Not Applicable.
The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to the inventors and/or the assignee of any royalties thereon.
1. Field of the Invention
The present invention relates to fuel mixtures utilized in hypergolic propulsion systems. More specifically, the invention relates to hypergolic fuel mixtures of tertiary amines and amine azides, or amines and imidic amides.
2. Description of the Related Art
A liquid or gel bipropellant rocket propulsion system consists of gas generators, oxidizer and fuel propellant tanks, plumbing, oxidizer and fuel valves, and an engine. The bipropellant rocket propulsion unit begins operation when the gas generators have been initiated and the gases from the gas generator pressurize oxidizer and fuel propellant tanks. When the oxidizer and fuel valves open, the pressurized oxidizer and fuel tanks then force the propellants through the plumbing into the engine where the propellants are mixed and ignited. The propellants can be ignited by either ignition aids or by hypergolic (spontaneously self-igniting) chemical reaction. Since ignition aids can take up valuable space in the propulsion system, a hypergolic chemical reaction is the preferred ignition method. Inhibited red fuming nitric acid (hereinafter, IRFNA) and monomethyl hydrazine (hereinafter, MMH) have been the preferred hypergolic rocket oxidizer and fuel for rocket propulsion systems for some time, by providing a high specific impulse and density specific impulse, and providing a short ignition delay of approximately 3 milliseconds or less to approximately 15 milliseconds (depending on test techniques), before ignition after combining of an oxidizer and MMH. A short ignition delay characteristic is important since a long ignition delay of approximately 25 millisecond or longer causes fuel and oxidizer to accumulate in the combustion chamber, so that when ignition does take place an overpressurization can occur with creation of a “hard start.” Overpressurization in the combustion chamber can be severe enough to destroy the rocket motor and negate achievement of the mission objective.
A main drawback of MMH is the high toxicity of the compound. Classified as a suspected human carcinogen, MMH requires exceptional safety precautions during handling which makes fueling of rocket motors both time consuming and expensive. A non-carcinogenic alternative to MMH which can be readily utilized in hypergolic bipropellant propulsion systems is preferred.
U.S. Pat. No. 6,013,143, issued to D. M. Thompson and assigned to the Secretary of the Army, discloses liquid or gel bipropellant fuel compounds which are alternatives to use of potentially carcinogenic compound MMH in rocket propulsion systems similar to a system illustrated in U.S. Pat. No. 5,133,183. The hypergolic fuel compounds disclosed in the '143 patent include three tertiary amine azide compounds consisting of 2-N,N-dimethylamino-ethylazide (identified as DMAZ), bis(ethyl azide) methylamine (identified as BAZ), and pyrrolidinylethylazide (also identified as 2-(N-pyrrolidinyl)ethylazide, or PYAZ). The '143 patent disclosed that use of MMH as a fuel mixture with IRFNA would deliver a specific impulse of 284 lbf sec/Ibm and a density impulse of 13.36 lbf sec/cubic inch. Under similar operating conditions, DMAZ delivered a specific impulse of 287 lbf sec/Ibm and a density impulse of 13.77 lbf sec/cubic inch. To achieve performance comparable to MMH used in a rocket propulsion system, the '143 patent disclosed each one of the tertiary amine azides (DMAZ, BAZ or PYAZ) were combined with an oxidizer selected from the group of oxidizers consisting of IRFNA, nitrogen tetroxide, hydrogen peroxide, hydroxylammonium nitrate, and liquid oxygen. The '143 patent did not disclose alternative oxidizer compounds which may provide similar or improved performance when combined with DMAZ, BAZ or PYAZ. A limitation of the compounds disclosed in the '143 patent included, for each of the three hydrocarbon moieties attached to the tertiary amine, that at least one but no more than two moieties contained an azide group. A further limitation of the '143 patent includes the tertiary amine azide molecule can have no more than seven carbon atoms for the compound to remain hypergolic, allowing the tertiary amine azides to produce adequate specific impulse or density specific impulse results when mixed with IRFNA.
