Patent Application
20200191389
This invention relates to gas grills.
Gas fueled infrared heating devices ignite propane or natural gas to heat an object such as a glass or ceramic tile. The heated object emits infrared radiation. Thermal radiation is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation in the infrared heat frequency range. Heat is uniformly distributed across the surface of the heated object. Examples of applications for infrared heating include grills for cooking applications, and industrial drying applications. Burners for these devices operate at higher temperatures than, for example, gas water heaters, meaning that flame retrogression is more likely.
Infrared radiation uses electromagnetic waves rather than heated air for cooking or drying. Heat may be more uniformly distributed than when heating air by burning gas, and with regard to cooking, there is less drying of the food.
Most gas grills transfer heat to food primarily by convective energy. Generally, not more than 20% of the heat energy is converted to infrared energy. These grills do not limit the quantity of secondary air introduced to the combustion process through the ports. Therefore, a large amount of excess air is supplied to the combustion process. The excess air dilutes the temperature of the gases (products of combustion) so that the temperature of the ports of the burners is usually below the auto ignition temperature of the gas air mixture. The ports of the burner stop retrogression of the flame when the burner is turned off. Retrogression of the flame through the ports is not a concern.
As an example, the theoretical required carbon dioxide (CO2) level for natural gas for stoichiometric combustion is 12.2%. Stoichiometric combustion is defined as ideal combustion. In the conventional grills the CO2 level of the products of combustion is usually less than 2%, which indicates that large volumes of excess air are present during combustion using a typical gas grill in common use.
Higher performance grills, such as grills that transfer energy to the food by infrared radiation, operate at temperatures higher than the auto ignition of the fuel, requiring larger ports for the burner(s). Therefore, the ports of these burners are not effective at preventing retrogression of the flame when the burner is turned off and the velocity of the gas air mixture through the ports is reduced. While some burners in some applications allow the flame to flow back to the orifice and result in a small noise, like a “puff” sound, this effect is not desirable and can be unsafe.
For an infrared type of grill that employs an infrared emitter (heated by the product of combustion), it is highly advantageous for the emitter to be heated to temperatures of 700° F.-1000° F. Convective heat transfer is linear with temperature, but infrared energy heat transfer is proportional to the forth power of the temperature of the emitter as demonstrated by the Stefan-Boltzman Law. For a black body R=0.173×10-3 BTU/(h FT2·R2)
There are burners available that directly produce infrared energy from the combustion surface (such as the burner described by U.S. Pat. No. 3,27,948). These burners are very effective when the energy is transferred at levels of the emitter surface temperature over 1000° F. However, these burners are incapable of operating at lower temperatures (under about 700° F.).
In recent years, there has been developed a need for an infrared burner for gas grills that can operate at very low temperatures and much higher temperatures—range from about 250° F.-1000° F. This need has developed because of a change in the market. In the present market, slow cooking is desirable to many consumers. Some cuts of pork such as hams or Boston butts are slow cooked for as much as 8-12 hours. This trend of slow grilling on gas grills has partly developed because of the interest in outdoor kitchens. Today more expensive homes are installing outdoor kitchens. These kitchens may cost between $50,000 and $125,000. Therefore, consumers want more flexibility in their cooking methods. Gas grills are the primary choice for outdoor kitchens. Some of the gas grills installed in outdoor kitchens cost in excess of $6,000.
Most producers of expensive gas grills (more than $2,000) have changed their designs to accommodate two types of burners: one type for slow cooking, and another type for fast cooking. A common description of this type of infrared burner for fast cooking is a sear burner. This construct means that the user must, at some point, move the food from one location on the grill to another location. It is more convenient to adjust the level of heat at a control knob of a burner. There is a need for a burner for a grill that will allow a full range of cooking temperatures and times.
Gas fueled infrared heating devices are subject to limitations of other gas fueled heating devices, since a fuel-air mixture is burned to provide heat for the plate or other infrared radiation emitting device. There is a need for a device that will improve the efficiency of gas fueled infrared heating devices, while retarding auto ignition from back flow of the flame.
The present invention is a gas burner for a grill having a mixture plenum that receives gas and air. A port plenum is positioned above the mixture plenum. The port plenum comprises a plurality of ports. The ports discharge a gas air mixture received from the mixture plenum for combustion that occurs externally to the port plenum and adjacent to the ports.
A quenching plate is positioned between the mixture plenum and the port plenum to separate the mixture plenum from the port plenum. The quenching plate comprises a plurality of apertures. The gas air mixture flows through the plurality of apertures and from the mixture plenum to the port plenum. The construction and arrangement of the mixture plenum, the port plenum, the quenching plate and the quenching plate apertures retard back flow and auto ignition, and provide cooling to the quenching plate for quenching flame in the event of back flow from the port plenum toward the mixture plenum.
The present invention allows the use of larger ports, allowing more primary air to be used in the combustion process and lowering the carbon monoxide level. Larger ports can be used since retrogression is not of concern. The use of separate plenums for the mixture and the discharge ports allows more primary air to be injected into the cooler mixture plenum.
