US3722421A

US3722421A - Solid bipropellant

Info

Publication number: US3722421A
Application number: US00185185A
Authority: US
Inventors: A Thrailkill; R Geene
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1962-04-04
Filing date: 1962-04-04
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27

Abstract

A solid bipropellant grain having a specific impulse of over 275 seconds comprising a slotted, single perforate, internal burning oxidizer grain and adjacent pressed lithium aluminum hydride plates in which the greatest surface is exposed to the flow of the combustion products of the oxidant.

Description

United States Patent v 1 Thrailkill et al. [451 Mar. 27, 1973 [54] SOLID BIPROPELLANT 2,759,418 8/1956 Ross et al. ..149/74 X 9 5 751 Inventors: Arthur E. Thrailkill, Bel Air; Robert w Geene Aberdeen bothofMd ox 2,977,885 4/1961 Perry et a1. ..149/15 [73] Assignee: The United States of America as represented by the Secretary of t Primary Examiner-Benjamin R. Padgett y Attorney-S. J. Rotondi and A. T. Dupont [22] Filed: Apr. 4, 1962 CT 57 ABSTRA [21] Appl. No.: 185,185

A solid bipropellant grain having a specific impulse of U S Cl 102/101 149/2 149/15 over 275 seconds comprising a slotted, single per- 511 In t. C1 I C06d 5706 F4 2b 1/00 Mate internal burning Miler grain and mil-em [58] Field of se;; ii 149/15 14 2- 60/354 Pressed lithium aluminum hydride Plates in which 1 2 greatest surface is exposed to the flow of the combustion products of the oxidant.

[5 6] References Cited UNITED STATES PATENTS 2 Claims, 3 Drawing Figures 2,408,252 9/1946 DeGanahl ..102 9s h o /der SOLID BIPROPELLANT The invention described herein may be manufactured and used by or for the Government for govemmental purposes without the payment to us of any royalty thereon.

The present invention relates to solid propellants for rockets and missiles which are composed of two essentially incompatible materials which will not react until a designated time.

The primary object of this invention is to combine highly reactive components into a high energy solid propellant grain.

Another object of this invention is to combine a powerful reducing agent with a powerful oxidizing agent and produce a propellant grain which is safe from failure. I I

A further object of this invention is to combine the highly reactive fuel and oxidizer components of a propellant grain in such a manner that the components will react in an efficient manner.

Other and further objects and advantages of this invention will become apparent to those skilled in the art from the following specification and claims taken in connection with the accompanying drawing.

Practical embodiments of the present invention may be further illustrated by the accompanying drawing, wherein:

FIG. 1 illustrates one embodiment whereby the twelve spoke wheel fuel grain is kept separate from the slotted, single perforate, internal burning oxidizer charge, and

FIG. 2 illustrates a single perforate, internal burning pressed polyethylene coated lithium aluminum hydride fuel disk with a restrictor coating, and

FIG. 3 illustrates a web of pressed polyethylene coated lithium aluminum hydride fuel disks in a lucite holder. 7

Referring to FIG. 1, the drawing shows the structure of the type of propellant grain which was employed in the tests run to compare the performance of the bipropellant system with the monopropellant. The oxidizer charge is a slottedintemal burning grain placed at the head of the composite grain so that theoxidizers products of combustion, high temperature reactive gases, pass over the surface of the fuel grain causing it to decompose and to then react with the oxidizers products. v

The pressed lithium aluminum hydride fuel grain configuration shown in FIG. 2 did not burn out. When this fuel grain was fired with the slotted, single perforate oxidizer, the burning surface of the fuel grain which was exposed to the oxidizers products of combustion was insufficient to permit complete consumption.

Referring to FIG. 3, the pressed lithium aluminum hydride fuel grain of disks or plates shown, was consumed at a slow rate during combustion. When this fuel grain was fired with the oxidizer, the burning surface of the grain which was exposed to the oxidizers products of combustion was greater than the configuration in FIG. 2 and permitted complete consumption at a slow rate. Thus, it is seen that thesurfaces over which the oxidizer propellant products of combustion pass are more readily consumed than those surfaces normal to the direction of gas flow.

Propellants currently in use or under active development fall into the 240-265 second specific impulse class. Future demands on performance will require propellants of the 280 second specific impulse class or greater. To fulfill these increased demands more potent fuels, such as powerful reducing agents of the metallic erting one or both of the components so that they will not react until commanded. A protective coating around each particle achieves, in part, at least, some measure of protection, however, it does not always maintain its protective character through mixing, storage and handling up to the time of firing.

A new technique which will provide maximum safety is now proposed. The fuel component and the oxidant component which have been incorporated into the same matrix in the past now affixed in the engine in two separate and distinct packages, a solid bipropellant. Thus, one package would contain an oxidant while the other package would contain a fuel. By this arrangement the two troublesome components are separated at all times during mixing, storage, and subsequent handling. To get the fueland oxidant together at the time of firing or rather to bring together their products of decomposition, the oxidant package must release oxygen rich products of combustion and the fuel package must release fuel rich products of decomposition, both at a known and predictable rate so that a reaction will occur in an efficient manner.

