WO2011001435A1

WO2011001435A1 - Hypergolic ignition system for gelled rocket propellant

Info

Publication number: WO2011001435A1
Application number: PCT/IL2010/000527
Authority: WO
Inventors: Benveniste Natan; Valeriano Perteghella; Yair Solomon
Original assignee: Technion Research And Development Foundation Ltd.
Priority date: 2009-07-01
Filing date: 2010-06-30
Publication date: 2011-01-06
Also published as: IL199643A0

Abstract

The present invention provides a composition and a system for hypergolic ignition of rocket propellant. The composition includes the suspension of catalytic or reactive particles in a gelled fuel. The catalytic or reactive particles initiate a reaction upon contact with an oxidizer.

Description

HYPERGOLIC IGNITION SYSTEM FOR GELLED ROCKET PROPELLANT

FIELD OF THE INVENTION

The present invention relates to the ignition of liquid rocket propellants. More specifically the invention relates to a hypergolic ignition system comprising at least one gelled fuel and at least one ignition agent suspended in said fuel.

BACKGROUND

Liquid rocket propellant systems produce thrust by the expulsion of high velocity exhaust gases produced by a self-sustaining reaction between a fuel and an oxidizer. Direct ignition of rocket propellant systems may be achieved using hypergolic fuels which ignite spontaneously upon contact with the oxidizer. However, hypergolic ignition systems often use a harmful component, fuel or oxidizer. The fuel, typically derived from hydrazine, such as monomethyl hydrazine, can be combined with oxidizers such as nitrogen tetroxide or inhibited red fuming nitric acid. These reactants are often harmful to humans, highly toxic, carcinogenic and extremely reactive. As such, hypergolic propellants pose significant environmental problems and are generally difficult to handle.

Alternatively, where non-hypergolic systems are used, the reaction may be initiated by using complex ignition systems, typically involving igniters and/or catalyst beds. Such complex ignition systems, however, are expensive and contain additional components, which increase the risk of failure. Furthermore, complex ignition systems introduce extra weight to the rocket thus reducing its energy efficiency.

Various proposed systems have been suggested for propellant ignition using catalytic agents which are dissolved in liquid fuels. US Patent No. 6,695,938 describes a system using reduced toxicity hypergolic bipropellants such as hydrogen peroxide and a reactive fuel which serves as a solvent for a catalyst or reactive material which is dissolved therein. Several catalytic agents, in particular sodium borohydride, which are soluble in various fuels including diglyme and triglyme are described.

US Patent No. 7,083,690 describes a method for preparing organic fuels.

According to the method, a mixture is prepared between an organic fuel and a catalyst in which the mixture is hypergolic with hydrogen peroxide. Novel catalysts capable of rendering both polar and non-polar organic fuels hypergolic with rocket-grade hydrogen peroxide are disclosed. These catalysts are complexes formed by reacting alkyl-substituted diamines or triamines, with metal salts of an aliphatic carboxylic acid or metal 1,3 dione chelates. In addition, the use of various acetylenic compounds as stability enhancing additives and/or promoters is described.

US Patent No. 5,932,837 describes an ignition system using a non-toxic hypergolic miscible fuel and a rocket grade hydrogen peroxide oxidizer. The nontoxic hypergolic miscible fuel contains three mutually soluble species: a) a polar organic species which is miscible with hydrogen peroxide, b) a propagator of substituted or unsubstituted amines, amides or diamines, and c) a catalyst of inorganic metal salt which reacts to form a catalyst in solution or as a colloid.

An issue common to liquid fuel systems which contain catalysts or reactive materials, is that fuel selection is based, at least partially, upon its miscibility characteristics. Other important factors, such as the fuel energy content and environmental footprint, may be compromised in favor of improved miscibility. In addition, solvent fuels which are capable of dissolving catalytic agents have relatively low heat of combustion. Thus, hypergolic ignition systems often show relatively low energetic performance, are environmentally hazardous and are difficult to handle.

