A monopropellant is a single liquid that serves as both fuel and oxidizer. A monopropellant decomposes into a hot gas in the presence of an appropriate catalyst, upon introduction of a high-energy spark, or upon introduction of similar point source ignition mechanism. Monopropellants, for example, can be used in a liquid-propellant rocket engine. A common example of a monopropellant is hydrazine, often used in spacecraft-attitude control jets. Another example is HAN (hydroxylammonium nitrate).
Another form of propellant is called a bipropellant, which consists of two substances usually stored separately: the fuel and the oxidizer. Anytime a combustion process is employed, pre-mixing of combustion components may be desirable. Examples of fuels which can benefit from pre-mixing prior to combustion include, without limitation, natural gas, gasoline, diesel, kerosene, ethane, ethylene, ethanol, methanol, methane, acetylene, and nitro methane. Examples of oxidizers that can be pre-mixed with said fuels include, without limitation, air, oxygen/inert gas mixes, oxygen, nitrous oxide, and hydrogen peroxide. Fuel components can be mixed with oxidizing components in many different ratios to make a pre-mixed bipropellant and thus obtain a desired combustion reaction. The flashback arrestor element described herein is specifically relevant to any situation where the combustion components are mixed prior to entering a combustion chamber.
Chemically reacting monopropellants and pre-mixed bipropellants contain constituents that liberate chemical energy through thermal decomposition and/or combustion. The chemical energy release is initiated by a mechanism designed within the chemical reaction chamber (where the majority of chemical energy release occurs). Commonly, this initiation mechanism is incorporated in the vicinity of a chemical reaction chamber's injector head.
Deflagration is a common form of combustion where the flame speed travels at velocities less than the speed of sound. Deflagration combustion is commonly associated with low pressures. However, contained or pressurized combustion may result in the more powerful detonation phenomenon.
A detonation is a phenomenon characterized by supersonic flame front propagation. Usually associated with detonation waves are pressure/temperature spikes and shock waves. The physics and corresponding reaction phenomenon are sufficiently different from a deflagration to warrant separate designations and analysis. The aforementioned conditions can result in a transient phenomenon containing immense power that can be used for destructive or carefully controlled constructive purposes.
An ignition source is any energy mechanism that causes a chemical combustion process to initiate. In combustion reactions, the reactants are at a higher energy state than the products following combustion. However, to release the energy stored within the chemical bonds of the reactants, a certain quantity of energy (activation energy) must first be provided. The sources of the initiation energy in a combustion process are referred to as ignition sources. Many ignition sources exist including, without limitation, electrical sparks, catalysts (substances which lower the activation energy by providing a surface which increases a reaction's chemical kinetics), heat sources, impact loads, compression, or any combination thereof.
If an ignition source exists downstream of a detonable mixture/detonable single component, in particular monopropellants and premixed bipropellants, flames can propagate (also known as “flashback”), through a feed line and into a storage container causing catastrophic system failure An ignition source downstream of a detonable mixture can cause a detonation to propagate upstream.
Rocket engines commonly operate with monopropellants that can have very high gas and/or liquid densities as compared to more conventional air/fuel mixtures or low-pressure fuel and oxidizer mixtures. Flashback at these much higher monopropellant energy densities is not readily controlled. As a result, high energy density monopropellants that have small quenching distances (e.g., fluid gap, pore, and/or effective fluid passageway diameters small enough such that flames cannot propagate through the passageway) have been traditionally avoided because of the flashback failure mechanism that is very difficult to control.
A tiered porosity flashback-suppressing element intended to advance safety in the use of highly combustible gases and liquids, particularly at high propellant densities (high gas pressure or liquid phase), in a tubing flow path is described herein. Such a flashback arrestor may be used, for example, in spacecraft propulsion, energy generation, work producing cycles, and general combustion reactions employing monopropellants and pre-mixed bipropellants. Accordingly, disclosed herein are materials, methods and devices relating to various components of such propulsion and work producing systems including, without limitation, micro-fluidic porous media elements, injector heads, flashback arrestors and shut-off valves in the field of rocket propulsion or other applications wherein combustible materials may be subject to flashback. The materials are variable density micro-fluidic porous media elements of sintered metal or other materials, and methods of making same. The flashback arrestors comprise such porous media elements and other elements to provide a flashback arrestor or shut-off valve for use with high temperature and pressure propellants in feed lines.
