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 
       [0001]    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 
       [0002]    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 a conventional combustion device  10 , having a housing  11  containing a combustion chamber  12 . The combustion chamber  12  communicates with a nozzle  13  and an exit passage  14 . An oxidizer, usually gaseous oxygen, is introduced into the combustion chamber  12  through an oxidizer orifice  15 . Fuel, either liquid or gas, enters the combustion chamber  12  through a fuel inlet  16  to mix with the oxidizer flow from the oxidizer orifice  15 . Ignition, often provided by a spark-plug (not shown), occurs to form an intense flame in the combustion chamber  12 . The width and length of the combustion chamber  12  are sized to provide essentially complete combustion of the fuel and oxidizer. Prior to entry into the nozzle  13 , the velocity of the hot combustion products is quite low. The combination of a restricting cross section of the nozzle  13  with an expanding cross section of the exit passage  14  serves to greatly accelerate the combustion gasses. This structure is termed a de Laval nozzle. 
         [0003]    Due to the extreme heat generated in the combustion device  10 , external cooling is required. An outer shell structure  20  is spaced a small distance away from the housing  11 , forming an annular coolant passage  21 . Water passes into the annular coolant passage  21  through a coolant inlet  22 , exiting through a coolant outlet  23 . 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 
       [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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. 
         [0010]    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. 
         [0011]    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. 
         [0012]    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. 
         [0013]    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 
         [0014]      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. 
           [0015]      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. 
           [0016]      FIG. 3  is an exploded isometric view of the embodiment shown in  FIG. 2 , with a portion of a housing sectioned to better show the oxidizer injection passage. 
           [0017]      FIG. 4  is an enlarged cross section of the embodiment shown in  FIGS. 2 and 3  better showing the action of fuel and oxidizer within a tube which forms part of the combustion apparatus shown in  FIG. 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. 
           [0018]      FIG. 5  is a cross section view of the combustion apparatus shown in  FIG. 4  after the composite stream in the tube has been ignited. 
           [0019]      FIG. 6  is an isometric section view of a combustion apparatus which is functionally similar to that shown in  FIGS. 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. 
           [0020]      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. 
           [0021]      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 in  FIGS. 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. 
           [0022]      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. 
           [0023]      FIG. 11  is a sectioned view of the embodiment shown in  FIG. 10  when assembled. 
           [0024]      FIG. 12  is a section view of another embodiment, which is similar to that shown in  FIGS. 2-5  but where a water-cooling jacket is provided around the tube to allow the use of a longer tube. 
           [0025]      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 
       [0026]      FIG. 2  illustrates one embodiment of the present invention, a combustion apparatus  30 .  FIG. 3  shows an exploded view of the same embodiment. This combustion apparatus  30  can be fabricated from three pieces of stock. A tube  32  is attached to a body section  34  which in turn attaches to a backing section  36 . The backing section  36  in turn has a fuel coupling  37  for connection to a conventional fuel supply line (not shown). The tube  32  is preferably of high conductivity copper to provide greater heat transfer, while the body section  34  and the backing section  36  can be formed of brass. The body section  34  also attaches to an oxidizer coupling  38  for connection to a conventional oxidizer supply line (not shown). 
         [0027]    While the structure of the combustion apparatus  30  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 the combustion apparatus  30 . 
         [0028]    The combustion apparatus  30  has a housing  40  that terminates at a proximal end  42  and a distal end  44 . The housing  40  has a cavity  46  symmetrically disposed about a central axis  48 . The cavity  46  is terminated in part by the proximal end  42 , defined by the backing section  36  which has a central fuel injection passage  50  therethrough which communicates with the fuel coupling  37 . The fuel injection passage  50  has a fuel passage axis  52  which coincides with the central axis  48 . The backing section  36  is provided with a fuel passage extension  53  which continues the fuel injection passage  50  into the cavity  46 . The cavity  46  has two sections, a central section  54  which is generally cylindrical, being radially terminated by a peripheral wall  56  that is a cylindrical surface symmetrically disposed about the central axis  48 , and a nozzle section  58  which connects the central section  54  to the distal end  44 . 
         [0029]    An oxidizer injection passage  60  is provided to inject an oxidizer from the oxidizer coupling  38  into the central section  54  of the cavity  46 . The oxidizer injection passage  60  is configured to direct the oxidizer into the central section  54  in a tangential manner so as to generate a vortex centered on the central axis  48 , the vortex subsequently passing through the nozzle section  58  and into a bore  62  of the tube  32 . 
