Abstract:
A stacked dual gas burner which achieves good performance at high firing rates as well as good simmer performance at low firing rates. The stacked dual gas burner includes a main burner and a second (simmer) burner. The main burner and second burner are positioned in a stacked relation in a burner assembly, with the second burner positioned coaxially with and below the main burner. The second burner radius is smaller than the main burner radius, such that a portion of the main burner overhangs the second burner adjacent to the second burner ports. Recirculation underneath the overhanging edge of the main burner above the simmer burner ports helps maintain flame attachment at the second burner ports. A valve may be used to provide separately controllable flows of fuel to each of the main and second burners.

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to gas burners of the type employed for cooking appliances such as gas cook tops, and more particularly to dual burners including separate main and simmer burner ports. 
     BACKGROUND OF THE INVENTION 
     A conventional gas cooking appliance, such as a gas cook top, includes a plurality of gas burners arranged in an array on the cook top. The burners are supplied from a manifold connected to a source of fuel gas, with individual user operated valve control dials for regulating the flow of gaseous fuel to the individual burners. Food to be cooked is placed in receptacles, e.g., pots and pans, which are positioned over the burners on the gas cook top. 
     Typical gas burners have an annular or generally ring-shaped configuration, with flame-generating ports disposed peripherally around the burner to provide a ring of discrete flames emanating from the burner ports when the user operates a control valve to provide a flow of gas to the burner. (The burner flame may be ignited by a continually burning pilot flame positioned in or near the burner or, more commonly, by an electrical flame ignition.) One limitation of such conventional burners is that they cannot provide a wide range of heating capability, ranging from very high firing rates (low-time-to-boil) to low (simmer) capability. If the burner ports are made large, to accommodate a high gas flow therethrough for providing high output, the flame provided by such ports will extinguish if the gas flow is reduced too much. Similarly, if the burner ports are made small, to support a low firing rate, for simmering, the flow through the burner ports will be restricted, causing the flames to lift off at higher gas flow levels, thereby limiting high firing rate capability of the burner. 
     A conventional dual gas burner attempts to achieve both good high firing rate and simmer performance by utilizing two burner rings in each burner. Concentric main and simmer burners are provided, with the main outer and larger burner having more and larger burner ports than the burner ports provided in the smaller and inner simmer burner. Gas flow to the main and simmer burners is controlled to provide high firing rates by providing gas flow at relatively high rates to the main burner, and low firing rates, for simmering, by providing gas flow at a lower rate to the simmer burner. In such configurations, the small inner burner has very good convective heat transfer to a container located over the burner in which food to be cooked is placed, thereby raising the effective simmer temperature. Simultaneously, the larger outer burner ring has poor convective heat transfer to the cooking container, thus increasing time to boil at high firing rates. Thus, this conventional burner configuration in itself is of limited effectiveness, providing more heat to a cooking container when it should be providing less (during simmering), and less heat when it should be provide more (at high firing rates). 
     Another method which has been used to achieve good simmer performance may be employed with a single conventional burner ring. To achieve low output from such a burner, without unintentional loss of flame, gas flow is maintained at a level to keep the flame burning, but the gas flow is cycled on and off at a low duty cycle to keep temperatures minimized. Shutting off the gas flow for variable short periods of time can reduce the average heat output below that output possible with the control of only the continuous flow rate, thereby providing good simmer performance. However, such burners require an additional control system and added hardware which increases the manufacturing costs and reduces the reliability of gas cook tops employing such burners. Also, the cyclic nature of the burner operation can be less safe than other methods. 
     What is desired, therefore, is a low-cost gas burner for a gas cook top or other gas cooking appliance which can achieve good performance (low-time to-boil, high efficiency, and low emissions) at high firing rates as well as good simmer performance at low firing rates. 
     SUMMARY OF THE INVENTION 
     The present invention provides a stacked dual gas burner which achieves good performance at high firing rates as well as good simmer performance at low firing rates. A stacked dual gas burner in accordance with the present invention achieves this wide range of operation by integrating a large main burner and slightly smaller second (simmer) burner into a single burner assembly. The control of gas flow to the burner assembly is provided by a valve, e.g., a two-stage valve. The main and second burners are positioned with respect to each other in the burner assembly so as to provide for recirculation above the simmer burner ports, to maintain flame attachment at the simmer burner ports even at very low gas flow levels. The main burner and second burner may be provided together as a single integrated piece, or as two separate pieces which are assembled together in a burner assembly. 