Disclosed are materials of variable density or tiered porosity micro-fluidic porous media structures of sintered metal or other materials, and methods of making same. While micro-fluidic materials may be used in filters, heat exchangers, catalyst beds, and lightweight structural materials, the disclosed tiered porosity materials and the corresponding processes for making these disclosed materials find particular use in components of rocket propulsion systems, such as injector heads, flashback arrestors and shut-off valves, and in similar components in other work producing systems where a detonation-susceptible fluid propellant or such energetic materials must be safely fed from a storage container to a chemical reaction chamber, a combustion chamber or the like where work is extracted from the resulting of heat of reaction.
Generally speaking, work extracting cycles that can implement the flashback arrestor element may include without limitation gas turbine cycles (e.g., Brayton similar cycles,) Otto cycles, diesel cycles, and constant pressure expansions of combusted products (e.g., similar to pneumatic machines). Accordingly, it should be understood that materials, devices, and methods described herein may have other applications in addition to rocket propulsion.
In an embodiment, the method of producing aluminum porous media disclosed herein comprises mixing a binding agent with aluminum powder to generate a first mixture, heating the first mixture to a sub aluminum sintering temperature to get a homogeneous composite of the metal powder, heating the homogeneous composite to an aluminum sintering temperature to sinter-bond the aluminum powder to get aluminum porous media of first porosity, and treating the aluminum porous media of first porosity to remove an oxide patina from the porous media of first porosity.
In an alternate embodiment, removing the oxide layer of the aluminum porous media of first porosity further comprises bathing the aluminum porous media of first porosity in an oxide removing acid such as muriatic acid. In yet another embodiment, the aluminum porous media bathed into the oxide removing acid is exposed to a jet of an inert gas such as argon, helium, etc. In yet alternate embodiment, at least one of silicon beads and silicon dioxide beads are added to the mixture and subsequently the at least one of silicon beads and silicon dioxide beads are dissolved using an etching process.
In an embodiment, an aluminum porous media of a first porosity and aluminum porous media of a second porosity are merged together to create an aluminum porous media of varying porosity, wherein the first porosity is different than the second porosity. The merging may comprise pressing the aluminum porous media of the first porosity with the aluminum porous media of the second porosity. In an alternate embodiment, the method of creating an aluminum porous media of a first porosity may further comprise striking-off a first layer of aluminum porous media of the first porosity before merging the aluminum porous media of the first porosity with the aluminum porous media of the second porosity.
An alternate embodiment of the method disclosed herein provides creating a layered micro-fluidic porous media element, the method comprising fabricating a plurality of micro-fluidic porous media slices, registering each of the plurality of micro-fluidic porous media slices, and bonding one or more of the plurality of micro-fluidic porous media slices, wherein fabricating a plurality of micro-fluidic porous media slices further comprises coating a thin film with a photoresist coating, covering the coated thin film with a mask, exposing the covered thin film to electromagnetic energy to develop the mask, etching the exposed thin film, and removing the mask.
An alternate embodiment of the method disclosed herein provides generating a plurality of metal foils with an array of micro-sized pores, and bonding the plurality of metal foils with an array of micro-sized pores. In an implementation of such a method, generating the plurality of metal foils may further comprise passing the laser source through a microlens array, and ablating a metal foil with the laser source passed through the microlens array. A yet alternate implementation may further comprise removing an oxide layer from each of the plurality of metal foils before bonding the plurality of metal foils.