In an effort to improve the safety of handling and storing of liquid propellants, various systems utilizing gel propellants have been suggested. The rheological characteristics of the gels as well as their tendency to harden when brought in contact with a gaseous environment render their use advantageous for reducing toxicity hazards. Hence, in cases of failure in the feeding system or during storage, the leakage rate of the fuel is reduced in comparison to liquids. Rahimi et al. (Journal of Propulsion and Power, Vol. 20, No. 1, 2004, pp. 93-100) examined the rheological characteristics of gelled inhibited red-fuming nitric acid (IRFNA) and monomethyl hydrazine (MMH) and conducted firing tests. C* efficiencies of 90% and significant improvements in storage and handling were reported.

GB 885410 discloses that liquid fuels for rocket motors, such as hydrazine, ethylene diamine and/or a fuel mixture of diethylene triamine (80%) and methylamine (20%), are gelled to a semi-solid or gel state by adding carboxyl vinyl polymer. Liquid oxidizers for the fuels, such as bromine pentafluoride, may be gelled by adding a fluorocarbon polymer while an oxidizer such as hydrogen peroxide may be gelled with a carboxyl vinyl polymer.

US Patent Application No. 2008/0202655 discloses a group of tertiary amine azides useful as hypergolic fuels for hypergolic bipropellant mixtures.

US Patent No. 2008/0127551 discloses a hypergolic fuel mixture in a propulsion system comprising: a first component including a hypergolic amine azide compound; and a second component including a hypergolic tertiary amine compound; whereby said first and second components form a liquid or gel fuel mixture in the propulsion system.

US Patent No. 6,013,143 discloses a hypergolic liquid or gel fuel propulsion system comprising: (i) a tertiary amine azide selected from the group of tertiary amine azides consisting of dimethylaminoethylazide, and pyrollidinylethylazide; and (ii) an oxidizer selected from the group of oxidizers consisting of inhibited red fuming nitric acid, nitrogen tetroxide, hydrogen peroxide, hydroxyl ammonium nitrate, and liquid oxygen.

US Patent No. 6,652,682 discloses a gelled bipropellant composition, comprising a liquid fuel; an oxidizing agent; and boron particles having a diameter of less than about 100 nanometers wherein the boron particles act as a gelling agent when mixed with the liquid fuel.

The combustion of gelled fuels was investigated for both organic and inorganic gellants. Nachmoni and Natan (Combustion Science and Technology, Vol.

156, 2000, pp. 139-157), and Arnold and Anderson (AIAA paper 2010-421, 2010) studied the ignition and combustion characteristics of inorganic gellant, nonmetallized, kerosene-based, gel fuels. In addition, calorimetric tests were conducted to evaluate the heat of vaporization of gels. In general, it has been demonstrated that gels obey the d -law of diffusion-controlled combustion and that the amount of the gelling agent correlates with the time of burning. In addition, an increase in the gellant content resulted in an increase in the ignition delay time and further resulted in an ignition which required a larger heat input. An ignition time formula of hypergolic gelled propellants is found in Williams (Journal of Propulsion and Power, Vol. 25, No. 6, 2009, pp. 1354-1356).

Solomon, Natan and Cohen (Combustion and Flame, Vol. 156, No. 1, 2009, pp. 261-268) studied the combustion of organic-gellant-based gel fuel droplets. It has been found that during the combustion, after the vaporization of part of the fuel, an elastic layer of gellant is formed around the droplet that prevents further fuel vaporization from the outer surface of the droplet. This causes the fuel to evaporate below the droplet surface producing bubbles, which results in droplet swelling, fuel jetting and finally collapse of the remaining droplet. The process was found to repeat itself in a periodic manner until complete consumption of the fuel and gellant.

In recent years, there has been a rise in the number of space vehicles launched yearly. This increase has led to a need to reduce the costs and the environmental hazards associated with propellant systems. The propellant toxicity, storability and handling costs of hydrazine based fuels as well as the extra weight, high costs and increased risk of failure associated with complex ignition systems has led to intensive research in finding alternatives to current rocket propellant systems.