         [0030]    The bore  62  of the tube  32  is symmetrical about a bore axis  64 , and the tube  32  is attached to the housing  40  such that the bore axis  64  aligns with the central axis  48  of the cavity  46  and with the fuel passage axis  52 . The joinder of the tube  32  with the housing  40  can be made by a variety of techniques. As depicted in  FIGS. 2 and 3 , the housing  40  of this embodiment is provided with an opening  65  in the distal end  44  which slidably accepts an insertable section  66  of the tube  32 . The insertable section  66  of the tube  32  has the bore  62  reshaped over the region thereof that is adjacent to the central section  54  of the cavity  46  when the tube  32  is properly inserted into the opening  65 , this shaping of the bore  62  forming the nozzle section  58  of the cavity  46 . The tube  32  in this embodiment is secured to the housing  40  by soldering or other appropriate joining technique. 
         [0031]      FIGS. 4 and 5  are sectional side views of the combustion apparatus  30  shown in  FIGS. 2 and 3 , to better illustrate one preferred spacial relationship between the fuel passage extension  53  and the bore  62  of the tube  32 . In this embodiment the fuel passage extension  53  continues beyond the nozzle section  58  into the bore  62 .  FIG. 4  illustrates the combustion apparatus  30  in an initial startup condition where the oxidizer is being provided to the combustion apparatus  30  and has established a vortex, schematically represented by  70 , having a low pressure core  72  or eye of the vortex  70  which is centered on the bore axis  64 . 
         [0032]      FIG. 5  illustrates the combustion apparatus  30  after fuel is being directed into the low pressure core  72  and is ignited to form a combustion region  74  that increases in cross section as the fuel passes down the bore  62 . The limit of the expansion will be determined by the length of the tube  32 , and should be maintained such that an unmixed sheath region  76  of the oxidizer surrounds the combustion region  74  throughout the length of the bore  62  to buffer the tube  32  from the heat generated by the combustion and to enhance the efficiency of the combustion apparatus  30 , since loss of thermal energy is reduced. Having the combustion apparatus  30  so operated results in greater acceleration of the combustion products. In fact, the output from combustion apparatus  30  exhibits shock diamonds  78 , indicating that the output stream has reached supersonic flow. The unmixed sheath region  76  results from operating the combustion apparatus  30  in such a manner that the radial advancement of flame in the combustion region  74  as it passes through the bore  62  is greater than the rate of diffusion of the unburned fuel radially outward into the oxidizer. It should be noted that the formation of the low pressure core  72  allows the combined fuel and oxidizer to be ignited after exiting the bore  62 , in which case the flame rapidly progresses upstream to form the combustion region  74  within the bore  62 . Alternatively, the combined fuel and oxidizer could be ignited within the bore  62 , such as by a spark plug (not shown). 
         [0033]      FIGS. 6 and 7  each illustrate an alternative embodiments of combustion apparatus ( 30 ′ and  30 ″, respectively) which each has a replaceable tube ( 32 ′ and  32 ″), but which is each functionally the same as the combustion apparatus  30  discussed above and shown in  FIGS. 2-5 . In the case of the combustion apparatus  30 ′ shown in  FIG. 6 , the tube  32 ′ fits into a socket  80  which extends the distal end  44 ′ of the housing  40 ′. A retention collar  82  threadably engages the distal end  44 ′ and forcibly engages an enlarged segment  84  of the tube  32 ′ to lock the tube  32 ′ in the socket  80 . 
         [0034]    In the combustion apparatus  30 ″ shown in  FIG. 7 , the tube  32 ″ threads directly into the socket  80 ′ of the housing  40 ″.  FIG. 7  also illustrates an alternate tube  32 ′″ that could be exchanged for the tube  32 ″ to provide a smaller bore  62 ′. 
         [0035]      FIGS. 8 and 9  illustrate an experimental approach for determining an appropriate length L of a tube  90  for a combustion apparatus  92  having a structure similar to that of the combustion apparatus  30  discussed above. The combustion apparatus  92  also has a housing  94  to which the tube  90  is affixed. For a particular set of operating parameters, a maximum practical length L MAX  for the tube  90  can be determined experimentally. To do this, a tube blank  90 ′ having an initial length L I  which is substantially longer than the final length L is attached to the housing  94  and fuel and oxidizer are introduced into the combustion apparatus  92  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 blank  90 ′, and at some point expand so as to be close enough to the tube blank  90 ′ that the sheath of cool oxidizer is no longer sufficient to prevent substantial heating of the tube blank  90 ′. At some point along the length of the tube blank  90 ′, indicated by the line A-A, the heat from the combustion gases causes a terminal portion  96  (shown in phantom) of the tube blank  90 ′ extending beyond the line A-A to melt, leaving a base portion  98  of the tube blank  90 ′ remaining. The length of the base portion  98  extending to the line A-A defines the maximum practical length L MAX  for the particular operating conditions employed. The length L of the tube  90  is then selected to be somewhat shorter than the maximum practical length L MAX . 