In an implementation, the aluminum porous media may be used in a monopropellant system comprising, a monopropellant tank with an internal surface made of an aluminum porous media element, a monopropellant delivery apparatus with an internal surface made of an aluminum porous media element, and a flashback arresting device having a microfluidic porous element adapted to deliver the monopropellant to an ignition device, wherein the internal surface of the monopropellant tank and the internal surface of the monopropellant delivery apparatus are bonded together. In an embodiment of such a monopropellant system, the porosity of the internal surface of the monopropellant tank is different from the porosity of the internal surface of the monopropellant delivery apparatus.
Other implementations are also described and recited herein.
In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. For example, while various features are ascribed to particular embodiments, it should be appreciated that the features described with respect to one embodiment may be incorporated with other embodiments as well. Similarly, however, no single feature or features of any described embodiment should be considered essential to the invention, as other embodiments of the invention may omit such features.
Equation 1 below covers gases and liquids, it uses the mass flux moving through the structure rather than the fluid velocity as there is no ambiguity in terms of what velocity you are speaking of when using “fluid velocity”. All combustion reactions (from which detonations could be derived) are most commonly based on mass or molar flow rates of constituents rather than fluid velocities.
Wherein dP/ds—Pressure change along a fluid streamline moving through the element, K—micro-fluid porous media permeability coefficient, C—micro-fluidic porous media Form coefficient, μ—Fluid dynamic viscosity, ρ—fluid density, {dot over (m)}″—mass flux of fluid moving through micro-fluidic porous media element.
The special case of further derivation of Equation 2 below, for ideal gases flowing through a structure of thickness, L (this equation is consistent with our
Wherein, P1—Pressure immediately upstream of micro-fluidic porous media element, P2—Pressure immediately downstream of micro-fluidic porous media element, L—micro-fluidic porous media element thickness, K—micro-fluid porous media permeability coefficient, C—micro-fluidic porous media Form coefficient, R—gas constant, T—gas temperature in micro-fluidic porous media element, μ—Fluid dynamic viscosity, ρ—fluid density, {dot over (m)}″—mass flux of fluid moving through micro-fluidic porous media element.
Propellant from the monopropellant tank 112 is fed to the combustion chamber 114 via monopropellant lines 118. Flashback-arresting shut-off valve 102 may shut off the fuel in the event of the flashback. A flashback arrestor 104 diverts the energy caused by a flashback away from the lines 118 and tank 112. Flashback-arresting ignition interface 106 may contain a micro-fluidic porous media structure of sintered metal or other heat resistance materials. Further, the shut-off valve 102 and/or the flashback arrestor 104 may also contain a micro-fluidic porous media structure. Note that while the flashback arresting devices 102, 104, 106 are disclosed in
In an embodiment of the space craft 100, substantial, or all, parts of the monopropellant propulsion system 110 may be made of aluminum porous media disclosed herein. Specifically, in such an embodiment, various components of the monopropellant propulsion system 110, such as the monopropellant tank 112, the lines 118, the combustion chamber 114, the nozzle 116, etc., may be made of the aluminum porous media disclosed herein. In an embodiment, the aluminum porous media may be made of variable density and the density of the aluminum porous media in each component of the monopropellant propulsion system 110 may be different from the density in other components. Moreover, the gradient of the density of the aluminum porous media may also be different in different components of the monopropellant propulsion system 110.
Thus, in an embodiment of the monopropellant propulsion system 110, various components, such as the monopropellant tank 112, the lines 118, the combustion chamber 114, the nozzle 116, etc., may be made of aluminum porous media in a manner so that there are no transition joints between the various components of the monopropellant propulsion system 110 between dissimilar materials.
Because aluminum is a very light-weight material, using aluminum porous media in one or more components of the monopropellant propulsion system 110 allows reducing overall weight of the monopropellant propulsion system 110. Similarly aluminum porous media may also be used in other engines, resulting in reduced mass of the engine. In one embodiment, the gradient of porosity of aluminum porous media used in various components of the vehicle 100, or components of other engines, may be determined based on the gradient of the temperatures that may affect one or more of such components. In yet another embodiment, one or more components of the monopropellant propulsion system 110, or components of other engines, may be constructed using regeneratively cooled micro-fluidic porous arrays of aluminum. These could include powerplant heat exchangers, generators, and piston engines requiring heat dissipation.
