Abstract:
A gas burner for an infrared oven provides fast and controllable infrared energy, the emitted spectrum of which varies continuously over a wide spectrum. The burner is assembled from an elongated fuel distribution chamber having an open top and into which a gaseous fuel and combustion air is introduced. As the fuel mixture is delivered into the fuel distribution chamber, it eventually fills the chamber and thereafter flow through a double-layer wire mesh burner plate set over the fuel distribution chamber. The fuel combusts above the wire mesh burner plates to heat a screen wire above the burner plates. The screen wire is heated to a temperature at which the screen wire emits IR. The emitted IR wavelength can be controlled by controlling the gas supply to turn the combustion on and off according to the amount of IR heated needed.

Description:
BACKGROUND  
       [0001]    Infrared (IR) energy is known to be able to cook certain types of foods faster than convection energy. Although IR is not as fast as microwave energy, IR energy is known to produce better cooking results than microwaves. 
         [0002]    A problem with cooking using IR is that generating short-wavelength IR, which penetrates food deeper than long wavelength energy, typically requires a relatively large amount of energy because high temperatures are needed to adequately heat a surface to emit short-wavelength IR. Because short-wavelength IR almost always requires a very high temperature surface, generating short-wavelength IR therefore often requires additional time to generate. Another problem with IR cooking is that it is more difficult to control than convection heating. 
         [0003]    An oven that is able to quickly, efficiently and controllably generate infrared energy for cooking different types of foods would be an improvement over the prior art. 
       SUMMARY  
       [0004]    A gas burner for an IR oven can quickly, efficiently and controllably generate short-wavelength IR as well as long-wavelength IR by combusting a gaseous fuel just below a low mass, low-specific heat burner screen until it emits IR. The gas supply is preferably cycled on and off, in order to allow the burner screen to absorb heat energy from combusting fuel until it reaches a desired temperature. The gas supply is then shut off to allow the burner screen to dissipate IR and cool, which testing shows will extend the burner screen&#39;s useful lifespan. 
     
    
     
       DRAWING DESCRIPTION  
         [0005]      FIG. 1  is an exploded perspective view of a gas burner; 
           [0006]      FIG. 2  shows a top view of the burner shown in  FIG. 1 ; 
           [0007]      FIG. 3  shows a cross sectional view through the burner of  FIG. 1  and  FIG. 2  through section lines III-III; and 
           [0008]      FIG. 4  shows an isolated view of the connection of wire mesh burner plates used in the burner. 
       
    
    
