U.S. patent number 3,730,093 [Application Number 04/607,129] was granted by the patent office on 1973-05-01 for explosive apparatus.
Invention is credited to Jerry W. Cummings.
United States Patent |
3,730,093 |
Cummings |
May 1, 1973 |
EXPLOSIVE APPARATUS
Abstract
In one embodiment a cylindrical mass of fuel is surrounded on
the sides by a layer of high explosive for implosive dissemination
of the fuel. Axially within the fuel is a frangible tube containing
a powdered igniter mixture of metal and metal oxide which are
exothermically reactive together. Gas voids are provided in the
igniter mixture for assuring initiation of reaction therein. Means
are provided for detonating the high explosive which sends an
implosive shock wave through the fuel and the metal-metal oxide
mixture. The mixture is thereby ignited and fragmented and the
heated mixture and the fuel are radially disseminated providing
ignition of the fuel as it is disseminated. The nature of the
arrangement permits use for fuel of a broad variety of materials
including materials known to be combustible and also a variety of
materials not normally considered combustible.
Inventors: |
Cummings; Jerry W. (Palos
Verdes Estates, CA) |
Family
ID: |
24430947 |
Appl.
No.: |
04/607,129 |
Filed: |
December 27, 1966 |
Current U.S.
Class: |
102/363;
149/15 |
Current CPC
Class: |
F42B
12/44 (20130101) |
Current International
Class: |
F42B
12/44 (20060101); F42B 12/02 (20060101); F42b
024/15 () |
Field of
Search: |
;102/6,57,90,66,24HZ,56
;149/2,19,15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Engle; Samuel W.
Claims
What is claimed is:
1. A fuel-air explosive device comprising:
a cylindrical body of fuel;
a housing around the fuel;
a layer of high explosive around the housing, the thickness of said
layer being sufficient to disseminate said fuel at a velocity
substantially greater than the combustion velocity of said fuel
with air;
means for detonating said high explosive;
an igniter for said fuel located within said body of fuel;
said igniter comprising:
a frangible tube substantially coaxial with said cylindrical body
of fuel;
a mixture of two materials within said tube, said two materials
being exothermically reactive together in response to detonation of
said high explosive, and
means forming a plurality of controlled void spaces within said
mixture of materials;
the first of said two materials being selected from the group
consisting of lithium, potassium, cesium, barium, calcium, sodium,
magnesium, beryllium, aluminum, titanium, zirconium, and
carbon;
the second of said two materials being selected from the group
consisting of oxides, halides, carbides, sulfides, borides,
nitrides, silicides, and phosphides of the metals magnesium,
beryllium, aluminum, titanium, zirconium, manganese, vanadium,
zinc, chromium, iron, cadmium, indium, cobalt, nickel, molybdenum,
tin, lead, copper, and mercury;
said first material being substantially more electropositive than
the metal of said second material;
first and second ductile end plates at opposite ends of said
cylindrical body of fuel, said end plates having a substantial
sonic velocity mismatch with said fuel for reflecting a shock wave;
and
said means for detonating the high explosive comprising a fuze and
detonator carried by the housing adjacent an end plate.
2. An explosive device as defined in claim 1 wherein said fuel is
selected from the group consisting of
propane, butane, pentane, hexane, heptane, octane, nonane, decane,
undecane, dodecane, ethylene oxide, polyethylene, propylene oxide,
polypropylene, polystyrene, styrene, butene, butadiene,
isobutylene, pentene, hexene, heptene, octene, ethylacetylene,
acetylene, dimethyl-acetylene, pentine, methyl butine, hexine,
benzene, toluene, naphthene, ethyl benzene, propylbenzene, butyl
benzene, xylene, mesitylene, mesityl oxide, cumene, pseudocumene,
indine, naphthalene, methyl naphthalene, diphenyl, acenaphthalene,
fluorene, phenanthrene, anthracene, fluoranthene, pyrene,
benzpyrene, chrysene, naphthacene, pyridine, picoline, quinoline,
quinaldine, indole, acridine, carbozole, allylbenzene, stilbene,
diphenylmethane, triphenyl methane, tetraphenyl methane, terphenyl,
camphor, methyl alcohol, ethyl alcohol, propyl alcohol, butyl
alcohol, amyl alcohol, hexyl alcohol, phenol, benzyl alcohol,
diethyl ether, methyl ethyl ether, dipropyl ether, diphenyl ether,
methyl phenyl ether, dioxane, methyl butyl ether, ethyl butyl
ether, dibutyl ether, diamyl ether, dihexyl ether, divinyl ether,
tetrahydrofuran, acetaldehyde, benzaldehyde, propionaldehyde,
butyraldehyde, valeraldehyde, acrolein, crotonaldehyde,
benzaldehyde, furfural, acetone, methyl ethyl ketone, methyl propyl
ketone, diethyl ketone, hexanone, methyl butyl ketone, dipropyl
ketone, dibutyl ketone, diamyl ketone, chloracetone, methyl amine,
dimethyl amine, trimethyl amine, ethylamine, diethylamine,
triethylamine, propylamine, dipropylamine, tripropylamine,
butylamine, amylamine, hexylamine, ethylene diamine, trimethylene
diamine, allylamine, aniline, acetamide, propionamide, benzamide,
nicotinonitrite, flour, glucose, fructose, sucrose, lactose,
maltose, cellulose (such as, for example, cotton, sawdust, straw,
paper), butyric acid, isovaleric acid, caproic acid, caprylic acid,
capric acid, lauric acid, myristic acid, palmitic acid, stearic
acid, paraffin, charcoal, coconut oil, palm oil, olive oil, castor
oil, peanut oil, corn oil, rape oil, beef tallow, lard, whale
blubber, cottonseed oil, soybean oil, tung oil, linseed oil,
gasoline, kerosene, jet engine fuel, bunker oil, gas oil,
lubricating oil, petroleum ether, mineral spirits, heavy ends from
petroleum refining, asphalt, waxes, lacquer, napalm, furan, ethyl
nitrate, furfurol, ethyl cellulose, nitromethane, nitrobenzene,
dinitrobenzene, nitroethane, nitropropane, nitrobutane,
nitropentane, light oil, carbolic oil, creosote oil, anthracene (or
green) oil, pitch, fusel oil, starch, polyvinyl chloride, polyvinyl
alcohol, epoxy polymers, mercaptons, and glycol, including cyclic
and branched chains, polymers, and saturated and unsaturated
isomers thereof, nitrate, ammonia, sulfhydride, and cyanide
substitutions thereon and heterocyclic chains with nitrogen,
oxygen, phosphorus, and sulfur.
Description
BACKGROUND
Military munitions in general offer many damage mechanisms such as,
for example, increased pressure or over-pressure maintained for
short-time intervals, fragmentation or flight of fragments, and
thermal effects, each of which will cause damage to either material
or personnel depending on intensity of the effect. The first of
these damage mechanisms is what is known as "blast" and is the
principal mechanism of destruction when a high explosive is
detonated. In many weapons a fragmentation mechanism is added
wherein a frangible container or prepared shrapnel is incorporated
in the weapon to provide a cloud of high velocity fragments or
shrapnel for damaging materiel or wounding personnel. Certain other
types of weapons rely principally on thermal effects such as the
conventional napalm weapons wherein a jelled gasoline, benzene, or
similar fuel is ignited and spared over an area it is desired to
burn.
The usual military weapons outside of nuclear devices rely on one
or two of these damage mechanisms with minimal presence of the
other mechanism or mechanisms. Thus, for example, a high explosive
device usually relies on blast effect alone or may include some
minor amount of fragmentation. Similarly, the usual fragmentation
weapons do not include more high explosive than is needed to propel
the fragments and a minimal amount of blast effectiveness or
over-pressure is noted at any substantial distance from the point
of detonation. In neither of these cases is a substantial thermal
effect noted. In the conventional napalm, on the other hand, the
thermal effects due to burning of the napalm are predominant and
very little fragmentation or blast destruction is obtained.
Another type of weapon is the so called fuel-air explosive (FAX)
weapon wherein a combustible material is dispersed as a vapor or
aerosol in a cloud so as to mix thoroughly with the naturally
occurring air to form a detonable or burnable mixture, and the
cloud is ignited. These weapons often produce both blast and
thermal effects for the mechanisms of destruction. The FAX type
weapon has an advantage in that the weight effectiveness is high
since only fuel is delivered and the oxidizer, namely air, is
virtually omnipresent. This is in contrast to explosives which do
not rely on combination with air to supply energy and the energy
per unit weight delivered is lower.
A substantial difficulty with the prior art fuel-air explosive
(FAX) weapon is that of the timing of ignition of the cloud of
combustible mixture. In order to obtain optimum effectiveness from
the weapon, it is desirable to ignite the fuel-air mixture in the
cloud when it is in the concentration range for detonation rather
than combustion. The time for the cloud to reach the optimum
concentration, however, varies with atmospheric conditions such as
temperature and pressure. Since these conditions will vary the time
for the fuel to be dispersed to the optimum concentration for
detonation, various fusing mechanisms have been suggested for FAX
weapons in order to obtain ignition of the fuel cloud at some
pre-selected time after dispersion of the fuel has commenced. Such
mechanisms have not been satisfactory since, for example, different
time intervals are required for dispersion of a fuel cloud in low
temperature, low altitude and in high temperature, high
altitude.
BRIEF SUMMARY OF THE INVENTION
According to a significant feature of this invention there is
provided a fuel selected from a broad class of materials that are
combustible with air after high energy implosive dissemination,
substantially surrounded by a high explosive of determined power.
According to another feature of the invention, a critical power of
explosive is not required and there is provided an igniter,
operable in response to detonation of explosive to disseminate high
temperature fragments of fuel igniting material in a direction
substantially the same as the direction a fuel is dispersed.
Thus, it is an object of this invention to provide an improved
fuel-air explosive device.
Other objects and many of the attendant advantages of this
invention will become apparent by examination of the following
detailed description and accompanying drawings wherein:
FIG. 1 illustrates in cutaway a mine constructed according to the
principles of this invention;
FIG. 2 illustrates a cloud of droplets dispersed according to the
principles of this invention;
FIG. 3 illustrates one of the droplets of FIG. 2;
FIG. 4 illustrates an aerial bomb constructed according to the
principles of this invention;
FIG. 5 transverse cross section of the aerial bomb of FIG. 4;
FIG. 6 illustrates in cutaway another embodiment of this invention;
and
FIG. 7 is a cutaway view of another embodiment of this
invention.
Throughout the drawings, like reference numerals refer to like
parts.
DETAILED DESCRIPTION
FIG. 1 illustrates a mine constructed according to the principles
of this invention. As provided in practice of this invention
according to a preferred embodiment, there is provided a
cylindrical plastic container 10 which may, for example, comprise
an open-ended polyethylene cylinder about 8 7/8 inches tall and 4
3/4 inch diameter, having a wall thickness of about 0.17 inch.