Moreover, one or more of these components include one or more micro-fluidic porous media structures, in particular one or more tiered porosity flashback suppressing elements made of materials and using methods as will be detailed below. It should be understood that while it is preferred to incorporate such tiered porosity elements into valve structures, blast deflector structures and the like, in some situations and with some monopropellants or pre-mixed bipropellants, it may be possible or even desirable to interpose such elements alone in the propellant flow path.
In a second depicted implementation, bipropellant tanks (i.e., fuel tank 228 and oxidizer tank 230) are premixed before injection into the power generation system 220, 222, or 224. Example fuels for such systems include, without limitation, natural gas, gasoline, diesel, kerosene, ethane, ethylene, ethanol, methanol, methane, acetylene, and nitro methane. Example oxidizers for such systems include, without limitation, air, oxygen/inert gas mixtures, oxygen, nitrous oxide, and hydrogen peroxide. Fuel components can be mixed with oxidizing components in many different ratios to obtain a desired combustion reaction.
Flashback valve 234, flashback arrestor 236, and/or the regulator 232 may contain flashback-arresting or suppressing technology as presently disclosed. The flashback arresting technology prevents or stops detonation waves from propagating upstream towards the tanks 226, 228, 230 and causing catastrophic system failure in feed lines downstream of where fuel is premixed with oxidizer. Further, the presently disclosed flashback arresting technology (e.g., flashback arrestor 236) may also include detonation wave arrestor/diverter to divert energy of the detonation waves away from the feed lines and/or fuel tank 228 and oxidizer tank 230.
Further,
In an embodiment of the components illustrated in flowchart 200, one or more of the components may be made of the aluminum porous media disclosed herein. For example, in an embodiment, the monopropellant tank 226, the injectors 238, and one or more sections of the regulator 232 and the flashback diverter 230 may be made of the aluminum porous media disclosed herein. In yet alternate embodiment, each of these components may be made of the aluminum porous media disclosed herein having porosity different from each other.
Each of the bottom compression fitting 310 and the top compression fitting 312 provides a path for propellant fluids (gases, liquids, or a combination thereof) through cavities in their bodies. The bottom compression fitting 310 may be designed so that it may be connected to tubes, pipes or other mechanism designed for transporting such fluids towards the bottom compression fitting 310 from the tanks 226, 228, 230. Similarly, the top compression fitting 312 may be designed so that it may be connected to tubes, pipes or other mechanism designed for transporting a fluid away from the bottom compression fitting 312 towards the injectors 238. The flame arrestor structure 306 may be designed to incorporate a receptor 326 on one of its surface to hold a tiered porosity element 330. Note that while in the embodiment illustrated in
The flashback arrestor assembly 300 is configured to be positioned in the path of fluid from a fluid reservoir such as the tanks 226, 228, 230 to the injectors 238. Thus, the fluid from a tank may travel through a connecting pipe, tube, or other mechanism towards the bottom compression fitting 310. The bottom compression fitting 310 is connected to the flame arrestor structure 306 in a manner so that the fluid from the bottom compression fitting 310 travels towards the receptor 326 containing the porous media element 330. As discussed above, the porous media element 330 allows the fluid to pass through it, but is structured to resist a flame front from progressing through it, as will be detailed below. Moreover, the fluid may also travel in the direction of the surface of the receptor 326 and thus, perpendicular to the flow of the fluid through the porous media. In
The bottom surface of the detonation wave deflector 302 is designed so that it deflects the fluid travelling thorough the porous media element 330 towards the periphery of the detonation wave deflector 302. Moreover, the side surface of the detonation wave deflector 302 is designed in a manner so that when the burst membrane 308 is fitted around the detonation wave deflector 302, a number of flow paths are formed along the side surface of the detonation wave deflector 302. The fluid coming from the porous media element 330 and the fluid traveling along the surface of the receptor 326 may travel through such flow paths formed between the detonation wave deflector 302 and the burst membrane 308 towards the cap 304. Directional arrows 336 denote such path of fluid flow between the detonation wave deflector 302 and the burst membrane 308.
