US20090286190A1 - Method and apparatus for combusting fuel employing vortex stabilization - Google Patents

Abstract

The present method and apparatus for producing a supersonic jet stream introduce an oxidizer in such a manner as to create a vortex, which is then restricted. Fuel is introduced into a reduced pressure eye of the vortex, forming a stratified composite stream of gases with unmixed oxidizer surrounding an inner mixture of fuel and oxidizer. This stratified composite stream is passed down a tube that exhausts to a low pressure environment. The combined fuel and oxidizer in the stratified stream is ignited to provide a high-velocity stream of combustion products. The outer layer of unmixed oxidizer in the vortex shields the tube and reduces or eliminates the need for additional cooling.

Description

FIELD OF THE INVENTION
• The present invention relates to a method and apparatus for combusting fuel with an oxidizer to obtain a high velocity jet of hot combustion gases, having particular utility for providing a thermal torch.
BACKGROUND OF THE INVENTION
• In a classical combustion apparatus for producing a high-velocity flame jet, a fuel and an oxidizer are combined in a combustion chamber. The combined fuel and oxidizer are then ignited to produce combustion gases, and these gases are then accelerated through a nozzle.FIG. 1 is a cross-section view that illustrates a typical example of aconventional combustion device10, having ahousing11 containing acombustion chamber12. Thecombustion chamber12 communicates with anozzle13 and anexit passage14. An oxidizer, usually gaseous oxygen, is introduced into thecombustion chamber12 through anoxidizer orifice15. Fuel, either liquid or gas, enters thecombustion chamber12 through afuel inlet16 to mix with the oxidizer flow from theoxidizer orifice15. Ignition, often provided by a spark-plug (not shown), occurs to form an intense flame in thecombustion chamber12. The width and length of thecombustion chamber12 are sized to provide essentially complete combustion of the fuel and oxidizer. Prior to entry into thenozzle13, the velocity of the hot combustion products is quite low. The combination of a restricting cross section of thenozzle13 with an expanding cross section of theexit passage14 serves to greatly accelerate the combustion gasses. This structure is termed a de Laval nozzle.
• Due to the extreme heat generated in thecombustion device10, external cooling is required. Anouter shell structure20 is spaced a small distance away from thehousing11, forming anannular coolant passage21. Water passes into theannular coolant passage21 through acoolant inlet22, exiting through acoolant outlet23. The requirement for water cooling complicates the structure and reduces thermal efficiency, since much of the energy generated by combustion is lost in the form of heat.
SUMMARY OF THE INVENTION
• The method of the present invention for producing a supersonic jet stream includes the step of creating a vortex of an oxidizing fluid having an eye with a reduced pressure. The vortex is constricted and fuel is passed into the eye of the vortex to form a stratified composite stream, with unmixed oxidizer surrounding an inner mixture of fuel and oxidizer. This stratified composite stream is passed down a tube having a bore that exhausts to a low pressure environment. The combined fuel and oxidizer in the stratified stream are ignited to provide a stream of combustion products which can reach velocities exceeding the speed of sound.
• While the method has general applicability, it can be conveniently practiced with a combustion and accelerator apparatus described hereafter which constitutes part of the invention. In general, the apparatus is configured such that it merges and expands a fuel stream and an oxidizer stream and forms a vortex-stabilized composite stream having a fuel-rich core surrounded by an outer sheath of the oxidizer, with the combined fuel and oxidizer in the fuel-rich core providing an intermediate combustible mixture that, when ignited, expands to provide a flame-stabilized high velocity jet.
• The apparatus has a housing which terminates in a proximal end and a distal end. The housing has a cavity which is symmetrically disposed about a central axis. The cavity has a central section which is generally cylindrical and nozzle section which extends to the distal end.
• A fuel passage is provided in the housing and passes through the proximal end of the housing and into the cavity. The fuel passage is so positioned such that it directs the fuel along the central axis.
• A tube having a bore attaches to the housing at the distal end of the housing, forming a continuation of the housing and terminating with a free end. The bore is symmetrically disposed about the central axis. The length of the tube is adjusted such that the oxidizer flow shrouds the wall of the tube extension along its entire length, assuring that it remains cool.
• A fuel passage extender extends into the central section of the cavity and preferably terminates in the nozzle section or in the bore of the tube. It is preferred that the fuel passage extender be a tapered structure having a cross section which, at least over a substantial portion of its length, reduces as a function of its distance from the proximal end of the housing.