The use of a quenching plate according to the invention is more reliable than preventing retrogression through the use of small ports. The quenching plate in the present invention is outside the combustion zone, and is unlikely to be overheated and allow retrogression as can happen where ports are used to prevent retrogression.
Higher temperatures are associated with infrared burners since hot gases from combustion must heat the emitter. Since the emitter temperature is preferred to be in the range of 700° F.-1000° on higher settings, for the emitter to maintain this temperature, hot gases must be produced at a much higher temperature to achieve the required heat transfer to the emitter. However, the invention allows energy to be decreased to very low levels for very slow cooking. Lower temperature can be achieved by reducing the temperature of the air, which reduces the cooking temperature to a desired low level. The temperature of the air may be adjusted by varying the fuel input.
The present invention according to a preferred embodiment is a gas burner 2 comprising a first plenum, or mixture plenum 4, for introduction of a gas air mixture to the burner, and a second plenum, or port plenum 6, having a plurality of ports formed therein that discharge the gas air mixture for combustion at an exterior of the port plenum.
The mixture plenum 4 and the port plenum 6 are preferably completely separated from each other by a quenching plate 8. The quenching plate has a plurality of apertures 12 therein. The apertures may be formed, for example, by perforations in the quenching plate, and/or a screen, such as a welded or woven wire mesh screen. The quenching plate is constructed to be capable allowing sufficient flow of air gas mixture from the mixture plenum to the port plenum, while also quenching any flame that undesirably enters the port plenum due to back flow. As shown in
The port plenum 6 comprising the plurality of ports 14 is preferred to be located within the combustion zone. A housing for the grill may form the combustion zone. The mixture plenum 4, which is positioned below the port plenum, may be located partially or entirely outside of the combustion zone. The quenching plate 8 separates the port plenum and mixture plenum. The quenching plate is positioned between the mixture plenum and the port plenum as shown.
The use of the multiple plenums allows the burner to be mounted to the bottom of the combustion chamber 16 or other similar enclosure that contains combustion.
In one embodiment, the mixture plenum is positioned generally below the combustion zone and below the port plenum. In another embodiment the mixture plenum is generally positioned beside the combustion zone of the heating device and beside the port plenum. The combustion zone of the heating device may be the area between the infrared energy emitter 26 and the gas burner 2, and including the port plenum 6.
The volume of the mixture plenum 4 provides an area for the gas and air to substantially uniformly mix to the desired ratio. The volume of the mixture plenum is preferred to be larger than the volume of the upper, port plenum. In a preferred embodiment, the port plenum 6 has a volume that is 15% to 35% of the volume of the mixture plenum, and more preferably 16% to 25% of the volume of the mixture plenum. In one embodiment, the port plenum has a depth of about ½ inch, while the mixture plenum has a depth of about 3 inches, when the length and width of each plenum is generally the same. The port plenum operates within the higher temperature of the combustion zone, with the burner structure preventing auto-ignition.
The preferred application for this burner is devices that require temperatures in excess of the auto ignition temperature of the gas air mixture. A gas grill is a preferred application of the burner. For some applications, the port plenum may be exposed to temperatures as high as 1650° F. In applications such as gas grills, the combustion chamber 24 is enclosed as shown in
In a preferred embodiment, the gas air mixture is transmitted at substantially uniform pressure and volume from the lower, mixture plenum 4 to the upper port plenum 6 along the length of the quenching plate. In many applications of combustion and heat transfer, it is necessary that the burner be substantially elongated relative to its cross sectional area. The result is that as combustible mixture flows from the mixture plenum 4 into the burner, the gas pressure drops along the length of the burner as the gas-air exits through ports along the length of the burner. The gas-air pressure and volume is therefore lower in many cases as the distance from the venturi increases. The result is inconsistent heating along the length of the burner.
This present invention overcomes this problem in a preferred embodiment by varying the flow area through the apertures 12 of the quenching plate 8. The size of the apertures, or the density of the apertures, or both, may be varied to increase or decrease the flow of combustible mixture to the upper or port plenum. Pressure and volume of the gas-air mixture may be measured at the quenching plate on the port plenum side to construct a plate that has substantially equal flow volume along the length of the plate.
In a preferred embodiment of the invention, the mixture plenum 4 and the port plenum 6 are constructed as separate units.
The area of the individual ports 14, as well as the collective area of the ports, may be increased as compared to ports of conventional burners. An increase in the port area allows more primary air to be introduced through a venturi 18 or other air injector than with previously known gas heating devices. It is neither a good nor safe practice to allow the flame to retrogress back to the orifice when the burner is turned off. If the port size is too large, and the velocity of the fuel air mixture is decreased below the flame velocity, retrogression of the flame into the ports will occur. For this reason, the diameter of the ports of a conventional burner must be small enough to quench the flame when the velocity of the mixture is below the flame velocity.
In the present invention, the diameter of the ports 14 may be formed to have a larger area than other gas fueled burners. When the burner is turned off, if the flame retrogresses through the ports into the upper plenum, the flame is quenched by the quenching plate between the plenums, and the flame cannot retrogress to the fuel source.