The outer surface of the detonation wave deflector 302 that is designed to be adjacent to the cap 304 may also be designed in a manner so as to form a number of flow paths 338 between the detonation wave deflector 302 and the cap 304. The fluid traveling between the detonation wave deflector 302 and the burst membrane 308 along paths 336 may flow though the path 338 towards the central opening in the body of the cap 304. Subsequently, the fluid may flow through the opening in the cap 304 towards the top compression fitting 312 and from there towards a pipe, tube, or other mechanism connecting the top compression fitting to the injector 238.
In an alternate embodiment, the tiered porosity flashback-suppressing element can be incorporated, either alone or in an arrestor assembly as described above, into a shut-off valve. For example, a shut-off valve may be placed adjacent to the receptor 326 and attached to the burst membrane 308 so that in the case of a flashback, the shutoff valve closes off the flow of fluid from the tank 226, 228, 230 to the injector 238. As discussed below, such a shut-off valve may be attached to the burst membrane 308 in a manner to trigger a shut-off in case of a bursting of the burst membrane 308.
An alternate implementation may provide a propellant shut-off assembly for isolating a propellant source in the event of a flashback, wherein the propellant shut-off assembly may include a burst membrane configured to fail in presence of the flashback and a biased closed shut-off valve attached to the burst membrane. Such a shut-off valve may be held open by the burst membrane while the burst member is intact. Yet another implementation may provide a method of isolating a propellant source in the event a flashback. In such an embodiment, while propellant moves through the propellant shut-off assembly in a propellant flow direction, the propellant shut-off assembly may experience a flashback. As a result, a burst membrane within the propellant shut-off assembly may be fractured to failure because of the flashback. Such a failure of the burst membrane causes the propellant shut-off assembly to close and isolate a propellant source from any components of the propellant delivery system that have failed as a result of the flashback.
In case of an incident causing flashback, the porous element 330 operates as a thermal sponge that absorbs combustion energy at rates higher than the rate at which a detonation wave can release combustion energy. As a result, the porous media element 330 provides a detonation quenching. However, because in the normal operation, the porous media element 330 is also providing a path for combustible fluid, the porous media element 330's effective microchannel diameter sizing and surface area are strategically chosen for each particular application based on combustible fluid mass flow rate requirements and allowable pressure drop. While the quenching distance of the porous media element 330 may be sufficient to arrest a primary detonation wave, the energy release from a line flashback can cause secondary ignitions through mechanical failures and/or heat transport through solid material. This conductive heat transport can produce hot spots in direct contact with un-combusted combustible fluid sufficient to ignite a propellant upstream of the flashback arrestor assembly 300.
However, the detonation wave deflector 302 together with the burst membrane 308 provides additional protection to the sources of combustible fluids from the potential harm caused by such additional detonation wave. Specifically, the detonation wave deflector 302, together with the burst membrane 308, allows the detonation products travelling from the opening in the top compression fitting 312 to be vented before they reach the porous media element 330 or at least in the immediate vicinity of the porous media element 330. Moreover, the detonation wave deflector 302, when hit by a combustion wave, disperses the shock wave away from the porous media element 330. Specifically, the detonation wave deflector 302 directs the shock wave energy towards the burst membrane 308.
