Abstract:
A gas cooking grill is disclosed. The cooking grill has a firebox having a combustive heat source near the bottom therein, a cooking surface disposed along an upper portion of the firebox, and a convex intermediate element interposing the burner and the cooking surface, the intermediate element having an apex near the cooking surface and sides spaced apart from the cooking surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of U.S. Provisional Patent Application No. 61/037,477 entitled “COOKING SYSTEM FOR GAS GRILLS,” filed Mar. 18, 2008, the contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to gas cooking grills in general and, more specifically to a device and method for providing even cooking temperatures on a gas grill. 
       BACKGROUND OF THE INVENTION 
       [0003]    Until recently, most gas grills were built using atmospheric gas burners that mixed gas and some (primary) air and then expelled that mixture through small burner ports where additional (secondary) air was mixed by contact and ignition produced sustained flame. The heated mixture of combustion products and air was then used to heat food on open grates above the burner. Various materials in various configurations were often placed between the burner and the food to manipulate the flow of hot air, control the flow of grease and water from the food products, provide a surface for grease vaporization that would induce specific flavor in the meat product, and provide some secondary heating by radiation. An exception to this construction was the cooking system using infrared radiation patented by Willie H. Best in U.S. Pat. No. 4,321,857. 
         [0004]    In recent years, following expiration of the &#39;857 patent, further developments in cooking systems have been made, including U.S. Pat. No. 6,114,666 awarded to Best, which features an infrared re-emitter between the heat source and the food. Further applications by Best have been made, including US2006/0021517 and 60/847,281, that describe two more methods of using infrared re-emitters. However, although representing many advantages over prior art, the new systems have some limitations. First, they are complex and difficult to build, requiring significant precision of manufacture. Second, by their nature they hide the burner flame, suppressing an intuitive visible indication to the operator about the state of the burner system. Third, there is no flame around the cooking meat in almost any condition, depriving the consumer of an important psychological signal of the cooking event. 
         [0005]    One attempt to address these shortcomings has been made in the patent application of Johnston, US 2007/0125357, that uses a perforated plate with food support ribs and cooks with a mixture of convective heat and infrared radiation. The perforations in the plate allow the burner flame to be seen, and to some extent grease dripping though the perforations and igniting below the perforated plate will be visible. Furthermore, the food support ribs and the perforated plate fairly effectively suppress any flame around the food. However, this type of construction is complex and difficult to manufacture and is particularly difficult to clean of food debris trapped between the food support ribs. 
         [0006]    What is needed is a device and method for addressing the above, and related, issues. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention disclosed and claimed herein, in one aspect thereof, comprises a gas cooking grill. The grill has a firebox with a combustive heat source near the bottom therein, and a cooking surface disposed along an upper portion of the firebox. A convex intermediate element interposes the burner and the cooking surface, the intermediate element having an apex near the cooking surface and sides spaced apart from the cooking surface. 
         [0008]    In some embodiments, the sides of the intermediate element have a plurality of holes defined therein. The holes may be defined proximate the sides of the intermediate element. 
         [0009]    In some embodiments, a distance from the apex of the intermediate element to a bottom of the sides of the intermediate element is from 60 to 100 percent of a distance from the heat source to the cooking surface. A distance from a plane containing the heat source to the bottom of the intermediate element may be from 0 to 55 percent of a distance from the plane to the cooking surface. A distance between the bottom sides of the intermediate element may be from 30 to 90 percent of the distance between two sides of the firebox at the level of the heat source. 
         [0010]    The intermediate element may be formed from a single radius, or formed from a plurality of blended radii. The intermediate element also may contain at least one tangent section and/or at least one parabolic section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a partial cutaway perspective view of one embodiment of a gas grill according to aspects of the present disclosure. 
           [0012]      FIG. 2  is a partial cutaway perspective view of another embodiment of a gas grill according to aspects of the present disclosure. 
           [0013]      FIG. 3  is a partial cutaway end view of the gas grill of  FIG. 2 . 
           [0014]      FIG. 4A  is a shaded illustration of a temperature distribution of a convex intermediate element of the present disclosure in a gas grill. 
           [0015]      FIG. 4B  is a shaded illustration of the intermediate element of  FIG. 4A  removed from the grill. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring now to  FIG. 1 , a partial cutaway perspective view of one embodiment of a gas grill according to aspects of the present disclosure is shown. The grill  100  has a burner  104  that may be adapted to burn propane, butane, natural gas, or any other gas commonly available to consumers. The burner  104  sits in a firebox  102  that may be supported by a stand (not shown). The firebox  102  could also be attached to a mobile platform or attached permanently (e.g., enclosed by masonry). 
         [0017]    An arched or convex intermediate element  106  may be placed around the burner  104 . A substantially rounded apex  110  of the element  106  may sit directly above the center of the burner  104 . Sides  112  of the element  106  may contain a number of small holes  108 . The exact geometry of the intermediate element  106  may be important to functionality of the grill  100  and will be described in greater detail below. The intermediate element  106  may be made from any food-safe fire resistant material. In one embodiment, the intermediate element  106  comprises porcelainized steel. 
         [0018]    Referring now to  FIG. 2 , a partial cutaway perspective view of another embodiment of a gas grill according to aspects of the present disclosure is shown. The grill  200  shares many similarities with grill  100  of  FIG. 1 . However, it can be seen that the shape of the firebox  102  has changed slightly relative to that of  FIG. 1 .  FIG. 2  also shows, in phantom, another embodiment of a convex intermediate element  202  having sides  212 , defining holes  208 , and an apex  210 . This element  210  could be used instead of the convex intermediate element  106 . It is understood that the grill  200  will have only one intermediate element  106  or  202 . However, two are shown in  FIGS. 2 and 3  to illustrate that a range of various sizes are possible. The geometries and sizes contemplated are discussed below with respect to  FIG. 3 . The grill  200  is also shown with the grating  204  in place in order to clarify that the intermediate elements  106  and  202  are convex toward the food support grate  204  above the burner  104 . 
