Combustion – Separately supplied or controlled – physically related flame... – Coaxial
Reexamination Certificate
2000-07-17
2001-11-27
Yeung, James C. (Department: 3743)
Combustion
Separately supplied or controlled, physically related flame...
Coaxial
C431S278000, C431S349000, C126S0390BA, C126S0390BA, C239S549000, C239S553500, C239S558000
Reexamination Certificate
active
06322354
ABSTRACT:
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
Bar-Ilan Amnon
Brekken Matthew
Carbone Philip
Hobson Steven
Reich Judith
Foley & Lardner
Wolf Appliance Company, LLC
Yeung James C.
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