For ideal detonation wave quenching, the micro-fluidic porous media must consist of sufficiently small fluid channel diameters and/or tortuous paths to quench effectively back propagation of a flame front. At the same time, the micro-fluidic porous media must be made sufficiently thin to avoid excessive pressure drop during normal operation (i.e., it permits the flow of propellant into the combustion chamber). To quench a flame, typical flame propagation into a medium is on the order of 1's to 100's of quenching diameters into the medium. For example, for a combustible fluid that requires 10 micron pores to quench a flame, the thickness of the membrane necessary to quench the flame may be as small as ˜100 microns. However, the combustion process may generate combustion pressures that drive the preferred membrane thickness to be significantly greater in order to provide mechanical strength during a combustion event. If the micro-fluidic porous media is nominally designed for both small quenching distances and very large thicknesses to accommodate the combustion pressures, very large fluid pressure drops may ensue when flowing a combustible fluid through the micro-fluidic porous media structure, i.e., a thick membrane of small pore size will interfere with the normal flow of propellant into the combustion chamber.
Therefore, a more optimal design for a flashback arrestor is one in which the pore diameters of the micro-fluidic porous media varies through the thickness of the micro-fluidic porous media. Near the front surface of the micro-fluidic porous media where the combustion event may be initiated (e.g., on the combustion chamber side of the flashback arrestor), the effective pore diameters should be much smaller than the much thicker porous structure which lies below (e.g., on the propellant tank side of the flashback arrestor). This micro-fluidic porous media structure transfers mechanical loads from near the surface where the combustion event has occurred and ensures that the overall structure does not mechanically fail. Therefore, the process for creating variable density micro-fluidic porous media should meet the requirements for preventing flashback with much lower pressure drops than micro-fluidic porous media structures that have uniform pore structures throughout.
The goal is to provide a porous media element that prevents flashback with minimum propellant flow pressure drop through the micro-fluidic porous media. This element may be composed of metal or other materials. In one embodiment, the membrane is composed of metal or other materials that are ductile, highly thermally conductive to dissipate heat, and can take many thermal cycles without cracking. The pores are approximately within a range of 10 nanometers to 100 microns in diameter.
One method for providing such characteristics with a very thin micro-fluidic porous media membrane to minimize fluid pressure drop through the membrane utilizes one or more of the fabrication processes disclosed below.
In one embodiment, in order to create very thin sintered metal membranes with reproducible thicknesses, a process is used in which a binding agent or other fluid medium is mixed with metal powders in a batch process. The binder (for example, a mixture of paraffin based waxes) has physical properties such that at slightly elevated temperatures, it will melt and become fluid, thus allowing conventional mixing with selected metal powders to create a homogenous blended composite. The system 1000 exemplifies one embodiment in which the mixing of the binder 1002 with the powder 1004 may be done by mechanical mixing apparatus 1006. At ambient or room temperature, the binder/metal mixture will remain in a plastic such as for example, clay-like, state. At this stage, the plasticity of the mix provides amenability to placement on a molding surface or substrate to form the composite material to a prescribed thicknesses and shape. Very thin structures may be reproducibly made using this method. For example, in one embodiment a structure of approximately 0.020 inches thickness may be made by using the method described above. Subsequently, the mixture may be heated at a temperature lower than that of the metal-sintering temperature, initially to melt out binding agent leaving a porous part of the prescribed thickness and shape. The part may then be subjected to higher temperatures to become sinter-bonded. A pressing mechanism may also be deployed at the time of sintering that will apply a force to the part for consolidation and strengthening.
Oxidation Reduction: Micro-fluidic porous media structures made of metals such as aluminum may be treated by an additional chemical process in which the aluminum oxide patina is at least partially reduced back to aluminum metal. An oxide patina reduces the particle to particle bond strength, which will compromise the strength of the micro-fluidic porous media structure. Reducing agents may be used to reduce the aluminum oxide patina during the mixing and/or sintering processes. Liquid reductants (i.e. ammonia and ammonia based compounds, oxalic acid, muriatic acid, formic acid, dilute nitric acid, sodium mercury amalgams, dilute hydrochloric acid containing amalgams), metal reductants (i.e. zinc, tin, magnesium), hydride reductants (i.e. LiAlH, NaBH, BiH3) powders or suspensions of powdered reductants may be mixed in prior to sintering. A releasing agent such as alkyl stearates or stearic acid may be used in order to release the micro-fluidic porous media structure from the mold.
