Patent Application
20140190599
The present invention relates generally to fuels and, more particularly, to hypergolic bipropellants.
Monomethyl hydrazine (MMH) with dinitrogen tetroxide (NTO) comprise a storable, bipropellant that is conventionally used for spacecraft because of its hypergolic properties. Hypergolicity, as used herein, refers to a fuel that is self-igniting after contact between the fuel (here, the MMH) and the oxidizer (here, the NTO). Hypergolic ignition is valuable because it offers high reliability, eliminates inert mass of a separate ignition system, and provides an ability to restart for missions having multi-pulse operation.
However, there are drawbacks to the use of MMH/NTO and other similar hypergolic fuels (such as those based on alcohols and alkyl- or azido-functional amines). For example, both of MMH and NTO have a high vapor toxicity, which creates a ground safety hazard. Additionally, the MMH/NTO fuel has a limited inherent energy density, which is related to the density of the fuel. Also, there are significant costs and operational constraints associated with handling MMH/NTO due, at least in part, to the very toxic vapor. Accordingly, there has been a desire to find bipropellants that are less toxic having similar, if not improved, performance characteristics as compared to NTO/MMH.
Some hypergolic bipropellant alternatives to hydrazines have been examined but fallen short due to two significant drawbacks: (1) the alternatives contain volatile, toxic components; (2) the alternatives do not impart improvements in volumetric impulse as comparison to MMH/NTO, or both. One difficulty in finding a suitable alternative has been that fuels having high vapor toxicity with significant vapor pressure present a severe technical challenge.
One approach has been the use of energetic, ionic compounds to replace vapor-toxic, nonionic fuels. Such ionic compounds generally have beneficial characteristics over neutral molecules, including, for example, higher density, greater thermal stability, and negligible vapor pressure. Of course, use of ionic compounds is not without difficulty. Specifically, ionic compounds typically have a melting point that is ordinarily high, or at least certainly well above the melting point of hydrazine compounds, such as MMH.
Accordingly, there is need for hypergolic bipropellants that overcome the above prior art shortcomings.
The present invention overcomes the foregoing problems and other shortcomings, drawbacks, and challenges of conventional hypergolic bipropellants. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. To the contrary, this invention includes all alternatives, modifications, and equivalents as may be included within the spirit and scope of the present invention.
According to one embodiment of the present invention, a hypergolic bipropellant includes an ionic liquid fuel and nitric acid, which is operable as an oxidizer. The ionic liquid fuel comprises an open chain amine having at least one quarternized nitrogen and a dicyanamide anion.
Yet another embodiment of the present invention includes a hypergolic bipropellant system having first and second components. The first component includes an ionic liquid fuel having an open chain amine having at least one quarternized nitrogen and a dicyanamide anion. The second component includes nitric acid operable as an oxidizer. The hypergolic bipropellant system, upon mixing the first component with the second component, is configured to cause an ignition.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be leaned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the sequence of operations as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration.
The present invention provides a storable, bipropellant fuel having lower vapor pressure and vapor toxicity as compared to conventional bipropellant fuels. According to one embodiment of the present invention, a bipropellant fuel comprises an ionic liquid, an oxidizer, and a volatile fuel. In particular, and according to embodiments of the present invention, the ionic liquid includes a hydrazinium nitrate, the oxidizer is nitric-acid based. For example, the hydrazinium nitrate may be 2-hydroxyalkyl hydrazinium, [HORN2H4]+[NO3]−, wherein R is a linear or cyclic alkyl, alkene, or alkyne hydrocarbons having 1-28 carbon atoms. According to one preferred embodiment, the hydrazinium nitrate is 2-hydroxyethyl hydrazinium nitrate, [HOCH2CH2N2H4]+[NO3]−, (“HEHN”). The volatile fuel may include, for example, a non-toxic homogenous miscible fuel (“NHMF”), including methanol, dimethylazidoehtylamine (hereafter, “CINCH”), furfuryl alcohol (2-furanmethanol), and JP-10.
According to another embodiment of the present invention, the bipropellant fuel may further include a catalyst, including, for example, ammonium vanadate.
The ionic liquid, for example, HEHN, may be synthesized, according to one embodiment of the present invention and as shown in flowchart 20 of
The oxidizer may be any nitric acid-based oxidizer, including, but not limited to, nitric acid, white fuming nitric acid (“WFNA”), red fuming nitric acid (“RFNA”), inhibited red fuming nitric acid (“IRFNA”), and combinations thereof. RFNA may be prepared, according to one embodiment of the present invention, from white fuming nitric acid containing 13% dinitrogen tetroxide and 2% ammonium vanadate.
