U.S. patent application number 12/152137 was filed with the patent office on 2009-12-31 for polyoxymethylene as structural support member and propellant.
This patent application is currently assigned to Physical Sciences, Inc.. Invention is credited to Alan H. Gelb, B. David Green, Prakash B. Joshi, Dean M. Lester, W. David Starrett, Bernard L. Upschulte, Ingvar A. Wallace.
Application Number | 20090320974 12/152137 |
Document ID | / |
Family ID | 34139806 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090320974 |
Kind Code |
A1 |
Joshi; Prakash B. ; et
al. |
December 31, 2009 |
Polyoxymethylene as structural support member and propellant
Abstract
A vehicle includes at least one polyoxymethylene structural
support member. The polyoxymethylene structural support member
includes a polyoxymethylene component that is a propellant that
provides thrust to the vehicle upon pyrolysis or combustion of the
polyoxymethylene component of the product of pyrolysis of the
polyoxymethylene component. The vehicle can be a satellite or other
type of spacecraft.
Inventors: |
Joshi; Prakash B.; (Andover,
MA) ; Upschulte; Bernard L.; (Nashua, NH) ;
Gelb; Alan H.; (Boston, MA) ; Green; B. David;
(Methuen, MA) ; Lester; Dean M.; (Brigham, UT)
; Starrett; W. David; (Roy, UT) ; Wallace; Ingvar
A.; (Brigham City, UT) |
Correspondence
Address: |
HAMILTON BROOK SMITH & REYNOLDS
530 VIRGINIA RD, P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Assignee: |
Physical Sciences, Inc.
Andover
MA
Alliant Techsystems Inc.
Edina
MN
|
Family ID: |
34139806 |
Appl. No.: |
12/152137 |
Filed: |
May 12, 2008 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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11086789 |
Mar 22, 2005 |
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12152137 |
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10884795 |
Jul 1, 2004 |
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11086789 |
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10688860 |
Oct 17, 2003 |
6904749 |
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10884795 |
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60419897 |
Oct 18, 2002 |
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60419898 |
Oct 18, 2002 |
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60419899 |
Oct 18, 2002 |
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Current U.S.
Class: |
149/13 ; 149/101;
149/105; 149/12; 149/88 |
Current CPC
Class: |
C06B 31/28 20130101;
B64G 1/22 20130101; F42B 5/16 20130101; C06D 5/00 20130101; Y10T
29/49622 20150115; B64G 1/403 20130101; B64G 1/421 20130101; F02K
9/32 20130101; C06B 45/10 20130101; F42B 3/02 20130101; C06B 21/005
20130101; F02K 9/36 20130101; F02K 9/08 20130101 |
Class at
Publication: |
149/13 ; 149/105;
149/101; 149/88; 149/12 |
International
Class: |
C06B 45/24 20060101
C06B045/24; C06B 25/04 20060101 C06B025/04; C06B 25/10 20060101
C06B025/10; C06B 25/00 20060101 C06B025/00; C06B 45/26 20060101
C06B045/26 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] Portions of this invention's development were supported
under two government contracts: 1) U.S. Air Force Research
Laboratory, Kirtland AFB, Contract No. F29601-99-C-0095; and 2)
Defense Advanced Research Project Agency, through Office of Naval
Research Contract No. N000014-00-C-0437. The Government has certain
rights in the invention.
Claims
1. A material comprising polyoxymethylene and at least one member
selected from the group consisting of an oxidant, a structural
reinforcement, and an energetic additive.
2. The material of claim 1, wherein the material defines at least
one channel for conducting oxidant or propellant through the
material.
3. The material of claim 1, wherein the oxidant is a solid.
4. The material of claim 1, wherein the energetic additive includes
at least one member selected from the group consisting of
2,4,6-trinitrotoluene, cyclotrimethylenetrinitramine,
1-acetyl-3,5-dinitrocyclotrimethylenetriamine,
cyclotetramethylenetetranitramine,
1-acetyl-3,5,7-trinitrocyclotetramethylenetetramine, nitroglycerin,
nitroguanidine, and nitrocellulose.
5. The material of claim 1, wherein the additional structural
reinforcement includes at least one member selected from the group
consisting of a metallic facesheet, a metallic tube, a metallic
mesh, a metallic cloth, carbon fiber, carbon cloth, carbon
nanotubes, a ceramic, boron fibers and boron cloth.
Description
RELATED APPLICATION(S)
[0001] This application is a divisional of U.S. application Ser.
No. 11/086,789, filed Mar. 22, 2005, which is a continuation of
U.S. application Ser. No. 10/884,795, filed Jul. 1, 2004, which is
a continuation of U.S. application Ser. No. 10/688,860, filed Oct.
17, 2003 which claims the benefit of U.S. Provisional Application
Nos. 60/419,897, 60/419,898, and 60/419,899 which were each filed
on Oct. 18, 2002. The entire teachings of the above applications
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] Structural components in aerospace and underwater vehicle
systems contain fluids or bear mechanical loads. They add mass to
the vehicle, which reduces the amount of onboard propellant the
vehicle is able to carry. This in turn limits the payload weight
that the vehicle is able to carry as well as its endurance, range,
and/or velocity.
[0004] In current aerospace and underwater vehicle systems,
structural components are often sized to withstand the acceleration
and vibration loads encountered during launch. After launch, the
vehicle experiences relatively insignificant loads and much of the
mass of the structural components is unnecessary, particularly for
those vehicles which are expendable, non-serviceable, or
non-reusable. In those cases, the momentum associated with the
structural mass constrains maneuverability and can limit mission
performance.
[0005] Past attempts at utilizing structural mass after launch
include the use of thermoplastics (e.g., fluoropolymers such as
polytetrafluoroethylene, which is currently used in pulsed plasma
thrusters). One limitation of these past approaches is that these
thermoplastic thrusters are designed for high impulse (e.g.,
thousands of seconds), but extremely low thrust, propulsion.
Generally, such thrusters are not suited for high thrust aerospace
and underwater propulsion, which require large flows of fuel to
produce the thrust. Furthermore, combustion of fluoropolymers
typically requires high pyrolysis temperatures (.about.500.degree.
C.), and results in production of soot that is unacceptable on many
missions, particularly space missions involving sensitive
equipment. Combustion of polytetrafluoroethylene also tends to
produce high molecular weight products that can limit propulsion
performance (i.e., specific impulse).
SUMMARY OF THE INVENTION
[0006] The invention generally is directed to a vehicle, a method
of propelling a vehicle, and a material, all of which employ
polyoxymethylene.
[0007] The vehicle includes at least one polyoxymethylene
structural support member, wherein the polyoxymethylene structural
support member includes a polyoxymethylene component that is a
propellant. The propellant provides thrust to the vehicle upon
pyrolysis or combustion of the polyoxymethylene component or of a
product of pyrolysis of the polyoxymethylene component. The
polyoxymethylene component includes a solid oxidant or an energetic
additive component.
[0008] The method of propelling a vehicle includes the steps of
employing at least a portion of a solid material, wherein the solid
material is a structural member and includes polyoxymethylene and a
solid oxidant or an energetic additive, to produce a propulsive
gas. At least a portion of the propulsive gas is directed away from
the vehicle to provide thrust, thereby propelling the vehicle. For
example, directing the propulsive gas from the vehicle in an
asymmetric manner can provide thrust.
[0009] The process for fabricating structural composites includes
placing a mold material between plates of a mold. The mold material
includes polyoxymethylene and at least one material selected from
the group consisting of an oxidant, a structural reinforcement and
an energetic additive. Pressure is applied to at least partially
cure the mold material and thereby form a polyoxymethylene rod. In
one embodiment, the polyoxymethylene rod is machined to produced
radial slots. Additional structural reinforcement is inserted into
the radial slots. The polyoxymethylene rod is then inserted into a
metallic cylinder and polyoxymethylene is further cured.
