US3213610A - Subzero temperature fuel and rocket ignition process - Google Patents

Description

United States Patent 3,213,610 SUBZERO TEMPERATURE FUEL AND ROCKET IGNITION PRUCESS John C. Grigger, Oreland, and Henry C. Miller, Hatfield, Pa., assignors to Pennsalt Chemicals Corporation, Philadelphia, lPa., a corporation of Pennsylvania No Drawing. Filed Apr. 27, 1962, Ser. No. 190,7918 12 Claims. (Cl. 6035.4)

This invention relates to methods and means useful in rocket propulsion and jet or thrust engines, particularly at subzero temperatures. In one of its specific aspects, it relates to a hypergolic igniter system. In another of its specific aspects, it relates to methods for using said system in the ignition of oxidizer-fuel systems in rocket motors and jet engines.

Hypergolic, or self-igniting, oxidizer-fuel systems are well-known as means for producing gaseous products useful as a source of thrust in rocket motors. A hypergolic oxidizer-fuel system chemically consists of an oxidizing component and a reducing component. The essence of the mode of operation of a hypergolic system is that the individual chemical components, which alone are not selfigniting in the atmosphere of a combustion chamber, will ignite spontaneously when brought into intimate contact with each other. The use of such a system, in addition to its economic advantages, generally avoids dangers and difficulties resulting from ignition system failures which can occur with a system which depends on a non-chemical ignition means.

Practically all hypergolic mixtures have delayed ignition periods of substantially less than one second and preferably not more than 50 milliseconds at ordinary ambient temperatures at ground level. At lower temperatures, this ignition delay period becomes longer. At subzero temperatures, i.e., below zero degrees on the centigrade temperature scale, the delay can become dangerously prolonged and disastrous through build-up of unignited combustible materials in a combustion chamber. Also, in some cases, complete failure of ignition can result with materials which become non-hypergolic in the presence of each other due to the low temperature.

The temperatures commonly encountered in high altitude operation of aircraft powered by jet or piston engines is in the range of 40 to 57 C. In outer space, it is expected that temperatures of about -100 C. are common. At these extremely low subzero temperatures, the problems of ignition, or re-ignition after a flame-out, of the components even of a system which is hypergolic at normal ambient temperatures at ground level become formidable.

We have now found a hypergolic igniter system which functions usefully for starting a fire by auto-ignition at a temperature at least as low as that of the freezing point of chlorine trifluoride, i.e., at about -83 C., and lower, e.g., at about -145 C., in a mixture of halogen fluoride with perchloryl fluoride (ClO F) or fluorine or a mixture thereof. We have found that on bringing together separately and substantially simultaneously an oxidizer comprising a halogen fluoride and a metal fuel comprising niobium or tantalum, auto-ignition of the resulting mixture occurs within a few seconds at about 100 C. and in much less than a second at higher temperatures, e.g., above around 75 C.

It is known in the prior art that certain metals will ignite at appreciably elevated temperatures, e.g., above about 150 C., in the presence of halogen fluorides. Thus, uranium will ignite at 150 C., 225 C., 250 C., and 260 C. in bromine trifluoride, bromine pentafluoride, chlorine trifluoride (GR) and fluorine, respectively, and zirconium ignites in chlorine trifluoride or fluorine gas at 331mm Patented Get. 26, 1965 about 340 C. On the other hand, thorium, aluminum, copper, iron, magnesium and platnium do not ignite in these oxidizers even at temperatures ranging at 410 C. See, for example, Stein and Vogel, Industrial and Engineering and Chemistry, volume 48, pages 418-21 (1956). Therefore, it was surprising to find that niobium and tantalum of the Group VA metals ignite spontaneously at subzero temperatures in the presence of an oxidizer comprising a halogen fluoride, e.g. chlorine trifluoride. It was also surprising to find that tantalum is more reactive than niobium in this respect.

The Group VA metals are vanadium, niobium and tantalum. Unlike niobium and tantalum, vanadium does not ignite spontaneously in a halogen fluoride even at room temperature, although vigorous chemical reaction occurs.

For the practice of the invention, niobium (columbium) and tantalum metal each can be used in commercially pure form. Each of these metals also can be used as an alloy consisting substantially of one of these metals with the other or with at least one other metal, e.g., iron, zirconium, tungsten or nickel. The metals, or their alloys, can be used in the form of pellets, preferably of about 0.1 gram in weight or lighter. The metals, or their alloys, also can be used in the form of shavings, turnings or fine powder. Also, the metals, or their alloys, can be used in the form of a suspension within a liquid fuel. They can also be used as an ingredient embedded with a binder in the surface of and within a solidified form of fuel, for example, in an extruded plastic oxidant-fuel composition containing the niobium or tantalum metal, or an alloy thereof, in pellet, shavings, turnings, powdered or other physical form, alone or in major proportion in combination with another metal.