Inside the bottom of the plastic container 10 is a circular bottom
end plate 11 which may, for example, be a one-half inch thick
aluminum plate. Although pure aluminum is preferred, it will be
apparent that aluminum alloys and other similar materials such as
copper, malleable iron and similar ductile materials can also be
employed as the bottom end plate 11. At the top of the plastic
container 10 there is provided a circular top end plate 12 having a
flange 13 at the periphery thereof for setting on top of the
plastic container 10 and closing the upper end thereof. The top
plate 12 is preferably a one-half inch aluminum plate substantially
the same as the bottom end plate 11.
Inside the plastic container 10 is a fuel 14 discussed in detail
hereinafter. The fuel 14 preferably comprises napthalene or may
also comprise, as discussed hereinafter, napalm, finally divided
polyethylene, dioxane, aviation gasoline, jet fuel, or other
hydrocarbons or red phosphorous or other materials pointed out
hereinafter.
Surrounding the sides of the plastic container 10 is a
substantially continuous layer of high explosive 16 about
three-eighths inch thick. The layer of explosive 16 can comprise,
for example, RDX (cyclotrimethylenetrinitramine) or PETN
(pentaerythritol tetranitrate) in a conventional flexible binder.
Such an explosive is readily available commercially from E. I.
duPont de Nemours, Wilmington, Del., under the trademark Detasheet.
It will be apparent to those skilled in the art that many other
kinds of high explosives can also be employed for the explosive
layer 16 such as tetryl, TNT, or conventional military high
explosives. At the bottom of the explosive layer 16 there are
provided four conventional detonators 17 equally spaced around the
periphery of the cylindrical mine. An individual strand of
conventional timed fuse or Primacord 18 is connected to each of the
detonators 17. The four strands of Primacord 18 are in turn
connected to a single detonator (not shown) which can, for example,
be an electric detonator fired from a control point. The four
strands of Primacord 18 are each cut to a uniform length so that
each of the detonators 17 is simultaneously initiated. If desired,
a weather-proof plastic or metal cover can be provided over the
mine for protection, camouflage and the like as will be apparent to
one skilled in the art.
In use of a mine as described and illustrated, it may be placed on
a defensive perimeter, for example; and upon recognition of
approach of enemy personnel, the mine can be detonated from a
control point by applying an electric signal to the electric
detonator (not shown) which ignites the strands of Primacord 18
which in turn initiate the detonators 17. The detonators 17 in turn
initiate the explosive 16 which causes a substantially cylindrical
shock wave to be propagated through the fuel 14 towards the center
of the cylindrical mine. As the shock wave travels inwardly through
the fuel, it is reinforced by its convergence. The high velocity
shock wave ejects the fuel 14 radially outwardly, that is, in a
direction normal to the shock wave and opposite to the direction of
travel of the shock wave. Such a dispersion of the fuel 14 can be
termed as implosion wherein the fuel is subjected to a converging
shock wave from the exterior. This is contrasted to explosive
dispersion wherein the fuel is dispersed by a centrally located
explosive and is dispersed partly by an expanding shock wave and
partly by action of expanding combustion products. The passage of a
high energy shock wave through a material accelerates the material,
and in an implosive device, the presence of relatively unyielding
material all around any given element of material causes a net
ejection of the material in an outward direction. By adapting this
principle in the practice of this invention, the effectiveness of
ordnance devices is vastly improved.
The front of propagation of the converging shock wave through the
fuel is not completely cylindrical since the explosive is initiated
at one end and the propagation velocity of detonation through the
explosive is in the order of 6,000 meters per second and the shock
wave velocity through the fuel may be in the order of 3,000 meters
per second for liquid fuels and may be considerably smaller for
other fuels, such as porous solids. This would indicate that some
of the fuel will be ejected in upward and downward directions from
the mine upon explosion thereof.
It is apparent, however, that most military targets, particularly
for mines, involve men and materiel which are within a few feet of
ground level and any of the weapon effects directed upwardly are
essentially wasted. It is for this reason that the end plates 11
and 12 are provided on the mine described and illustrated in FIG.
1. The end plates are appreciably reflective to the shock waves
since aluminum has a very substantial impedance mismatch with
substantially any material forming the fuel and shock waves are
therefore reflected therefrom. The reflected shock wave causes the
shock wave traveling through the fuel to behave in a manner similar
to what would be obtained if an infinite column of fuel and
explosive were exploded. It is for this reason that a substantial
quantity of the fuel is ejected radially from the mine and a
relatively small quantity of fuel is ejected longitudinally, that
is, upwardly or downwardly. The end plates, particularly the top
end plate 12, also assist in ejecting fuel radially since a
substantial pressure is generated in the interior of the fuel due
to the surrounding explosive 16, and the inertial properties of the
end plates prevent the fuel from traveling longitudinally and,
instead, cause it to be dispersed radially.
According to another significant feature of the invention an
igniter may be incorporated in the explosive device illustrated in
FIG. 1 in order to assure that adequate ignition energy is
available within the cloud of disseminating fuel at whatever time
after the beginning of dissemination the cloud enters the detonable
region. With this arrangement the described criticality of power
level of the explosive may not be required. The igniter herein
described initiates combustion substantially at the same time as
the fuel is disseminated in the cloud by disseminating high
temperature igniter particles together with the disseminating fuel
cloud and there is no reliance on secondary sequential igniting
sources. Thus, in a preferred embodiment as illustrated in FIG. 1,
the igniter takes the form of a centrally located tube 6 whose
symmetry axis coincides with the axis of the container 10. The tube
6 is filled with a mixture of reactive materials 7, hereinafter
described, which is highly exothermic. A plastic cap 8 is provided
at the upper end of the tube 6 containing the reactive mixture or,
if preferred, a plug or a closed end tube can be employed. At the
lower end of the tube 6, there is provided a rubber or similar plug
9 embedded in a shallow recess in the bottom plate 11. The rubber
plug 9 provides a loose closure of the tube 6 to prevent mixing of
the fuel 14 with the reactive mixture 7. In the case of liquid
fuels, the tube 6 can be sealed by the end covers 8 and 9,
respectively. It is preferred that the tube 6 be constructed of a
frangible material, such as Micarta, or other brittle plastic, or
glass or the like can be employed.
As hereinabove mentioned, one of the problems with prior art FAX
type weapons is the timing of ignition in order to assure
detonation in the disseminated cloud of fuel vapor. It is also
significant that the means for initiating detonation in the cloud
of disseminated fuel be contained within the cloud at the time it
is desired to initiate detonation. Thus, if a sequential detonator
is employed, it may be ejected from the cloud prior to the time at
which detonation is desired and be quite ineffective. The igniter
provided in the practice of this invention is contained within the
fuel cloud for several milliseconds after initiation of
dissemination, thereby assuring detonation at whatever time a
detonable composition is reached. Such a result is obtained by
providing a substantial number of initiation or ignition sources
within the cloud, said sources having a spectrum of velocities so
that it is assured that at least some of the igniting sources are
within the cloud when a detonable mixture is attained.
It is therefore a broad function of the preferred igniter to
provide a source of a plurality of high velocity, high temperature
particles within the fuel cloud. The general means for providing
such ignition sources is the positioning of reactive materials 7
which are highly exothermic in an intimate mixture in such a
position in the explosive device that a high energy shock wave is
passed therethrough. In the preferred embodiment, the converging
shock wave from the explosive 16 shatters the frangible tube 6 and
converges through the reactive materials 7. The passage of the high
energy shock wave therethrough initiates a chemical reaction
between the intimately mixed reactive materials, fragments the
products of the reaction, and imparts momentum to the products of
the reaction so that they acquire an outward velocity within the
cloud of disseminated fuel. Since the imploding shock wave is the
same one as has just disseminated the fuel 14 in a dispersing
cloud, the initiation of the igniter is substantially simultaneous
with initiation of dissemination.
The reactive materials of the igniter are preferably contained in a
frangible holder or tube in order to obtain a wide dissemination of
relatively small fragments. If a malleable or otherwise resilient
tube is used to contain the reactive materials a substantial
portion of the products of the reaction may be trapped within a
compressed or squeezed container in such a manner that the entire
mass moves relatively slowly through the cloud. Thus, for example,
when an aluminum tube was employed to contain the reactive mixture
a large white, hot portion of the tube was seen being ejected from
the fuel cloud. If it is desired to introduce an ignition source
with a substantial delay time a malleable or resilient tube may be
employed. By appropriately sizing or shaping the containing device
or tube substantial sizes of hot mass may be emitted which have
delay times within the volume of the cloud in the order of 500
milliseconds. Frangible tubes are, however, preferred for quick
introduction of a high number of hot ignition particles. Glass as
well as plastic materials such as hard phenolics which exhibit
brittle characteristics may be employed.
The mixture of reactive materials 7 in the igniter preferably
comprises a compound AB and an element C which undergo an
exothermic reaction of the type AB + C = AC + B. In particular,
these reactions are typified by the Goldschmidt reaction wherein a
stable metal oxide is mixed with a metal. In this type of reaction,
the second metal replaces the metal in the compound with the
liberation of considerable heat which elevates the reaction
products of metal oxide and metal to an elevated temperature. A
familiar example of this type of reaction is the so called Thermit
reaction in which finely divided iron oxide and aluminum are caused
to react to produce high temperature aluminum oxide and molten
iron. In order to be useful in an igniter, the quantity of heat
generated by the reaction must be sufficient to elevate the
reaction product to a temperature substantially in excess of the
temperature required to cause ignition of the fuel-air mixture.
When aluminum is the element C in the reaction of AB and C, the
metal oxide, in which B is the metal and A is oxygen, may comprise
one or more of the oxides of copper, cobalt, nickel, chromium,
manganese, zinc, and the like as well as iron. When the element C
is magnesium, zirconium oxide can also be employed and, as will be
apparent, when the metal C is sodium, potassium barium, calcium, or
similar highly active material, many other metal oxides AB can be
employed.
By the choice of metals B and C, in the reactive chemical mixture,
metallic particles of B and compound AC provide for variations in
the velocity with which such particles are emitted. A choice of
high density material in the product of reaction results in the
arrival of the fragments of reaction product at any given radius in
the fuel cloud later than fragments of a low density material.
Thus, for example, relatively light weight fragments of aluminum
arrive at a given radius sooner than heavier density particles of
copper. Thus the choice for a selected explosive thickness and
geometry permits an adjustment of the time at which hot metal and
metal compound fragments arrive at a substantial distance from the
point of origin. Inherent in this selection of materials is the
ability to control the time at which ignition sources are presented
to some substantially large fraction of cloud mass.