[0010] This invention provides a material that has utility during
both launch and post-launch portions of a vehicle's mission. During
launch, the material can provide structural support to at least a
portion of the vehicle. In the vehicle's post-launch phase, the
material can provide propulsive force.
[0011] The present invention has many advantages. For example,
polyoxymethylene (POM) possesses many favorable mechanical
characteristics. POM has a tensile strength that is about
two-thirds that of elemental aluminum, yet POM only has about half
the density (POM's density is about 1.4 g/cm.sup.3). Also, POM is
stable in low pressure environments. This allows the fuel to
withstand large changes in pressure without significant
degradation. POM also has a low coefficient of thermal
conductivity, which ensures that as parts of the vehicle are
converted into fuels, the remaining structure does not heat
excessively.
[0012] The polyoxymethylene material of the invention pyrolyzes at
relatively low temperatures (beginning at about 120 C), leaving
little residue and creating little or no soot. The material can be
employed to produce clean gaseous fuels, which can be used to
produce thrust or energy, or it can be combusted with a separate
liquid, solid or gaseous oxidizer to produce thrust or energy. This
makes it particularly advantageous for vehicles having
contaminant-sensitive systems, such as spacecraft possessing
sensitive optical devices. The decomposition products tend to be
relatively low molecular weight materials, which means that the
fuel provides a relatively large amount of thrust and specific
impulse compared to conventional materials.
[0013] Some additional advantages of this invention include the
capacity to provide, for example, light-weight, multi-functional
materials; decreased vehicle mass and launch weights; increased
payload capacity; enhanced vehicle maneuverability; increased
vehicular life spans; and the ability to provide end-of-lifetime
orbit-raising (or deorbiting) capacity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing will be apparent from the following more
particular description of example embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating embodiments of the present invention.
[0015] FIG. 1 schematically illustrates the concept of pyrolyzing
polyoxymethylene by the method of the invention and then combusting
the resulting products with an oxidizer to produce gases for
propulsion.
[0016] FIG. 2 schematically illustrates an example of a general
reaction scheme for a bipropellant embodiment where the fuel of the
invention is pyrolyzed to produce propulsion.
[0017] FIG. 3 illustrates one embodiment of a vehicle of the
invention that utilizes a polyoxymethylene composition material as
a structural material and as a propellant source.
[0018] FIG. 4 illustrates a cross-sectional side view of one
embodiment of a stringer/thruster of the invention, wherein the
polyoxymethylene is segmented to provide restart capability.
[0019] FIG. 5 depicts a cross-sectional radial view of another
embodiment of a stringer/thruster of the invention, wherein a
liquid and a gaseous oxidizer is introduced through multiple axial
passages.
[0020] FIG. 6 shows a schematic representation of yet another
embodiment of a stringer/thruster of the invention where a fluid
oxidant is introduced through a single axial passage.
[0021] FIG. 7 depicts a cross-sectional radial view of the
stringer/thruster of the invention shown in FIG. 5.
[0022] FIG. 8 illustrates a cross-sectional side view of yet
another embodiment of a stringer/thruster of the invention, shown
in FIG. 5.
[0023] FIG. 9 illustrates a cross-sectional side view of still
another embodiment of the stringer/thruster of the invention,
wherein a solid oxidant is embedded within the
polyoxymethylene.
[0024] FIG. 10 depicts a portion of an embodiment of a
panel/thruster of the invention.
[0025] FIG. 11 depicts an overhead view of the panel/thruster of
FIG. 10.
[0026] FIG. 12 depicts a cross-sectional side view of another
embodiment of a panel/thruster of the invention.
[0027] FIG. 13 depicts a cross-sectional view of the panel/thruster
of FIG. 12.
[0028] FIG. 14 depicts a cross-sectional view of an embodiment of a
rod of the invention.
[0029] FIG. 15 is a representation of the amounts of formaldehyde
and carbon monoxide products of thermal decomposition of POM at
various temperatures. The molar concentration of hydrogen, also a
pyrolysis product, is equal to the molar concentration of carbon
monoxide.
[0030] FIG. 16 is a plot of the pressure and temperature of a
chamber as POM is pyrolyzed and the resulting formaldehyde vapor
that is produced by the pyrolysis fills the storage chamber.
[0031] FIG. 17 is a plot of thermocouple measurements obtained
during combustion of polyoxymethylene in oxygen as oxidant flow
rate is varied, demonstrating controllability of the combustion
reaction.
[0032] FIG. 18 is a plot of thermocouple measurements from a
Simulated Bulk Autoignition Test (SBAT) of POM-A.
[0033] FIG. 19 is a plot of thermocouple measurements from a SBAT
of cyclotetramethylenetetranitramine (HMX).
[0034] FIG. 20 is a plot of thermocouple measurements from a SBAT
of a mixture of POM-A and HMX.
[0035] FIG. 21 is a plot of thermocouple measurements from a SBAT
of POM-B.
[0036] FIG. 22 is a plot of thermocouple measurements from a SBAT
of a mixture of POM-B and HMX.
[0037] FIG. 23 is a plot of pressure as a function of time from the
sustained combustion of a POM composite with oxygen in one
embodiment of a stinger/thruster configuration of the
invention.
[0038] FIG. 24 is a plot of pressure data from the sustained
combustion of POM with hydrogen peroxide in one embodiment of a
stinger/thruster configuration of the invention.
[0039] FIG. 25 is a plot of pressure data from the sustained
combustion of POM with hydrogen peroxide in one embodiment of a
stinger/thruster configuration of the invention.
[0040] FIG. 26 is a plot of pressure data from the sustained
combustion of POM with hydrogen peroxide in one embodiment of a
stinger/thruster configuration of the invention.
[0041] FIG. 27 is a plot of pressure data from a 3-pulse thrust
profile obtained during the combustion of POM with hydrogen
peroxide in one embodiment of a stinger/thruster configuration of
the invention.
[0042] FIG. 28 is a plot of the combustion pressure and temperature
during combustion of a POM composite with hydrogen peroxide in one
embodiment of a stinger/thruster configuration of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0043] A description of example embodiments of the invention
follows.
[0044] The teachings of all patents, published applications and
references cited herein are incorporated by reference in their
entirety.
[0045] The foregoing and other objects, features, and advantages of
the invention will be apparent from the following, more particular,
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0046] This invention provides for a vehicle comprising at least
one polyoxymethylene structural support member that provides thrust
to the vehicle upon pyrolysis or combustion of the polyoxymethylene
or of a product of pyrolysis of the polyoxymethylene. In some
embodiments, the polyoxymethylene structural support member has a
dual-use in that it provides support to some portion of the vehicle
and also can be used as a fuel.
[0047] In some embodiments, the present invention generally relates
to a fuel comprising polyoxymethylene ("POM") that is employed to
produce a propulsive gas. As used herein, a "fuel" is a material
that is able to be employed as a propellant to produce a gas which
is used to create energy or to produce thrust or propulsive force.
The propulsive force can be produced directly by release of gases
caused by pyrolysis or combustion of the fuel, or indirectly by
accumulation and delayed release or combustion of products of
pyrolysis or products of products of combustion of the fuel.
[0048] In some embodiments, the fuel of this invention includes at
one additional material such as, for example, a combustible
material (e.g., an oxidant or an energetic additive) and/or a
structural support material. The fuel is then referred to as a
"composite material."
[0049] The fuel is a solid that includes POM, which is a family of
acetal polymers with the general formula (CH.sub.2O).sub.n.
Compositions of POM are available commercially, often including
various additives and thermal stabilizers. One composition,
DELRIN.RTM. ("POM-A"), is available from E.I. du Pont de Nemours
& Co. (Wilmington, Del.) and includes at least one proprietary
additive and/or thermal stabilizer. In another embodiment, the fuel
includes one or more stabilizing materials. In still another
embodiment, the stabilizing materials are chemically bound to the
POM in the fuel (e.g., copolymers and/or substituents of the POM
polymer).