The oxidizer which is used in practice of the invention preferably is halogen fluoride, including chlorine trifluoride, chlorine monofluoride, bromine trifluoride, and bromine pentafluoride. The oxidizer can also be halogen fluoride in combination with fluorine or with perchloryl fluoride, or with a mixture of both of the latter materials. Preferably, the oxidizer is a mixture of halogen fluoride with perchloryl fluoride. In such a mixture, the ratio of perchloryl fluoride to the halogen fluoride can range from about 2421 to 1:5 by weight, more perchloryl fluoride being required to keep the oxidizer in fluid form as the temperature of use is lowered. A mixture of oxidizer containing from about 25% to about 50% by weight of perchloryl fluoride in the halogen fluoride is preferred. Mixtures of perchloryl fluoride with halogen fluoride which are hypergolic to certain fuels at ordinary ambient temperatures are disclosed and claimed in Gall, US. Patent 3,066,058. A mixture of halogen fluoride with fluorine in similar proportions can be used. Also, fluorine and perchloryl fluoride can be mixed and the mixture used with a halogen fluoride, e.g., chlorine trifluoride, in similar proportions as when perchloryl fluoride is used alone with the halogen fluoride oxidizer.

In practicing the invention in accordance with one embodiment in rocket propulsion, chlorine trifluoride and tantalum in the form of fine shot are separately and simultaneously charged into the combustion chamber of a rocket motor in a way which will be obvious to one skilled in the art such that they immediately come into intimate contact, thereby spontaneously igniting. For example, the chlorine trifluoride is pumped into the chamber and the shot is blown in with a combustible gaseous material. The gaseous reaction products of combustion are discharged through the exit orifice of said motor to propel the rocket.

The halogen fluorides have little or no vapor pressure at 0 C. Therefore, auxiliary means are usually necessary to charge the halogen fluoride to the combustion chamber. A pump can be used for this purpose if means for driving the pump are available at the subzero temperature. Preferably, however, since pumping means could become inoperative, the halogen fluoride is pressurized by means of a gaseous material to a pressure above that of the combustion chamber. An inert gas, e.g., nitrogen or helium, can be used for this purpose. However, in some cases it is preferred to use a reactive gaseous material, e.g., perchloryl fluoride or fluorine. Also, since in some cases the temperature of use of the halogen fluoride may be below the freezing point of the halogen fluoride, e.g., below 83 C. in the case of chlorine trifluoride, an auxiliary liquified gaseous ma terial, such as one of the above group, provides a fluid medium in which the halogen fluoride can be charged into the combustion chamber in the form of a slurry of crystals and thus brought into contact with the metal component of our igniter system, e.g., tantalum in powdered form. Despite the fact that the halogen fluoride is in crystalline form, when it is brought into contact with our metal fuel, the reactivity of the metal with the halogen fluoride is sufliciently vigorous soon to cause spontaneous ignition of the metal. On ignition, the auxiliary material, e.g., perchloryl fluoride, also supports combustion of the metal. Therefore, the oxidizer of our invention can be charged to a combustion chamber at extremely low subzero temperatures Without need for auxiliary mechanical means.

A metal component of our igniter mixture, e.g., niobium, also can be charged to the combustion chamber without need for auxiliary mechanical means by fluidizing a powder of the metal with a gas, e.g., carbon monoxide, which is non-reactive with the metal in its powdered form. Accordingly, by means of our invention, positive starting of a fire in the combustion chamber of a rocket motor or of a jet engine can be achieved even at extremely low subzero temperatures without depending on mechanical means for charging the components of the igniter mixture to the combustion chamber.