The hot, metallic fragments are preferably selected so as to
preclude chain stopping. Certain elements are known to have an
affinity for organic radicals such as, for example, sodium. The
sodium may react directly with organic radicals and limit
combustion thereof with air and hence lower the yield of a FAX type
weapon. Thus, the free metal produced in the ignition source should
avoid a type which energetically engages in reactions with organic
radicals typical of chain stopping. Among the materials
satisfactory from this standpoint, cobalt, nickel, zinc, chromium,
copper, iron and manganese, are examples. The selection of
materials not acting as chain stoppers can be of significance since
a substantial portion of f the free metal after the reactive yield
may be at sufficiently elevated temperatures to be in the vapor
form and as such, reactivity with organic radicals is particularly
high.
Preferred materials to employ in the igniter comprise an intimate
mixture of copper oxide and aluminum or an intimate mixture of
magnesium and zirconium oxide all in a size range of about 100
microns. Copper oxide and aluminum is a desirable mixture since the
reaction products, aluminum oxide and molten copper, have favorable
temperatures and densities after reaction and provide a good
spectrum of particle velocities. The magnesium and zirconium oxide
mixture is also preferred since one of the reaction products is hot
metallic zirconium which additionally reacts with the nitrogen,
oxygen, and water vapor in air in order to produce additional
thermal yield. In addition to the metal oxides, it will be apparent
to one skilled in the art that combinations of metal and metal
halide, such as sodium and aluminum chloride or magnesium and
copper chloride, can also be employed. Similarly, ammonia
compounds, sulfides, nitrides, borides, carbides, hydrides,
phosphides, peroxides and the like can be employed in the practice
of this invention so long as the free metal is substantially more
electropositive relative to the anion than is the metal originally
compounded therewith. Thus, for example, a mixture of barium
peroxide and magnesium provides a highly exothermic reaction that
is relatively easily initiated. Calcium carbide is an inexpensive
and useful material.
In general it is preferred to employ a stoichiometric mixture of
the reactive materials so that a maximum temperature is obtained.
It may be desirable in some instances to introduce a substantially
inert material in the igniter mixture so that more massive
fragments are ejected at a somewhat lower temperature. This effect
may be obtained, for example, by incorporating an excess of one of
the reactants in the mixture. If excess aluminum is mixed with a
metal oxide, molten aluminum is produced and ejected. The presence
of inert materials may also slow the reaction and make the
fragments of igniter material persist at elevated temperature for a
longer time. In order to initiate reaction of the reactive mixture
7, it is preferred that the materials have controlled voids
therein. Thus, they may be in the form of fine powders or similar
arrangements so that a substantial amount of gas filled void space
is provided in the mixture. The gas filled voids act in
substantially the same manner as the gas filled voids hereinafter
described in relation to powdered fuels. Broadly the gas is heated
to an elevated temperature by passage of the shock wave
therethrough and the hot gas, in turn, heats the reactive
materials. Goldschmidt type reactions employing metals and metal
oxides are relatively slow to start and propagate under usual
conditions since there is a substantial requirement for sensible
heat for elevating the temperature of the reactants to a point
where the reaction can commence. Such a difficulty was noted, for
example, in Thermit type incendiary bombs wherein it was required
to initiate the reaction in the Thermit upon impact of the bomb and
after an appreciable time to permit thorough reaction, explode a
center burster for scattering the burning Thermit mixture. By
employing a substantial amount of gas filled void spaced within the
reactive mixture in the practice of this invention and providing
means for passing a high energy shock wave through the gas filled
voids, there is provided a means for elevating the temperature of
the entire reactive mixture to a temperature at which the reaction
can commence. There is, then, substantially no time lag between
initiation of the reaction and propagation thereof throughout the
entire reactive mixture.
It is found with fine, dense powders, such as a metal and metal
oxide, that there is relatively dense packing and a relatively
small amount of gas filled void space is left between the
individual particles. This is, in part, also due to the spectrum of
particle sizes occurring in these powders which contributes to
dense packing. It is therefore preferred that a controlled
proportion of extra void spaces be specially provided in the
reactive mixture for promoting the initiation of reaction thereof;
that is, voids that are in addition to the small gas filled voids
between particles of the mixed powders. Reaction can be initiated
by addition to the reactive mixture of controlled voids in the form
of small, hollow particles such as the so called microspheres which
comprise hollow spheres of plastic such as phenolic resin or the
like. Similarly, controlled gas voids can be provided by plastic
foams, glass foams or other materials having a substantial gas
volume therein. It is preferred that the controlled void space
within the reactive mixture be in the range of about from 5 to 35
percent of the volume of reactive mixture; in addition to the
inherent void space between the particles of powder, and it is also
preferred that the gas filled extra voids be in the size range of
from about one one-hundredth to one-fourth inch in order to assist
in fragmentation of the reactive mass. In order to provide ignition
sources throughout the expanding cloud of fuel in a preferred
embodiment, it is desirable to fragment the reactive mixture into
substantial particles or clusters of powder grains which are at
elevated temperature during their transition through the cloud of
fuel. This assures a distribution of ignition sources within the
cloud, both in space and in time, so that an ignition source is
assuredly available at the time the cloud reaches a detonable
mixture.
Thus, for example, a suitable igniter employs a mixture of copper
oxide and aluminum or magnesium oxide and zirconium with about 10
to 20 percent of additional void space provided in the form of
organic foam. Typical foam particles are in the order of about 3/16
inch diameter and may comprise, for example, bits of Styrofoam
(polystyrene foam), epoxy bubbles, polyethylene foam, or heat
expanded rice granules (Puffed Rice) which are uniformly mixed
within the mixture of reactive powders. When such particles of foam
are distributed approximately uniformly in the reactive powders,
the particles are on approximately 1/2 inch centers and since
fragmentation of the mixture generally occurs through the foam,
fragments of reactive mixture having sizes in the range of from
one-fourth to one-half inch are produced. It should be recognized
that when fragments of the mixture are provided, these comprise
large clusters of the reactive powders, possibly sintered together
by the extreme temperatures and pressures of the shock wave, along
with reacting materials and the products of the reaction which are
heated to an elevated temperature. Similarly pressed pellets of
reactive mixture can be employed with the inherent large void space
therebetween. This also permits good control of fragment size. It
is found that upon ejection of such fragments from an igniter as
provided in the practice of this invention, the particles are at an
intense white heat.
Thus, controlled void spaces filled with gas are provided within
the mixture of reactive powders for providing "hot spots" within
the mixture of reactive powders, and these hot spots provide
sources of ignition for the reactive mixture in case reaction does
not commence within the main bulk of the reactive mixture due to
dense packing of the powders. The controlled voids also serve to
promote fragmentation of the reactive materials in a controlled
manner for providing a selected particle size. Fragmentation in a
controlled manner and ignition hot spots can also be obtained by
using hollow, frangible tubes or the like within the reactive
mixture in lieu of the foam particles hereinabove described.
The fragments of reacting mixture, preferably in the size range of
from about one-fourth to one-half inch, are ejected from the
igniter so as to pass through the expanding cloud of fuel at high
velocity. Since there is a spectrum of fragment sizes of reacting
mixture which are acted upon by the converging shock wave, these
fragments have a spectrum of velocities. Generally speaking,
smaller size fragments have higher velocity than larger size
fragments of similar material and fragments nearer the center of
the converging shock wave may have somewhat higher velocity than
fragments further out in the igniter. It has been found that hot
fragments from the igniter are ejected from the surface of an
expanding cloud of fuel of the size provided by a mine as described
and illustrated in FIG. 1, throughout the time interval from 10 to
50 milliseconds after initiation of dissemination of the cloud.
Thus, it is assured that the distribution of hot fragments in time
and hence in the space of the cloud assures the presence of a
plurality of ignition sources within the cloud at whatever time the
cloud of expanding fuel enters the detonable region.
The fragments of igniter mixture apparently have a lower initial
velocity than the fuel forming the disseminating cloud due to the
heavier fragments which must be accelerated. However, because the
fragments of igniter mixture are heavy they tend to remain at high
velocity longer than the light droplets and vapor of the fuel.
Thus, although the fragments are initially slower, the fuel is
slowed by drag and the fragments eventually emerge from the cloud.
In practice, a number of white hot "sparklers" are seen emerging
from the cloud of fuel about 10-15 milliseconds after initiation.
The emergence of new sparklers continues for at least an additional
40-80 milliseconds thereafter. The continued presence of hot
fragments in the cloud assures detonation thereof when a detonable
mixture is reached.
The advantages of imploding the reactive mixture as compared with
an explosion thereof by means of a center burster of explosive are
impressive. Thus, in the implosion of an igniter as provided in the
practice of this invention, the entire reactive mixture is heated
to an elevated temperature due to passage of a high energy shock
wave through gas filled voids amongst the particles thereof. In
addition, the implosion compresses and possibly coalesces the
mixture of powders. In addition, when controlled void spaces, as
provided by foam particles or the like, are present, hot spots are
generated in the igniter for deliberately initiating the reaction
at specific locations within the mixture. The imploding shock wave
also fragments the mixture of reactive powders at the void
locations so that the fragment size of reacting material is
controlled. These particles are finally ejected at a spectrum of
high velocities to provide ignition sources within an expanding
cloud of fuel.
Explosive type of dissemination of a reactive mixture, on the other
hand, may heat a small amount of the mixture to an elevated
temperature sufficient to initiate reaction. No substantial amount
of heating is obtained, however, by the shock wave alone as
evidenced by the relatively poor performance of Thermit type
incendiary weapons employing a center burster. In addition, an
explosive dissemination of the reactive mixture tends to separate
the individual particles of reactive mixture so that no reaction
therebetween can occur. Even if the individual pieces of powder are
not disseminated, the fragment size of the mixture is relatively
small when explosive dissemination is employed and few of the
fragments may be undergoing reaction.
The reason for the lack of heating of the reactive mixture and the
small fragment size may lie in the relatively short time that an
expanding shock wave acts on the reactive mixture as compared with
the relatively longer dwell time of the reactive mixture within the
influence of an imploding shock wave. With an exploding or
expanding shock wave, the material is ejected at substantially the
same time it is undergoing heating to initiate reaction, whereas in
the imploding shock wave situation as provided in the practice of
this invention, the shock wave first acts to heat the reactive
mixture and a very short time thereafter causes ejection thereof.
This dwell time, even though short, gives sufficient time for
heating of the reactive mixture and the initiation of reaction
thereof. The strength or energy of the shock wave in the implosion
is continually increasing due to convergence thereof, thereby
giving high heating rates. The explosion shock wave, on the other
hand, is diverging and losing energy per unit area as the square of
the distance from the point of initiation, and therefore the energy
available to impart to the reactive mixture is continually
decreasing.
The fuel contained in the mine of FIG. 1 or an aerial bomb or
similar explosive device of similar construction can be in one or
more of two classes of material. The first class comprises
materials normally subject to explosive reaction or detonation when
mixed with air and ignited. Typical materials in this class include
conventional aviation gasoline, pentane, hexane, octane, benzene,
and similar materials forming explosive compositions when mixed
with air. It is preferred that the heat of combustion of such
materials be greater than about 750,000 BTU per cubic foot of fuel.