[0050] As used herein, "POM" refers to any of the polyoxymethylene
family of polymers that may or may not include chain stabilizers
and/or terminating additives. "POM-A" refers to DELRIN.RTM..
"POM-B" refers to POM with acetate end caps and no additives or
thermal stabilizers. "POM" can be combusted with, for example,
hydrogen peroxide or hot gaseous oxygen. POM-B can be combusted
with, for example, nitrogen tetroxide.
[0051] In one embodiment, the fuel includes one or more oxidants
and/or one or more energetic additives. In another embodiment, the
oxidant is in a liquid form and is in contact with the fuel. In a
further embodiment, the oxidant is a solid that is incorporated
directly into the fuel.
[0052] Suitable oxidants can include hydrogen peroxide, nitrogen
tetroxide, oxygen, nitrous oxide, nitrates (e.g., potassium
nitrate, barium nitrate, sodium nitrate, hydroxylammonium nitrate,
and strontium nitrate), chlorates (e.g., potassium chlorate,
magnesium chlorate, and sodium chlorate), and perchlorates (e.g.,
ammonium perchlorate and potassium perchlorate).
[0053] "Energetic additives" are materials that enhance the
pyrolysis or combustion of the fuel by, for example, increasing the
fuel value of the fuel, the pyrolysis or combustion rate,
increasing the amount of energy released during pyrolysis or
combustion, and/or decreasing the amount of external energy needed
to initiate pyrolysis or combustion. In one embodiment, the
energetic additives are chemically compatible with the other
materials of the fuel so that they may be incorporated directly
into the fuel and will not react with the other materials at
sub-pyrolytic or sub-combustion temperatures (e.g., the
temperatures experienced during the fabrication of the fuel).
[0054] Examples of energetic additives include TNT
(2,4,6-trinitrotoluene), RDX (cyclotrimethylenetrinitramine), TAX
(1-acetyl-3,5-dinitrocyclotrimethylenetriamine), HMX, SEX
(1-acetyl-3,5,7-trinitrocyclotetramethylenetetramine),
nitroglycerin, nitroguanidine, nitrocellulose, and Composition B (a
castable explosive, usually made with RDX and/or TNT as the main
ingredient).
[0055] In one embodiment, the fuel includes at least one additional
structural support material. The additional structural support
material can increase the structural strength of the fuel. For
example, the tensile strength of the fuel can be increased by
inclusion of at least one structural support material embedded in
the POM of the fuel. In a further embodiment, at least one
additional structural support material is included to increase the
fuel's in-plane or axial stiffness. In another embodiment, the
structural support material encases the POM to contain products of
pyrolysis and combustion and to shield it from degrading
environmental effects such as solar UV radiation, ionizing
radiation, or atomic oxygen erosion. In a further embodiment, the
structural support material forms a conduit through which the
products of pyrolysis are directed. Examples of suitable structural
support materials include metallic facesheets (e.g., titanium
facesheets), metallic meshes, metallic tubes, metallic cloth,
carbon or boron fibers, carbon cloth, carbon nanotubes, and ceramic
materials. The term "non-combustible reinforced material" can
include, for example, an external shell through which an oxidizing
material, or oxidizer, may flow.
[0056] In a preferred embodiment, the additional structural support
material is made of a material that will be consumed along with the
POM during pyrolysis. Examples of suitable materials for such an
embodiment include those made from carbon, such as carbon fibers
(in a chopped or continuous form or woven into cloth), carbon
nanotubes and boron. In an especially preferred embodiment, the
additional structural support materials are chemically stable with
(i.e., the support materials will not react with) the other
materials in the fuel at sub-pyrolytic and/or sub-combustion
temperatures so as to permit an all-solid state material that
includes POM, the additional structural support material, and at
least one solid oxidant and/or energetic additive.
[0057] The fuel is employed to produce a propulsive gas. For
example, the fuel can be heated, pyrolyzed, combusted, and/or
reacted to produce the propulsive gas.
[0058] In one embodiment, the fuel is heated to pyrolyze the POM
and produce a propulsive gas. FIG. 1 schematically illustrates
process 10, which is an examples of a general reaction scheme for
pyrolyzing fuel 12 to produce propulsive gas 18.
[0059] During pyrolysis, the POM component of fuel 12 dissociates
into first pyrolysis product 14, a gas composed mostly of
formaldehyde. As used herein, the term "first pyrolysis products"
refers to the gas or gases produced by the pyrolysis of the solid
fuel and the POM included in the solid fuel. The general reaction
is:
##STR00001##
The conversion is accomplished with small expenditures of energy,
.about.2 kJ per gram of POM included in fuel 12. Solid POM is able
to withstand the typical operating temperatures of spacecraft
systems (from about -40.degree. C. to about 70.degree. C.),
however, it will pyrolytically decompose at temperatures above its
melting point (.about.175.degree. C.), starting around 250.degree.
C. and completing around 400.degree. C.
[0060] In some embodiments, other gases, in addition to the first
pyrolysis products, are formed during the pyrolysis of the fuel.
For example, gasses other than formaldehyde can be formed from the
decomposition products of side groups on the POM polymer,
copolymers in the POM polymer, and/or any additional material
included in or reacted with the fuel (e.g., oxidants, energetic
additives, and/or additional structural support materials consumed
during pyrolysis).
[0061] Optionally, at least a portion of first pyrolysis product 14
is further pyrolyzed into second pyrolysis product 16. As used
herein, the term "second pyrolysis products" refers to the gas or
gases formed by further pyrolyzing the first pyrolysis products.
For example, the formaldehyde gas in first pyrolysis product 14 can
be converted to carbon monoxide and hydrogen gas by heating in the
presence of a catalyst (e.g., platinum and/or ruthenium) in the
general reaction:
##STR00002##
In this reaction, about 0.2 kJ of heat is needed per kilogram of
formaldehyde. The composition of the second pyrolysis product will
vary depending on reaction conditions, the composition of the first
pyrolysis product, and whether the first pyrolysis products are
reacted with any additional materials. Examples of component gases
of the second pyrolysis product include hydrogen, water, carbon
monoxide, carbon dioxide, nitrogen, nitrous oxide, nitrogen
monoxide, and/or nitrogen dioxide.
[0062] In process 10, first and/or second pyrolysis product 14, 16
are released, or directed away, from a vehicle as propulsive gas
18. As used herein, the term "propulsive gas" refers to gases which
produce a propulsive force or energy, and can include the first
pyrolysis products, second pyrolysis products, their combustion
products, and any other materials mixed and/or reacted with the
first and second pyrolysis products.
[0063] In some embodiment, this invention provides a method of
propelling a vehicle. In one example, the method includes the steps
of employing at least a portion of a solid fuel to produce a
propulsive gas, and directing at least a portion of the propulsive
gas away from the vehicle to provide thrust, thereby propelling the
vehicle. In further embodiments, the solid fuel is a structural
member.
[0064] In some embodiments, the fuel is used as a monopropellant
(i.e., no additional materials, such as an oxidant, need be reacted
with the fuel or the pyrolysis products in order to provide thrust
to a vehicle). In one monopropellant embodiment, the fuel is
pyrolyzed and the resulting first pyrolysis product is directed
through a nozzle as a propulsive gas to produce thrust, much like a
conventional cold gas thruster on a spacecraft. Such an embodiment
can be useful, for example, for those applications that require a
low thrust and low specific impulse (.about.50 s) propulsive force,
such as attitude control and station-keeping applications. In yet
another embodiment, at least a portion of the first pyrolysis
product is further pyrolyzed to produce a second pyrolysis product
which is then directed through a nozzle as propulsive gas to
produce thrust. This embodiment can be useful, for example, for
those applications that require a moderate thrust and moderate
specific impulse (.about.130 s) propulsive force, such as orbital
maneuver applications.