The need remains for a cost effective, reliable and safe ignition system for rocket propellants which does not compromise the energetic performance of the propellant system. Furthermore, there is an unmet need for a hypergolic rocket propellant system which is easy to handle and which remains stable during long term storage.

SUMMARY OF THE INVENTION

The present invention provides a composition comprising a gelled fuel in which catalyst or reactive particles are suspended. The particles can ignite hypergolically (upon contact) with an oxidizer. The fuel and the oxidizer can be chosen from a wide spectrum of materials that are environmentally friendly (green propellants) without the need of carrying a complex ignition system. These propellants can provide the necessary energy for propulsion of any air/space vehicle.

The present invention is based in part on the unexpected finding that catalyst or reactive particles can be uniformly suspended in a gelled fuel without the occurrence of sedimentation or coagulation. The catalyst or reactive particles can react spontaneously with an oxidizer or can serve as catalysts to promote the ignition reaction. The rheological properties of the gelled fuel, e.g. the yield stress and the high viscosity while at rest, assure that no particle sedimentation takes place even at high acceleration levels of the vehicle. The uniform suspension of reactive solid particles in a gelled fuel obviates the need for the use of highly reactive fuels which pose significant safety hazards and further obviates the need for complicated and heavy ignition systems without compromising the energetic performance of the system. Upon contact with the particles, the oxidizer reacts spontaneously or decomposes exothermally, producing high temperature gases. This results in fuel vaporization and decomposition and consequent reaction of fuel vapors with the oxidizer.

According to a first aspect the present invention provides a hypergolic composition for rocket propellant, comprising: (a) at least one fuel in the form of a gel, and (b) at least one particulate ignition agent suspended in the fuel.

In one embodiment, the ignition agent reacts upon contact with an oxidizer to produce an energetic reaction.

According to another aspect, the present invention provides a hypergolic propulsion system comprising: (a) at least one fuel in the form of a gel, (b) at least one particulate ignition agent suspended in the fuel, and (c) at least one oxidizer.

In some embodiments, the ignition agent is selected from the group consisting of hydrazine, a hydrazine derivative, and a metal hydride. Each possibility represents a separate embodiment of the invention. In particular embodiments, the metal hydride is selected from the group consisting of sodium borohydride, lithium borohydride, and potassium borohydride. Each possibility represents a separate embodiment of the invention. Alternatively or additionally, the ignition agent comprises a hypergolic catalyst. According to various embodiments, the ignition agent comprises a complex of an alkyl-substituted amine and a metal salt. In some embodiments, the alkyl- substituted amine is selected from the group consisting of an alkyl-substituted diamine and an alkyl-substituted triamine and the metal salt is the metal salt of an aliphatic carboxylic acid. In particular embodiments, the aliphatic carboxylic acid is selected from the group consisting of an acetate, a propionate and a butyrate. Each possibility represents a separate embodiment of the invention.

According to certain embodiments, the fuel is selected from the group consisting of hydrocarbons, alcohols, amines, amides, metal-organic liquid compounds, alkaloids, and liquid hydrogen. Each possibility represents a separate embodiment of the invention. In an exemplary embodiment the hydrocarbon-based fuel is kerosene.

In various embodiments, the liquid fuel is gelled using a gelling agent. In accordance with these embodiments, the hypergolic composition of the present invention comprises: (a) at least one fuel in the form of a gel; (b) a gelling agent, and

(c) at least one particulate ignition agent suspended in said fuel. In particular embodiments, the gelling agent is selected from the group consisting of nano-silica fumed powder, aluminum stearate and gelling polymers. Each possibility represents a separate embodiment of the invention. Without being bound by any theory or mechanism of action it is contemplated that the gelled fuel has viscosity and yield stress large enough to prevent sedimentation and/or coagulation of the ignition agents under high acceleration.