The ionic liquid and the oxidizer may be stored separately and safely, which reduces costs associated with handling and moving the bipropellant. In use, and when ignition is desired, a first portion of oxidizer is mixed with a second portion of ionic liquid. A ratio of the first and second portions may vary; however, for optimum performance, the ratio may depend on the selected ionic liquid and can be determined by those of ordinary skill in the art. Furthermore, a first injection rate of the oxidizer and a second injection rate of the ionic liquid may vary (ab initio, after ignition, or both) and depends, largely, on a desired thrust.
According to another embodiment of the present invention, a bipropellant fuel comprises an ionic liquid and an oxidizer, wherein the ionic liquid includes an open chain ammonium-based dicyanamide. More particularly, the ionic liquid comprises a dicyanamide anion [N(CN)2]− and an ammonium-based cation. Exemplary ammonium-based cations may include, for example, ammonium, hydrazinium, guanidinium, and formadinium, having the respective formulae:
and wherein each of R1, R2, R3, R4, and R5, where present, is separately selected from the group consisting of H, NH2, alkenyl, alkylnyl, a strained-ring (e.g., a cycloalkyl), and high-nitrogen moieties (e.g., azidoalkyl, cyanoalkyl, aminoalkyl, or hydrazinoalkyl). Substituents may be selected to confer a low melting point, a low viscosity, or both. Additionally, substituents may be selected to increase heat of combustion.
Cations of the ionic liquid and having a quarternized nitrogen atom, that is, an aprotic ionic liquid, facilitate fast ignition. For similar reasons, hydroxyl-functionality of the cation side chain may be avoided.
As was noted above, the oxidizer may be a nitric acid, including, for example, nitric acid, WFNA, RFNA, IRFNA, and combinations thereof.
As was noted above, the ionic liquid and the oxidizer may be stored separately and safely, which reduces costs associated with handling and moving the bipropellant. In use, and when ignition is desired, a first portion of oxidizer is mixed with a second portion of ionic liquid. A ratio of the first and second portions may vary; however, for optimum performance, the ratio may depend on the selected ionic liquid and can be determined by those of ordinary skill in the art. Furthermore, a first injection rate of the oxidizer and a second injection rate of the ionic liquid may vary (ab initio, after ignition, or both) and depends, largely, on a desired thrust.
The following examples illustrate particular properties and advantages of some of the embodiments of the present invention. Furthermore, these are examples of reduction to practice of the present invention and confirmation that the principles described in the present invention are therefore valid but should not be construed as in any way limiting the scope of the invention.
HEHN was synthesized according to the method of
The theoretical performance (specific impulse and volumetric impulse) for HEHN with an oxidizer (dinitrogen tetroxide, RFNA, and 98% hydrogen peroxide) was computed and compared against theoretical performances of MMH, NHMF (a volatile fuel), CINCH (dimethylazidoethylamine), and JP-10 (a synthetic hydrocarbon fuel) with the same oxidizers.
Ignition delays of HEHN with an oxidizer and conventional fuel/oxidizer combinations were evaluated using Pino testing, as described in M. A. PINO, “A versatile ignition delay tester for self-igniting rocket propellants,” Jet Propulsion. (2005) 463-466.
The reactivity of substituted ammonium dicyanamides with WFNA was evaluated by drop test, monitored with a high speed video camera, and the results are shown, below, in Table 2.
Table 3, below, summarizes ignition test results for two protic ionic liquids and an aprotic ionic liquid having a hydroxyethyl sidechain in the cation with WFNA. Ignition responses are compared to two related aprotic ionic liquids.
Trimethyl-azidoethyl ammonium iodide (17.40 g; 67.99 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield trimethyl-azidoethyl ammonium dicyanamide, as shown in Equation 2, wherein X is iodide, each of three R group is methyl, and one R group is —CH2N3.
The yield was 86%; melting point was 16° C.; onset of decomposition occurred at 180° C.; and the viscosity was determined to be 81 cp.
Trimethyl-allyl ammonium bromide (2.66 g; 11.72 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield trimethyl-allyl ammonium dicyanamide, as shown in Equation 2, wherein X is bromide, each of three R groups is methyl, and one R group is —CH2CH═CH2.
The yield was 87%; melting point was 28° C.; onset of decomposition occurred at 210° C.; and the viscosity was determined to be 26 cp.
Dimethyl-diallyl ammonium bromide (3.19 g; 15.47 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield dimethyl-diallyl ammonium dicyanamide, as shown in Equation 2, wherein X is bromide, each of two R groups is methyl, and each of two R groups is —CH2CH═CH2.