[0065] In other embodiments, the fuel is employed as one component
of a bi- or multi-propellant system (i.e., at least one additional
material is reacted with the fuel or the pyrolysis products in
order to provide thrust to a vehicle). In some bipropellant
embodiments, a reactive chemical (e.g., an oxidant) is contacted
with the fuel to initiate and/or sustain the combustion of the
pyrolysis products.
[0066] In some embodiments, a fluid oxidant is contacted with the
fuel and a combustion process results in the formation of a
propulsive gas. For example, in one embodiment, a fluid oxidant
(e.g., hydrogen peroxide, hydroxylammonium nitrate) is passed over
a catalyst (such as silver or irridium), causing the oxidant to
decompose. The products of the catalytic decomposition reaction and
any uncatalyzed oxidant are combusted with the solid fuel material,
creating combustion gases that include carbon dioxide and water.
These combustion gases are directed away from the propellant system
or vehicle to provide thrust.
[0067] In some embodiments, an ignition and/or heating means (e.g.,
a spark or a hot filament) is used to initiate the combustion
process. In one embodiment, a heating or ignition source is exposed
to the fuel while in the presence of a fluid oxidant, resulting in
combustion that forms the propulsive gas. In other embodiments, the
catalytic reaction heats the oxidant and reaction products to a
sufficient temperature so that they combust with the fuel on
contact (i.e., hypergolically) and ignition or heating means are
not required and the combustion process continues until the fuel or
oxidant supply is restricted or exhausted. In such a hypergolic
embodiment, the flow of fluid oxidant can be controlled to increase
or decrease the combustion rate, and in turn, control the amount of
thrust or energy produced.
[0068] In some embodiments, the fluid oxidant and/or catalytic
reaction products are directed to the site of combustion or
pyrolysis through channels defined by the fuel. The fluid oxidant
can be directed through the channels with the use of, for example,
a pump or compressor. In another embodiment, a fluid oxidant is
directed to a site of combustion that is remote from the site of
pyrolysis to initiate and/or sustain the combustion of pyrolysis
products. One example of this embodiment includes directing the
pyrolysis products away from the fuel and into a separate
combustion chamber where they contact and combust with a reactive
chemical.
[0069] In some embodiments, the fuel includes a POM and a solid
oxidant (e.g., potassium perchlorate). The fuel is combusted to
form propulsive gases. These combustion gases are directed away
from the propellant system or vehicle to provide thrust. In some
embodiments, an ignition and/or heating means (e.g., a spark or a
hot filament) is used to ignite or initiate the combustion process.
Optionally, or in addition, a heated fluid oxidant is contacted
with a fuel that includes a solid oxidant to initiate
combustion.
[0070] In another embodiment, the fuel is pyrolyzed in the presence
of at least one liquid or gaseous oxidant. At least a portion of
the resulting first and/or second pyrolysis products contacts and
combusts with the oxidant, and the heat released in the combustion
reactions assists in further pyrolyzing the fuel and/or first
pyrolysis products. The combustion products, along with any
uncombusted pyrolysis products, are directed away from the vehicle
as propulsive gas. In some embodiments, the oxidant is the
rate-limiting reactant and combustion continues until the supply of
oxidant is exhausted. These embodiments would be useful for those
applications that require a high thrust and high specific impulse
(e.g., greater than 250 seconds) propulsive force, such as
applications involving orbital plane changes, orbit-raising, or
deorbiting.
[0071] In some embodiments, the heat released during combustion is
recycled as energy to drive pyrolysis. In those embodiments, the
flow of the oxident is controlled in order to manipulate the rate
of combustion and the amount of energy released. Manipulating the
amount of energy released from combustion in turn increases or
decreases the amount of energy available to drive pyrolysis of the
fuel and/or the first pyrolysis product, thereby controlling the
amount of propulsive gas and thrust produced.
[0072] In one embodiment, the nozzle is fabricated from a
high-temperature material in order to withstand the combustion
pressures and temperatures. Examples of high-temperature material
include tungsten, graphite, rhenium coated graphite, or silica
phenolic (such as DUREZ.RTM., available from Occidental Chem.
Corp., Dallas Tex.).
[0073] FIG. 2 schematically illustrates process 20, which is a
general reaction scheme for a bipropellant embodiment where fuel 12
is pyrolyzed to produce propulsive gas 18. At least a portion of
first and/or second pyrolysis product 14, 16 are combusted with
oxidant 22, as described earlier.
[0074] The combustion products, along with any uncombusted first
pyrolysis product 14, second pyrolysis product 16, and oxidant 22,
are then released from the vehicle as propulsive gas 18. The
combustion process is sufficiently exothermic to at least partially
pyrolyze uncombusted fuel and first pyrolysis products. About 18 kJ
of heat is released per gram of first and/or second pyrolysis
products combusted, depending on the specific composition of the
first and/or second pyrolysis products and whether any other
reactants are used. In one embodiment, the heat released during the
combustion is recycled as energy to drive the pyrolysis of the fuel
and/or first pyrolysis products.
[0075] The exact composition of the propulsive gas depends, for
example, on the original composition of materials utilized during
the propulsive gas production process and the reaction conditions.
Examples of individual gases comprising the propulsive gas include,
but are not limited to, formaldehyde, hydrogen, carbon monoxide,
water, carbon dioxide, nitrogen, nitrous oxide, nitrogen monoxide,
and/or nitrogen dioxide.
[0076] In one embodiment, the pyrolysis and/or combustion of the
fuel is initiated and/or sustained by a heat source. In another
embodiment, further pyrolysis and/or combustion of the pyrolysis
products is initiated and/or sustained by a heat source. Some
examples of heat sources include a hot filament, a squib, or a bag
igniter. In a preferred embodiment, the heat source is controlled
in order to manipulate the amount of pyrolysis products formed,
combustion products formed, and/or the amount of energy released
during combustion, and in turn, control the amount of propulsive
force produced. For example, modifying the amount of energy
released from a heat source will decrease or increase the rate of
pyrolysis and the amount of pyrolysis products formed, and
consequently change the amount of propulsive gas released to
generate propulsive force. If combustion of pyrolysis products is
also involved, increasing or decreasing the amount pyrolysis
products formed will impact the amount of material fed to the
combustion process, and in turn, modify the amount of combustion
products available for use as propulsive gas.
[0077] In another embodiment, the heat source also acts as an
additional structural support material. For example, an additional
structural support material in the form of a metallic mesh or wire
included in the fuel could conduct electricity and act as a hot
filament to initiate and/or sustain the pyrolysis reactions.
[0078] In one embodiment, the oxidant is a fluid. In yet another
embodiment, the oxidant is a fluid stored in at least one storage
tank positioned on or in the vehicle. In still another embodiment,
the oxidant is withdrawn from the vehicle's operating environment.
For example, a vehicle could draw atmospheric oxygen from its
operating environment and react it with the fuel, the first
pyrolysis product, and/or the second pyrolysis product. In a
further embodiment, the fluid oxidant is directed to the site of
pyrolysis and/or combustion. In yet another embodiment, the fluid
oxidant is directed to the site of pyrolysis and/or combustion
through at least one channel defined by the fuel.
[0079] In one embodiment, the vehicle is autophagous so that the
propulsion continues as long as the oxidizer is contained within
the vehicle or there is a sufficient supply of oxidant in the
operating environment.
[0080] In another embodiment, the first pyrolysis product and/or
the second pyrolysis product are stored in a container (e.g., a
titanium storage tank) for use at a latter time. For example, the
vapor pressure of formaldehyde is about 5 atm at 300 K and about 10
atm at 350 K, which allows it to be stored in a liquid-vapor
equilibrium mixture at moderate pressures (e.g., about 300 to 500
psia) and temperatures (e.g., above about 60.degree. C.). In one
embodiment, a suitable titanium storage tank could be made with
relatively thin walls, for example, walls about 10 mils or about
0.25 millimeters thick.