U.S. Pat. No. 6,210,504, issued to D. M. Thompson and assigned to the Secretary of the Army, discloses a gas generator fuel source for a liquid or gel gas generator system, including the three tertiary amine azide compounds disclosed in the '143 patent, specifically DMAZ, BAZ, and PYAZ. The '504 patent discloses that any one of the three tertiary amine azide compounds is contained and heated in an iridium catalytic reactor bed to achieve a self sustaining decomposition reaction to yield gaseous products for pressurization of the liquid or gel gas generator system. The '504 patent does not disclose alternative tertiary amine azide compounds which may provide similar or improved performance when used instead of, or in combination with DMAZ, BAZ or PYAZ. Limitations of the structure and radicals attached to the tertiary amine azide compounds are relevant to the '504 patent as also disclosed in the '143 patent. The '504 patent discloses solid additives and gellant additives consistent with the additives disclosed in the '143 patent, including use of a gallant such as silicon dioxide, clay, carbon, and polymeric gallant.
It is desirable to provide a plurality of hypergolic fuel mixtures exhibiting minimal toxicity, classified as a non-carcinogen, and having a short ignition delay when mixed in a propulsion system. It is also desirable to provide a plurality of fuel mixtures having a short ignition delay and a density specific impulse competitive with MMH fuel. It is further desirable to provide a plurality of hypergolic fuel mixtures containing a tertiary diamine, tertiary tri-amine or a tetra-amine compound, any of which is mixed with an amine azide compound, a monocyclic amidine compound, or a multi-cyclic amidine compound, for use in propulsion systems as replacements for MMH fuel.
A fuel mixture is disclosed for use as hypergolic liquid or gel fuel in bipropellant propulsion systems, with the chemical compounds preferably having similar ignition characteristics as MMH, and preferably the compounds not being toxic or classified as a suspected human carcinogen. One compound disclosed includes N,N,N′,N′-tetramethylethylenediamine (hereinafter, TMEDA), a tertiary diamine, mixed with any one of a family of hypergolic amine azides, with one compound being DMAZ. Laboratory test data for TMEDA provides an ignition delay of approximately 14 milliseconds, and laboratory test data for DMAZ provides an ignition delay of approximately 26 milliseconds. Combination of TMEDA and DMAZ in a hypergolic liquid or gel fuel provides an unexpected reduction for ignition delay values to a range of about 9 milliseconds to about 10 milliseconds depending on the percentage of DMAZ mixed with TMEDA.
An alternative compound includes a mixture of a hypergolic tertiary diamine such as TMEDA, and an amine azide such as tris(2-azidoethyl) amine (TAEA). Laboratory test data for unmixed TMEDA provides an ignition delay of about 14 milliseconds, and laboratory test data for unmixed TAEA provides an ignition delay of about 43 milliseconds. Combination of TMEDA and TAEA in a hypergolic liquid or gel fuel provides an unexpected reduction for ignition delay times to a range of about 8 milliseconds to about 9 milliseconds depending on percentage of TAEA mixed with TMEDA.
Additional combinations of chemical compounds to form a hypergolic fuel mixture include numerous cyclic amidine (also identified as imidic amide) compounds, such as 1,5-diazabicyclo(4.3.0)non-5-ene (hereinafter, DBN), mixed with a hypergolic tertiary diamine such as TMEDA, or a 1,8-Diazabicyclo(5.4.1) undec-7-ene (hereinafter, DBU), mixed with a hypergolic tertiary diamine such as TMEDA. A monocyclic analog of bi-cyclic DBN but having the non-nitrogen containing cyclic structure opened along with isomers thereof, are additional compounds utilized to form a hypergolic fuel mixture when mixed with a hypergolic tertiary diamine such as TMEDA. Compounds containing one or more tertiary tri-amine structures, such as N,N,N′,N″,N″-pentamethyldiethylenetriamine (hereinafter, PMDETA), and compounds containing tetra-amine, such as hexamethyl-triethylene-tetra-amine (HMETA), or larger amine structures, when mixed with amine azide or imidic amide compounds, are also capable of providing favorable short ignition delay values to serve as hypergolic fuel mixtures with minimal toxicity and lacking suspicion as a human carcinogen.