The use of larger ports allows increased thermal efficiency and increased heating of the infrared energy emitter 26. More air for combustion is provided by primary air through the ports. Less secondary air is required through the secondary air ports 22. Therefore, less heat from the burner is applied to air moving through the heating device or grill 28, and more heat from the burner is available to heat the infrared energy emitter. The ports 14 are preferred to be equal to or greater than 0.10 inches and are even more preferred to be equal to or greater than 0.15 inches in diameter.
The above discussion is based upon a gas fueled heating device having naturally aspirated primary air for mixing with gas in the mixture plenum and in some embodiments a means to supply secondary air to the combustion chamber 16 such as ports 22. However, this burner may also operate with the same benefits using a premixed air and gas composition, as is frequently the case in industrial applications.
The flame quenching plate allows a flow of gas from the mixture plenum to the port plenum, but does not allow a flame to pass through the quenching plate. Apertures in the quenching plate may be formed by perforating a sheet of metal that forms the plate, or by disposing one or more screens, including wire mesh screens, in the quenching plate. The apertures are small enough to stop the passage of the flame, while permitting sufficient flow of the gas through the quenching plate. The individual apertures are preferred to be not larger than 0.050 inches, and are more preferred to be not larger than 0.025 inches. Wire mesh may be used to form the apertures. This method of quenching a flame provides for a change in the molecular carriers.
In this embodiment, flame quenching occurs between the two plenums that are separated by the quenching plate 8. Therefore, there is unlimited flow area available. When the port diameter of a burner is used to prevent retrogression of the flame, the restrictions imposed can create other problems. The ability to inject primary air is dependent on the pressure in the burner tube or the burner plenum. Decreasing the flow area of the ports increases the pressure, which decreases the volume of primary air that is injected. The present invention does not depend on quenching the flame at the ports. Therefore, more latitude is available in selecting the diameter of the ports.
The burner as described herein provides flexibility in heating devices where the temperature of the combustion zone is in excess of the auto ignition. This temperature varies with the type of gas, but the temperature in the mixture plenum may be 500° F. to 600° F. less, and up to 800° F. less, than the temperature in the port plenum under some conditions. The burner of the present invention can operate in an environment up to about 1650° F., which is above the auto ignition temperature for natural gas and propane gas.
The quenching plate quenches flame flashback or retrogression since it is cooler than the combustion zone and port plenum, and the use of small apertures, which may be wire mesh in a preferred embodiment. The cooler quenching plate is sufficiently cool to quench a flame, while the apertures retard back flow.
In a preferred embodiment of the burner construct, the mixture plenum 4 is exposed to cooler, ambient air.
The quenching plate may also be connected to the housing of the heating device or grill 28 so that the housing conducts heat away from the quenching plate.
A preferred structure of the quenching plate also encourages thermal conductivity. The apertures 12 are surrounded by the material from which the quenching plate 8 is formed. In one embodiment, a plurality of areas comprising apertures 12 are each surrounded by a solid structure that conducts heat from the apertures.
The areas of the quenching plate comprising the apertures 12 are spaced apart from each other and disposed within the solid thermally conductive areas of the quenching plate 8 in one embodiment. The wire mesh conducts heat into the solid perimeters of the areas formed of wire mesh that together form the quenching plate. The solid areas of the quenching plate are constructed of materials that encourage thermal conductivity, such as metal, and particularly, stainless steel. The quenching plate is cooled by thermal conductivity to the cooler mixture plenum, and in some embodiments, also by the housing of the heating device or grill 28, as described above, and particularly by thermal conductivity from the solid areas of the quenching plate to the mixture plenum and/or housing. The apertures in the quenching plate, such as the wire mesh, retard backflow into the mixture plenum, and if flame is present in any backflow, the cooler quenching plate quenches the flame. The area of the quenching plate dedicated to apertures should not be more than ⅓ of the surface area of the quenching plate, with the solid area(s) 30 comprising the remainder of the surface area of the quenching plate. In one embodiment, if wire mesh is used to provide apertures, then the wire mesh should not occupy more than ⅓ of the surface area of the quenching plate. In some embodiments the apertures may occupy as little as six (6%) percent of the surface area of the quenching plate.
Other preferred applications of the present invention include the situation in which a burner greater than about 2 feet in length is required and the fuel air entrance to the burner is required to be at one end of the burner. Also, the burner may be used in the food cooking applications, such as gas grills and commercial griddles. The burner may be used in the heating of water and other liquids.
An embodiment of a burner having a fuel air entrance (such as venturi 32) at one end of the burner is shown in
This application is a continuation in part of U.S. patent application Ser. No. 15/055,964 filed Feb. 29, 2016, and which claimed the benefit of U.S. Provisional Application Ser. No. 62/127,300 filed Mar. 3, 2015.
| Number | Date | Country | |
|---|---|---|---|
| 62127300 | Mar 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15055964 | Feb 2016 | US |
| Child | 16795654 | US |