• The combustion apparatus is provided with a means for injecting the oxidizer into the central section of the cavity so as to create a vortex in the central section having a low pressure eye centered on the central axis. The nozzle section serves to constrict the vortex as it advances through the housing.
• This means for injecting the oxidizer can be provided by employing one or more oxidizer passages that terminate in the central section of the cavity, each of the oxidizer passages being substantially tangent to a circle centered on the central axis and residing substantially in a plane normal to the central axis. By so introducing the oxidizer, a vortex will be created in the central section of the cavity.
• The vortex passes through the nozzle section and into the bore and, at some point along this portion of the path, the fuel is released into the eye of the vortex in a manner such that the fuel remains directed along the central axis as it passes along the bore of the tube, thus providing a vortex-stabilized stratified fuel and oxidizer stream which remains stratified as the oxidizer and fuel flow through the remainder of the structure.
• In some embodiments, the cross section of the bore increases as the distance from the distal end of the housing increases. This increase can be a continuous function of the distance or can be a stepwise increase.
BRIEF DESCRIPTION OF THE FIGURES
• FIG. 1 is a section view of a prior art combustion apparatus, which is a chamber-stabilized torch suitable for depositing a layer of material on a target.
• FIG. 2 is an isometric section view of a combustion apparatus that forms one embodiment of the present invention, which employs a single oxidizer injection passage to provide a vortex-stabilized stratified fuel and oxidizer stream.
• FIG. 3 is an exploded isometric view of the embodiment shown inFIG. 2, with a portion of a housing sectioned to better show the oxidizer injection passage.
• FIG. 4 is an enlarged cross section of the embodiment shown inFIGS. 2 and 3 better showing the action of fuel and oxidizer within a tube which forms part of the combustion apparatus shown inFIG. 2. The tube is illustrated with a schematic representation of a stratified stream of fuel and oxidizer passing through and exiting a bore of the tube.
• FIG. 5 is a cross section view of the combustion apparatus shown inFIG. 4 after the composite stream in the tube has been ignited.
• FIG. 6 is an isometric section view of a combustion apparatus which is functionally similar to that shown inFIGS. 2-5, but where the tube can be readily replaced. The tube has an enlarged segment that slidably engages a socket in a housing of the combustion apparatus, and a retention collar threadably engages the housing to secure the tube in the socket.
• FIG. 7 is an isometric section view of another combustion apparatus that allows the tube to be readily replaced. In this embodiment, the housing has a socket that is threaded and the tube has threads that engage the threads of the socket to attach the tube to the housing. An alternative tube having a smaller bore is also illustrated, which can be interchanged with the first tube to allow the bore size to be varied to suit the desired operating parameters for the combustion apparatus.
• FIGS. 8 and 9 are section views that schematically illustrate one method for experimentally determining an appropriate length of a tube for a combustion apparatus such as those shown inFIGS. 2-7. In this method, a tube blank that is longer than the anticipated tube length is employed and is operated in a combustion apparatus under the desired operating conditions. The tube blank melts off at a point which indicates the maximum practical length, and the tube is then made somewhat shorter than this maximum practical length.
• FIG. 10 is a partially exploded isometric view of a combustion apparatus that forms another embodiment of the present invention, where the housing and the extension are formed as an integral unit and the oxidizer is preheated by passing it through the wall of the extension. In this embodiment, the oxidizer is injected into a central section of a cavity via a plurality of oxidizer passages that communicate between an oxidizer manifold and the central section. The tube of this embodiment has a bore with a stepped profile so as to enhance the acceleration of the combusting gases and reduce noise.
• FIG. 11 is a sectioned view of the embodiment shown inFIG. 10 when assembled.
• FIG. 12 is a section view of another embodiment, which is similar to that shown inFIGS. 2-5 but where a water-cooling jacket is provided around the tube to allow the use of a longer tube.