     A stacked dual gas burner in accordance with the present invention includes a main burner and a second (simmer) burner. The main burner and second burner may be provided together as a single integrated piece, or as two separate pieces which are assembled together in a burner assembly. The main burner and second burner are positioned in a stacked relation in the burner assembly, with the second burner positioned coaxially with and below the main burner in the burner assembly. The main burner may have a generally circular configuration, with a first radius, and have a plurality of main burner ports formed on an outwardly facing radial surface thereof. The second burner, positioned below the main burner, is preferably also circular in shape, with a second radius, and has a plurality of second burner ports formed on an outwardly facing radial surface thereof. The second burner radius is preferably smaller than the main burner radius, such that a portion of the main burner overhangs the second burner adjacent to the second burner ports. The overhanging portion of the main burner provides for stabilization of flames provided at the second burner ports. Recirculation underneath the overhanging edge of the main burner above the simmer burner ports helps maintain flame attachment at the second burner ports. 
     The main burner ports are preferably round in shape and may be grouped into clusters of burner ports wherein the distance between burner ports within a cluster is smaller than the distance between clusters. The second burner ports on the second burner may be either round in shape or have a slot design. The second burner ports may also include a plurality of pairs of burner ports, wherein one of the burner ports in each pair is positioned above another of the burner ports in each pair. The main burner ports in the main burner are larger than the second burner ports in the second burner. The relative sizes of the ports in the two burners are preferably designed to minimize the step change in performance which occurs when switching between the sets of ports. The main ports in the main burner and the second ports in the second burner may be aligned radially with each other. The main burner preferably also may include secondary main burner ports formed therein adjacent to the main burner ports. The secondary main burner ports are preferably smaller than the main burner ports, and reduce port loading for greater flame stability at high firing rates (especially for a cold burner) and enhance flame carryover between the burner ports. 
     The flow of gas to the burner assembly is preferably controlled by a two-stage valve. When the valve is turned by different amounts, the flow of fuel to the second and main burner ports is controlled at various levels. Preferably, the fuel provided to the main burner is a partially pre-mixed gas-air mixture. The second burner is preferably a diffusion flame burner, for enhanced flame stability. 
     A stacked dual gas burner in accordance with the present invention achieves several advantages over conventional dual burners and other gas burners. By positioning the second burner below the main burner, simmer flames from the second burner are moved away from a cooking container, thereby reducing heat transfer from the second burner relative to the main burner. Since the second burner is positioned below the main burner, and not merely concentrically thereto, the relative diameter of the main burner can be decreased and the relative diameter of the second burner increased, thereby further reducing convective heat transfer to a container from the second burner and increasing convective heat transfer to a container from the main burner. By providing a main burner which overhangs the second burner ports of a second burner, recirculation underneath the overhanging edge of the main burner adjacent to the second burner ports is provided, which stabilizes simmer burner flames provided by the second burner ports, thereby maintaining flame attachment at the second burner ports even at very low gas flow levels. A stacked dual gas burner in accordance with the present invention also produces minimal CO, due to a large amount of air provided underneath both the main and second burners, providing sufficient burn-out, and operation in natural draft mode. A single igniter can be used to ignite either burner, further minimizing the cost of the burner assembly in accordance with the present invention. 
     Further objects, features, and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a perspective view of an exemplary stacked dual gas burner in accordance with the present invention. 
     FIG. 2 is a side view of the exemplary stacked dual gas burner of FIG.  1 . 
     FIG. 3 is a first side cross-sectional view of the exemplary stacked dual gas burner of FIG.  1 . 
     FIG. 4 is a second side cross-sectional view of the exemplary stacked dual gas burner of FIG.  1 . 
     FIG. 5 illustrates in detailed cross-section a portion of the stacked dual gas burner illustrated in FIG.  4 . 
     FIG. 6 is an exploded perspective view of an exemplary stacked dual gas burner in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An exemplary stacked dual gas burner  10  in accordance with the present invention will be described in detail with reference to FIGS. 1-4. A stacked dual gas burner  10  in accordance with the present invention includes two burners, a main burner  12  and a second or simmer burner  14 . The main  12  and second  14  burners are stacked together, along with a base portion  16 , to form the stacked dual gas burner assembly  10 . (Note that the main burner  12  and second burner  14  may be provided together as a single integrated piece, or as two separate pieces which are assembled together in the burner assembly  10 .) One or more such assemblies  10  may be mounted in a conventional manner in a gas cooking appliance, such as a gas cook top. The main burner  12  and second burner  14  are preferably circular in configuration. (Although the main burner  12  and second burner  14  may have other than a circular shape, the main burner  12  and second burner  14  preferably have the same shape.) 