[0081] In some embodiments, the fuel is able to provide structural
support to at least a portion of the vehicle for at least a portion
of a mission, and this invention is suitable for any vehicle that
would derive utility from such a material. Examples of portions of
a vehicle suitable for this invention include structural members or
composites which are needed for structural support during an early
portion of a vehicle's mission, such as launching of a vehicle.
Suitable structural members and composites include structural
paneling, support beams and support rods.
[0082] In one embodiment, the vehicle is one that travels under
water for at least a portion of its mission such as, for example, a
torpedo or a rocket launched from a submerged platform. In another
embodiment, the vehicle is one that travels through the atmosphere
for at least a portion of its mission such as, for example, a
rocket or a munition. In yet another embodiment, the vehicle is one
that travels through outer space for at least a portion of its
mission such as, for example, a satellite or a rocket.
[0083] In still more embodiments, this invention includes a
vehicle. In one example, the vehicle comprising at least one
polyoxymethylene structural support member that provides thrust to
the vehicle upon pyrolysis or combustion of the polyoxymethylene or
of a product of pyrolysis of the polyoxymethylene. In other
embodiments, the vehicle is or includes a thruster. In further
embodiments, the thruster includes a noncombustible shell and a
fuel and/or a polyoxymethylene structural support member is
contained within the noncombustible shell.
[0084] In yet other embodiments, this invention includes a vehicle
propulsion system that provides propulsion to a vehicle. In one
example, the vehicle propulsion system includes a fuel that
includes polyoxymethylene and produces a propulsive gas when
pyrolyzed, a noncombustible support material structurally
supporting the fuel, and an exhaust channel through which the
propulsive gas flows, wherein the exhaust channel is in fluid
communication with the fuel.
[0085] FIGS. 3-10 illustrate representative embodiments of vehicles
or portions of vehicles of the invention that utilize the fuel and
are capable of operating in low pressure environments, such as
outer space.
[0086] FIG. 3 illustrates one possible embodiment of a vehicle of
the invention that utilizes a fuel of the invention. Spacecraft 30
includes a vehicular propulsion system that produces thrust by
directing a propulsive fluid (not shown) away from itself.
Spacecraft 30 includes solar array 32, self-consuming
stringer/thruster 34, self-consuming panel/thruster 36, and payload
module 38. Self-consuming stringer/thruster 34 and panel/thruster
36 include the fuel of this invention. Inclusion of the fuel grants
the self-consuming stringer/thrusters 34 and panel/thrusters 36
some form of additional structural support such as, for example,
increased rigidity. When spacecraft 30 reaches a point in its
mission where those fuel-bearing components have greater utility as
a fuel source than as an additional structural support,
self-consuming stringer/thrusters 34 and panel/thrusters 36 are
employed to consume at least a portion of their fuel material via
the processes and methods of this invention. The resulting gas or
gases are directed away from spacecraft 30 as a propulsive gas,
thereby producing a propulsive force.
[0087] FIG. 4 illustrates a cross-sectional side view of one
embodiment of a stringer/thruster of the invention. Self-consuming
stringer/thruster 40 includes shell 42, made of a noncombustible
material capable of withstanding the temperatures and pressures
produced during pyrolysis or combustion (e.g., titanium). Shell 42
protects fuel 41 within stringer/thruster 40. Dividers 44 span the
inner width of shell 42, providing internal structural support to
stringer/thruster 40 as well as segmenting fuel 41 into propellant
cores. Fuel 41 is pyrolyzed via the processes and methods of this
invention, and the resulting first pyrolysis product, second
pyrolysis product, and/or their combustion products are directed
away 48 from stringer/thruster 40 through nozzle 46, thereby
producing thrust 49 in the opposite direction.
[0088] FIG. 5 depicts a cross-sectional radial view of another
embodiment of a stringer/thruster of the invention. Self-consuming
stringer/thruster 50 includes channels 52. Channels 52, which are
defined by fuel 56, can carry at least one oxidant to the site of
ignition and/or combustion. Shell 58 protects fuel 56. Fuel 56
includes additional structural support material, in the form of
mesh 54. In one embodiment, the mesh is made from a material that
functions as an electrical heater/igniter to initiate and/or
sustain the thermal decomposition and combustion of the fuel, the
first pyrolysis product, and/or the second pyrolysis product. Both
the oxident and the pyrolysis product flow through channels 52,
including the center channel.
[0089] FIG. 6 shows a schematic representation of yet another
embodiment of a stringer/thruster of the invention. Self-consuming
stringer/thruster 60 utilizes a fluid oxidant. The fluid oxidant is
stored in oxidant tank 62 and directed into self-consuming
stringer/thruster 60 through flow control valve 64, which regulates
the flow of oxidant into forward closure 66. In some embodiments,
the forward closure is also used as an attachment point in order to
secure the self-consuming stringer/thruster to a vehicle. Forward
closure 66 includes heat source 68 and catalyst bed 70. Heat source
68 heats the oxidant as it enters forward closure 66. Catalyst bed
70 facilitates decomposition of the fluid oxidant 78, the first
pyrolysis product, and/or second pyrolysis product. The oxidant
flows through channel 72, contacting and reacting with fuel 78. The
reaction products flow to combustion chamber 74 where they can
react further. In some embodiments, the combustion chamber, as well
as other portions of a self-consuming stringer/thruster, are lined
with insulation in order to protect sensitive portions of the
stringer/thruster or an attached vehicle from high combustion
temperatures and/or pressures. The resulting gases are directed
from stringer/thruster 60 through nozzle 76 as propulsive gas.
Nozzle 76 is incorporated inside shell 79.
[0090] In one embodiment, if self-consuming stringer/thruster 60
depicted in FIG. 6 is sized to be about 44 inches long with an
outer diameter of about 2 inches, the total mass of the
thruster/stringer should be approximately 6 pounds, with a fuel
mass of about 4 pounds. This would give a fuel mass fraction of
about 0.67.
[0091] FIG. 7 depicts a cross-sectional radial view of
self-consuming stringer/thruster 80. In addition to the oxidant
that flows through channels 89, a secondary oxidant is introduced
through secondary oxidant passages 82, which in this embodiment are
shown as a series of grooves through which a second oxidant can
flow. The second oxidant is injected towards the site of pyrolysis
and/or combustion by secondary oxidant injectors 84, which
perforate shell 88. The second oxidant assists in the pyrolysis
and/or combustion of fuel 86, the first pyrolysis product, and/or
the second pyrolysis product.
[0092] FIG. 8 illustrates a cross-sectional side view of
self-consuming stringer/thruster 90 in a configuration where the
propulsive gas is combusted at a site downstream from where fuel 99
is initially pyrolyzed. Solid fuel 99 is contained in portion I of
self-consuming stringer/thruster 90, where it is pyrolyzed to form
the first pyrolysis product. In one embodiment, an oxidant is
directed into portion I through channels 92 where it promotes the
pyrolysis and/or combustion of fuel 99 and at least a portion of
the resulting first and/or second pyrolysis product. The first
and/or second pyrolysis product is directed to portion II of
self-consuming stringer/thruster 90, where it undergoes further
pyrolysis and/or combustion in combustion chamber 94. In one
embodiment, an oxidant is directed into combustion chamber 94
through secondary oxidant passages 96, where it reacts with the
first and/or the second pyrolysis product. The reaction products
are directed away from stringer/thruster 90 through nozzle 98 as
propulsive gas to provide thrust to stringer/thruster 90 and any
attached vehicle.
[0093] FIG. 9 illustrates a schematic of all-solid state thruster
100. All-solid state thruster 100 includes fuel 108. Fuel 108 is
formed in a predetermined shape in order to permit a desired thrust
profile and flow efficiency. Fuel 108 incorporates an embedded
solid oxidant. Examples of predetermined shapes include a tapered
pattern or a star pattern. Fuel 108 is encased within shell 109,
which is capable of withstanding combustion pressures and
temperatures. In some embodiments, the pyrolysis and combustion
reactions produce a low enough flame temperature that shell 109 is
uninsulated, which reduces thruster mass.