In another embodiment, the hypergolic igniter system of this invention can be used as an igniter system for a separate propellant system which is to provide thrust in a rocket motor. In such use, an amount of metal from about 0.1 gram to 1.0 gram in wire or particle form is generally adequate to provide sufficient heat and flame on spontaneous ignition in an oxidizer comprising halogen fluoride to ignite the thrust-providing propellant system. The propellant can be in solid form, for example, such as that disclosed and claimed in Guth, US. 2,963,356, but containing, in addition to the ingredients of the Guth type of propellant, an effective amount of tantalum, niobium or an alloy of either in divided form dispersed in the propellant and embedded in the surface thereof so that it is readily accessible to our oxidizer. The amount of niobium or tantalum metal or alloy thereof in the propellant can be from 0.5 to 10 parts per 100 parts by weight of propellant. For example, a stream of oxidizer of this invention, e.g., chlorine trifluoride, is directed against the exposed surface of a solid propellant containing an alloy of niobium in the combustion chamber of a rocket motor. Upon contact with the chlorine trifluoride, hypergolic ignition of the niobium alloy is achieved even at temperatures of about l C. When the combustion of the propellant becomes selfsustaining, the flow of the oxidizer of our hypergolic ignition system can be discontinued. The products of combustion are discharged through the exit orifice of the motor to propel the rocket.

In the event that the thrust-providing propellant system comprises a liquid or powdered fuel in combination with a liquid or powdered oxidizer in combustible proportions, the hypergolic igniter system of this invention can be used to achieve positive ignition of such a propellant system at subzero temperatures. For example, an oxidizer useful in the practice of our invention, e.g. chlorine trifluoride containing 50\% by weight of perchloryl fluoride, and pellets of commercially pure tantalum of about 0.1" diameter are charged separately and substantially simultaneously into the combustion chamber of a rocket motor so that the oxidizer envelops the pellets, thereby causing spontaneous ignition of the tantalum. Separately and substantially simultaneously, a thrust-providing propellant mixture consisting of another fuel, e.g., kerosene (]P4), and another oxidizer, e.g., oxygen, are charged into the combustion chamber. The latter propellant mixture ignites in the products of combustion of the hypergolic igniter system of this invention. After the combustion of the thrustproviding propellant mixture becomes self-sustaining, the

flow of the components of our hypergolic igniter system can be discontinued. The gaseous products of reaction are discharged through the exit orifice of the rocket motor to propel the rocket.

In view of the reactivity of niobium and tantalum metal and their alloys in halogen fluoride, use of these metals as materials of construction in the combustion chamber must be avoided. However, this fact presents no great problem because other metals, particularly those forming a protective fluoride film, e.g., Monel or nickel or 18-8 stainless steel can be used in the combustion chamber where the halogen fluoride is present.

The niobium or tantalum metal or one of their alloys can also be dispersed as a stream of fine fluidized powder into the path of a liquid or of a powdered solid fuel which is to be burned in the combustion chamber solely with an oxidizer useful in the practice of this invention to produce the thrust for operation of the rocket motor. The mixed stream of metal, e.g., niobium, and fuel, e.g., powdered coal fluidized with carbon dioxide gas, ignites spontaneously in a stream of an oxidizer of this invention, e.g., chlorine trifluoride, at a subzero temperature, e.g. in the range of about -1 to 83 C.

Similarly, the mixed stream of our metal fuel and another fuel, e.g. unsymmetrical dimethyl hydrazine (UDMH) or hydrogen, can be used with an oxidizer comprising halogen fluoride, e.g., chlorine trifluoride, to provide intermittent bursts of thrust in vector rockets attached to a space vehicle. Thus, positive ignition of the vector rockets at extremely subzero temperatures, e.g., C. and lower, is made possible by the practice of our invention.

The same technique as described in the preceding paragraph can be employed also in the ignition of jet engine motors using J P4 fuel at ordinary ambient temperatures, as well as at subzero temperatures, in order to overcome the dangers arising from flame-out in commercial airliner engines during takeoff or in flight.

Many flame-propagating materials will rapidly burn, after ignition by the hypergolic igniter system of this invention, at a subzero temperature, in the presence of an oxidizer of the system. These materials include all materials which burn at an elevated temperature in an atmosphere containing halogen or oxygen and halogen, but which may not ignite spontaneously with a halogen fluoride at a subzero temperature. Examples of such combustible materials are hydrogen; ammonia; hydra- Zines; carbon compounds, particularly alkyl hydrazines, e.g., symmetrical and unsymmetrical dimethyl hydrazines, aryl hydrazines, alcohols, mercaptans, ketones, ethers and hydrocarbons, e.g., acetylene, ethane, propane, hexane and kerosenes; carbonaceous materials of all kinds, e.g., wood, coal, coke, carbon, graphite, cellulosic fibers, and synthetic polymers; alkali metals, e.g., lithium, sodium and potassium; alkaline earth metals, e.g., beryllium, magnesium, calcium, strontium and barium; aluminum; iron; phosphorus and its lower valence compounds; sulfur; boron; silicon; and hydrides and alkyls of the listed chemical elements. After any of these flame-propagating materials has been ignited at subzero temperatures by means of our hypergolic igniter system,

for example as disclosed in any of the preceding embodiments, the oxidizer of our system comprising halogen fluoride can be used alone with the above material to maintain a flame and to produce products of combustion It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention Without departing from the scope and spirit thereof, and the invention includes all such modificauseful in operation of thrust devices. 5 tions.