When the energy available from combustion of the fuel is in this
order of magnitude or greater, a reasonable effect can be obtained
from an explosive device having a useful volume. It is found that
the measure of heat of combustion in terms of the volume of fuel
available is a more useful measure than the heat of combustion per
unit weight since the limiting factor in many military ordnance
devices is volume rather than weight. Gasoline is a particularly
desirable fuel since the explosive devices can be loaded in the
field rather than requiring preloading.
A second class of fuel materials comprises compounds not normally
detonable, having relatively longer chains or larger numbers or
rings that are broken into relatively shorter chains or smaller
molecules which form detonable mixtures with air after being
subjected to the pressures and temperatures associated with the
high energy shock waves provided in the practice of this invention.
An example of such material is acetaldehyde which is apparently
decomposed upon passage of a shock wave therethrough into molecules
of methane and carbon monoxide and possibly other molecular
fragments which are highly explosive when disseminated in air.
Another highly useful material in this class is, for example, solid
naphthalene which has a heat combustion of about 1,200,000 BTU per
cubic foot, but which is not readily detonable in air. Upon passage
of a shock wave through naphthalene, the relatively larger
molecules are apparently broken into many smaller molecular
fragments of the decomposed ring structure, and probably free
radicals which are extremely reactive due to the deficiency of
hydrogen. As a matter of fact, one of the highest yields obtained
in FAX-type ordnance devices constructed according to the
principles of this invention is obtained with naphthalene as the
fuel and with a layer of explosive around the naphthalene greater
than about one-fourth inch. The advantages of a solid fuel as
compared with a liquid in an ordnance device are apparent.
Another particularly valuable fuel for use in such a device
comprises polyethylene which upon passage of a high energy shock
wave therethrough under suitable conditions, is broken into shorter
chain lengths comprising ethylene and short chains of polyethylene,
all of which have broken chain ends which are highly reactive.
Polyethylene is a particularly desirable fuel material because of
its substantial inertness for handling before explosive
decomposition thereof, and because of the high energy available. It
is found that polyethylene gives effects substantially as good as
naphthalene.
Decomposition of longer chains into shorter chains upon application
of shock wave energy is a completely reasonable phenomenon. Thus,
it would appear to fit within a class of decompositions of very
complex molecules already known. Thus, for example, complex
molecules can be broken or decomposed by the application of
ultraviolet radiation. Application of a very small pulse of energy
in an extremely short period of time as represented by a photon of
ultraviolet applied at the speed of light is known to break complex
molecules. Similarly, statistical application of energy to complex
molecules over relatively longer periods of time is provided in
conventional petroleum cracking, wherein long and complex molecules
are subjected to elevated temperature and pressure and undergo
cracking. It would appear that the application of high energy by
means of a shock wave fits somewhere in between decomposition by
photons and thermal cracking. The decomposition of molecules
therefore includes ultraviolet decomposition wherein a small energy
is added within an extremely short period of time, a shock wave
wherein a much larger pulse of energy is added in a somewhat longer
period of time, and thermal cracking wherein a substantial energy
is added over a very long period of time.
An explosive shock wave generated by high explosives can be
represented as a wave of pressure as a function of time at a given
arbitrary location within a material through which the shock wave
passes. It is the nature of a shock wave that at the given location
the pressure virtually instantaneously rises to a high peak and
thereafter exponentially decays to approximately the original
pressure in a total elapsed time measured in microseconds. In
general, the peak pressure generated is independent of the
thickness of explosive employed, however, the shape of the decay
curve following the peak is a function of the thickness of high
explosive generating the shock wave. As the thickness of the
explosive increases the time that the pressure remains near the
peak is prolonged, and the time to which an element of material
through which a shock wave passes is subjected to the highly
energetic condiditons of the shock wave is also prolonged.
Thus, it has been found that by increasing the thickness of high
explosive surrounding a fuel above about one-quarter inch the fuel
is subjected to elevated pressure for a sufficient time that
thermal decomposition of organic molecules may occur. Although for
purposes of discussion the shock wave can be considered as a
pressure peak this is merely a manifestation of the energetic
conditions in the shock wave which include high temperatures and
rapid viscous shearing of the matter through which the shock wave
is passing. In addition to the increased time interval for transit
of the shock wave due to the thickness of explosive there is also
an increased time interval in an implosive arrangement due to the
transit of the shock wave into the fuel from the surrounding
explosive and return of the shock wave back out again after
reaching the center, which at least effectively doubles the time of
exposure to the elevated pressure and other energetic
conditions.
In the usual arrangement the increase in thickness of high
explosive does not increase the peak pressure obtained by a shock
wave but only influences the decay of pressure after the passing of
the peak. The peak height is determined only by the nature of the
explosive employed. In an imploding shock wave situation, however,
the peak pressure increases due to convergence of the shock wave as
the wave travels inwardly. As the peak pressure increases due to
convergence of the shock wave the velocity at which the leading
edge of the shock wave travels also increases. The pressure pulse
behind the shock front does not increase in velocity in the same
manner as the leading edge of the shock wave and this further
contributes to the time an element of matter through which the
shock wave is passing is subjected to the energetic conditions of
the shock wave in an imploding situation.
If mathematical wave equations are applied to the situation of a
shock wave converging through a material several possible
mathematical solutions for the transit time of the shock front
through a fuel to the center and back out again are obtained. In
one of these mathematical solutions the transit time from the
exterior of the fuel to the center and back out again is
substantially independent of the radius of the fuel within the
explosive when the explosive thickness is in excess of about
one-quarter inch of high explosive. Although it is not certain that
this mathematical solution is applicable to the imploding
situation, it is certainly plausible. Evidence that it may be
applicable is found in the fact that substantially similar effects
are noted when the explosive thickness is in excess of about
one-quarter inch when the diameter of the FAX type weapon is about
4 3/4 inches and when the FAX type weapon is as large as 15 inches
in diameter.
Other evidence of the criticality of an explosive thickness in
order of about one-fourth inch is from an examination of the cloud
diameter at a selected time after detonation of the explosive.
Thus, if the cloud diameter at 5 milliseconds after initiation of
the explosive is examined, it is found that there is a regular
increase in cloud diameter with increase in explosive thickness up
to about one-fourth inch; however, above about 1/4 inch up to about
3/8 inch explosive thickness, an increase in cloud diameter of only
about 5 percent is noted. Since at least 50 percent additional
energy is available due to the increased explosive thickness, and
there is no appreciable increase in cloud diameter, it is
reasonable to assume that the excess energy is expended in
decomposition of complex organic molecules in the fuel.
Although the critical limit of explosive thickness has been
determined to be about one-fourth inch it is particularly preferred
that the explosive surrounding a stable fuel in an imploding FAX
type weapon be in the order of about three-eighths inch so that a
substantial margin of surplus explosive is present to assure the
presence of the effect under all conceivable conditions in which
the explosive device might be employed.
It is found that the mere passage of shock waves through massive
pieces of polyethylene and similar solid materials may not be
sufficient to initiate the chemical changes hereinabove indicated.
The breaking of the complex chemical molecule into simpler
substances is an effect which may be obtained by proper combination
of elevated temperature and elevated pressure. In order to obtain
extreme elevated temperatures in many solids, it is preferable to
provide the solids as porous materials having controlled void
spaces therein and having air or other gas in the voids. The
passage of the shock wave through the gas in the voids raises the
gas to an elevated temperature which persists after passage of the
shock wave therethrough.
If it is considered that a small element or particle of the solid
fuel is substantially completely surrounded by a film of gas, the
shock wave passing therethrough heats the gas to an elevated
temperature and presents a boundary condition on the fuel particles
which is essentially a step function wherein the particle is
suddenly exposed to temperatures of 2,000.degree.F or more
depending on the wave velocity, gas viscosity, and similar factors.
As is well known, any solid material has some thermal lag when
subjected to an elevated temperature environment, that is, there is
a certain time interval for a pulse of heat to pass from the
outside to the center of the particle of solid fuel as the
temperature suddenly increases at the boundary. The time interval
is inversely proportional to the radius of the particle, squared.
Thus, as the particle size or the distance separating adjacent gas
films becomes increasingly smaller, the thermal lag or time
constant for the thermal pulse to reach the center of the solid
material becomes very short. Thus, a small particle is rapidly
heated to the temperature of the gas within the boundary between
the particles. When the individual particles of solid fuel are
extremely small, any chemical changes due to thermal and pressure
effects occur rapidly since the necessary temperature elevation is
substantially concurrent with passage by the shock wave or
generation of high pressure, and very rapid thermal decomposition
of complex molecules can occur. When massive solids or large
particles are used, the temperature pulse may lag the pressure
pulse within the solid and conditions may not be proper for
decomposition of relatively stable molecules such as
polyethylene.
In the instance of solid fuel materials, a suitable arrangement
comprises fine powders, or a foam structure of coalesced material
can be employed. If desired, the fine particles which are
preferably spherical powders can be sintered in order to provide a
substantially solid mass of material. In any event a porous solid
is preferred wherein the thermal lag between the boundary of the
gas and the center of the particle is relatively low. It is
apparent that solid non-porous masses of some materials, such as
naphthalene, which are decomposed by transition of the shock wave
therethrough can be employed. It should also be noted that sintered
pellets of powders can be employed in substantially the same manner
as hereinabove described in relation to the igniter.