[0094] Forward closure 102 is used for vehicle attachment and
optionally includes ports for instrumentation and/or heat source
104. Thruster 100 can include one or more heat sources 104 which
initiate or sustains the pyrolysis and/or combustion reactions.
Examples of suitable heat sources include a hot filament, a squib,
or a bag igniter.
[0095] The reaction products are directed away from all-solid state
thruster 100 by passing them through a simple homogeneous nozzle
106 which is contained within the titanium sleeve of shell 109.
[0096] In one embodiment, all-solid state thruster/stringer with a
similar configuration as thruster 100 depicted in FIG. 9 is sized
to be about 40 inches long with an outer diameter of about 2 inches
and a nozzle throat diameter of about 0.25 to 0.5. The total mass
of the thruster/stringer is less than about 5 pounds, with a fuel
mass of about 4 pounds. The fuel mass fraction is about 0.8 or
greater. Actual thruster design dimensions and weights will vary
depending on the application.
[0097] Another embodiment of the invention is illustrated in FIG.
10 which depicts a more detailed view of a portion of
panel/thruster 36. Shown in FIG. 3, panel/thruster 36 includes a
layer of fuel 12 sandwiched by facesheets 110. In some embodiments,
the facesheets are made from a material able to withstand the
temperatures reached during pyrolysis and/or combustion, such as
titanium. In other embodiments, the panel/thruster also
incorporates other additional structural support material (e.g., a
metallic or carbon mesh); oxidizing materials; channels for the
flow of oxidant; heat sources; and/or insulating material. The
layer of fuel 12 in panel/thruster 36 is partitioned into
individual cells by dividers 112.
[0098] FIG. 11 depicts an overhead view of self-consuming
panel/thruster 36 with facesheets 110 omitted in order to more
clearly illustrated how fuel 12 is partitioned by dividers 112.
Propulsive gases are formed by the previously mentioned methods and
processes of this invention, and directed away from panel/thruster
36 through a suitable device, such as a nozzle (not shown), to
produce thrust 120. In the embodiment illustrated in FIG. 11, the
propulsive gas is directed in two directions at a right angle to
one another so as to generate thrust along both the X and Y axes.
In some embodiments, the panel/thruster is constructed so that the
propulsive gas is capable of being directed by suitable means, such
as a controllable and, optionally, multiported nozzle, at virtually
any angle or combination of angles to provide thrust in a desired
direction. For example, in one embodiment, the self-consuming
panel/thruster is constructed to direct propulsive gas in the Z
axis as well. In that way, the thrust is produced in any desired
direction by, for example, controlling the amount of propulsive gas
directed in either the X, Y, and/or Z axes.
[0099] FIGS. 12 and 13 depict a cross-sectional side view and a
cross-sectional lateral view, respectively, of panel/thruster 130.
Fuel 138 defines channels 132, which carry oxidizer to the site of
pyrolysis and/or combustion. Panel/thruster 130 also includes
facesheets 134, which sandwich fuel 138. Fuel 138 incorporates
additional structural support materials, such as mesh 136, that
also can operate as an ignition or heat source.
[0100] In some embodiments, this invention includes a method of
producing work. For example, the method can comprise the steps of
heating at least a portion of a material that includes
polyoxymethylene to produce a gas and directing the gas to a means
for producing work, thereby producing work.
[0101] An example of means for producing work is a turbine. A
combustion and/or pyrolyzation reaction produces a gas from the
fuels of this invention, and the gas is directed towards the
turbine. The gas produces work, which the turbine uses to produce,
for example, an electric current or other forms of energy.
[0102] This invention also includes a process for fabricating
structural composites that include the fuel. In one embodiment, the
processes includes the steps of placing a mold material that
includes POM between plates of a mold, and applying pressure until
the mold material has been cured. In another embodiment, the
process includes heating the mold material until it has been cured
at a temperature below the ignition temperature of the mold
material. Preferably the temperature is between 160.degree. C. to
185.degree. C. Most preferably, the temperature is between
170.degree. C. and 175.degree. C. In yet another embodiment, a
plurality of plates are used to produce more than one structural
composite during a single curing process.
[0103] In one embodiment, additional materials are included in the
mold material such as, for example, energetic additives, oxidants,
and/or additional structural support materials. In another
embodiment, the plates are lined with additional structural support
material so that the finished structural composite is encased in
the additional structural support material.
[0104] The pressure and/or heat of the mold is maintained until the
mold material has been cured to the desired extent. Determining the
extent to which the mold material should be cured and what
combination or pressure and temperature to use can be accomplished
through a variety of methods (e.g., visual inspection and testing
of physical properties) and will depend on the physical properties
required for a given application. For example, if tensile strength
is a relatively important property of the finished structural
composite, the cure time which gives the necessary strength can be
found by testing structural composites cured for various periods of
time and at various temperatures and pressures. In one embodiment,
the cured structural composite is machined to the correct size and
shape necessary for the application of interest.
[0105] In one embodiment, the process for fabricating structural
composites include placing a mold material between plates of a
mold, wherein the mold material includes polyoxymethylene and at
least one material selected from the group consisting of an
oxidant, a structural reinforcement, and an energetic additive, and
applying pressure to the mold material to at least partially cure
the mold material and thereby form a POM rod. In a further
embodiment, the process includes machining the POM rod to produce
radial slots, inserting additional structural reinforcement into
the radial slots (e.g., carbon fiber structural reinforcement), and
inserting the POM rod into a sleeve or cylinder. In some
embodiments, the POM rod and cylinder can be heated to further cure
the POM material. Suitable temperatures for further curing will
vary with the demands of a given application. Examples of suitable
temperature ranges for further curing include a range from about
160.degree. C. to about 185.degree. C., or a range from about
170.degree. C. to about 175.degree. C.
[0106] Example of cylindrical component 300, formed by the
previously described methods, is shown in FIG. 14. Cylindrical
component 300 includes POM material 304 encased by outer sleeve
302. In some embodiments, the outer sleeve is metallic or is a
carbon tube made from carbon fibers and carbon cloth. Optionally,
POM material 304 is reinforced with additional materials (e.g.,
carbon fibers, carbon cloth, boron fibers, boron cloth, metallic
mesh, etc.). The particular method of fabrication will depend on
the type of reinforcement material used and the type of outer
sleeve material.
[0107] The following examples are not intended to limit the
invention in any way.
Example 1
Fabrication of Cylindrical Component
[0108] A cylindrical component similar to that shown in FIG. 14 was
formed by machining a commercially available rod of POM material
304 to produce center bore 306 and radial slots, into which
longitudinal webs of reinforcement material 308 are inserted.
Examples of suitable reinforcement material include carbon cloth or
fiber within an epoxy or phenolic matrix.) The resulting reinforced
POM rod was then cooled to a temperature of between about
-10.degree. C. to about 0.degree. C. to induce shrinkage. Metallic
sleeve 302 was heated above .about.100.degree. C. to induce radial
thermal expansion. The POM rod was then inserted into the metallic
sleeve and the assembly cured at temperatures in the range of about
100.degree. C. to about 150.degree. C. for over an hour to allow
consolidation of reinforcement material 308 with the surrounding
POM matrix. A tight mechanical force fit of the POM rod within the
metallic sleeve was thus accomplished. Optionally, the bond between
the POM rod and the metallic sleeve can be improved by application
of commercially available bonding agents such as, for example, the
rubber-based CHEMLOCK thermosetting adhesive and NARMCO
thermosetting adhesive, epoxy-based RESINWELD thermosetting
adhesive, and phenolic-based Phenoweld.RTM. thermosetting
adhesive.
Example 2
Summary of Open Burning Results
[0109] An amount of POM-A and POM-B was warmed in the presence of
various oxidants to measure melting, pyrolysis, and self-ignition
points.