Dissolvable pore space occupiers: Silicon or silicon dioxide beads may be mixed into the homogenous batch process shown in
For aluminum fabrication using PSMP, reduction oxidation-reduction agents are used to reduce the surface oxidation of the particles and performed in an inert, non-oxidizing environment.
The process illustrated in
The process of registering each slice is shown in
Mechanical alteration to an existing porous element can minimize flow alteration while increasing the element's flashback resistance. A number of post manufacturing processes may effectively achieve the same result of reduction in mean pore diameter. These post manufacturing processes may include, without limitation, cold pressing, water hammering, ball peening, or detonation “burn in” of a first porosity medium to form a layer of having a second, preferably smaller porosity. In one embodiment, the method of detonation burn in has produced desirable results. In this process, a detonable fluid is loaded within a fixture to a density below the predicted flashback failure point of the porous element and the fluid is intentionally detonated. If this process is repeated with progressively higher combustible fluid density, mechanical alteration particularly near the surface structure on the combustion side of a porous element can be achieved to effectively decrease the pore size of the membrane near this surface. In addition to mechanical alteration of the structure, this process can be used to validate a flashback arresting device's characteristics prior to use as a flashback arresting device.
Specifically,
Therefore, in an embodiment, micro-fluidic porous media elements are repeatedly exposed to detonation waves of weak but progressively increasing strength. Thus, for example, a micro-fluidic porous media element may be first exposed to a detonation wave of 0.015 g/cc detonation wave. If the exposure does not result in the failure, it may be subsequently exposed to a detonation wave of 0.016 g/cc, etc. Based on the characteristics of the micro-fluidic porous media element, it may be empirically decided as to what point the exposure to detonation wave of increasing strength should stop.
Not only must the micro-fluidic porous media element be able to quench the detonation wave by dissipating heat in the micro-fluidic structure at a higher rate than it is being chemically released, but the structure must also be designed to tolerate the high transient combustion wave (e.g. detonation) pressures that ultimately will be incident on the micro-fluidic porous media element. This structural requirement can be met through a number of design means including, without limitation, working with geometries that minimize exposure of the micro-fluidic porous media elements to maximum strength combustion waves, and providing sufficient material of a given type to dissipate the energy of the combustion wave without causing material failure or alteration of the micro-fluidic structure.
For example, it is possible simply to increase the thickness of a micro-fluidic porous media element in order to effectively dissipate the detonation wave shock energy without mechanically failing. However, this method would also increase the pressure drop through the micro porous element. As discussed above, any design must balance the needs of desired flow of propellants to the combustion chamber with the ability to provide flashback protection characteristics. However, if the issues of pressure drop and the scale of the element can be overcome, there are valid methods by which to increase the mechanical strength of the micro porous element.
To achieve this end, mechanical backing reinforcement may be placed in strategic locations to increase the micro-fluidic porous media element's (and backing structure's) tolerance to shock energy without mechanically failing. In this configuration, a very thin membrane-like structure that quenches the combustion wave is bonded onto a stronger mechanical substrate that is also permeable and/or contains fluid passageways to the thinner micro-fluidic porous media element. This backing structure could be, for example, a higher permeability porous media element bonded to the much thinner micro-fluidic porous media element. Alternatively, the micro-fluidic porous media element's permeability may be designed to vary continuously. In another configuration, the very thin membrane and/or a variable density micro-fluidic porous media element can be placed on a solid backing structure that allows high load transfer without micro-fluidic porous media element failure and simultaneously contains fluid passageways to distribute fluid across the micro-fluidic porous media element. To achieve this end, mechanical reinforcement should be placed in strategic locations to minimize the internal stresses, yet maximize the porous element's fluid throughput. Such backing structures are shown as integrally formed in flame arrestor structure 306 as described above.