According to another aspect, the present invention provides a hypergolic propulsion system comprising: (a) at least one fuel in the form of a gel, (b) at least one particulate ignition agent suspended in the fuel, (c) a gelling agent; and (d) at least one oxidizer.

In some embodiments, the oxidizer is selected from the group consisting of hydrogen peroxide, liquid oxygen, nitrous oxide, nitrous acid, nitric acid, perchloric acid, cerium compounds, chlorites, bromites, fluorites, chlorates, bromates, fluorates and hyperchlorites. Each possibility represents a separate embodiment of the invention.

According to additional embodiments, the present invention provides a method of preparing a hypergolic composition for rocket propellant, comprising the steps of: (a) obtaining a liquid fuel, (b) adding a gelling agent, and (c) suspending a particulate ignition agent in the fuel such that upon contact with an oxidizer the ignition agent initiates a reaction between the fuel and the oxidizer.

Further embodiments and the full scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the invention and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings.

With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented with the purpose of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention; the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings: Fig. 1 is a schematic representation of a hypergolic propulsion system (100). 120 represents gelled fuel; 160 represents particulate ignition agent; and 140 represents an oxidizer.

Fig. 2 is a flowchart representing a method of preparing hypergolic ignition composition.

Fig. 3 is a schematic representation of the experimental system.

Fig. 4 is a picture of a test cell.

Fig. 5 is a picture of a test cell interior.

Fig. 6 is a sequence of high-speed photographs demonstrating hypergolic ignition of hydrogen peroxide with a kerosene gel containing NaBH₄ suspended particles. The time interval between sequent pictures is 2 μs.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a hypergolic ignition system comprising fuel in the form of a gel and a particulate ignition agent suspended therein. The system of the present invention is designed to provide hypergolic ignition of the gelled fuel upon contact of the ignition agent with an oxidizer. Methods of preparing said system are disclosed as well.

Gellation of liquid fuel and suspension of reactive or catalyst particles in the fuel enables hypergolic ignition of almost any fuel-oxidizer combination. No specific restrictions due to miscibility characterizes of the fuel are present. Hence, fuels having high energetic performance are suitable within the scope of the present invention. The present invention thus provides the use of environmentally safe hypergolic bipropellants (e.g. hydrogen peroxide and kerosene).

Reference is now made to Fig. 1 which shows a schematic representation of a hypergolic ignition system for rocket propellant according to an exemplary embodiment of the invention. The ignition system 100 includes a gelled fuel 120, an oxidizer 140 and an ignition agent 160 which is held in suspension in the gelled fuel 120. The ignition agent 160 and the oxidizer 140 may be selected such that they react hypergolically thus triggering a self-sustained reaction between the fuel 120 and the oxidizer 140. Ignition agents within the scope of the present invention include, but are not limited to, hydrazines and derivatives thereof, and metal hydrides. Each possibility represents a separate embodiment of the invention. Suitable metal hydrides include, but are not limited to, sodium borohydride, lithium borohydride, and potassium borohydride. Each possibility represents a separate embodiment of the invention. Other ignition agents such as hydrazine and hydrazine derivatives can also be used. The term "hydrazine derivative" as used herein refers to any substituted hydrazine including, but not limited to, monomethylhydrazine, 1,1- dimethylhydrazine, 1,2- dimethylhydrazine, phenyl hydrazine and the like. Each possibility represents a separate embodiement of the invention.

Alternatively, the ignition agent 160 may catalytically initiate a reaction between the fuel 120 and the oxidizer 140. Hypergolic catalysts within the scope of the present invention include, but are not limited to, complexes of alkyl-substituted amine and metal salts. Suitable complexes include, but are not limited to, alkyl- substituted diamines or alkyl-substituted triamines mixed with metal salts of aliphatic carboxylic acids. Suitable salts include, but are not limited to, manganese acetate, manganese propionate, manganese butyrate, cobalt acetate, cobalt propionate, cobalt butyrate, copper acetate, copper propionate, copper butyrate, silver acetate, silver propionate, silver butyrate and combinations thereof. Each possibility represents a separate embodiment of the invention.