         [0036]    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 a combustion apparatus  100  that forms one embodiment of the present invention that employs such an oxidizer manifold. 
         [0037]    The combustion apparatus  100  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. The combustion apparatus  100  has a structure with only three parts, each of which is designed to be readily fabricated by machining. 
         [0038]    The combustion apparatus  100  has a main body  102  and a proximal body  104  which, in combination, form a housing with a cavity  106 . In this embodiment, the cavity  106  is surrounded by an oxidizer manifold  108 . The main body  102  also serves as a tube, having a bore  110  therethrough which communicates with the cavity  106 . The main body  102  and the proximal body  104  are attached together at a single body joint  112 , which can be sealed by soldering to seal the oxidizer manifold  108 . While there is no sealed joint between the cavity  106  and the oxidizer manifold  108 , the effect of any oxidizer leakage through this joint should be negligible. 
         [0039]    The oxidizer manifold  108  introduces oxidizer into a central section  113  of the cavity  106  via a series of tangentially-directed oxidizer passages  114  passing through a wall  116  that defines the periphery of the central section  113 , forming a vortex that is then constricted by passing through a nozzle  117 . 
         [0040]    The oxidizer is introduced into the oxidizer manifold  108  from an oxidizer inlet  118  through a series of passages which run alongside the bore  110 . The oxidizer inlet  118  can connect to an oxidizer coupling such as that shown in  FIGS. 2 and 3 . From the oxidizer inlet  118 , the oxidizer is first passed forward by a forward conduit  120  to a forward annular space  122 . The forward annular space  122  is formed by a forward ring  124  that is sealably attached to the main body  102  at two forward ring joints  126 ; again, these joints  126  can be soldered. The forward annular space  122  circumscribes the bore  110 . 
         [0041]    From the forward annular space  122 , the oxidizer is passed rearward to the oxidizer manifold  108  through a number of side conduits  128  that extend through the main body  102  parallel to the bore  110 . The side conduits  128  communicate between the forward annular space  122  and the oxidizer manifold  108 . 
         [0042]    In the combustion apparatus  100 , the bore  110  expands in cross section as the distance from the cavity  106  increases. Such could be provided by a gradually expanding cross section; however, for ease of machining the embodiment illustrated, the bore  110  is expanded by forming a series of bore cylindrical sections  130 , where the diameter of each of the bore cylindrical sections  130  increases as the distance of the bore cylindrical section  130  from the cavity  106  increases. 
         [0043]    When the combustion apparatus  100  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-guiding passage  132  extending through the main body  102 . The wire-guiding passage  132  is inclined with respect to a central axis  134 , about which the cavity  106  and the bore  110  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 the bore  110 . 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. 
         [0044]    An alternative approach to introducing a coating material would be to introduce a powder into the stream of fuel which is introduced into the cavity  106  through a fuel passage  136  that extends through the proximal body  104  and is aligned with the central axis  134 . In the combustion apparatus  100 , introducing powder into the oxidizer stream would be impractical in view of the number of passages and spaces ( 120 ,  122 ,  128 ,  108 , and  114 ) through which the oxidizer passes before reaching the cavity  106 . In any case, it is preferred for the fuel passage  136  to be extended into the cavity  106  by a fuel passage extender  138 . 
         [0045]    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. 
         [0046]      FIG. 12  illustrates a combustion apparatus  200  which has a housing  202  and a tube  204  attached thereto. The tube  204  is encased in a water cooling jacket  206  which provides an annular water passage  208  around the tube  204 . The jacket  206  is provided with a water inlet  210 , into which cooling water is introduced, and a water outlet  212  where the water exits the jacket  206 . The water is heated as it passes along a terminal portion  214  of the tube  204 , the terminal portion  214  being the portion which is beyond a self-cooling section  216  of the tube  204  where the tube  204  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 the tube  204  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 the tube  204 . 
         [0047]      FIG. 13  illustrates another combustion apparatus  300  which has a housing  302  and a tube  304  attached thereto. In this embodiment, a water inlet  306  is provided which allows water to be injected into a vortex that is formed by the oxidizer as it passes down the tube  304 . The water introduced into the vortex is spun to a bore surface  308  of the tube  304 , since the water is more dense than that oxidizer; this spun water forms a water film  310  on the bore surface  308 . As the combustion products expand radially, the oxidizer is exhausted and the water film  310  initially provides shielding over the additional length and, for this additional length, provides shielding of the tube  304 . By adjusting the flow of the water into the tube  304 , one can adjust the water flow such that a dry output will be provided without overheating of the tube  304 . 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. 
         [0048]    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.