The present invention is disclosed to include mixtures of chemicals referenced herein, with performance test results illustrated in graphs of ignition delay in milliseconds (msec) vs. % ratios of chemicals, including:
Referring now to
Previously disclosed alternative fuel compounds proposed for replacement of MMH in fuel, specifically DMAZ, BAZ and PYAZ mixed with IRFNA, have been investigated and found by laboratory drop testing of individual compounds to each provide significant longer ignition delays than that of MMH, as illustrated by data generated as a result of laboratory testing and provided in Table 1. Testing to determine ignition delay values of compounds was achieved using a laboratory drop test known to those skilled in the art involved in testing, such as drop testing utilized by the U.S. Army Research, Development and Engineering Command at the Redstone Arsenal, Ala., and government contractors including ERC, Incorporated, in Huntsville, Ala. The following ignition delay results for individual compounds are tested separately as mixtures with oxidant IRFNA, to allow comparisons with the ignition delay data for fuel mixtures in various combinations as disclosed herein (see
Fuel combinations of the present invention consist of one or more of a family of hypergolic amine azides or hypergolic imidic amide compounds (also referenced as a first component), mixed with one or more hypergolic tertiary diamine compound(s) (also referenced as a second component), and/or one or more tertiary tri- or tetra-amine compound(s) (an alternate second component). The hypergolic amine azides have the general structure (R1)(R2)(R3)N, in which R1, R2, and R3 is selected from the element of hydrogen, and an aliphatic, alkene, alkyne, or cycloalkyl group, any of which may or may not contain heteroatoms or heterocyclic atoms, but where at least one of the R groups selected contains an azide. The amine azides thus need not be tertiary amines and may have three azide-containing groups attached to the amine. The disclosed description of the amine azide differs from, and is broader than, that prior art relating to liquid or gel fuels, in which the disclosures of azides are limited to tertiary amine azides in which a maximum of two attached groups contain an azide. Examples of hypergolic amine azides defined by this invention include but are not limited to 2-(N,N-dimethylamino) ethylazide (DMAZ), 2-(N-cyclo-propylamino)ethylazide, bis(2-azidoethyl)methylamine, bis(2-azidoethyl)ethylamine (BAZ), tris(2-azidoethyl)amine (TAEA), 2-(N-pyrrolidinyl)ethylazide (PYAZ), N-(2-azidoethyl)morpholine, and 1,2-bis(N-(2-azidoethyl)-N-methylamino)ethane.
The tertiary diamines have the general formula R4R5N—R6—NR7R8, where R4, R5, R7, and R8 are aliphatic groups and R6 may be an aliphatic, alkene, or alkyne group. The hypergolic diamines include but are not limited to, N,N,N′,N′-tetramethyl-ethylene-diamine (TMEDA), N,N,N′,N′-tetramethyl-1,3-diaminopropane (TMPDA), N,N,N′,N′-tetramethyl-1,4-diaminobutane (TMBDA), N,N,N′,N′-tetramethyl-1,4-diaminobut-2-ene (cis or trans isomers or mixtures of cis/trans isomers), and N,N,N′,N′-tetramethyl-1,4-diaminobut-2-yne.