The ignition agent, according to the principles of the present invention, is in particulate form. Within the scope of the present invention are particles having a diameter in the nanometer and/or micrometer range. Exemplary diameters include, but are not limited to, about 50 run, about lOOnm, about 200 nm, about 400 nm, about 800 nm, about lμm, about 2μm, about 5μm, about lOμm, about 50μm, about lOOμm and about 200μm. Particle sizes can be determined by a skilled artisan according to various parameters including, e.g. the ignition agent and the oxidizer which are used.

The ignition agent which is suspended in the gelled fuel is provided in an amount sufficient to induce a hypergolic reaction between the fuel 120 and the oxidizer 140 as is known in the art. Exemplary amounts include e.g. about 1%, about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35% or about 40% by weight of the composition. According to a particular embodiment, the amount of the ignition agent is about 10% by weight of the composition.

In some non-limiting embodiments of the invention, sodium borohydride is used as the ignition agent 160 and hydrogen peroxide is used as the oxidizer 140. Sodium borohydride is a substance known to be hypergolic with hydrogen peroxide generating sufficient heat to initiate reaction between the oxidizer and the fuel 120.

It is noted that hypergolic ignition is initiated by the action of the oxidizer 140 and the ignition agent 160. Because the fuel 120 used with embodiments of the invention is not selected for its hypergolic characteristics, safe or "green" propellants may be used. Suitable fuels within the scope of the present invention include, but are not limited to, hydrocarbons (e.g. various fractions of petroleum), alcohols (e.g. ethanol, isopropanol), amines (e.g. ethylene diamine, diethylene triamine, methylamine, cyclotetramethylenetetranitramine), amides (e.g. dicyanamide), metal- organic liquid compounds, alkaloids (e.g. imidazolium), and liquid hydrogen. Each possibility represents a separate embodiment of the invention. In particular, any kind of liquid hydrocarbon is suitable according to the principles of the present invention. Accoring to one exemplary embodiment, the fuel is kerosene. The term "kerosene" as used herein refers to the lighter fraction of crude petroleum that boils approximately in the range of 145° C to 300° C and is composed mainly of Cg-C₁₆ hydrocarbons. Included by this term are aviation turbine fuels for civilian (Jet A or Jet A-I) and military (JP-8 or JP-5) aircrafts, and military turbine fuel grades such as JP-5, JP-8 and RP/ 1. Each possibility represents a separate embodiemt of the invention.

According to the principles of the present invention, the fuel is in the form of a gel. In one embodiment, the gelled fuel can be obtained without the use of a gelling agent, however, it is contemplated that the fuel is gelled using a gelling agent. Thus, in some embodiments, the composition and system of the present invention further comprise a gelling agent. The gelling agent may be selected to suit the fuel 120; for example, nano-silica fumed powder is known to be suitable for inducing gellation of kerosene fuel. Other suitable gelling agents including, but not limited to, aluminum stearate, gelling polymers and the like may be used to induce gelation according to the principles of the present invention. The fuel may initially be in gelatin-like state or may be gelled using the selected gelling agent with the ignition agent 160 held in suspension.

The amount of gelling agent used for inducing gellation of the fuel can be determined by a person skilled in the art. According to certain embodiments, only a very small amount of gelling agent is required to induce gellation of the fuel 120. A small amount, according to the principles of the present invention, refers to an amount of about 1%, about 2.5%, about 5%, about 7.5%, about 10%, about 15%, about 20%, about 25% or about 30% (w/w). Without being bound by any theory or mechanism of action, the small amount of the gelling agent causes no significant loss in the total energy output of the gelled propellant 120. Additional embodiments include the use of a gelling agent which does not cause any loss of energy.