• FIG. 13 is a section view of another embodiment that uses water cooling, but where the water is introduced into the vortex of uncombined oxidizer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIG. 2 illustrates one embodiment of the present invention, acombustion apparatus30.FIG. 3 shows an exploded view of the same embodiment. Thiscombustion apparatus30 can be fabricated from three pieces of stock. Atube32 is attached to abody section34 which in turn attaches to abacking section36. Thebacking section36 in turn has afuel coupling37 for connection to a conventional fuel supply line (not shown). Thetube32 is preferably of high conductivity copper to provide greater heat transfer, while thebody section34 and thebacking section36 can be formed of brass. Thebody section34 also attaches to anoxidizer coupling38 for connection to a conventional oxidizer supply line (not shown).
• While the structure of thecombustion apparatus30 can be defined in terms of the pieces from which it can be fabricated, it is more convenient to discuss the structure in terms of the functional elements which provide certain functions on the oxidizer stream and the fuel stream as they pass through thecombustion apparatus30.
• Thecombustion apparatus30 has ahousing40 that terminates at aproximal end42 and adistal end44. Thehousing40 has acavity46 symmetrically disposed about acentral axis48. Thecavity46 is terminated in part by theproximal end42, defined by thebacking section36 which has a centralfuel injection passage50 therethrough which communicates with thefuel coupling37. Thefuel injection passage50 has afuel passage axis52 which coincides with thecentral axis48. Thebacking section36 is provided with afuel passage extension53 which continues thefuel injection passage50 into thecavity46. Thecavity46 has two sections, acentral section54 which is generally cylindrical, being radially terminated by aperipheral wall56 that is a cylindrical surface symmetrically disposed about thecentral axis48, and anozzle section58 which connects thecentral section54 to thedistal end44.
• Anoxidizer injection passage60 is provided to inject an oxidizer from theoxidizer coupling38 into thecentral section54 of thecavity46. Theoxidizer injection passage60 is configured to direct the oxidizer into thecentral section54 in a tangential manner so as to generate a vortex centered on thecentral axis48, the vortex subsequently passing through thenozzle section58 and into abore62 of thetube32.
• Thebore62 of thetube32 is symmetrical about abore axis64, and thetube32 is attached to thehousing40 such that thebore axis64 aligns with thecentral axis48 of thecavity46 and with thefuel passage axis52. The joinder of thetube32 with thehousing40 can be made by a variety of techniques. As depicted inFIGS. 2 and 3, thehousing40 of this embodiment is provided with anopening65 in thedistal end44 which slidably accepts aninsertable section66 of thetube32. Theinsertable section66 of thetube32 has thebore62 reshaped over the region thereof that is adjacent to thecentral section54 of thecavity46 when thetube32 is properly inserted into theopening65, this shaping of thebore62 forming thenozzle section58 of thecavity46. Thetube32 in this embodiment is secured to thehousing40 by soldering or other appropriate joining technique.
• FIGS. 4 and 5 are sectional side views of thecombustion apparatus30 shown inFIGS. 2 and 3, to better illustrate one preferred spacial relationship between thefuel passage extension53 and thebore62 of thetube32. In this embodiment thefuel passage extension53 continues beyond thenozzle section58 into thebore62.FIG. 4 illustrates thecombustion apparatus30 in an initial startup condition where the oxidizer is being provided to thecombustion apparatus30 and has established a vortex, schematically represented by70, having alow pressure core72 or eye of thevortex70 which is centered on thebore axis64.
• FIG. 5 illustrates thecombustion apparatus30 after fuel is being directed into thelow pressure core72 and is ignited to form acombustion region74 that increases in cross section as the fuel passes down thebore62. The limit of the expansion will be determined by the length of thetube32, and should be maintained such that anunmixed sheath region76 of the oxidizer surrounds thecombustion region74 throughout the length of thebore62 to buffer thetube32 from the heat generated by the combustion and to enhance the efficiency of thecombustion apparatus30, since loss of thermal energy is reduced. Having thecombustion apparatus30 so operated results in greater acceleration of the combustion products. In fact, the output fromcombustion apparatus30 exhibits shockdiamonds78, indicating that the output stream has reached supersonic flow. Theunmixed sheath region76 results from operating thecombustion apparatus30 in such a manner that the radial advancement of flame in thecombustion region74 as it passes through thebore62 is greater than the rate of diffusion of the unburned fuel radially outward into the oxidizer. It should be noted that the formation of thelow pressure core72 allows the combined fuel and oxidizer to be ignited after exiting thebore62, in which case the flame rapidly progresses upstream to form thecombustion region74 within thebore62. Alternatively, the combined fuel and oxidizer could be ignited within thebore62, such as by a spark plug (not shown).