The relative proportion of the hypergolic amine azide compound in the fuel may vary from about 1% to about 99%, and the proportion of the hypergolic tertiary diamine, tria-mine or tetra-amine compounds in the fuel may vary from about 1% to about 99% (dependent on amount of amine azide compound mixed wherewith). For optimal motor specific impulse and density specific impulse it is generally desirable to incorporate into the fuel the maximize percentage of amine azide compound which will still allow an acceptably low ignition delay of about 3 milliseconds to about 15 milliseconds. The tertiary diamine component of the fuel will optimally have a relatively short ignition delay when mixed with the oxidizer and have a relatively high content of tertiary amine groups in the molecule. An example of one embodiment is a fuel containing about 33.3% DMAZ and about 66.7% TMEDA (see
An unexpected characteristic of the new fuel combinations is illustrated by the test data for shortened ignition delay times of mixtures of an amine azide and a tertiary amine as compared to test data for ignition delay times for either of the unmixed individual components. This synergistic effect of shortened ignition delay times is illustrated in
A process for producing an improved hypergolic fuel mixture having shortened ignition delay times includes selecting an optimal proportion of DMAZ, a cyclic amine azide or an imidic amide compound, combined with a proportion of TMEDA or a tri- or tetra-amine, and further includes adding an oxidizer to the fuel mixture to initiate a reaction which is sufficiently exothermic to cause spontaneous ignition of the fuel in a propulsion system. The ignition delay is caused by several factors including production of sufficient heat by the initial oxidizer when mixed with the first component and second component to cause ignition of the fuel mixture. An ideal situation for fast ignition (i.e. shortened ignition delay) is one in which the fuel gives off a large amount of heat upon initial reaction with the oxidizer and also has a relatively low ignition temperature. In the two component mixture described herein, the amine azide (component one) releases a relatively low amount of heat upon initial reaction with an oxidizer because of its relatively low amine content and the relatively low basicity of the amine, therefore the amine azide has a relatively low ignition temperature. In contrast, the tertiary amine (component two) releases a greater amount of heat upon initial reaction with an oxidizer because of its relatively high amine content and its relatively high basicity, although the tertiary amine has a relatively high ignition temperature. A step of selecting appropriate first and second components, followed by adding the selected first and second components with an oxidizer in a propulsion system, allows the process to take advantage of the favorable characteristics of the first and second components, namely low ignition temperature of the amine azide, and high initial heat production of the tertiary amine.
Examples of test results for proportions of TAEA compound as a first component of a hypergolic fuel mixture, when mixed with TMEDA compound as a second component are illustrated in
Examples of test results for proportions of a DBN cyclic compound used as a first component of a hypergolic fuel mixture, when mixed with TMEDA compound as a second component are illustrated in
Any of the above described hypergolic amine azide compounds or imidic amide compounds as first components can be mixed with an alternative second component of N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), to provide favorably short ignition delay times. One embodiment of the fuel mixture is illustrated in
A source for inducing reaction of the first compound and the second compound is stored with the fuel propulsion system and is readily injected in the mixture of the first and second compound at a time when ignition of the first and second compound is required for proper operation of the propulsion system. The source for inducing reaction is an oxidizer selected from the group consisting of liquid oxygen, hydrogen peroxide, nitric acid, nitrogen dioxide and inhibited red fuming nitric acid (IRFNA).
Additives to a fluid mixture of first and second components are available for forming a gel mixture. The additive gellant is provided in the mixture in a proportion of between about 0.5% to about 10% additive selected from silicon dioxide, clay, carbon, and polymeric gel. The gelled fuel mixture can also include solid additives which improve the specific impulse and density specific impulse. The solid additives are known to those skilled in the art of rocket fuels and include, but are not limited to, carbon, aluminum, silicon, boron, tungsten, triamino-trinitrobenzene or tetramethyl-ammoniumazide. The gelled fuel mixtures can include between about 1% to about 80% solid additives, between about 98.5% to about 10% amine azide and tertiary amine fuel mixtures in varying ratios (see
While numerous embodiments of mixtures of chemical compounds and processes for combining the chemical compounds for this invention are illustrated and disclosed herein, it will be recognized that various additional embodiments utilizing the primary chemicals of the invention may be employed without departing from the spirit and scope of the invention as set forth in the appended claims. Further, the disclosed invention is intended to cover all stereoisomer chemical compositions and alternate processes falling within the spirit and scope of the invention as set forth in the appended claims.