[0110] POM-A, combined with either N.sub.2O.sub.4, NO.sub.2, or
air, melted at about 175.degree. C. Pyrolysis began at about
235.degree. C. POM-A, combined with either N.sub.2O.sub.4 or
NO.sub.2, self-ignited at around 235-275.degree. C., and at around
350-400.degree. C. when mixed with air. These values are in line
with known values, which cite a melting point of about 175.degree.
C., a pyrolysis point of between about 200.degree. C. and about
400.degree. C., and a self-ignition point with air in the range of
about 323-375.degree. C.
[0111] POM-B, combined with either N.sub.2O.sub.4, NO.sub.2, or
air, melted at about 165.degree. C. Pyrolysis began at about
215.degree. C. POM-B, combined with either N.sub.2O.sub.4 or
NO.sub.2, self-ignited at around 250-275.degree. C. POM-B, combined
with air, self-ignited at a temperature greater than about
350.degree. C.
Example 3
Mass Spectrometry Data of Thermal Decomposition Products
[0112] FIG. 15 shows mass spectrometry data for products (measured
in .mu.g) produced during the thermal decomposition of POM at
various temperatures. The products include carbon monoxide,
formaldehyde, and other compounds (such as water or carbon dioxide)
that were formed in side reactions or were initially present as
impurities in the reaction materials. The presence of hydrogen was
inferred from the presence of carbon monoxide. The trial runs
listed as 1-3 were conducted at a temperature of .about.400 C,
those listed as 5-8 were conducted at .about.500 C, those listed as
10-12 were conducted at .about.750 C, and those listed as 14-17
were conducted at .about.1000 C. The data clearly demonstrates that
at temperatures of .about.500.degree. C. or less, the primary fuel
product is formaldehyde. For decompositions at temperatures above
.about.750.degree. C. the primary fuel products are carbon monoxide
and hydrogen.
Example 4
Measurements of Pressure and Temperature in Formaldehyde Storage
Chamber
[0113] In order to evaluate the feasibility of storing formaldehyde
vapors produced from POM pyrolysis, 13 grams of solid POM was
placed in a heating chamber. The temperature of the POM was raised
to approximately 350.degree. C. so that predominantly formaldehyde
was produced. The resulting formaldehyde vapor was admitted into a
storage chamber which was maintained at a different temperature.
The temperature and pressure of the gas in the storage chamber was
continuously monitored. FIG. 16 shows the pressure of the vapor
mass as a function of time. As the POM material was pyrolyzed, the
vapor pressure increased until an equilibrium point was
reached.
[0114] FIG. 16 also shows the pressure and temperature of the
storage chamber, which was maintained initially at 70.degree. C.
and increased gradually as POM was pyrolyzed and formaldehyde vapor
filled the storage chamber. About 12 grams of the solid POM was
pyrolyzed, leaving 1 gram in the heating chamber. The mass of the
formaldehyde in the vapor phase stabilized at about 9 grams. As the
vapor's temperature equilibrated to approximately 75.degree. C.,
the pressure stopped rising and remained constant as POM continued
to pyrolyze. The value of this equilibrium pressure (.about.290
psi) corresponds to the vapor pressure of formaldehyde at
75.degree. C. (indicated by the horizontal bar). It was concluded
that the storage chamber contained an equilibrium mixture of
gaseous formaldehyde (.about.9 g) and liquid formaldehyde (.about.2
g) at 75.degree. C. at about 20 atm. This shows that solid POM can
be converted to gas which can be stored at moderate temperature and
pressure, and that this gas can be utilized for propulsion.
Example 5
Flow Burn Combustion of POM-A and POM-B with N.sub.2O.sub.4
[0115] Flow burn experiments were conducted to demonstrate
sustained combustion of POM materials with oxidizers.
[0116] Oxidizer (N.sub.2O.sub.4) from a tank flowed through a
PYREX.RTM. glass tube, filled with solid POM-A (available
commercially as a rod). The tube was three-fourths of an inch in
outer diameter and four inches in length. To initiate combustion, a
thin-wire electrical heater/igniter was introduced within the
tube.
[0117] First, N.sub.2O.sub.4 was directed from the tank to the
tube. The heater was then turned on and the POM began to pyrolyze.
The resulting pyrolyzation products, mixed with N.sub.2O.sub.4,
ignited around the hot wire, as was evidenced by a clearly
observable glow within the tube. The oxidizer flow was then
adjusted so that there was no brown gas emanating from the open end
of the tube, indicating that all of the oxidant entering the tube
was consumed (i.e., there was no excess oxidant). Once this
condition was reached, the heater was turned off and the glow
within the tube persisted, indicating self-sustained
combustion.
[0118] A similar experiment was performed using air as the oxidant
rather than N.sub.2O.sub.4. The POM-A material was also shown to
achieve a self-sustaining combustion. This demonstrates that a
dual-functional POM material would be capable of drawing a supply
of oxidant from the atmosphere and that an air-breathing vehicular
propulsion system is feasible.
[0119] Similar experiments were performed on POM-B. However, since
POM-B was only available in powder form, the experiments were
conducted in a horizontal PYREX.RTM. glass tube enclosing a
cylinder, made from stainless steel mesh, along its axis. The mesh
was sufficiently fine to prevent the powder from entering the
central cylinder through which N.sub.2O.sub.4 was introduced. The
heater/igniter assembly was inserted into the mesh tube from the
bottom end, such that the igniter was placed near the top end of
the tube. A thermocouple was also inserted into the mesh cylinder
from the top end and then the glass tube was closed with a metallic
fitting.
[0120] As before, an oxidant (N.sub.2O.sub.4) flowed through the
glass tube filled with powdered POM-B and the same ignition-burn
procedures were followed. Upon ignition, the burn zone first spread
radially from the steel cylinder to the glass surface, and then
proceeded axially along the length of the tube. POM-B burned very
smoothly and evenly, leaving the glass surface very clean, with
little or no remaining residue from the combustion process.
[0121] FIG. 17 shows the thermocouple measurements obtained during
the POM-B flow-burn experiment. The measurements give the
temperature of the products of combustion versus time. As shown,
the heater was turned on at about the 40 second mark. The heater
was turned off after about five seconds when ignition of the POM-B
material occurred. The large temperature jump at about the 50
second mark indicated that the combustion was self-sustaining. As
the N.sub.2O.sub.4 flow rate was varied the temperature of
combustion increased or decreased, demonstrating the
controllability of the combustion process.
Example 6
Flow Calorimetry Combustion of POM-B with N.sub.2O
[0122] Flow calorimetry experiments were performed to show the
combustion of POM-B with N.sub.2O, measure the energy released
during the combustion, and validate thermochemistry predictions.
Thermochemistry predictions indicated two possible reactions for
the POM-N.sub.2O bipropellant system, and are listed in Table
1.
TABLE-US-00001 TABLE 1 Energy Release Reaction # Products (kJ/g
mixture) 1 CO, H.sub.2O, N.sub.2 7.0 2 CO.sub.2, H.sub.2O, N.sub.2
21.0
[0123] The apparatus consisted of a PYREX.RTM. glass tube of
propellant POM-B through which the oxidizer (N.sub.2O) was
introduced from an oxidizer mass flow controller. A stainless steel
tube was connected at the bottom of the PYREX.RTM. glass tube and
wound through a water-filled thermos in order to act as a heat
exchanger. A thermocouple was used to monitored the temperature of
the water. A second thermocouple monitored the temperature of the
exhaust gases to ensure that it was close to the temperature of the
water, thus indicating that almost all of the heat of reaction had
been transferred to the water. Mass loss of the tube material and
the total amount of oxidizer utilized was also measured. A heater
was installed inside of the PYREX.RTM. glass tube to initiate the
reaction.