The yield was 71%; melting point was −90° C. (glass); onset of decomposition occurred at 160° C.; and the viscosity was determined to be 37 cp.
Dimethyl-allyl-propargyl ammonium bromide (5.57 g; 27.31 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield dimethyl-allyl-propargyl ammonium dicyanamide, as shown in Equation 2, wherein X is bromide, each of two R groups is methyl, one R group is —CH2CH═CH2, and one R group is —CH2C≡CH.
The yield was 73%; melting point was 22° C.; onset of decomposition occurred at 127° C.; and the viscosity was determined to be 111 cp.
Allylammonium chloride (8.79 g; 94.11 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield allylammonium dicyanamide, as shown in Equation 2, wherein X is chloride.
The yield was 92%; melting point was 11° C.; onset of decomposition occurred at 75° C.; and the viscosity was determined to be 95 cp.
Diallylammonium chloride (3.26 g; 24.47 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield diallylammonium dicyanamide, as shown in Equation 2, wherein X is chloride.
The yield was 81%; melting point was 37° C.; onset of decomposition occurred at 65° C.; and the viscosity was determined to be 185 cp.
Dimethyl-azidoethyl ammonium bromide (3.49 g; 23.32 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield dimethyl-azidoethylammonium dicyanamide, as shown in Equation 2.
The yield was 84%; melting point was 16° C.; onset of decomposition occurred at 82° C.; and the viscosity was determined to be 74 cp.
1,1,1-trimethyl hydrazinium iodide (1.1062 g; 5.48 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield 1,1,1-trimethyl hydrazinium dicyanamide, as shown in Equation 3, wherein X is iodide and each of three R groups is methyl.
The yield was 70%; melting point was 64° C.; and the onset of decomposition occurred at 217° C.
Aminoguanidinium chloride (2.69 g; 24.34 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield aminoguanidinium dicyanamide, as shown in Equation 4, wherein X is chloride.
The yield was 92%; melting point was 55° C.; and the onset of decomposition occurred at 120° C.
Formadinium chloride (1.959 g; 24.32 mmol) was added to a 100 mL Schlenk flask equipped with a TEFLON stir bar, purged with dry nitrogen, and dissolved in ca. 30 mL of methanol. In the dark, a ca. 5% excess of freshly prepared silver dicyanamide was added to the stirred solution. Stirring continued overnight. Insoluble silver halide and excess silver dicyanamide were removed by filtration. The solvent was removed under reduced pressure to yield formadinium dicyanamide, as shown in Equation 5, wherein X is chloride.
The yield was 88%; melting point was −74° C. (glass); onset of decomposition occurred at 69° C.; and the viscosity was determined to be 60 cp.
Hypergolic bipropellants, as provided herein, are particularly useful for volume limited types of propulsion systems. The hypergolic bipropellants have a volumetric impulse that is superior to conventional bipropellants with a reduced vapor toxicity hazard. The latter of which significantly improves safety of handling, particularly with loading and unloading of propellant, which in turn lowers costs of use and storage. Use of open-chain cations, according to embodiments of the present invention and as compared to heterocycle-based cations, may provide further cost savings.
Hypergolic bipropellants, as provided herein, have potential as a replacement for bipropellant used in on-orbit spacecraft propulsion, liquid engines for boost and divert propulsion, and other high performance/limited volume systems. For example, hydrazinium dicyanamide ionic liquids, as describe herein, have a density of about 1.483 g/cm3 at 173 K while the density of hydrazine is 1.0059 g/cm3 at 296.24 K. As a result, hydrazinium dicyamaide may confer a greater energy density to a bipropulsion system.
While the present invention has been illustrated by a description of one or more embodiments thereof and while these embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.
This application is a Continuation-In-Part of U.S. application Ser. No. 10/816,032, entitled HYPERGOLIC BIPROPELLANTS, and filed on Apr. 2, 2004 and U.S. application Ser. No. 12/567,110, entitled BIPROPELLANTS BASED ON SELECTED SALTS, and filed on Sep. 25, 2009. This application is also related to U.S. application Ser. No. 14/047,529, entitled HYPERGOLIC BIPROPELLANTS, Air Force Docket Number AFB-671CIP1, filed on even date herewith; and U.S. application Ser. No. 12/567,136, entitled BIPROPELLANTS BASED ON CHOSEN SALTS, filed on Sep. 25, 2009. The disclosure of each of these applications is incorporated herein by reference, in its entirety.
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10816032 | Apr 2004 | US |
| Child | 14047529 | US | |
| Parent | 12567110 | Sep 2009 | US |
| Child | 10816032 | US |