Gelatinization of the fuel 120 is directed to producing a gelatinous medium suitable for supporting suspended particles of the ignition agent 160. Typically, a gelatinous mixture comprising the propellant and particulate ignition agents suspended therein is formed, hi exemplary embodiments, the gelatinous mixture is supported by a continuous skeleton formed by the gelling agent (e.g. nano-silica fumed powder).

It will be appreciated that the operational conditions for rocket propellant often involve extremely high acceleration forces. The mechanical properties of the gelatinous mixture are preferably such that no sedimentation or coagulation occurs even under such conditions.

Accordingly, the amount of gelling agent is tailored in order to achieve gel viscosity which is sufficient to prevent or substantially reduce the occurrence of sedimentation/coagulation. According to the principles of the present invention, the viscosity of the composition of the present invention is at least about 0.01 Pascal- seconds (Pa s), alternatively at least about 0.1 Pa s, about 1 Pa s, about 5 Pa s, about 10 Pa-s, about 50 Pa s, about 100 Pa-s, about 500 Pa-s, about 1000 Pa s, about 5,000 Pa-s, or further alternatively at least about 10,000 Pa-s. Viscosity can be measured using e.g. a rotating spindle viscometer.

It is therefore contemplated that the gelatinous composition of the present invention has viscosity which is large enough to prevent or substantially reduce the occurrence of sedimentation and/or coagulation of the ignition agent under high acceleration. It is further contemplated that the gelatinous composition of the present invention has yield stress which is large enough to prevent or substantially reduce the occurrence of sedimentation and/or coagulation of the ignition agent under high acceleration.

The oxidizer 140, according to the principles of the present invention, is selected to produce a self-sustained reaction with the fuel 120. Suitable oxidizers include, but are not limited to, chlorites, bromites, fluorites, chlorates, bromates, fluorates, hyperchlorites, peroxides, nitrates and liquid oxygen. Each possibility represents a separate embodiment of the invention. Exemplary oxidizers include, but are not limited to, hydrogen peroxide, liquid oxygen, nitrous oxide, nitrous acid, nitric acid, hydroxyl ammonium nitrate, ammonium nitrate, ammonium dinitramide, perchloric acid, hydroxyl ammonium perchlorate, ammonium perchlorate, cerium compounds, and combinations thereof. Each possibility represents a separate embodiment of the invention. According to a particular embodiment, hydrogen peroxide is used as the oxidizing agent. Hydrogen peroxide is a high density liquid oxidizer that decomposes exothermically into steam and oxygen. It is environmentally safe, relatively easy to handle, and can be used with a variety of fuels and ignition agents.

Reference is now made to Fig. 2 which shows a flowchart representing a method for preparing a composition for hypergolic ignition of rocket propulsion according to an exemplary embodiment of the present invention.

The present invention further provides a method of preparing a hypergolic composition for rocket propellant. The method includes the following principle steps: step (a) obtaining a liquid fuel, step (b) adding a gelling agent, and step (c) suspending a particulate ignition agent in the fuel. Upon contact with an oxidizer, the ignition agent initiates a reaction between the fuel and the oxidizer.

In some embodiments, the ignition agent is selected so as to provide a hyperbolic reaction with the oxidizer. Alternatively, the ignition agent is a catalyst which induces the reaction between the fuel and the oxidizer.

The following examples are presented in order to more fully illustrate certain embodiments of the invention. They should in no way, however, be construed as limiting the broad scope of the invention. One skilled in the art can readily devise many variations and modifications of the principles disclosed herein without departing from the scope of the invention.

EXAMPLES:

EXAMPLE 1: Manufacturing of hvpergolic fuel by gelation and suspension of reactive or catalyst particles

Chemicals

• Kerosene based fuel (e.g. JP-8, JP-5 etc) having a density of 810 kg/m³; a flash point of 52 ⁰C; boiling point in the range of 165-265 °C; and auto-ignition temperature of 220 ⁰C.

• Nano-Silica fumed powder, 0.014 μm (SIGMA).