• FIGS. 6 and 7 each illustrate an alternative embodiments of combustion apparatus (30′ and30″, respectively) which each has a replaceable tube (32′ and32″), but which is each functionally the same as thecombustion apparatus30 discussed above and shown inFIGS. 2-5. In the case of thecombustion apparatus30′ shown inFIG. 6, thetube32′ fits into asocket80 which extends thedistal end44′ of thehousing40′. Aretention collar82 threadably engages thedistal end44′ and forcibly engages anenlarged segment84 of thetube32′ to lock thetube32′ in thesocket80.
• In thecombustion apparatus30″ shown inFIG. 7, thetube32″ threads directly into thesocket80′ of thehousing40″.FIG. 7 also illustrates analternate tube32′″ that could be exchanged for thetube32″ to provide asmaller bore62′.
• FIGS. 8 and 9 illustrate an experimental approach for determining an appropriate length L of atube90 for acombustion apparatus92 having a structure similar to that of thecombustion apparatus30 discussed above. Thecombustion apparatus92 also has ahousing94 to which thetube90 is affixed. For a particular set of operating parameters, a maximum practical length L_MAXfor thetube90 can be determined experimentally. To do this, a tube blank90′ having an initial length L_Iwhich is substantially longer than the final length L is attached to thehousing94 and fuel and oxidizer are introduced into thecombustion apparatus92 according to the desired operating parameters. When the combined fuel and oxidizer is ignited and burns, the combustion gases expand as they progress down the tube blank90′, and at some point expand so as to be close enough to the tube blank90′ that the sheath of cool oxidizer is no longer sufficient to prevent substantial heating of the tube blank90′. At some point along the length of the tube blank90′, indicated by the line A-A, the heat from the combustion gases causes a terminal portion96 (shown in phantom) of the tube blank90′ extending beyond the line A-A to melt, leaving abase portion98 of the tube blank90′ remaining. The length of thebase portion98 extending to the line A-A defines the maximum practical length L_MAXfor the particular operating conditions employed. The length L of thetube90 is then selected to be somewhat shorter than the maximum practical length L_MAX.
• While all the embodiments discussed above have a single oxidizer passage for introduction of the oxidizer into the cavity so as to form a vortex that travels through the chamber, in some instances it is preferred to employ multiple passages to introduce the oxidizer into the chamber. In such cases, it is frequently advantageous to provide an annular manifold for the oxidizer, this manifold encircling the at least a portion of the cavity and serving as the connector between the oxidizer source and the passages.FIGS. 10 and 11 illustrate acombustion apparatus100 that forms one embodiment of the present invention that employs such an oxidizer manifold.
• Thecombustion apparatus100 again is designed to swirl the oxidizer as it is introduced; however, in this embodiment the oxidizer is introduced into the cavity through multiple passages. Thecombustion apparatus100 has a structure with only three parts, each of which is designed to be readily fabricated by machining.
• Thecombustion apparatus100 has amain body102 and aproximal body104 which, in combination, form a housing with acavity106. In this embodiment, thecavity106 is surrounded by anoxidizer manifold108. Themain body102 also serves as a tube, having abore110 therethrough which communicates with thecavity106. Themain body102 and theproximal body104 are attached together at asingle body joint112, which can be sealed by soldering to seal theoxidizer manifold108. While there is no sealed joint between thecavity106 and theoxidizer manifold108, the effect of any oxidizer leakage through this joint should be negligible.
• Theoxidizer manifold108 introduces oxidizer into acentral section113 of thecavity106 via a series of tangentially-directedoxidizer passages114 passing through awall116 that defines the periphery of thecentral section113, forming a vortex that is then constricted by passing through anozzle117.
• The oxidizer is introduced into theoxidizer manifold108 from anoxidizer inlet118 through a series of passages which run alongside thebore110. Theoxidizer inlet118 can connect to an oxidizer coupling such as that shown inFIGS. 2 and 3. From theoxidizer inlet118, the oxidizer is first passed forward by aforward conduit120 to a forwardannular space122. The forwardannular space122 is formed by aforward ring124 that is sealably attached to themain body102 at two forward ring joints126; again, thesejoints126 can be soldered. The forwardannular space122 circumscribes thebore110.
• From the forwardannular space122, the oxidizer is passed rearward to theoxidizer manifold108 through a number ofside conduits128 that extend through themain body102 parallel to thebore110. Theside conduits128 communicate between the forwardannular space122 and theoxidizer manifold108.
• In thecombustion apparatus100, thebore110 expands in cross section as the distance from thecavity106 increases. Such could be provided by a gradually expanding cross section; however, for ease of machining the embodiment illustrated, thebore110 is expanded by forming a series of borecylindrical sections130, where the diameter of each of the borecylindrical sections130 increases as the distance of the borecylindrical section130 from thecavity106 increases.