Table I Ex- Periodic ample Metal Table Oxidizer Ignition Temperature Results and Comments No. Group 1 Niobium, 3 x 5 x VA ClFa, 4 g Above liquid nitrogen tempera- Violent, incendiary reaction and bright ture, but below MP. of 011%. bluish-white flame observed before f01F:i was observed to melt. Tube use 2 do VA OIFa, 2 g., (31031, 2 g- About 148 F During air-warming of tube from liquid nitrogen temperature, white flash of light was observed, followed after a few seconds by bright flame lasting for about seconds. Some fusion of tube. N0 biobium left.

3 do VA Fluorine, 4g N o ignition Liquidfluorine boiledoftatroomtemperature. N o combustion. Metal gained 0.0007 g. weight over original 0.2075 g.

4 Tantalum x x 34... VA .ClFa, 4 g Slightly above liquid nitrogen Violent ignition observed as with temperature. niobium, but earlier.

5 Vanadium, 0.218 g. in fine VA ClFa, 7.6 g No ignition Vigorous bubbling reaction began on granular form. melting of 01113 and continued until all ClFa had boiled 011 while warming to about 55 F.

6 Bismuth, 0.024 wire VB 011%, 6.6 g.-. do Liquid 01F; boiled off at room temperature. No combustion. Metal gained 0.0002 g. over original 0.2591 g.

Zirconium IVA ClFa. Liquid ClF; boiled oif at room temperature. N0 combustion. Tungsten VIA ClF3 Do.

This invention is further illustrated by Examples 1-8 We claim:

shown in Table I. In carrying out the demonstration of our invention as disclosed by the examples, a translucent test tube A1. diameter by 6" long, made of polychlorotrifluoroethylene was used as a vessel for holding liquid oxidizer. The test tube was suspended in and cooled in a liquid nitrogen bath (-196 C.). A small piece of metal was placed in the test tube and cooled to the temperature of the bath. Oxidizer was then quickly condensed into the chilled test tube, the oxidizer cover ing the chilled metal test piece and freezing instantly to the temperature of the bath. The liquid nitrogen bath was then removed and the tube allowed to stand at room temperature. The contents of the test tube were observed as the oxidizer warmed. All test work was conducted behind safety glass barricades in a vented hood.

The results, as shown in Table I, show that, of the metals tested, only niobium and tantalum ignite in chlorine trifluoride at subzero temperatures. The results also show that fluorine does not ignite niobium in the absence of chlorine trifluoride even at room temperatures. Further, the results show that neither a Group IVA nor a Group VIA metal nor a Group VB non-metal element ignites even at room temperature in chlorine trifluoride. Also, the results show that a chlorine trichloride-perchloryl fluoride oxidizer mixture ignites below the freezing point of chlorine trifluoride (F.P. -83.5 C.). The results, taken in view of the known art, accordingly amply demonstrate the unobvious and unexpected ignition properties of the hypergolic igniter system of the invention.

Although the practice of the invention has been described principally in connection with its use in rocket engines at subzero temperatures, the invention can also be practiced at above zero temperatures wherever it is desired to obtain positive ignition of a combustible material, using the hypergolic igniter system of this invention to ensure such ignition. Thus, our hypergolic igniter system can be used in chemical cutting tools or devices such as those described in Sweetman, US. 2,918,125 and Gall, above, by using the niobium or tantalum metal or their alloys of our igniter system in combination with the halogen fluoride of Sweetman or the halogen-perchloryl fluoride mixture of Gall.

1. An oxidizer-fuel propellant system which is selfigniting at a subzero temperature when the oxidizer and fuel are brought in contact with each other said oxidizer being selected from the group consisting of (a) halogen fluoride and (b) a mixture of halogen fluoride With at least one member of the group consisting of fluorine and perchloryl fluoride, said mixture containing at least 4% by weight of halogen fluoride; said fuel consisting of (a) from about 0.5 to about 10 parts by weight of a divided form of metal selected from the group consisting essentially of niobium, tantalum, an alloy of niobium with tantalum, an alloy consisting substantially of niobium, and an alloy consisting substantially of tantalum in combination with (b) parts by weight of other material combustible in said oxidizer.