     The main burner  12  includes a plurality of main burner ports  18  formed on a radially outward facing surface thereof. The main burner ports  18  are preferably round in shape. The main burner ports  18  may be evenly spaced around the main burner  12 , or grouped into clusters. For example, the main burner ports  18  may be grouped into four clusters, wherein the distance between each burner port  18  within a cluster is smaller than the distance between clusters. Secondary main burner ports  19  preferably may also be formed on the radially outward facing surface of the main burner  12 , adjacent to the main burner ports  18 . The secondary main burner ports  19  are preferably smaller than the main burner ports  18 , and are positioned on the radially outward facing surface of the main burner  12  between, and preferably slightly below, the main burner ports  18 . The secondary main burner ports  19  reduce port loading for greater flame stability (especially for a cold burner) and enhance flame carryover between the burner ports. As shown, e.g., in FIG. 3, the main burner  12  may be formed as a main burner ring  20 , having the main burner ports  18  (and secondary main burner ports  19 ) extending therethrough from an outside thereof to an inside thereof, and a cover portion  21 , enclosing the top of the main burner ring  20 . The bottom of the main burner ring  20  is thus left open. The cover portion  21  of the main burner  12  may have a larger radius than, and thus extend over, the main burner ring  20 . 
     The second burner  14  includes a plurality of second burner ports  22  formed on a radially outward facing surface thereof. The second burner ports  22  may have either a round or slot shaped design. The round second burner ports  22  may be provided as dual round second burner ports, i.e., pairs of round burner ports with one of the burner ports in each pair positioned above the other. (Both dual round and slot shaped second burner ports  22  are illustrated in FIG. 2 on a single stacked dual gas burner  10  for exemplary purposes only. In real world applications, the second burner ports  22  on a single stacked gas burner assembly  10  are preferably either round or slot shaped in configuration, not both.) As shown in FIG. 4, and in more detail in FIG. 5, the second burner  14  is preferably formed as a ring. The second burner ports  22  preferably extend into the second burner ring and are in fluid communication with a circumferential channel  24  formed in the second burner ring  14 . The circumferential channel  24  preferably opens downward. 
     The main burner  12  and second burner  14  may have the same number of burner ports  18  and  22 , respectively, with the main  18  and second  22  burner ports aligned radially with each other in the stacked dual gas burner assembly  10 . The main burner ports  18  are preferably larger than the second burner ports  22 , with the relative sizes of the ports in the two burners selected to minimize the step change in performance which occurs when switching between the two sets of ports. 
     A distribution ring  25  is provided below the second burner ring  14 . The distribution ring  25  has a U-shaped cross-section, forming a channel  26  in fluid communication with the circumferential channel  24  of the second burner ring. As will be discussed in more detail below, a flow of gas is provided into the circumferential channel  24  and out of the second burner ports  22 , via the channel  26  in the distribution ring  25 , for providing, e.g., simmer flames from the second burner ports  22 . Note that the floor of the U-shaped cross-section is preferably sloped to improve proper gas distribution through the channel  26  (see FIG.  3 ). 
     In accordance with the present invention, the main burner  12  and second burner  14  are mounted together (or formed in a single piece) in a stacked relationship on the base portion  16  to form the stacked dual gas burner assembly  10 . For example, as illustrated, the main burner  12  is positioned coaxially with and on top of or above the second burner  14 . The second burner ring  14  is, in turn, placed on top of the distribution ring  25 , such that the distribution ring channel  26  is in fluid communication with the circumferential channel  24  in the second burner ring. The stacked first  12  and second  14  burner rings, and distribution ring  25 , are mounted on the base portion  16  such that the base portion  16  and the inside surfaces of the first burner  12 , second burner  14 , and distribution ring  25  form a central main fuel chamber  27 . 
     The changes made to the foregoing paragraph of the specification from the paragraph as originally filed is shown on a separate sheet attached hereto. 