Typical examples of materials decomposable into detonable molecules
or molecular fragments include: propane, butane, pentane, hexane,
heptane, octane, nonane, decane, undecane, dodecane, ethylene
oxide, polyethylene, propylene oxide, polypropylene, polystyrene,
styrene, butene, butadiene, isobutylene, pentene, hexene, heptene,
octene, ethylacetylene, acetylene, dimethyl-acetylene, pentine,
methyl butine, hexine, benzene, toluene, naphthene, ethyl benzene,
propyl benzene, butyl benzene, xylene, mesitylene, mesityl oxide,
cumene, pseudocumene, indine, naphthalene, methyl naphthalene,
diphenyl, acenaphthalene, fluorene, phenanthrene, anthracene,
fluoranthene, pyrene, benzpyrene, chrysene, naphthacene, pyridine,
picoline, quinoline, quinaldine, indole, acridine, carbozole,
allylbenzene, stilbene, diphenylmethane, triphenylmethane,
tetraphenylmethane, terphenyl, camphor, methyl alcohol, ethyl
alcohol, propyl alcohol, butyl alcohol, amyl alcohol, hexyl
alcohol, phenol, benzyl alcohol, diethyl ether, methyl ethyl ether,
dipropyl ether, diphenyl ether, methyl phenyl ether, dioxane,
methyl butyl ether, ethyl butyl ether, dibutyl ether, diamyl ether,
dihexyl ether, divinyl ether, tetrahydrofuran, acetaldehyde,
benzaldehyde, propionaldehyde, butyraldehyde, valeraldehyde,
acrolein, crotonaldehyde, benzaldehyde, furfural, acetone, methyl
ethyl ketone, methyl propyl ketone, diethyl ketone, hexanone,
methyl butyl ketone, dipropyl ketone, dibutyl ketone, diamyl
ketone, chloracetone, methyl amine, dimethyl amine, trimethyl
amine, ethylamine, diethylamine, triethylamine, propylamine,
dipropylamine, tripropylamine, butylamine, amylamine, hexylamine,
ethylene diamine, trimethylene diamine, allylamine, aniline,
acetamide, propionamide, bensamide, nicotinonitrite, flour,
glucose, fructose, sucrose, lactose, maltose, cellulose (such as,
for example, cotton, sawdust, straw, paper), dioxane, butyric acid,
isovaleric acid, caproic acid, caprylic acid, capric acid, lauric
acid, myristic acid, palmitic acid, stearic acid, paraffin,
charcoal, coconut oil, palm oil, oliver oil, castor oil, peanut
oil, corn oil, rape oil, beef tallow, lard, whale blubber,
cottonseed oil, soybean oil, tung oil, linseed oil, gasoline,
kerosene, jet engine fuel, bunker oil, gas oil, lubricating oil,
petroleum ether, mineral spirits, heavy ends from petroleum
refining, asphalt, waxes, lacquer, napalm, furan, ethyl nitrate,
furfurol, ethyl cellulose, nitromethane, nitrobenzene,
dinitrobenzene, nitroethane, nitropropane, nitrobutane,
nitropentane, light oil, carbolic oil, creosote oil, anthracene (or
green) oil, pitch, fusel oil, starch, polyvinyl chloride, polyvinyl
alcohol, epoxy polymers, mercaptons, and glycol, including cyclic
and branched chains, polymers, and saturated and unsaturated
isomers thereof, nitrate, ammonia, sulfhydride, and cyanide
substitutions thereon and heterocyclic chains with nitrogen,
oxygen, phosphorus, and sulfur.
It has been found that in addition to the hydrocarbon fuels
hereinabove described that red phosphorus, boron, and calcium make
excellent fuel materials when employed in an implosive type
ordnance device. Red phosphorus is particularly advantageous since
it is normally a stable material difficult to ignite and normally
of little use in military munitions. Phosphorus, however, can be
allotropically transformed into what is known as white phosphorus
which provides an effective military munition since white
phosphorus reacts rapidly and exothermically with air. White
phosphorus munitions are well known and widely used but may be
difficult to handle because of the high reactivity of white
phosphorus with air. It is found that red phosphorus when subjected
to high dynamic pressure as obtains in the implosive type device
herein described and illustrated, converts to white phosphorus.
After release from the transient high pressure environment in the
implosion, the white phosphorus produced tends to convert back to
the red form, however, the vigorous ejection by implosive
dissemination permits the white phosphorus to react with air prior
to the completion of the transition back to the red phosphorous
state. The incendiary and obscuration effects of white phosphorus
are thereby obtained with implosive dissemination when normally
stable red phosphorus is employed as the fuel.
In order to obtain a maximum effectiveness of the cloud of fuel
prior to ignition thereof in the prior art FAX weapon, the fuel is
disseminated to substantially the optimum cloud size and detonation
is then initiated in the fuel.
When a combustible fuel is mixed with air, there is a certain range
of concentration of dispersed fuel in the air that is combustible.
This concentration can be expressed, for example, as the ratio of
the weight of air to the weight of fuel dispersed therein. For a
typical hydrocarbon such as gasoline, for example, the ratio may
run from slightly above 0 to about 25 parts by weight of air per
part of fuel by weight and combustion may occur throughout that
region. Encompassed within the region of combustion for a typical
hydrocarbon, there is often a so-called detonation region or ratio
which for a typical hydrocarbon, such as gasoline, may run from a
ratio of about 10 to about 16 parts by weight of air per part by
weight of fuel.
When the concentration of fuel dispersed in air is outside of the
combustible region, no burning occurs and a stable flame is not
maintained. When the concentration is within the combustion region,
the fuel chemically combines with air with the liberation of
energy. The rate of propagation of a flame through the mixture is
subsonic in the combustion region, and the flame is accompanied by
chemical intermediates, combustion products, and the like that
cause the reactions which are typically combustion to occur. In the
detonation region, the rate of propagation of the reaction through
the mixture is supersonic, that is, higher than the acoustic
velocity in the explosive material. This creates a shock wave
characterized by a steep pressure rise with accompanying
temperature rise followed by a fall in pressure. The sharp increase
in pressure and temperature at the shock wave causes the chemical
reaction to proceed, thereby adding energy to sustain and augment
the shock wave.
The usual high-explosive source of over-pressure in conventional
explosive devices is essentially a point source (or relatively
small volume) of a detonation which causes a shock wave to
propagate radially outward. The traveling shock wave is slowed down
in passing through the air because of various losses such as
conductivity, viscosity of the air, and the like. After the shock
wave has passed a sufficient distance from its starting point, its
propagation velocity is subsonic, and at this point there is no
longer any over-pressure. It is apparent that increasing the weight
of high explosive causes initially higher over-pressure to be
generated. However, at a short distance from the explosive the
influence of increased weight is realizable only by the cube root
of the increased weight. Thus, to generate very high over-pressure
at any substantial distance from a detonation, very large weights
of high explosive must be used.
The fuel-air explosive (FAX) weapon, however, differs
substantially. In the FAX weapon a quantity of fuel is distributed
through the air so that the mixture of fuel and air is detonable in
a large volume or cloud. When a detonation is started in such a
cloud, it travels at substantially undiminished propagation
velocity throughout the extent of the cloud. In this manner, large
over-pressures may be generated at substantial distances from the
point of initiation of the dissemination rather than propagated to
substantial distances. Although the maximum over-pressure values at
the center of the detonation are not as large as the maximum value
to be expected from a high explosive, large levels of over-pressure
may be generated over substantial areas, and damage caused over a
larger area than possible with the same weight of high
explosive.
There is a limit to the volume of such a detonable cloud which is
determined by the weight of fuel which is dispersed and the
detonable limits of weights of air to weight of fuel. The detonable
limits are principally determined by the chemical composition of
the fuel being dispersed.
Thus, for example, when gasoline is employed as the fuel the
detonable limit lies between about 10 and 16 parts of air to 1 part
of gasoline by weight. Assuming that the gasoline is uniformly
mixed as a vapor with the air and assuming the specific weight of
air as 0.08 pounds per cubic foot, the range of a cloud size which
would be detonable can be calculated. Thus, the ratio of the weight
of air over the weight of fuel (W.sub.a /W.sub.f) is between 10 and
16 and
W.sub.a /W.sub. f = (D.sup.2 /4 ) .sup.. H .sup.. 0.08/W.sub.f
where D is the diameter of the cloud and H is the height of the
cloud. If it is assumed that the cloud has a height of about 4 feet
and 3 pounds of gasoline are employed, it is found that the
diameter of the cloud is between 10.7 and 13.8 feet for a detonable
mixture. Thus, a cloud between about 5- and 7-foot radius would be
detonable and outside those limits; namely, for larger or smaller
diameters the cloud would burn or if too lean or too rich a mixture
is obtained in larger or smaller clouds, nothing in the way of a
noticeable reaction could be made to occur. It is apparent that if
the process of dispersing a fuel produces a content of dust or
droplets of fuel in addition to vapor, the diameter of the
detonable cloud will decrease from the above-mentioned values.
In prior art FAX-type devices, the cloud is dispersed with
particular care being taken to prevent burning of the fuel during
dispersion and secondary detonators are fired at a carefully
selected time interval after the beginning of dispersion when the
cloud is at the optimal diameter for detonation; that is, the cloud
is at a proper air-to-fuel mixture ratio within the detonable
limits. The secondary detonator approach in prior art FAX weapons
is difficult to put into practice because the growth rate of the
cloud, as well as the detonable limits of the composition, are
dependent on the ambient temperature of the munition as well as the
atmospheric pressure and temperature at the point of detonation.
The extremes of temperature of the fuel between polar and tropical
use and the extremes of pressure between high and low altitude air
are apparent. In order to obtain optimal results, therefore, it is
desirable to have a variable timing arrangement which, for
practical considerations, is difficult in application.
The objection usually presented to cloud burning prior to
detonation involves the loss by burning of a portion of the fuel at
the expense of the total energy available for detonation yield
which is preferred. It is found with an explosive device
constructed according to the principles of this invention that the
fraction of fuel loss by burning is, at a maximum, only about 11
percent. The amount of fuel burned can be calculated from the
equation
where V.sub.c is the combustion velocity, V.sub.g is the cloud
growth velocity, the subscript cr is for combustion rich and the
subscript dr is for detonation rich; that is, the ratio of the
weight of air to the weight of fuel is too rich for combustion or
detonation, respectively.
In an explosive device constructed according to the principles of
this invention, the velocity of cloud growth V.sub.g is made very
large by the use of a layer of high explosive surrounding the fuel.
The explosive causes a converging high energy shock wave to pass
through the fuel thereby dispersing the fuel at very high velocity.
This assures a rapid rate of cloud growth which is relatively
independent of uncontrolled variables such as temperature and
pressure. It is preferred to employ an explosive thickness in
excess of about one-fourth inch and of about three-eighths inch for
an explosive device in the size range of from about 4 to 15 inches
in diameter; below this thickness the velocity of cloud growth is
lower and greater amounts of the fuel are burned prior to
detonation.
Thus, for example, the combustion velocity for a gasoline-air
mixture is in the order of less than 1,000 feet per second. The
detonation velocity of such a mixture is in the order of 5,000 feet
per second, and in an ordnance device constructed according to the
principles of this invention the initial velocity of dissemination
of fuel is in the order of 12,000 feet per second, about an order
of magnitude higher than the combustion velocity. In the prior FAX
type devices the velocity of cloud growth is in the order of 1,000
feet per second or less, that is, about the same velocity as the
combustion velocity and as hereinabove described the dissemination
velocity slows down as the material disseminates.
In an explosive device constructed according to the principles of
this invention, however, due to augmentation by burning fuel
adjacent to the shock front, the high velocity shock wave does not
slow down below the detonation velocity until most of the fuel has
been expended by reaction in a detonation mixture region rather
than by combustion. Optimum over-pressure yield over a large area
is therefore obtained from such an explosive device with minimal
loss of energy due to unwanted combustion. It is found that
reduction in high explosive thickness below about one-fourth inch
for a device about 5 inches diameter causes some reduction in the
over-pressure yield and also in the thermal effects obtained from
the ordnance device.