• Sodium Borohydride (NaBH₄) p.a., >96 % (SIGMA) having a density of 1074 kg/m³; a flash point of 70 ⁰C; boiling point of 500 °C; and auto-ignition temperature of 220 °C.

• Hydrogen Peroxide (H₂O₂) p.a., 92 %; melting point of -43°C; boiling point of 150°C; and density of 1460 kg/m³.

The fuel (kerosene) was gelled using nano-silica fumed powder and the sodium borohydride particles (10% wt) were suspended in the fuel in a mixing process.

EXAMPLE 2: Combustion system

In order to test the reaction characteristics of hvpergolic substances, a test apparatus was designed to enable reliable measurements on a drop-like quantity of fuel. A hermetically sealed cell, in which temperature and pressure were controlled, was used to conduct the ignition tests. The test cell can be pressurized up to 20 atm using nitrogen as an inert ambient gas. Ambient temperature was controlled by an electrical resistance inside the cell and it was measured using a thermocouple located at the upper part of the cell. The gel fuel composition of Example 1 was placed on a glass plate and a hydrogen peroxide droplet was dropped from a syringe on the gel fuel composition. Two thick circular optical glass windows have been fitted into two holes in the cell walls along the same axis in order to enable view through the cell and focus the high speed camera on the fuel and oxidizer droplet impingement point. The experimental system is presented in Figs. 3, 4 and 5.

The ignition delay, defined as the time interval between the moment the oxidizer drop and the fuel drop come into contact and the moment the fuel ignites, was measured by a high-speed camera which was set to a frame rate of 500 fps (i.e., the time interval between sequent pictures was 2μs). Figure 6 depicts high-speed photographs of a hypergolicity test of 92% hydrogen peroxide with a kerosene gel containing NaBH₄ suspended particles. The ignition delay mesured was less than 8μs.

The scope of the present invention is defined by the appended claims and includes both combinations and sub-combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description.

In the claims, the word "comprise", and variations thereof such as

"comprises", "comprising" and the like indicate that the components listed are included, but not generally to the exclusion of other components.

While certain embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to the embodiments described herein. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the present invention as described by the claims, which follow.

Claims

1. A hypergolic composition for rocket propellant, comprising:

(a) at least one fuel in the form of a gel, and

(b) at least one particulate ignition agent suspended in said fuel.

2. The hypergolic composition of claim 1, wherein said ignition agent reacts upon contact with an oxidizer to produce an energetic reaction.

3. The hypergolic composition of claim 2, wherein said oxidizer is selected from the group consisting of hydrogen peroxide, liquid oxygen, nitrous oxide, nitrous acid, nitric acid, perchloric acid, cerium compounds, chlorites, bromites, fluorites, chlorates, bromates, fluorates and hyperchlorites.

4. The hypergolic composition of claim 1, wherein said fuel is selected from the group consisting of hydrocarbons, alcohols, amines, amides, metal-organic liquid compounds, alkaloids, and liquid hydrogen.

5. The hypergolic composition of claim 4, wherein said fuel is kerosene.

6. The hypergolic composition of claim 1, further comprising a gelling agent.

7. The hypergolic composition of claim 6, wherein the gelling agent is selected from the group consisting of nano-silica fumed powder, aluminum stearate and gelling polymers.

8. The hypergolic composition of claim 1, wherein said ignition agent is selected from the group consisting of hydrazine, a hydrazine derivative, and a metal hydride.

9. The hypergolic composition of claim 8, wherein the metal hydride is selected from the group consisting of sodium borohydride, lithium borohydride, and potassium borohydride.

10. The hypergolic composition of claim 1, wherein said ignition agent comprises a hypergolic catalyst.

11. The hypergolic composition of claim 10, wherein said catalyst comprises a complex of an alkyl-substituted amine and a metal salt.

12. The hypergolic composition of claim 11, wherein said alkyl-substituted amine is selected from the group consisting of an alkyl-substituted diamine and an alkyl- substituted triamine.