The most critical factor affecting the release and subsequent combination of the products of combustion is the geometry of the fuel grain with respect to that of the oxidizer grain. In order to have the fuel consumed at-a reasonable linear rate, the fuel grain geometry, with respect to the oxidizer grain, must be of such a configuration that the fuels surface being consumed is in the main stream of the oxidizers products of combustion. To effect this action, several grain geometries were investigated for the performance studies of the bipropellant. A monopropellant and a standard DDP- propellant were used as controls. The simplest and most satisfactory grain design under the circumstances was a one-eighth inch slotted, 0.6 inch diameter single perforate, internal burning grain'which was used for the design of the monopropellant, the DDP-70 grain design was essentially completely consumed during the burning of the oxidizer grain. The designs of the pressed polyethylene coated lithium aluminum hydride shown in FIG. 2 and '3 which were tested were disks 1 35 inches in diameter and one-half inch and one-eighth inch thick, respectively.

In evaluating grain design, it was found that the end surfaces of the grain could be neglected so that the computed burning surface of the fuel grain was only that surface parallel to the axis of the motor. It is recognized that the grain geometries employed were selected on the basis of rather simplified assumptions regarding the mode of consumption of the fuel grain and therefore the conditions under which the experiments were conducted were other than optimum. The specific impulse values therefore obtained do not indicate the maximum efficiency possible. Greater efficiency may be obtained with other arrangements of the bipropellant components, such as, for example, placing the fuel grain between the two oxidizer grains so that the first oxidizer would cause the fuel grain to be consumed and the second oxidizer would act as an afterbumer delivering the desired products of combustion to the nonle.

While it is to be understood that the present invention is not drawn to any particular composition but places novelty upon the idea of separating a solid fuel package from an incompatible solid oxidizer package, a few examples of the compositions used in these tests are set forth merely as guides for workers in the art and are not to be considered limiting in any way. The following compositions were employed in tests conducted in connection with this invention.

BIPROPELLANT Oxidizer Weight Percent Nitroglyeerine 32.1%

Ammonium Perchlorate 56.1%

Polyurethane 1 1.8% 100.0%

Fuel

Magnesium 73.0%

Polyurethane 24.9%

Carbon Black 2.1% 100.0%

Fuel/oxidizer ration 1:4

MONOPROPELLANT Nitroglycerine 26.75%

Ammonium Perchlorate 46.75%

Polyurethane 13.98%

Magnesium 12.17%

Carbon Black 0.35%

DDP-7O Powder Nitrocellulose (13.15N) 30.0%

Nitroglyccrine 10.0%

Ammonium Perchlorate 28.0%

Aluminum 29.0%

2 nitrodiphenylamine 1.0

Resorcinol 2.0% 100.0%

Solvent Nitroglycerine 70.0%

Triacetin 29.0%

2 nitrophenylamine 1.0% 100.0%

Powder/Solvent 72/28 Pressed polyethylene coated lithium aluminum hydride disks illustrated in FIGS. 2 and 3 were fired with the above bipropellant oxidizer composition.

A specific impulse of 275-279 seconds was predicted for fuel/oxidizer ratios over the range of 25/75 to 35/65.

Binders may be used, and in the case of metallic hydrides and powdered oxidizers, are necessary, to put the ingredients into useful forms. The binders must be carefully chosen so that they do not react with the metal hydride. This precludes, in general, binders which contain oxygen, halides and carbon to carbon double bonds. The fuel package having these restrictions will not be self consuming, and thus the geometry of the fuel must be such that the products of the oxidants combustion will pass over the fuel to effect combustion of the latter.

All firings were made in a two inch static test motor in the range facilities of the Interior Ballistics Laboratory. Graphite nozzles were used with an expansion ratio of six and a divergent half angle of 10. Each firing was monitored with two Dynamic Instruments Co., Inc., Model TCPT 31 SP-35, 0-3000 psi pressure gauges and a double Alleghany Instrument Company, Alinco Load Cell, Model 3441,000 lbs. All rounds were ignited with a US. Flare Squib 107-A and 3 grams of FFFG black powder.

The average results of several test runs which were made are'set forth in the following table for comparison.

The comparison between the solid bipropellant firing results and the monopropellant firing results appeared to be quite good. The solid bipropellants average measured specific impulse corrected to standard conditions is 96 percent of the monopropellants average measured specific impulse corrected to standard conditions and the average measured characteristic velocity of the solid bipropellant is 98 percent of the monopropellants average characteristic velocity. This demonstrates that the combustion and performance of the two-package propellant, i.e., the bipropellant, can be achieved with good efficiency. Better efficiencies are undoubtedly possible with more refined fuel grain geometries, however, these tests proved the feasibility of the principal of separation of fuel and oxidizer in a propellant grain.

Of course, it is to be understood that the present concept may be equally applicable to compatible ingredients as well as to incompatible ingredients. These grain designs are only exemplary, and numerous modifications are possible so long as the basic concept of the separation of fuel and oxidizer into distinct packages is maintained.

We claim:

pulse of over 275 seconds, comprising a slotted, single perforate, internal burning oxidizer grain and pressed lithium aluminum hydride plates adjacent thereto having their longitudinal axes parallel to the direction of

Claims

2. A solid bipropellant grain having a specific impulse of over 275 seconds, comprising a slotted, single perforate, internal burning oxidizer grain and pressed lithium aluminum hydride plates adjacent thereto having their longitudinal axes parallel to the direction of gas flow.