The thermal effects of this mode of dissemination of fuel can be
compared with conventional napalm type burning weapons. Napalm
employs a hydrocarbon, such as benzene, gasoline, or the like,
which is jelled in order to increase the viscosity so that the
material leaves a substantial smear on surfaces to be burned. The
burning occurs in contact with the surface leading to damage
thereof. The high viscosity also helps to maintain a continuity
between parts of the burning fuel streak in order to assure the
spread of combustion. The burning time in conventional napalm
weapons is in the order of 5 minutes so that substantial heat
transfer occurs over a long time. The surface temperatures achieved
are in the order of 500.degree.F or less.
In one embodiment of an ordnance device constructed according to
the principles of this invention, however, low viscosity materials
are dispersed as a cloud of high velocity droplets mixed with
vapor. Burning is developed throughout a pancake-shaped volume and
extremely high heat flux rates are obtained in the process. Among
other things high speed droplets of low viscosity fuel tend to
penetrate and make a "wick" of a wide variety of materials rather
than clinging to the external surface. Droplets, along with vapor,
burn in the cloud although no target is encountered, thereby
yielding a strong pulse of heat in the cloud with the result that
any target objects are also essentially surrounded by a source of
heat at very high temperature. Thus, even though the burning time
is in the order of a second or less, the energy flux rates are
extremely high and surface temperatures in the order of
1,500.degree.F or higher can be obtained. Temperatures have been
measured inside the flame cloud of a device constructed according
to the principles of this invention by using thermocouples. The
thermocouple surface is driven to temperatures of about
2,200.degree.F in a very short time.
The mechanism of burning of a target occuring with a weapon as
described and illustrated is to a large extent so called flash
burning. This is a damage mechanism wherein burning is due to a
very high heat flux for a short period of time as contrasted to the
low heat flux and long time burning of conventional napalm weapons.
Previously the only weapons giving any appreciable flash burning
have been nuclear devices wherein the intense heat flux from the
fireball causes burning of surfaces exposed thereto. It is found
with a weapon as described and illustrated that the heat flux is
sufficiently high to give flash burning of the nature found with
nuclear devices. Thus the described weapon gives an effect not
previously available from non-nuclear weapons and further gives
blast and fragmentation effects of the same order as prior art high
explosive weapons of comparable size.
In an ordnance device employing a thick layer of explosive
surrounding a fuel, it is hypothesized that initial ignition of the
fuel occurs substantially simultaneously with the dissemination
thereof. That is, there are no requirements for secondary
sequential detonation. The ignition of the fuel simultaneously or
substantially simultaneously with dissemination thereof occurs
because of the high quantity of explosive surrounding the fuel.
This generates a large magnitude shock wave passing through the
fuel which raises the temperature thereof to a regime wherein
reaction occurs when the fuel contacts air. In a FAX type weapon
with a center explosive burster, if initiation of combustion occurs
at the commencement of dissemination of the fuel, the mixture of
fuel with air is too rich, that is, the concentration of fuel is
too high relative to the air to support combustion and it is
definitely too high for detonation so that no explosive effects are
obtained beyond the range of the high explosive itself in the
absence of a secondary detonator. In the weapon described herein,
on the other hand, the periphery of the cloud of disseminating fuel
has a thin zone at which the ratio of the weight of air to the
weight of fuel is within the detonation region. Chemical
combination between the fuel and air therefore occurs in this
region and because of the larger quantity of explosive contained in
the ordnance device herein described, the fuel is traveling at
supersonic velocity during initial dissemination of the cloud.
The hypothesized mechanism of the effect is better understood by
reference to FIG. 2 wherein there is illustrated a plurality of
droplets 19 traveling from left to right. Immediately preceding
each of the droplets 19 by a distance of only a few microns is a
small shock wave 21 since the droplets 19 are traveling at a
supersonic velocity. The shock waves 21 act in concert to provide a
large scale shock wave substantially at the boundary of the
expanding cloud of fuel. As is well known from shock tube
measurements there is a combustion zone about 0.3 to 3.0
millimeters thick behind a shock front traveling through a
detonable mixture.
Examining a single droplet 19 and its associated shock wave 21 as
illustrated in FIG. 3, there will be a combustion region 22
adjacent the droplet 19 wherein the concentration of fuel in the
air is in the region of detonation, that is, the flame propagation
rate is supersonic. The droplet 19 is well within the combustion
region behind the shock front and the combustion region 22 is a
portion of the overall combustion zone of the shock wave. It should
also be noted that the shock wave 21 in traveling through the air
is losing energy due to viscosity of the air, expansion, and
conduction of heat therefrom. Energy is available, however, from
the combustion region immediately behind the shock wave and this
energy augments the energy of the shock wave. It therefore occurs
that an energy balance is present across the shock wave wherein the
reaction yield in the combustion zone is substantially equal to the
shock wave energy losses due to viscosity, conduction, and
expansion. When this balance is present, the shock wave will
continue to propagate at substantially the same velocity instead of
slowing down as energy is dissipated. In a conventional shock wave
without additional energy augmentation, the velocity continually
and rapidly decreases until no shock wave exists. Thus, in the
described device the shock wave is augmented by continually burning
fuel and the flame continues to propagate at supersonic velocity.
This is possible since the droplets of fuel are initially ejected
at a supersonic velocity due to the large quantity of explosive
surrounding the fuel.
It is apparent that combustion of fuel from the droplet 19 in the
combustion zone 22 depletes the quantity of fuel therein due to
high evaporation rate in the high temperature environment of the
shock wave and the droplets 19 are continuously decreased in size.
The droplets 19 are traveling through air or a mixture of fuel
vapor, combustion products, and air with a velocity that gives an
apparent wind direction as shown by the arrow in FIG. 3. This
apparent wind direction aerodynamically drags on the fuel droplets
19 and as the droplets get smaller, the affect of aerodynamic drag
is proportionately larger with respect to the droplet mass and the
droplets slow more rapidly.
It is apparent, however, that not all of the fuel is at the
periphery of the cloud of disseminating fuel since the implosive
shock wave traveling through the fuel from the explosive affects
the fuel at different times. Following the leading droplets 19 as
illustrated in FIG. 2 are a succession of following supersonic
droplets 23 each with its associated shock wave 24. The following
droplets 23 are traveling faster than the droplets 19 adjacent the
shock front since the fuel has not been dissipated therefrom by
combustion and the droplets are therefore larger and not as yet
slowed so much by aerodynamic drag.
Thus, as the droplets 19 (FIG. 2) are depleted by combustion,
additional droplets 23 arrive at the shock front and are in turn
slowed by aerodynamic drag and dissipated by combustion as droplets
19. The droplets 23 following the leading edge of the disseminating
cloud are not burned before reaching the shock front for
substantially the same reason that the fuel does not burn in a
conventional FAX weapon when the ignition is at the beginning of
dissemination of the cloud, namely the mixture within the cloud
behind the front is too rich for combustion. This is the case since
the gases behind the shock front comprise the combustion products
of the fuel, excess fuel vapor, and air that is substantially
depleted in oxygen.
Although it cannot be stated with certainty that the hypothesized
mechanism set forth hereinabove is actually occurring in the
expanding cloud of fuel, it is known that a substantial shock wave
accompanies the expanding cloud of fuel in the above described
weapon and that a very substantial over-pressure is generated out
to substantial distances, thereby giving blast effects as well as a
severe thermal effect due to the combustion zone.
A further hypothesis concerning the mechanism of reaction when a
fuel is subjected to a high energy implosion wherein the implosion
is sufficiently energetic to initiate combustion in the cloud of
disseminated fuel, also involves high rate dissemination of the
fuel. According to this phenomenon the outwardly traveling shock
wave from the high explosive surrounding the fuel creates a low
pressure region behind the shock wave. The initial quantity of fuel
traversing this low pressure region may rapidly deplete the
remaining oxygen therein, leaving an extremely fuel-rich or choked
environment within the expanding fuel cloud which will not burn.
The low pressure behind the shock wave also permits the dispersing
fuel to travel at high velocity with minimized aerodynamic drag. As
the fuel cloud further expands the concentration of fuel relative
to the air decreases until the cloud enters a detonable region at
which time the reaction between fuel and air progresses at
supersonic velocity across the entire cloud volume producing a
substantial blast effect as well as high thermal yield.
Despite the exact mechanism of reaction, the effects thereof can be
observed in operation of such an explosive device. Thus, for
example, in one instance an implosion type device was tested
wherein 37 gallons of pentane was contained and surrounded by a
layer of high explosive about three-eighths inch thick. For the
first 2 or 3 milliseconds after firing such a device the principal
effect noticed was that of the outwardly traveling shock wave from
the high explosive surrounding the fuel. By about 6 milliseconds
after initiation, however, the fuel had spread to a cloud diameter
of about 60 feet which represents a velocity of the forefront of
the fuel cloud of about 5,000 ft/sec; at about 10 milliseconds
after initiation the fuel cloud was over 88 ft in diameter and a
relatively small amount of burning was observed and what burning
was occuring was largely obscured by the unburned fuel surrounding
the implosion fireball. Shortly thereafter the cloud of expanding
fuel reached a detonable mixture and the flame front rapidly
propagated across the entire cloud volume. At 150 milliseconds
after initiation of implosion a large fireball at extremely high
temperature is spread across the ground over approximately a 100 ft
circle. The fireball continues to hug the ground for a time of
about one-third second to provide considerable flash burning on a
target and then commences to rise from the ground. A substantial
blast effect was obtained and substantial burning in the fuel cloud
was still occurring after a full second. A vehicle located about 30
feet from the point of initiation of the FAX device was overturned
and continued to burn for a substantial period of time after
dissipation of the fireball.
It has been found that there is a threshold thickness for the
explosive 16 surrounding the fuel 14 below which high energy shock
waves sufficient to initiate ignition without a separate igniter
are not obtained. Below the threshold, ignition may occur but the
large over-pressure wave described may not be obtained. This lower
threshold is found to be about one-fourth inch for conventional
high explosives and can be stated as a thickness equivalent to at
least one-fourth inch of explosive having a power or detonation
velocity in the range of 1.0 to 1.6 relative to
alphatrinitrotoluene (TNT) which is the power range of conventional
high explosives that are relatively safe to handle, that is, are
not unduly sensitive, and are suitable for military applications.
It will be apparent that explosives such as nitroglycerin having
higher power may be employed in thinner layers around the fuel.
Similarly lower power explosives may be employed in correspondingly
thicker layers. It would appear, however, that explosives having a
power substantially below that of TNT may not be completely
suitable since the detonation velocity in the explosive is also
low.
It is found with thicknesses of high explosive less than about
one-fourth inch that substantial blast effects at large distances
from the center are not obtained. Large thermal effects are still
present, however. On the other hand, when the thickness of
explosive surrounding the fuel is greater than about 1/4 inch
equivalent thickness of high explosive, there is a substantial
blast effect associated with explosion of the FAX type weapon
hereinabove described, and also a substantial thermal effect since
a very high temperature combustion zone is associated with the
shock front so that the energy transfer from the extremely hot
combustion zone is quite high. There is also continued burning
after the shock front is dissipated due to burning of the fuel rich
mixture behind the shock front. Such continued burning may persist
for more than 500 milliseconds, thereby causing further thermal
damage.
