-rings made from thermally stable elastomers (e.g. FKM, FFKM) can be used in low load scenarios, otherwise metallic C-rings might be used at high loads.

[0041] Certain embodiments of the propellant include, for example, ionic monopropellants of the following compositions:

[0042] Formulation 1: [0043] 80 % n-propylammonium nitrate [0044] 18% propargylammonium nitrate [0045] 1 % anhydrous copper(II) chloride [0046] 1 % graphite powder (< 5 .Math.m)

[0047] Formulation 2: [0048] 65 % ethylammonium nitrate [0049] 24 % lithium perchlorate [0050] 6 % imidazole [0051] 3 % zinc powder (< 10 .Math.m) [0052] 2 % copper(II) perchlorate

TABLE-US-00001 1 propellant supply line 2 combustion chamber 3 electrical contact 4 injector housing 5 injector electrode 6 counter electrode 7 insulator 8 compression spring 9 injector screw 10 injector seal 11 combustion chamber seal 12 injector socket 13 injector nut (end stop for compression spring) 14 power supply 15 electrical switch