         [0019]    For both grills  100 ,  200  convective heat generated by the gas burner  104  is trapped in the intermediate element  106 ,  202  in the apex  110 ,  210  and primarily escapes through the holes  108 ,  208  in the sides  112 ,  212  of the intermediate element  106 ,  202 , though some convective heat may exit at the ends of the arch in the gap between the intermediate element and the firebox  102  in which the burner  104  is located. Convective heating may also occur from around the sides  112 ,  212  of the intermediate element  106 ,  202 . 
         [0020]    The trapped heat and the passage of heat through the small holes  108 ,  208  heats the material of the intermediate element  106 ,  202  until it emits very significantly in the infrared, of an order of magnitude of 50% of the burner input energy based on measurements and calculations of the area, temperature, and emissivity of the intermediate element material. Food on the cooking grate  204  may be heated by a combination of radiant heat and convective heat, with radiant heat providing in the order of 50% of the heating to the food. 
         [0021]    The sides  112 ,  212  of the intermediate element  106 ,  202  may be hotter than the apex  110 ,  210  because the convective heat vent holes  108 ,  208  create a greater heat transfer to the material than the stagnant, though still hot, gas trapped in the apex  110 ,  210  of the intermediate element  106 ,  202 . Because of the convex shape of the intermediate element  106 ,  202  relative to the food support grate  204 , the hotter surfaces of the side  112 ,  212  are further away from the food support grate  204  than the cooler surfaces of the apex  110 ,  210  of the element  106 ,  202 . By well known laws of physics, the greater distance attenuates the radiative heating and so the temperature distribution from radiation across the surface or grate  204  is relatively even. 
         [0022]    Referring now to  FIG. 3 , a partial cutaway end view of the gas grill of  FIG. 2  is shown. The distance from a row of burner ports on burner  104  (where combustion takes place as the gaseous fuel mixture exits the burner) to the bottom of the cooking grate is shown as distance D. In some embodiments, the location and size of this arched or convex intermediate element  106 ,  202  will be defined in terms of the distance D and a further distance W, which is the distance between the sides of the firebox  102  at the level of the burner ports on the burner  104 . Only certain sets of parameters allow maximum control of flare-ups, even distribution of combined convective and radiant heat, and proper combustion characteristics.  FIG. 3  illustrates two of a number of intermediate elements that satisfy these characteristics. 
         [0023]    The shape of the intermediate element  106  or  202  can be defined as follows for one embodiment: 
         [0024]    A=the distance from the vertical location of the burner ports to the top of the arched structure and is 60% to 100% of the distance D. 
         [0025]    B=the distance from the plane of the burner ports to the bottom edges of the arched structure and is 0% to 55% of the distance D. 
         [0026]    C=the distance between the bottom of the two sides  112  of the intermediate element  106  and is 30% to 90% of W. 
         [0027]    The convex shape of the intermediate element  106 ,  202  may be formed by a single radius, by several blended radii, by a combination of a radius and tangent sections, by a parabola and by several other means known to the art to produce a generally smooth convex curved envelope that defines the intermediate element  106 ,  202 . 
         [0028]    Variation of these parameters discussed above requires variation of the number, size and spacing of holes  108 ,  208  shown in the sides  112 ,  212  of the intermediate element  106 ,  202 . In some combinations of parameters, satisfactory performance can be achieved without any of these ventilation holes  108 ,  208  in the sides  112 ,  212 . 
         [0029]    One characteristic of an intermediate element  106 ,  202  constructed to the geometry described is that the lower parts of the intermediate element  106 ,  202  become hotter than the upper part of the intermediate element. Since the lower parts are further away from the cooking grate than the upper parts, the heat transferred by radiation is diminished so that the total heat transfer to the grate tends to be equalized between the cooler parts closer to the grate and the hotter parts farther away from the grate. Although radiant heat is only part of the heating effect produced, the overall effect is more even heat distribution across the cooking area defined by the grate  204 . 
         [0030]    Methods of constructing a cooking system according to the present disclosure are simple and uncomplicated. In one embodiment, the customary vaporizer bar/port shield described initially in current art is replaced with the special convex intermediate element  106 ,  202  of the present disclosure. The burner flames are visible to the operator through the small holes  108 ,  208  on the sides  112 ,  212  of the arch  106 ,  202 , providing feedback about operating condition of the burner  106 ,  202 . 
         [0031]    Meat or other foods cooking on the food support grate  204  may shed grease onto the hot surface of the element  106 ,  202 . This may provide visible flame and smoke around the food. However, since the grease rapidly travels down the steep sides  112 ,  212  of the arch  106 ,  202 , persistent flame does not contact the food, which is favorable to avoid charring (especially of the meat surface). 
         [0032]    The high level of infrared heat as described above produces benefits with respect to greater moisture retention due to less heat being transferred convectively, which tends to pull moisture out of the meat. The heat transfer mechanism of the present grill  100 , with all convective heat being sent to the periphery of the cooking chamber and infrared heat in the center, provides measurably better evenness of heat across the cooking surface  204 . 
         [0033]    The performance of the intermediate element  106  in a cooking application can be shown by comparing performance of a traditional grill, in which the intermediate element is an inverted V shaped member, with a grill having the aforedescribed intermediate element  106 . Substitution of the convex intermediate element as described showed results in Table 1 where the difference in standard deviation and coefficient of variation of the range of temperatures is provided. This shows a 61.7% reduction in the coefficient of variation, a commonly used statistical measurement of performance. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Heat distribution measured with thermocouple 
               
