Patent Application
20110314791
This disclosure relates to combustible, solid metal fuels for use in propulsion systems.
Conventional propulsion systems, such as those used for ramjet projectiles, aircraft or other vehicles, typically utilize liquid hydrocarbon fuel. However, hydrocarbon fuels have a relatively low energy density compared to other materials, such as metals. There have been attempts to use metal materials as fuels in propulsion systems. For instance, metal fuels have been combined with liquid hydrocarbon fuels to produce a fuel slurry or combined with organic binders and solid oxidizers to produce a fuel composite.
An example method of fabricating a combustion system includes cold depositing a starting material onto a substrate as a solid metal fuel to produce a combustion structure.
An example propulsion system disclosed herein includes a combustion chamber having an inlet, an exhaust, and a passage that extends between the inlet and the exhaust. A consumable lining extends along the passage of the combustion chamber. The consumable lining includes a solid metal fuel that is combustible to generate propulsion force.
The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.
As also illustrated schematically in
A consumable lining 34 extends along the passage 30 of the combustion chamber 24. The consumable lining 34 includes a combustible, solid metal fuel 36 that may be selectively burned during operation of the vehicle 20 to propel the vehicle 20 forward.
As illustrated in
The solid metal fuel 36 provides the benefit of a much greater energy density than conventional hydrocarbon fuels, hydrocarbon slurries, or hydrocarbon composites. Depending on the composition, architecture, combustion kinetics, heat transfer, and oxide formation of the burning metal, the use of the solid metal fuel 36 has the potential to achieve a significant improvement in speed, range, and payload of the vehicle 20 compared to using hydrocarbon fuels.
In general, metals may burn in two different modes, depending on the properties of the metal oxide compared to the metal itself. One mode is vapor phase combustion, in which metal vapor driven off of the molten metal surface mixes with oxidizer above the metal surface and reacts to form a diffusion flame. The other mode is surface combustion where the oxidation reactions occur on the metal surface. Thus, the composition and architecture of the consumable lining 34 may be controlled to achieve a particular desired mode of burning to facilitate sustained combustion in the propulsion system 22.
The solid metal fuel 36 of the consumable lining 34 (e.g., combustion structure) may be fabricated by cold depositing a starting material onto a substrate as a solid metal fuel to produce the combustion structure with a high-combustibility. That is, the starting materials are deposited in a composition or architecture that renders the solid metal fuel of the consumable lining 34 sustainably combustible. For example, the starting material is cold deposited from at least one kind of powder material using cold spraying, also known as cold gas dynamic spraying, to achieve a composition, architecture, or combination thereof having high combustibility. Cold spraying provides the ability to control the deposition to achieve a composition and/or architecture that is suitable for sustainable combustion.
The cold spray process may utilize compressed nitrogen or helium gas to carry powder particles through a specially designed nozzle that accelerates the powder to a speed on the order of Mach 3. The powder may be heated slightly as a result of coming into contact with the compressed, hot carrier gas. However, the resonant time in the gas prior to rapid expansion and cooling of the gas is short and the powder does not significantly increase in temperature. That is, deposition of the powder relies substantially on kinetic energy, rather than high temperature melting or partial melting, to plastically deform and consolidate the powder onto a suitable substrate. The gas temperature, pressure, and particle size may be controlled to adjust the porosity of the deposited structure. One benefit of utilizing the cold spray process is that the materials being deposited are not heated and therefore do not melt, oxidize or anneal as part of the deposition process. Moreover, materials having different characteristics can be co-deposited without interacting, such as a metal and a non-metal (e.g., a polymeric material as an igniter material) or a metal and another different metal. Also, cold spray can be used to deposit or control the density of the consumable lining, and the cohesive and adhesive strengths between the deposited particles. For instance, the combustion structure can be formed with less than 5 vol % porosity, and in some examples may be formed with a nominal porosity close to 0 vol %. The following examples illustrate compositions and/or architectures that may be achieved by cold spraying at least one kind of powder as the starting material.
The solid metal fuel 36 of the consumable lining 34 may be made substantially of or include a combustible, high-energy density metal, such as beryllium, boron, magnesium, aluminum, silicon, scandium, titanium, vanadium, chromium, manganese, iron, yttrium, zirconium, molybdenum, lanthanum, hafnium, and tungsten. As will be described in further detail, the consumable lining 34 may include one or more of the metals listed above as the solid metal fuel 36. Generally, some of these metals may be more attractive for use as the solid metal fuel 36 because of higher energy density and ability to sustain combustion.
In some examples, the consumable lining 34 may have a single or multiphase composition of the above-listed metals, or include a multilayered structure of single and/or multiphase layers. For instance, cold spraying allows the consumable lining 34 to be formed from metal grains or metal particles that are weakly adhered together such that the grains or particles break-off or are released into the passage 30 during operation of the vehicle 20, to sustain combustion. The carrier gas temperature, pressure and particles size may be selected to achieve a suitable bonding force between the metal grains.
Additionally, the consumable lining 34 may include ignition materials to control combustion of the solid metal fuel 36 or to enable self-sustained combustion in low-oxygen environments, such as under water. In further examples, the solid metal fuel 36 may also serve as a structural, load-bearing member in the combustion chamber 24. That is, the solid metal fuel 36 may be formed with features or geometry that facilitate supporting other structures in the vehicle 20, unlike liquid or hydrocarbon fuels.
The constituents may be selected from beryllium, boron, magnesium, aluminum, silicon, scandium, titanium, vanadium, chromium, manganese, iron, yttrium, zirconium, molybdenum, lanthanum, hafnium, tungsten, and a thermite material, e.g. a metal/oxidizer composition. In one particular example, the first constituent 40a is aluminum and the second constituent 40b is boron. In another example, the first constituent 40a is titanium and the second constituent 40b is silicon. In other examples, one of the constituents 40a or 40b may serve as an ignition material, such as magnesium or a thermite material. The ignition material may be blended with one or more metals of the solid metal fuel 136 and serve to sustain or initiate burning of the solid metal fuel 136. The technique of cold spraying allows multiple kinds of powders to be deposited in a composition and structure that is desired for sustainable combustion.
In operation, the titanium and silicon of the second layer 344b react to form titanium silicide. The reaction results in open porosity in the second layer 344b, which allows gaseous oxidant, such as air, to move to the first layer 344a. Upon achieving a threshold level of porosity in the second layer 344b, the metal of the first layer 344a may ignite. Thus, the second layer 344b provides the benefit of controlling ignition and combustion of the first layer 344a.
The regions 770a-c each have a different composition. For instance, the compositions of the regions 770a-c may be single phase, multiphase, multilayered, or have any of the structures or compositions disclosed herein. Cold spraying may be used to fabricate such an architecture and composition by using different kinds of powders as the starting material to form the different regions 77-a-c. Additionally, the ignition material 660 may extend through the solid metal fuel 736. As an example, a layer 772 may extend through the solid metal fuel 736 to facilitate sustaining combustion of the solid metal fuel 736 and opening a passageway for exposure of the solid metal fuel composition to oxidant gas from the passage 30 of the combustion chamber 24. As an example, the ignition material of the layer 772 may be the same as or different than the ignition material 660. In one example, the ignition material of the layer 772 is a thermite material.
Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.