     DETAILED DESCRIPTION  
       [0009]      FIG. 1  shows a perspective view of a gas burner  10  for an oven, not shown. The burner  10  is comprised of a fuel distribution chamber  12 . In one embodiment, the distribution chamber is in the shape of a cuboid or rectangular parallelepiped having a bottom  14 , four sides  16 A- 16 D, but having an open top  18  through which a gas/fuel mixture flows as described below. The fuel distribution chamber  12  has a length, L, width W, and a depth D. 
         [0010]    A fuel inlet pipe  20 , with first and second opposing and open ends  22  and  24 , extends through one of the sides  16 A of the distribution chamber  12 . As can be seen in  FIG. 3 , the fuel inlet pipe  30  length, is more than half the length, L, of the distribution chamber  12  such that its second end  24  is between about 4 and 10 inches from a gas flow diverter  28 . A gaseous fuel, such as natural gas or liquid propane, is introduced into the open end  22 , which is outside the distribution chamber  12 . Combustion air is also introduced into the open end  22  of the fuel inlet pipe  20  from a blower, not shown, which supplies combustion air and which forces the fuel gas and combustion air mixture through the fuel inlet pipe  20 , causing the mixed gases to strike the diverter  28  and move back toward the first side  16 A of the chamber  12 . 
         [0011]    In  FIG. 3 , it can be seen that the fuel inlet pipe  20  is constructed by telescoping a short section of pipe S 1  inside a larger-diameter and longer second pipe S 2 . Close inspection of  FIG. 3  reveals that the first section of pipe S 1  fits just inside the second and longer second section of pipe S 2 . Since the outside diameter of the first section of pipe S 1  is less than the inside diameter of the second section S 2 , the inside diameter of section S 1  is also less than the inside diameter of the longer section of pipe S 2 . 
         [0012]    At a point  21  located approximately half-way between the first end  22  and second end  24  of the fuel inlet pipe  20 , a discontinuity in the S 1 /S 2  pipe diameters is formed by the termination of the pipe section S 1  within S 2 . In other words, at the point identified by reference numeral  21 , the inside diameter of the fuel distribution pipe  20  is stepped up or increased, causing a small but non-zero pressure drop at point  21 . The discontinuity  21  is believed to create additional turbulence, which aids in the mixing of fuel and combustion air together. At the second or distal end  24  of the fuel inlet pipe  20 , the fuel and combustion air leave the fuel inlet pipe  20 , strikes the diverter  28  and from which it can evenly fill the distribution chamber  12 . 
         [0013]    As can be seen in  FIG. 3 , the fuel inlet pipe  20  runs along almost the entire length of the distribution chamber  12 . Fuel and air that leaves the fuel inlet pipe  20  at its second end  24 , strikes the diverter  28 , which is sized, shaped and arranged to re-direct or divert gases leaving the fuel inlet pipe  20 , back toward the first side  16 A of the distribution chamber  12 . The diverter  28  is semi-circular or U-shaped, having a radius of curvature that is just slightly less than the one-half the distribution chamber depth D. 
         [0014]    It is important that an oven be heated evenly and uniformly so that the oven&#39;s interior space can be fully utilized, especially so in a commercial oven, such as those used to cook pizza. In order to provide even and uniform heat, the fuel and air that leaves the second opening  24  fills the fuel distribution chamber  12  and flows upwardly into one or more wire mesh burner plates  32 , that are placed over the open top  18  of the distribution chamber  12 . 
         [0015]    As shown in  FIG. 1  and  FIG. 3 , the wire mesh burner plate assembly  30  is comprised of several individual wire mesh burner plates  32  that are attached to each other so that they abut each other. The assembly  30  of wire mesh burner plates  32  is laid over the open top  18  of the burner  10  distribution chamber  12 . The wire mesh burner plates  32  and the composite plate  30  formed of several individual burner plates  32 , are both described and claimed in the applicant&#39;s co-pending U.S. patent application having Ser. No. [ t.b.a.] and which is entitled WIRE MESH BURNER PLATE FOR A GAS OVEN BURNER. The entire disclosure of U.S. patent application Ser. No. [t.b.a.] is incorporated herein by reference. As can be seen in the co-pending application Ser. No. [t.b.a.] for the Wire Mesh Burner Plate for a Gas Oven Burner and as can be seen in  FIG. 3 , several individual wire mesh burner plates  32  are coupled together over the open top of the burner distribution chamber  12 . Fuel combustion takes place above the wire mesh burner plates  32 . 
         [0016]    Fuel and combustion air from the distribution chamber  12  enters open space within the wire mesh burner plates  32  where they mix together. As the fuel and air continue to flow into the burner plates  32 , the fuel and air eventually flows out of the “top” of the burner plates  32  where it is ignited by a pilot flame (not shown), which is lit by an electric igniter controlled by a controller. The pilot light causes the fuel and air mixture leaving the top of the burner plates  32  to ignite and combust. The continued supply of fuel gas and combustion air from the distribution chamber  12  allows the combustion to continue, which in turn heats a wire mesh burner screen  36  spaced above the burner plates  32  and the burner plate assembly  30 . A gasket  34  that surrounds the burner plates  32  (See  FIG. 2 .) prevents the fuel and combustion air mixture from leaking from the sides of the burner plates  32  and helps to insure that all of the fuel is burned. 
         [0017]    Infrared heat energy is quickly and controllably generated by the combustion of fuel gas below the wire burner screen  36 , which preferably of a low mass and therefore quickly heated. The combustion of the fuel beats the wire burner screen  36  until it is hot enough to emit infrared. Once a desired IR emission is reached, the fuel gas is preferably shut off by a computer (not shown), after which IR will continue to be emitted as the burner screen  36  temperature drops. When IR emission drops to some empirically determined value, the burner can be re-lit by the controller (not shown) to re-heat the screen  36  and generate more IR. Since the burner screen  36  will be cooler when the burner  10  is re-lit, heat transfer efficiency from the combusting fuel to the screen  36  will be greater than when the burner screen  36  is continuously heated. By cycling the gas supply on and off, the energy transfer into the screen  36  can be improved over what it would be if the gas supply were simply left on during a cooking process. In addition, by cycling the wire screen  36  temperatures, the IR wavelength emitted from the wire screen  36  cyclically varies from relatively short-wavelength and deeply-penetrating visible IR emitted at high temperatures, to relatively long-wavelength, less-penetrating IR emitted at relatively low temperatures. By cycling the gas supply, the screen  36  can be made to emit IR across a continuously varying spectrum of wavelengths. 
         [0018]    The fuel combustion that heats the burner screen  36  takes place above the burner plates  32  but below the burner plate screen  36 , which is held in a spaced-apart relation above the burner plates by spacers as shown, with the preferred space being about one-half inch. The spacing between the burner plate screen  36  and the burner plate assembly  30  (or the individual burner plates  32 ) define a combustion space  38 , the height of which is chosen to provide a space large enough to allow the fuel to fully combust below the burner plate screen  36  in order to maximize heat transfer into the burner plate screen  36 . 
         [0019]    As the height of the combustion space  38  decreases, some of the combustion process will occur above the burner plate screen  36 , reducing heat transfer into the screen  38 . Conversely, as the combustion space  38  increases, the combustion process will finish below the burner plate screen  38 , allowing the combustion products to cool and external air to be drawn into the combustion space  38 , thereby reducing heat transfer into the screen  38 . Thus, there is an optimal spacing of the heat transfer screen  36  above the burner plates  32  that will maximize heat transfer for a given flow rate of fuel and combustion air into the burner  10 . In a preferred embodiment, the burner plate screen  36  is about one-half inch above the burner plates  32 , however, spacing as small as about one-quarter inch up to about one inch can also be used. 
         [0020]    In one embodiment, the burner plate screen  36  is nichrome wire, however, alternate embodiments include using steel and stainless steel wire, with and without heat-tolerant coatings such as ceramic. In yet another embodiment, the burner plate screen  36  is made entirely of ceramic. 
         [0021]    By combusting gas below a low-mass, low-specific heat screen, the screen  36  can be quickly heated to temperatures where the screen will emit short-wavelength and deep-penetrating infrared energy. By cycling the fuel supply on and off, the screen  36  is allowed to cool during gas-off time periods, during which time it will emit increasingly longer wavelength IR. Testing shows that rapid heating and cooling cycles also extends the screen&#39;s  36  life beyond the life it would have if the screen  36  were heated continuously. 
         [0022]    The foregoing description is for illustration and not for limitation. The scope of the invention is defined by the following claims.