Another method by which to mitigate the mechanical failure is to utilize structural design of the micro-fluidic porous media elements that can handle much higher compressive pressure loads. Such structures may consist without limitation geometries such as a cone or hemisphere. The bulk of these shapes may have a porosity with relatively high propellant fluid flow, but likely inadequate to suppress flashback in that fluid, while the first or outer surface of such shapes have been made or treated to have the requisite mean porosity to dependably suppress such a flashback. The first or outer surface would be facing “downstream” i.e., away from the propellant storage vessel or vessels and towards the ignition source i.e., combustion chamber of a rocket engine, gas generator or power plant.
At step 1802, a binding agent such as wax is mixed with a metal powder such as aluminum. Such mixing is illustrated in further detail in
A porous media element created in the above manner may have a surface patina created due to an oxidation-reduction. At step 1810, the porous media element may be treated to remove the patina surface. Such removal of patina may include, for example, treating the porous media element with a reducing agents to reduce the aluminum oxide patina during the mixing and/or sintering processes. Again, treating the porous media element with reducing agent may be done concurrently with one of the steps 1804-1808. Subsequently, at a step 1812, an EDM wire or plunge may be used to strike-off a layer of material from the porous media element.
At step 1814, one or more films of porous media element may be merged together. Such merging is disclosed in further detail in
The tiered porosity flashback suppressing elements can be thought of crudely as a thermal sponge that absorbs the combustion energy at rates higher than the detonation wave can release. The rate of energy absorption of a micro-fluidic porous media element increases with smaller flow passage effective diameter and to some extent the tortuosity and geometry of the fluid path. It should be noted that supersonic detonation wave quenching distances can typically be significantly smaller than the subsonic deflagration wave quenching distances given the dramatically different rates of thermal release associated with the speed of the wave. Many high energy density propellants have submicron to 100-micron detonation wave quenching distances. The disclosed elements, created by sintering pre-sorted metal media, can effectively create flow paths as small as 0.1 micron and can conceivably eventually be manufactured down into nanometer scales. The described flashback arrestor creates sufficiently small flow paths to quench high-pressure closed line detonations preventing ignition past said flashback arrestor.
Preferably, then, the porous elements of whatever shape can be made of a precursor particles or sheets and should be of a material that is physically robust, has a high thermal conductivity and thermal diffusivity, and can be bonded to form a porous body having a controllable mean pore diameter. Such materials should also be chemically inert with regard to the propellant flowing therethrough. Alternatively, some reactive or catalytic but otherwise desirable precursor materials can be made inert by isolating the surfaces of the elements with an inert coating. Without limitation, inert coatings for a particular propellant (e.g. MgO, Al2O3, and Yttria) may be applied to allow use of materials that may be catalytic with the propellant.
In an embodiment, the bathing and bonding process described above with respect to
The above specification, examples, and data provide a complete description of the structure and use of example embodiments of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Furthermore, structural features of the different embodiments may be combined in yet another embodiment without departing from the recited claims.
The present application claims benefit of priority to U.S. Provisional Patent Application No. 61/223,611, entitled “Propulsion Systems and Components Thereof” and filed on Jul. 7, 2009, which is specifically incorporated by reference herein for all that it discloses or teaches. Further, the present application is related to U.S. patent application Ser. No. 11/950,174, entitled “Spark-Integrated Propellant Injector Head With Flashback Barrier”, filed on Dec. 4, 2007 and to U.S. patent application Ser. No. 12/633,770 entitled “Regeneratively Cooled Porous Media Jacket” filed on Dec. 8, 2009. Further, the present application is related to: U.S. patent application Ser. No. ______, entitled “Tiered Porosity Flashback Suppressing Elements For Monopropellant Or Pre-Mixed Bipropellant Systems” (Attorney Docket No. 488-011-USP1), U.S. patent application Ser. No. 12/831,767, entitled “Flashback Shut-off” (Attorney Docket No. 488-011-USP3), and U.S. patent application Ser. No. 12/831,703, entitled “Detonation Wave Arrestor” (Attorney Docket No. 488-011-USP2), all three of which are filed on Jul. 7, 2010, which are also specifically incorporated by reference herein for all they disclose or teach.
Number | Date | Country | |
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61223611 | Jul 2009 | US |