2. The propellant according to claim 1 in which the metal is niobium.

3. The propellant according to claim 1 in which the metal is tantalum.

4. The propellant according to claim 1 in which the oxidizer is chlorine trifluoride.

5. A method for initiating rocket propulsion at a subzero temperature which method comprises (a) bringing together separately and substantially simultaneously into the combustion chamber of a rocket motor a hypergolic igniter system comprising an oxidizer selected from the group consisting of halogen fluoride and a mixture of halogen fluoride with at least one member of the group consisting of fluorine and perchloryl fluoride, said mixture containing at least about 4% by weight of halogen fluoride, and a fuel comprising a metal selected from the group consisting essentially of niobium, tantalum and their alloys with each other and at least one other metal, thereby causing spontaneous ignition of said metal in said oxidizer; (b) substantially simultaneously providing in said combustion chamber a propellant mixture consisting of other fuel and oxidizer therefor in combustible proportions; (c) mixing the combustion products of said hypergolic igniter system with said propellant mixture in the combustion chamber, thereby causing ignition of said propellant mixture; and (d) discharging the gaseous reaction products through the exit orifice of said motor.

6. A method according to claim 5 in which the metal is niobium.

7. A method according to claim 5 in which the metal is tantalum.

8. A method according to claim 5 in which the oxidizer is chlorine trifluoride.

9. A method for starting a fire at a subzero temperature by auto-ignition which method comprises bringing together separately and substantially simultaneously an oxidizer comprising halogen fluoride and a fuel comprising at least 0.5 part per 100 .parts of fuel of a divided form of a metal selected from the group consisting essentially of niobium, tantalum and their alloys with each other and with at least one other metal, thereby causing a fire by spontaneous ignition of said metal in said oxidizer.

10. The method according to claim 9 in which the met l is n bium '8 11. The method according to claim 9 in which the metal is tantalum.

12. The method according to claim 9 in which the oxidizer is chlorine trifluoride.

5 References Cited by the Examiner UNITED STATES PATENTS 2,974,484 3/61 Cooley 60-354 X 10 OTHER REFERENCES Rosenberg et al., Ind. & Eng. Chem, vol. 45, No. 10, pp. 2283-86, October 1953.

Lang, Handbook of Chemistry, 1946, pp. 58-9.

15 CARL D. QUARFORT-H, Primary Examiner.

LEON D. ROSDOL, Examiner.

Claims (1)

1. 5. A METHOD FOR INITIATING ROCKET PROPULSION AT A SUBZERO TEMPERATURE WHICH METHOD COMPRISES (A) BRINGING TOGETHER SEPARATELY AND SUBSTANTIALLY SIMUTANEOUSLY INTO THE COMBUSTION CHAMBER OF A ROCKET MOTOR A HYPERGOLIC IGNITER SYSTEM COMPRISING AN OXIDIZER SELECTED FRO THE GROUP CONSISTING OF HALOGEN FLUORIDE AND A MIXTURE OF HALOGEN FLUORIDE WITH AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF FLUORINE AND PERCHLORYL FLUORIDE, SAID MIXTURE CONTAINING AT LEAST ABOUT 4% BY WEIGHT OF HALOGEN FLUORIDE, AND A FUEL COMPRISING A METAL SELECTED FROM THE GROUP CONSISTING ESSENTIALLY OF NIOBIUM, TANTALUM AND THEIR ALLOYS WITH EACH OTHER AND AT LEAST ONE OTHER METAL, THEREBY CAUSING SPONTANEROUS IGNITION OF SAID METAL IN SAID OXIDIZER; (B) SUBSTANTIALLY SIMULTANEOUSLY PROVIDING IN SAID COMBUSTION CHAMBER A PROPELLANT MIXTURE CONSISTING OF OTHER FUEL AND OSIDIZER THEREFOR IN COMBUSTIBLE PROPORTIONS; (C) MIXING THE COMBUSTION PRODUCTS OF SAID HYPERGOLIC IGNITER SYSTEM WITH SAID PROPELLANT MIXTURE IN THE COMBUSTION CHAMBER, THEREBY CAUSING IGNITION OF SAID PROPELLANT MIXTURE; AND (D) DISCHARGING THE GASEOUS REACTION PRODUCTS THROUGH THE EXIT ORIFICE OF SAID MOTOR.