13. The hypergolic composition of claim 11, wherein said metal salt is a metal salt of an aliphatic carboxylic acid.

14. A hypergolic propulsion system comprising:

(a) at least one fuel in the form of a gel,

(b) at least one particulate ignition agent suspended in the fuel, and

(c) at least one oxidizer.

15. The hypergolic propulsion system of claim 14, wherein said ignition agent reacts upon contact with the oxidizer to produce an energetic reaction.

16. The hypergolic propulsion system of claim 15, wherein said oxidizer is selected from the group consisting of hydrogen peroxide, liquid oxygen, nitrous oxide, nitrous acid, nitric acid, perchloric acid, cerium compounds, chlorites, bromites, fluorites, chlorates, bromates, fluorates and hyperchlorites.

17. The hypergolic propulsion system of claim 14, wherein said fuel is selected from the group consisting of hydrocarbons, alcohols, amines, amides, metal-organic liquid compounds, alkaloids, and liquid hydrogen.

18. The hypergolic propulsion system of claim 17, wherein said fuel is kerosene.

19. The hypergolic propulsion system of claim 14, further comprising a gelling agent.

20. The hypergolic propulsion system of claim 19, wherein the gelling agent is selected from the group consisting of nano-silica fumed powder, aluminum stearate and gelling polymers.

21. The hypergolic propulsion system of claim 14, wherein said ignition agent is selected from the group consisting of hydrazine, a hydrazine derivative, and a metal hydride.

22. The hypergolic propulsion system of claim 21, wherein the metal hydride is selected from the group consisting of sodium borohydride, lithium borohydride, and potassium borohydride.

23. The hypergolic propulsion system of claim 14, wherein said ignition agent comprises a hypergolic catalyst.

24. The hypergolic propulsion system of claim 23, wherein said catalyst comprises a complex of an alkyl-substituted amine and a metal salt.

25. The hypergolic propulsion system of claim 24, wherein said alkyl-substituted amine is selected from the group consisting of an alkyl-substituted diamine and an alkyl-substituted triamine.

26. The hypergolic propulsion system of claim 24, wherein said metal salt is a metal salt of an aliphatic carboxylic acid.

27. A method of preparing a hypergolic composition for rocket propellant comprising the following steps:

(a) obtaining a liquid fuel,

(b) adding a gelling agent, and

(c) suspending a particulate ignition agent in the fuel,

such that upon contact with an oxidizer said ignition agent initiates a reaction between said fuel and said oxidizer.

28. The method of claim 27, wherein said oxidizer is selected from the group consisting of hydrogen peroxide, liquid oxygen, nitrous oxide, nitrous acid, nitric acid, perchloric acid, cerium compounds, chlorites, bromites, fluorites, chlorates, bromates, fluorates and hyperchlorites.

29. The method of claim 27, wherein said fuel is selected from the group consisting of hydrocarbons, alcohols, amines, amides, metal-organic liquid compounds, alkaloids, and liquid hydrogen.

30. The method of claim 29, wherein said fuel is kerosene.

31. The method of claim 27, wherein the gelling agent is selected from the group consisting of nano-silica fumed powder, aluminum stearate and gelling polymers.

32. The method of claim 27, wherein said ignition agent is selected from the group consisting of hydrazine, a hydrazine derivative, and a metal hydride.

33. The method of claim 32, wherein the metal hydride is selected from the group consisting of sodium borohydride, lithium borohydride, and potassium borohydride.

34. The method of claim 27, wherein said ignition agent comprises a hypergolic catalyst.

35. The method of claim 34, wherein said catalyst comprises a complex of an alkyl- substituted amine and a metal salt.

36. The method of claim 35, wherein said alkyl-substituted amine is selected from the group consisting of an alkyl-substituted diamine and an alkyl-substituted triamine.

37. The method of claim 35, wherein said metal salt is a metal salt of an aliphatic carboxylic acid.