Thus, in a land mine of the type described and illustrated in
relation to FIG. 1, substantial blast effects are obtained with
large over-pressures over large distances, also accompanied with
substantial thermal effects. Because of the above described
effects, a weapon constructed according to the principles of this
invention provides greater destructive capability than previously
known weapons whether measured on the basis of effectiveness per
unit weight of the explosive device or unit cost of the explosive
device. This latter factor is because of the relatively smaller
quantity of high explosive required in the FAX type weapon as
compared with the high explosive weapon and the relatively cheap
fuel employed to obtain the effect as well as the increase in area
of effective coverage per unit weight.
In addition to the blast and thermal effects obtained from an
explosive device as hereinabove described, extensive fragmentation
effectiveness is also readily obtained. If desired an outer
frangible container can be provided to form shrapnel which is
ejected at high velocity by the high explosive surrounding the
fuel. In a preferred arrangement, a plastic foam layer is provided
around the high explosive, either with or without a container.
Imbedded within the foam are a plurality of flechette type darts
which cause severe shrapnel damage. Similarly belts of flechette
fragments can be wrapped about the FAX type weapon or other
fragmentation means provided. It has been found that with a mine as
described, a density of fragments of 0.5 per square foot is readily
obtained at a distance of 60 feet from the center.
It will be apparent since the ordnance device herein described is
highly effective from the point of view of weight and volume, that
it is also particularly suitable as an aerial bomb, artillery
shell, mortar shell, missile warhead or the like. A typical aerial
bomb is illustrated in FIGS. 4 and 5 which comprise respectively
longitudinal and transverse sections of a preferred aerial bomb.
Thus, as illustrated in FIG. 4, there is provided a cylindrical
aluminum case or canister 26 about 5 inches in diameter and 9
inches long which may, for example, be one-eighth inch thick or
slightly less. In order to provide a structural container for the
aerial bomb, a top end plate 27 which preferably comprises an
aluminum plate approximately one-half inch thick is either formed
integral with the cylindrical housing 26 or can be otherwise
secured thereto as will be apparent to one skilled in the art.
On the outside of the top end plate 27 there is provided a
detachable pusher cap 28 which can be employed for ejecting the
aerial bomb from its attachment to an aircraft. Within the pusher
cap 28 is preferably a small conventional parachute 29 which is
secured to the top end plate 27 by way of riser lugs 31. The
parachute is employed not so much for decreasing the vertical
velocity of the aerial bomb as for reducing horizontal velocity and
thereby providing stabilization thereof so that it falls
substantially vertically with the top end plate upward and the axis
of the cylindrical device substantially vertical upon impact. It
will be apparent that in lieu of a conventional parachute, other
suitable drag devices or stabilization means can be employed.
Centered within the cylindrical canister 26 is a liner 32 which is
constructed of conventional plastic material or preferably
nitrocellulose. Nitrocellulose is preferred so that most of the
materials of construction are explosively effective and the
nitrocellulose has sufficient structural strength to support other
elements of the aerial bomb. The liner 32 is preferably bonded to
the upper end plate 27 by conventional epoxy resin so that an
effective seal is obtained therebetween. The liner 32 is closed at
the bottom end thereof so that a substantially closed chamber is
obtained. A small hole 33 is provided in the bottom of the liner 32
for filling thereof as described hereinafter. An explosive 34 such
as RDX, PETN or other suitable military high explosive is cast or
otherwise placed between the liner 32 and the outer metal canister
26. The thickness of explosive 34 is preferably at least one-fourth
inch in order to obtain the described effects. Within the liner 32,
there is provided a body of fuel 36 which is preferably
naphthalene, polyethylene, gasoline, or other fuels as described
hereinabove. Within the liner 32 and in contact with the fuel 36
there is provided a closed gas containing or evacuated volume as
defined by a bellows 35. This resilient volume is provided for
accommodating thermal expansion differences due to operation of the
aerial bomb in various temperature regimes, thereby preventing
damage to the aerial bomb.
Axially located within the liner 32 is a frangible tube 37 of a
brittle plastic material such as Micarta or polystyrene, or glass
or nitrocellulose. Within the frangible tube 37 there is a mixture
of powdered materials capable of undergoing an exothermic reaction
therebetween as described hereinabove. Preferred mixtures of
materials are stoichimetric mixtures of copper oxide and aluminum
or magnesium and zirconium oxide. As is well known, these materials
will react when initiated to produce aluminum oxide and copper, or
zirconium and magnesium oxide, respectively, at elevated
temperature. It is also preferred that controlled void spaces be
provided within the mixture of reactive materials for elevating the
temperature thereof and initiating reaction as described
hereinabove.
At the bottom end of the aerial bomb there is provided a bottom end
plate or base plate 39 which is also illustrated in the sectional
view of FIG. 5. The base plate 39 is secured to the canister 26
peripherally by shear pins 41 or other means as will be apparent to
those skilled in the art. It is preferred that the bottom end plate
39 be aluminum or aluminum alloy about five-eighths inch thick and
have a 1 inch by 3/8-inch well 42 running transversely thereof for
containing a fuse and detonator assembly 43 and an electrical power
supply 45. The explosive portion of the detonator assembly 43 is
arranged adjacent a hole 44 extending between the transverse well
42 and the upper surface of the bottom end plate 39. A shallow slot
46 runs from the hole 44 toward the center of the bottom end plate
39 and four radially extending shallow slots 47 extend from the
center of the plate to the periphery thereof. As assembled, a strip
of explosive is laid in each of the grooves 46 and 47 so that when
the explosive portion of the detonator 43 is initiated the
detonation traverses the hole 44 and initiates detonation in the
explosive strip in the groove 46. The detonation wave in the
explosion then follows the explosive strips in the grooves 47 so as
to arrive at the periphery of the bottom plate and the primary
explosive 34 at four points around the periphery thereof
substantially simultaneously. This assures that a symmetrical
detonation wave propagates upwardly through the primary explosive
34 for disseminating the fuel 36 and initiating ignition thereof as
hereinabove described.
The detonator assembly comprises a conventional electric detonator
43 and conventional electric power supply 45 such as a battery as
will be apparent to those skilled in the art. At the periphery of
the bottom end plate and arranged to extend through the canister
26, there are one or more arming switches 48 actuated upon ejection
of the aerial bomb from the aircraft carrying it. The arming
switches 48 may be used to unshunt the electric detonator for
arming the aerial bomb. On the bottom surface of the bottom end
plate 39, there is provided a contact switch assembly comprising an
inner dish shaped resilient plastic member 49 and an outer dish
shaped resilient plastic member 51 substantially concentric
therewith. A conductive metal layer 52 is provided on the outer
surface of the inner dish shaped member 49 and a conductive metal
surface 53 is provided on the inner surface of the outer dish
shaped switch member 51. The dish shaped plastic members 49 and 51
and the metallic layers 52 and 53 thereon are illustrated as
relatively thick in FIG. 4 only for purposes of illustration. In a
typical embodiment the plastic members may be about 0.05 inch thick
or less and the metallic layer about 0.001 inch or less. The inner
and outer metallic layers 52 and 53 are electrically insulated from
each other and are electrically connected in series between the
power supply 45 and electric detonator 43. When the metallic layers
52 and 53 are out of contact, they act as an open switch and
prevent firing of the detonator. Upon impact with a target, the
outer dish shaped plastic member 51 is deformed against the inner
dish shaped plastic member 49, thereby closing the contact between
the metallic layers 52 and 53 and acting as a switch applying power
to the detonator and initiating explosion of the aerial bomb.
In fabricating the aerial bomb described and illustrated in FIGS. 4
and 5, the canister 26 and top end plate 27 are formed integrally
or joined together and the parachute 29 is rigged and packed within
the pusher cap 28. The igniter assembly 37 and 38 is bonded to the
top end plate and the pressure accommodating bellows 35 attached
thereto. The nitrocellulose liner 32 is bonded in place to the top
end plate 27 and also to the end of the igniter assembly 37.
Conventional epoxy resins have been found suitable for the various
bonding procedures. After the liner is installed, the fuel 36 is
placed within the liner and the hole 33 plugged. After this
operation, the high explosive 34 is cast between the liner 32 and
the canister 26 and the previously assembled bottom end plate 39 is
installed with the detonator assembly 43 already in place.
After assembling the aerial bomb as described and illustrated, it
is ready for use. In the usual application, the aerial bomb is
inserted in a tube or housing on an aircraft so that the arming
switches 48 are depressed thereby shorting the detonator and
preventing accidental detonation of the bomb. In use, the bomb is
ejected from the housing (not shown) thereby releasing the arming
switches 48 and unshorting the detonator 43. On contact with the
ground or other objective the plastic dish-shaped member 51 is
deformed against the inner dish-shaped member 49 thereby applying
power to the detonator as hereinabove described. The explosion from
the detonator traverses the hole 44 in the baseplate and along the
grooves 46 and 47, respectively, to detonate the explosive 34. The
imploding shockwave from the high explosive 34 acts on the fuel 36
and reactive mixture 38 in the same manner as hereinabove described
in relation to the mine of FIG. 1.
In another embodiment, the principles of this invention are applied
to a napalm weapon. A difficulty with conventional napalm weapons
has been in initiating combustion of all portions of the scattered
napalm. Napalm comprises a jelled mixture of gasoline or benzene
which has a high viscosity and smears and sticks to surfaces for
prolonged burning. Napalm bombs in the past have dispersed the
napalm over a target by either of two mechanisms. For high altitude
delivery a napalm bomb is provided with a center burster of high
explosive which scatters the napalm over a substantial area. For
low altitude delivery the forward momentum of the bomb is employed
for dispersal. In either case an igniter may be provided for
initiating combustion of the napalm and many of the scattered
masses of jelled napalm are burning upon dissemination. Additional
ignition of scattered masses of napalm is provided by combustion of
evaporated fuel mixed with air in the vicinity of the napalm. In
order to promote such combustion relatively volatile hydrocarbons
such as benzene or pentane are incorporated in the napalm to
provide a combustible fuel mixture with air. It is found, however,
that high altitude delivery of napalm bombs with centrally located
explosive bursters is not highly effective and it is preferred that
low level, high speed drops of napalm bombs be made. It is found,
however, with either high altitude, center burster bombs or with
low altitude bombs that substantial quantities of napalm are often
present on the target area after combustion is completed. This
unburned napalm represents a diminished effectiveness of the napalm
weapons.