[0124] The heat released in the calorimetry experiments of POM-B
with N.sub.2O is consistent with the predominance of reaction 2,
i.e., POM is fully oxidized to CO.sub.2 and H.sub.2O while N.sub.2O
is reduced completely to N.sub.2. This demonstrates complete
combustion for the POM-N.sub.2O system, accompanied by high heat
release, which is important for the design of high performance
thrusters.
Example 7
Combustion of POM with HMX and N.sub.2O.sub.4
[0125] Energetic material HMX, which combines both a fuel and/or an
oxidant within its molecular structure, can be added to enhance the
performance of POM combustion. Before mixing HMX with POM-A, it was
necessary to ensure their chemical compatibility and estimate their
long-term stability. This was accomplished using a Simulated Bulk
Autoignition Tests (SBAT).
[0126] A few grams of a mixture of POM propellant and HMX were put
within a crucible which was then placed inside an aluminum block.
The crucible was kept thermally insulated from the block. The
aluminum block was heated slowly while thermocouples monitored the
temperature of both the mixture and the block. As the mixture
melted, its temperature was lower relative to the block
temperature. As the material was gradually heated, the POM-A and
HMX began to react with each other. As they reacted, they released
heat and the mixture temperature rose relative to the block
temperature. The data obtained from a SBAT is plotted as the
difference between the mixture temperature and block temperature
versus the block temperature.
[0127] FIG. 18 shows the SBAT results for POM-A alone. An endotherm
(i.e., a beginning of rapid negative temperature difference) began
at about 340.degree. F. (.about.171.degree. C.), which is
consistent with the melting temperature of POM-A.
[0128] FIG. 19 shows the SBAT results for HMX alone. At
approximately 355.degree. F. (.about.179.degree. C.), a slight
endotherm was observed. This is consistent with HMX's phase
transition from what is known as the .beta. crystalline structure
to the .delta. crystalline structure. A peak in an exotherm
(beginning of rapid positive temperature difference due to energy
release by the testing material) was observed at about 460.degree.
F. (.about.238.degree. C.).
[0129] FIG. 20 shows the SBAT results for a mixture composed of an
equal amount of POM-A and HMX. An endotherm began around
340.degree. F. (.about.170.degree. C.), which marked the melting of
POM-A as observed in the SBAT of POM-A alone. A second endotherm
was observed at about 370.degree. F. (.about.188.degree. C.),
marking the HMX phase shift. The peak exotherm occurred around
430.degree. F. (.about.220.degree. C.), about 30.degree. F. lower
(.about.17.degree. C. lower) than the exotherm observed in the SBAT
of HMX alone. This indicates that HMX is somewhat less stable when
mixed with POM-A. However, the peak exotherm of the mixture was
still about 90.degree. F. higher (.about.50.degree. C. higher) than
the melting temperature of POM-A. These differences indicate that
there is a sufficient safe range of temperatures where POM-A and
HMX may be mixed and processes during a fuel production
process.
[0130] FIG. 21 shows the SBAT results for POM-B alone. An endotherm
began about 37.degree. F. (.about.20.degree. C.) lower than that
recorded for POM-A alone.
[0131] FIG. 22 shows the SBAT results for a mixture composed of an
equal amount of both POM-B and HMX. An endotherm began around
320.degree. F. (.about.160.degree. C.), which marked the melting of
POM-B as observed in the SBAT of POM-B alone. As with POM-A, the
peak exotherm occurred around 430.degree. F. (.about.221.degree.
C.).
Example 8
Bomb Calorimetry Combustion of POM with HMX and N.sub.2O.sub.4
[0132] Following the demonstration of chemical compatibility
between POM-A and HMX, standard bomb calorimetry experiments were
conducted to measure the heat released during a reaction between a
POM-A/HMX mixture (75/25 wt %) and N.sub.2O.sub.4. Table 2 lists
some of the possible products of a POM-A/HMX reaction.
TABLE-US-00002 TABLE 2 Energy Released Reaction # Oxidizer Products
(kJ/g mixture) 1 N.sub.2O.sub.4 CO, H.sub.2O, NO 4.63 2
N.sub.2O.sub.4 CO, H.sub.2O, N.sub.2 5.93 3 N.sub.2O.sub.4
CO.sub.2, H.sub.2O, NO 9.75 4 N.sub.2O.sub.4 CO.sub.2, H.sub.2O,
N.sub.2 13.9
Based on the stoichiometry of reactions 1 and 4, a 1 gram portion
of the POM-A/HMX mixture (with a 75-25 molar ratio of POM-A to HMX)
was placed into a ceramic crucible. Chilled liquid N.sub.2O.sub.4
was added to the sample. The bomb calorimetry chamber was
pressurized with argon to 5 atm and the materials were electrically
ignited. Heat was transferred to the water bath and the resulting
temperature rise was measured. It was determined that the
combustion released 12.7 kJ/g of heat. The experiment was repeated,
and all measured values were within 3% of 12.7 kJ/g. This indicates
that when mixed with the energetic additive HMX and combusted with
the oxidizer N.sub.2O.sub.4, reaction 4 dominates and POM-A can be
fully oxidized to CO.sub.2 and H.sub.2O with N.sub.2O.sub.4 being
completely reduced to N.sub.2. This also indicates that POM-based
fuels can combust completely and give off a large amount of heat in
the process, both of these characteristics are important to the
design of high performance thrusters.
Example 9
Sustained Stable Combustion of POM and Carbon-Reinforced POM
Composites with Oxygen
[0133] A POM composite was constructed with DELRIN.RTM. reinforced
with a carbon cloth. The POM composite was combusted with oxygen
inside a thruster/stringer configuration similar to that
exemplified in FIG. 6. FIG. 23 shows pressure data as a function of
time from the sustained stable combustion (after ignition by a
squib) of the POM composite in the thruster/stinger
configuration.
Example 10
Sustained Stable Combustion of POM Composite with Hydrogen
Peroxide
[0134] A POM composite was combusted with liquid hydrogen peroxide
in a stringer/thruster configuration similar to that exemplified in
FIG. 6. FIGS. 24-27 show pressure data from a sustained stable
combustion as a function of time (measured in seconds). A catalyst
bed was encased within the shell of the stringer/thruster. The
catalyst bed was preheated and hydrogen peroxide directed through
it. The hydrogen peroxide decomposed into hot oxygen and steam,
which entered channel 72 within the self-consuming
stringer/thruster and reacted with the fuel.
[0135] The internal pressure of the stringer/thruster began at
atmospheric and increased quickly as the pyrolysis and combustion
products were formed. The pressure data from one test run is shown
in FIG. 24. The internal pressure of the stringer/thruster climbed
to more than 300 psia in about 12 seconds. FIG. 25 shows another
test run, where the internal pressure reached about 110 psia. FIG.
26 shows yet another test run where the internal pressure was
maintained at slightly less than 160 psia. The thruster/stringer
exhibited smooth, sustained combustion in all cases.
[0136] FIG. 27 shows still another test run where hydrogen peroxide
was supplied to the stringer/thruster in 3 separate pulses. The
internal pressure profile shows three spikes in internal pressure.
All three followed the change in oxidant flow relatively quickly,
with a lag time of only a few seconds or less.
[0137] FIG. 28 shows the pressure and temperature data obtained
from yet another run, including the pressure and temperature of the
hydrogen peroxide, the temperature of the catalyst, the combustion
inlet gas temperature, and the chamber pressure. Pressure (psia)
and temperature (F) are both shown on the Y-axis as a function of
time (sec). The pressure of the oxidant supply tank was kept
constant. Hydrogen peroxide was used as the oxidant. During the
preheat of the first 10 seconds, the catalyst temperature remained
relatively low. Ignition occurred at about 11 seconds. With
ignition, the catalyst temperature, as well as chamber pressure and
combustion inlet gas temperature, rises rapidly.
EQUIVALENTS
[0138] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims. For
example, all dimensions and weights identified with respect to
FIGS. 3 through 14 are nominal dimensions and weights; the
invention is not constrained by these dimensions and weights.
* * * * *