               
                 array on top of cooking grate 
               
               
                   
               
             
             
               
                 Standard grill with V shaped intermediate element 
               
             
          
           
               
                 644 
                 830 
                 732 
                 743 
                 622 
                 714 average temp F. 
               
               
                 669 
                 710 
                 730 
                 707 
                 656 
                 69.4 standard deviation temp F. 
               
               
                 659 
                 867 
                 762 
                 758 
                 626 
                 9.7% coefficient of variation, % 
               
             
          
           
               
                 Grill with convex intermediate element 
               
             
          
           
               
                 622 
                 637 
                 640 
                 643 
                 602 
                 640 average temp F. 
               
               
                 672 
                 668 
                 663 
                 679 
                 662 
                 23.9 standard deviation temp F. 
               
               
                 626 
                 636 
                 625 
                 637 
                 596 
                 3.7% coefficient of variation % 
               
               
                   
               
             
          
         
       
     
         [0034]    Viewing the actual heating characteristics of the intermediate member  106  is also instructive. Referring now to  FIG. 4A , a shaded illustration of a temperature distribution of a convex heating element of the present disclosure in a gas grill is shown. Referring also to  FIG. 4B , a shaded illustration of the heating element of  FIG. 4A  removed from the grill is shown. The figures are the result of a computational fluid dynamics study of heat transfer to the convex intermediate element. Here, the elevated temperatures along the bottom and reduced temperatures in the upper portions can be seen. 
         [0035]    Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.