• When thecombustion apparatus100 is to be employed to apply a coating, means are provided for introducing a coating material into the stream of combustion gases. In the embodiment illustrated, such means are provided by a wire-guidingpassage132 extending through themain body102. The wire-guidingpassage132 is inclined with respect to acentral axis134, about which thecavity106 and thebore110 are symmetrically disposed. The wire-guiding passage serves to direct a wire (not shown) passed therethrough such that the wire will intersect the stream of combustion gases exiting from thebore110. The hot combustion gases can then melt the end of the wire to introduce molten droplets of the coating material into the stream of gases, which then accelerates these droplets to impact against a workpiece to be coated.
• An alternative approach to introducing a coating material would be to introduce a powder into the stream of fuel which is introduced into thecavity106 through afuel passage136 that extends through theproximal body104 and is aligned with thecentral axis134. In thecombustion apparatus100, introducing powder into the oxidizer stream would be impractical in view of the number of passages and spaces (120,122,128,108, and114) through which the oxidizer passes before reaching thecavity106. In any case, it is preferred for thefuel passage136 to be extended into thecavity106 by afuel passage extender138.
• The above examples have been for combustion apparatus embodiments that do not employ water cooling, and hence limit the length of the tube in which the combustion occurs to assure that a layer of unmixed oxidizer resides against the tube along its length, this layer serving to protect the tube from the heat of the combustion gasses. The length of the tube can be increased if the tube is water-cooled. The water cooling can be accomplished by employing a water jacket and/or by injecting water into the vortex of the oxidizer, as discussed below.
• FIG. 12 illustrates acombustion apparatus200 which has ahousing202 and atube204 attached thereto. Thetube204 is encased in awater cooling jacket206 which provides anannular water passage208 around thetube204. Thejacket206 is provided with awater inlet210, into which cooling water is introduced, and awater outlet212 where the water exits thejacket206. The water is heated as it passes along aterminal portion214 of thetube204, theterminal portion214 being the portion which is beyond a self-coolingsection216 of thetube204 where thetube204 is cooled by the oxidizer. Thus, the heat input that is extracted by the water is substantially less than the heat extracted by water jacket of the prior art, since much of thetube204 is shielded by the vortex of the oxidizer, and therefore most of the heat generated by the burning remains in the combustion products as they pass down thetube204.
• FIG. 13 illustrates anothercombustion apparatus300 which has ahousing302 and atube304 attached thereto. In this embodiment, awater inlet306 is provided which allows water to be injected into a vortex that is formed by the oxidizer as it passes down thetube304. The water introduced into the vortex is spun to abore surface308 of thetube304, since the water is more dense than that oxidizer; this spun water forms awater film310 on thebore surface308. As the combustion products expand radially, the oxidizer is exhausted and thewater film310 initially provides shielding over the additional length and, for this additional length, provides shielding of thetube304. By adjusting the flow of the water into thetube304, one can adjust the water flow such that a dry output will be provided without overheating of thetube304. This technique has an additional benefit in that it changes the character of the output combustion products and maintains a less oxidizing output. In fact, one can obtain the desired flow by monitoring the color of the output of the torch while adjusting the input water flow.
• While the novel features of the present invention have been described in terms of particular embodiments and preferred applications, it should be appreciated by one skilled in the art that substitution of materials and modification of details can be made without departing from the spirit of the invention.

Claims (3)

1-10. (canceled)

11. A method for producing a supersonic jet stream, comprising the steps of creating a vortex of an oxidizer within and through a constricting bore, the vortex having a low pressure eye axially positioned within the bore;

passing a fuel into the eye of the continuously constricted vortex flow to form a stratified composite stream:

passing the vortex and stratified composite stream through and out of said constricting bore;

igniting the stratified composite stream;

and, limiting the length of said constricting bore to that length which maintains an annular sheath of cold oxidizer completely surrounding the exiting flame jet to prevent over-heating the material containing said bore.

12-20. (canceled)

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