     The main burner  12  has a radius which is larger than the radius of the second burner  14 , such that when the main burner  12  is positioned over the second burner  14  in the burner assembly  10 , an extending edge  28  of the main burner  12  extends radially outward beyond the outer periphery of the second burner  14  adjacent to the second burner ports  22 . Thus, the overhanging edge  28  of the main burner  12  extends radially outward beyond the second burner ports  22  formed in the second burner  14 . As will be discussed in more detail below, this extending portion  28  of the main burner  12  provides for recirculation, which stabilizes the flames produced from the second burner ports  22 , thereby helping to maintain flame attachment at the second burner ports  22  even at low simmer levels. To provide for such recirculation, the relative sizes of the main  12  and second  14  burners are selected such that the main burner edge  28  extends over the second burner  14  by an amount of, e.g., approximately ⅛″. This provides enough overhang  28  to provide recirculation, while maintaining the relative sizes of the main  12  and second  14  burners relatively similar. Thus, the relative size of the main burner  12  may be reduced and the second burner  14  increased, for a given burner size, to improve convective heat transfer from the main burner  12  while reducing convective heat transfer to a container placed above the burner  10  from the second burner  14 . Positioning the second burner  14  below the main burner  12  also increases the distance between the second burner ports  22  and a container placed above the burner. This further reduces the amount of heat that is provided from the second burner  14  to the container. These features, in combination, allow a stacked dual gas burner in accordance with the present invention to achieve a very high turndown ratio. For example, a turn-down ratio of up to 12 to 1 may be achieved with a stacked dual gas burner in accordance with the present invention. 
     Operation of a stacked dual gas burner  10  in accordance with the present invention, to provide a wide range of performance from a very high firing rate (low-time-to-boil) to low simmer operation will now be described in detail with reference to FIGS. 3-6. As shown in FIG. 6, in accordance with the present invention, separate flows of gaseous fuel  29  and  30  are provided to the main  18  (and secondary main  19 ) and second  22  burner ports, respectively. The flow of fuel  29  through the main burner ports  18  (and secondary main burner ports  19 ) is larger than the maximum flow of fuel through the second burner ports  22 . Thus, the main burner ports  18  (and secondary main burner ports  19 ) on the main burner  12  are used for high firing rate operation, to provide high temperature and rapid heating of a container placed above the burner  10 , and the second burner ports  22  in the second burner  14  are used to provide low firing rate operation, e.g., for simmering. 
     The main  29  and second  30  gaseous fuel flows are preferably provided from a gas source  32 . The gas source  32  may, for example, be a gas supply manifold in a gas cooking appliance, such as a gas cook top, which is provided, e.g., natural gas, propane, or some other gaseous fuel from a conventional source. Gas from the gas supply  32  is provided to a valve  34 , which may be controlled by an operator to control the main fuel flow  29  through the main burner ports  18  (and the secondary main burner ports  19 ) and the second fuel flow  30  through the second burner ports  22 . The valve  34  is preferably a conventional two-stage valve, which allows the main  29  and second  30  fuel flows to be controlled. For example, the valve  34  may be used to control the second fuel flow  30  and the main fuel flow  29  by turning the valve by different amounts in one direction. 
     The main  29  and second  30  gas flows are provided from the valve  34  via conventional conduits  36  and  38 , respectively, into the base portion  16  of the gas burner assembly  10 . The main fuel conduit  36  opens in fluid communication with the central fuel chamber  27 , which, in turn, is in fluid communication with the main burner ports  18  (and secondary main burner ports  19 ) in the main burner  12 . Thus, the main fuel flow  29  is provided to the main burner ports  18  (and secondary main burner ports  19 ) via the central fuel chamber  27  formed in the burner assembly  10 . Fuel entering the central fuel chamber is preferably a partially premixed gas-air mixture, which may be provided by a conventional venturi structure provided along the main fuel conduit  36 . 
     The second fuel conduit  38  opens in fluid communication with the channel  26  formed in the distribution ring (via an aperture  40  formed in the bottom of the distribution ring). Gas from the second fuel flow  30  thus diffuses around the distribution ring  25 , into the circumferential channel  24  formed in the second burner ring  14 , which is in fluid communication therewith, and out of the second burner ports  22 . Thus, the second fuel flow  30  is provided to the second burner ports  22  via the distribution ring channel  26 . Thus, the second burner  14  is preferably operated as a diffusion flame apparatus, for enhanced flame stability. The sloping floor of the distribution ring channel  26  ensures proper distribution of fuel among the second burner ports. 
     It is understood that the present invention is not limited to the particular embodiments, examples, and applications illustrated and described herein, but embraces all such modified forms thereof as come within the scope of the following claims.