In addition to the relative ineffectiveness of napalm weapons due
to unburned fuel, the delivery problem of aerial bombs is
considerable. Thus, low altitude airplane flights which provide the
most effective distribution of napalm also subjects the aircraft to
dangerous ground fire. It is, therefore, desirable that a highly
effective high altitude napalm weapon be available. It is also
found with low altitude deliveries that the area covered by a
napalm bomb in the order of 200 lbs, for example, is about 8 feet
wide and 150 feet long. This elongated pattern is due to the high
horizontal velocity of the bomb upon striking the ground.
FIG. 6 comprises a cutaway section of a portion of a cylindrical
ordnance device constructed according to the principles of this
invention, illustrating both transverse and longitudinal sections
of the device. It will be apparent to one skilled in the art that
conventional arming, fusing, and detonating means can be provided
with a device of this type in the same manner as hereinabove
described. In a preferred embodiment the ordnance device of FIG. 6
comprises an aerially delivered high altitude napalm bomb or the
like.
Thus there is provided a metal or plastic case 56 forming the outer
shell of the aerial bomb which may be about 15 inches diameter and
weigh 200 pounds. Within the container 56 is a quantity of napalm
57 or similar combustible fuel. Coaxially with the container 56
there is provided an igniter and burster which comprises a
frangible tube 58 within which is contained a layer of high
explosive 59. Within the layer of high explosive 59 is a second
frangible tube 61 which, in turn contains a reactive mixture 62
which preferably comprises a mixture of aluminum and copper oxide
or magnesium and zirconium oxide having controlled void spaces
filled with gas therein as hereinabove described. The tube 61 is
preferably about five-eighths to 1 1/4 inch in diameter. The
frangible tubes 58 and 61 can, for example, comprise Micarta,
phenolic resin, or other relatively brittle plastic that is inert
to the napalm fuel 57; the tube 58 thereby prevents leaching action
of the fuel on the high explosive 59 and also provides structural
support therefore. In a typical aerial bomb the layer of high
explosive 59 may be about 0.05 inch thick so as to provide a high
energy converging shock wave in the reactive mixture 62 for
initiation of reaction therein and an outwardly traveling wave for
disseminating the napalm.
It is found with a 200 pound weapon as described and illustrated in
FIG. 6 having napalm and a combined center burster and igniter that
an effective area of coverage of napalm is obtained over a 200 ft
diameter circle. Thus the effective area of coverage is over 15
times as large as with a conventional, low level, 200 pound napalm
weapon which covers an area of about 8 by 150 feet.
The high effectiveness of the napalm weapon described and
illustrated in FIG. 6 is largely due to the implosive center
burster and igniter present in the center of the aerial bomb. If an
equivalent amount of high explosive were employed as a cylindrical
center burster without the reactive mixture contained therein, some
dispersion of the napalm occurs but not to the large extent
obtained with the implosive burster and igniter. In addition,
because of the quenching effect of the large quantity of napalm, no
substantial amount of ignition thereof occurs due to the explosive
alone. When an implosive arrangement of high explosive having a
reactive mixture in the center thereof is employed in a napalm
weapon, on the other hand, the high explosive serves to commence
dissemination of the napalm in somewhat the same manner as a center
burster due to the action of an outwardly traveling shock wave from
the high explosive and expanding reaction products. However,
concurrent with the outwardly traveling shock wave there is an
imploding shock wave traveling through the reactive mixture. An
extremely high pressure is obtained due to the convergence of the
shock wave, higher than the peak pressure from cylinder of high
explosive, and this wave follows the outwardly traveling shock wave
a short time thereafter, and a very large force is thereby produced
for further propelling the napalm outward. The fragments of
reactive mixture in the igniter which are ejected by the imploding
shock wave also tend to accelerate the napalm outwardly and further
break up the mass of napalm for uniform distribution. Further, as
hereinabove described, the fragments of reactive mixture from the
igniter serve to initiate combustion of isolated masses of the
napalm mixture and clouds of evaporated fuel after dissemination
has progressed a substantial distance from the point of
initiation.
In still another embodiment of this invention organic materials
which react to produce elevated temperatures may be employed as
igniters. Thus, for example, concentrically oriented tubes of
hypergolic fuels along the axis of symmetry produces an evolving
cloud of very high temperature gas which functions as a source of
ignition. By purposefully producing deviations from symmetry in the
tubes and the explosive, jets of the hypergolic liquids may be
produced which enhance the ignition effects by a turbulent mixing
within the jets. The hot, gas jets so produced travel at high
velocities and provide a multiplicity of ignition sources within a
dispersing cloud of fuel.
Thus FIG. 7 illustrates in partial cutaway section another
embodiment of a fuel-air explosive apparatus incorporating the
principles of this invention. According to this embodiment a metal
or plastic cylindrical case 66 is provided as a container for the
explosive device. Within the container 66 there is located a
quantity of combustible fuel 67 such as gasoline, napalm or the
like. Coaxially arranged within the container is a central burster
and igniter which comprises three concentric tubes 68, 69, and 70
respectively, each of which is preferably constructed of a
frangible material, such as brittle plastic as hereinabove
described. The outermost of the tubes 68 preferably comprises a
square cross-section uniform along its length. The innermost tube
70 preferably comprises a uniform cylindrical tube. The
intermediate tube 69 has a generally square cross-section with a
plurality of convolutions along the length thereof; that is, the
tube is periodically pinched together on two or four of its sides.
In another embodiment the tube 69 may comprise a member having a
helical convolution which provides substantially the same effect as
the periodic convolutions described and illustrated.
Between the outermost tube 68 and the intermediate tube 69 there is
provided a high explosive 71 which is preferably cast in place so
as to conform to the convolutions of the intermediate tube 69.
Between the intermediate tube 69 and the inner tube 70 there is
provided a first hypergolic material 72 and within the innermost
tube 70 there is provided a second hypergolic material 73.
Hypergolic materials 72 and 73 are selected from pairs of materials
that are spontaneously and exothermically reactive merely upon
contact therebetween. Many pairs of hypergolic materials are known
which generate extremely high temperatures upon chemical reaction
therebetween. The temperatures produced may be several thousand
degrees Fahrenheit and the products of the hypergolic reaction may
in turn be combustible with air. Typical pairs of hypergolic
materials suitable for use in the practice of this invention
include: unsymmetrical di-methyl hydrazine, and nitrogen tetroxide;
penta borane and tetranitro methane; and alpha-penane and chlorine
pentafluoride.
In use of an ordnance device as described and illustrated in FIG. 7
the high explosive 71 is detonated by a conventional detonator as
will be apparent to one skilled in the art. The detonation of the
high explosive causes an expanding shock wave to travel outwardly
through the fuel 67 followed by a substantial volume of explosive
reaction products, both of which tend to accelerate the fuel
outwardly as has been described hereinabove. The inner surface of
the high explosive 71 is convoluted to conform to the convolutions
of the tube 69 and therefore the high explosive acts as a plurality
of shaped charges arranged adjacent to each other. These shaped
charges create a plurality of very vigorously mixed regions of the
hypergolic fuels 72 and 73 and create a plurality of radiating jets
of the mixed and mixing hypergolic materials. Thus there is
provided a large number of very high temperature jets of the
hypergolic materials traveling outwardly through the expanding
cloud of fuel 67 for providing a plurality of ignition sources
within the cloud in a manner analogous to the ignition sources
providing by the reactive mixtures hereinabove described. The
hypergolic materials may be preferred in many applications because
of the high energies available per unit weight, and because of the
elevated temperatures of the reaction, they may contribute
substantially to the thermal effects obtained from a FAX type
weapon.
It will be apparent to one skilled in the art that an igniter alone
without surrounding fuel also makes a highly desirable ordnance
device. In this type of device a reactive mixture as hereinabove
described and illustrated is contained within, and substantially
surrounded by, a layer of high explosive sufficient to initiate
reaction in the reactive mixture and cause dissemination thereof.
Such a weapon has a minimal blast effect which is due only to the
high explosive employed. However, substantial fragmentation can be
provided in addition to the fragmentation due to the reactive
material alone. As hereinabove pointed out, the reactive material
is ejected in a plurality of fragments, each of which may penetrate
structural material and each of which is at extremely elevated
temperature. The fragments of reactive mixture thus serve as a very
effective incendiary material. It will also be apparent to one
skilled in the art that in addition to the mine and aerial bomb
described and illustrated, that the principles of this invention
are readily applicable to artillery and mortar shells, missile
warheads and the like merely by changing the containing structures
and fuzing in conventional ways.
It will also be apparent to one skilled in the art that other
arrangements of igniter are possible using a converging shock wave.
Thus, for example, the igniter mixture described can be combined
with a conventional conical shaped charge of high explosive. The
igniter mixture is arranged as a thin layer within a conical cavity
in the explosive in substantially the same manner as copper or
other metals have been employed in the past. Firing of such a
device produces a jet of reacting and reacted igniter material at
very elevated temperature. As such the shaped charge having an
igniter mix has greater penetrating power than a conventional
shaped charge of high explosive.
In effect what is described above in relation to the igniter and
the powdered fuel is a means for heating the solid materials to
elevated temperature in a very short time. There is provided a
porous solid and means for passing a high energy shock wave through
said solid so that the gas which is in the void spaces in the solid
is heated to an elevated temperature and the heat is, in turn,
passed to the solid. If desired additional dispersed gas filled
void spaces of controlled size and proportion may be provided in
the porous solid. Such a solid, rapidly heated to elevated
temperature by a shock wave, may be employed in other manners than
in a military weapon such as, for example, for generating high
pressure, high temperature vaporized solids for research purposes,
driving projectiles, or the like. As such it will be recognized
that it may not be necessary in every instance to provide a
converging shock wave. If a high explosive of sufficient size is
employed a high energy flat shock wave may be satisfactorily
produced. Further, if the porous solid is bounded, at least on some
sides, by materials having a high impedance mismatch for shock
waves, intense heating is obtained and substantial dwell times of
the shock waves in the porous solids are obtained.
A preferred embodiment employs a reactive porous solid subject to a
shock wave for generating additional energy by exothermic reaction
after initiation by the shock wave. The reactive porous solid is
preferably a powdered element of the variety consisting of lithium,
potassium, cesium, barium, calcium, sodium, magnesium, beryllium,
aluminum, titanium, zirconium, and carbon and a powdered compound
such as an oxide, halide, carbide, sulfide, boride, nitride,
silicide or phosphide of a metal such as magnesium, beryllium,
aluminum, titanium, zirconium, manganese, vanadium, zinc, chromium,
iron, cadmium, indium, cobalt, nickel, molybdenum, tin, lead,
copper and mercury. The free element is preferably substantially
more electropositive than the metal in the compound so that a large
amount of energy is released by the reaction and the reaction
products are heated to an elevated temperature.
It is to be understood that the above described embodiments are
merely illustrative of application of the principles of this
invention. Those skilled in the art may readily devise other
variations that will embody the principles of the invention. It is,
therefore, to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
* * * * *