INFRARED EMITTING GAS BURNER

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

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.

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.

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

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's useful lifespan.

DRAWING DESCRIPTION

FIG. 1 is an exploded perspective view of a gas burner;

FIG. 2 shows a top view of the burner shown in FIG. 1;

FIG. 3 shows a cross sectional view through the burner of FIG. 1 and FIG. 2 through section lines III-III; and

FIG. 4 shows an isolated view of the connection of wire mesh burner plates used in the burner.

DETAILED DESCRIPTION

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 16A-16D, 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.

A fuel inlet pipe 20, with first and second opposing and open ends 22 and 24, extends through one of the sides 16A 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 16A of the chamber 12.

In FIG. 3, it can be seen that the fuel inlet pipe 20 is constructed by telescoping a short section of pipe S1 inside a larger-diameter and longer second pipe S2. Close inspection of FIG. 3 reveals that the first section of pipe S1 fits just inside the second and longer second section of pipe S2. Since the outside diameter of the first section of pipe S1 is less than the inside diameter of the second section S2, the inside diameter of section S1 is also less than the inside diameter of the longer section of pipe S2.

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 S1/S2 pipe diameters is formed by the termination of the pipe section S1 within S2. 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.

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 16A 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.

It is important that an oven be heated evenly and uniformly so that the oven'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.

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'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.

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.

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.

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.

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.

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.

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's 36 life beyond the life it would have if the screen 36 were heated continuously.

The foregoing description is for illustration and not for limitation. The scope of the invention is defined by the following claims.

Claims

1. A gas burner for an oven comprising:

an elongated fuel distribution chamber (distribution chamber) having an open top;

a fuel inlet pipe that extends through the distribution chamber by a first distance, said fuel inlet pipe having a first open end outside the distribution chamber into which gas fuel is introduced, said fuel inlet pipe having a second open end opposite the first open end from which fuel enters the distribution chamber;

at least one wire mesh burner plate, which extends over the open top of the distribution chamber;

a burner plate screen, spaced above and extending over at least part of the at least one wire mesh burner plate;

wherein a fuel/air mixture combusts substantially above the at least one wire mesh burner plate in order to heat the burner plate screen to emit infrared heat.

2. The gas burner of claim 1, further comprising a gas flow deflector within the distribution chambers said fuel being directed toward the gas flow deflector, the gas flow director redirecting at least some of the fuel and air within the distribution chamber.

3. The gas burner for an oven of claim 1, wherein the burner plate screen is spaced above the at least one wire mesh burner plate by a first distance that defines a space wherein the fuel/air mixture combusts.

4. The gas burner of claim 1, further comprised of a gasket around the at least one wire mesh burner plate.

5. The gas burner of claim 3, wherein the first distance is between about three-fifths of an inch and about one inch.

6. The gas burner of claim 3, wherein the first distance is approximately one-half inch.

7. The gas burner of claim 1, wherein the burner plate screen is comprised of a nichrome wire.

8. The gas burner of claim 1, wherein the burner plate screen is comprises of a ceramic-coated metal.

9. The gas burner of claim 1, wherein the burner plate screen is comprised of ceramic.

10. The gas burner of claim 1, wherein the combustion chamber is comprised of stainless steel.

11. A gas burner for an oven comprising:

an elongated fuel distribution chamber (distribution chamber) having a bottom, four sides and an open top, the fuel distribution chamber having a length, width and depth;

a fuel inlet pipe having that extends through a first side of the distribution chamber and through the distribution chamber by a first distance that is less than the distribution chamber length, said fuel inlet pipe having a first open end located outside the distribution chamber and into which gas fuel and combustion air is introduced, said fuel inlet pipe having a second open end opposite the first open end and from which fuel and combustion air enters the distribution chamber, said fuel inlet pipe also having an inside diameter and a discontinuity in said inside diameter;

at least one wire mesh burner plate, which extends over the open top of the distribution chamber;

a burner plate screen, spaced above and extending over the at least one wire mesh burner plate;

wherein a fuel/air mixture combusts above the at least one wire mesh burner plate after the fuel/air mixture passes through the at least one wire mesh burner plate and the distribution chamber.

12. The gas burner of claim 11, further comprising a gas flow deflector spaced away from the second open end of the fuel inlet pipe and located within the distribution chamber, said gas flow director directing at least some of the fuel exiting the second open end of the fuel distribution pipe to travel through the distribution chamber toward the first end of the distribution chamber.

13. The gas burner for an oven of claim 11, wherein the burner plate screen is spaced above the at least one wire mesh burner plate by a first distance, the first distance defining a space between the at least one wire mesh burner plate and the burner plate screen wherein the fuel/air mixture combusts.

14. The gas burner of claim 11, further comprised of a gasket around the at least one wire mesh burner plate.

15. The gas burner of claim 13, wherein the first distance is between about three-fifths of an inch and about one inch.

16. The gas burner of claim 13, wherein the first distance is approximately one-half inch.

17. The gas burner of claim 11, wherein the burner plate screen is comprised of a nichrome wire.

18. The gas burner of claim 11, wherein the burner plate screen is comprises of a ceramic-coated metal.

19. The gas burner of claim 11, wherein the burner plate screen is comprised of ceramic.

20. The gas burner of claim 11, wherein the combustion chamber is comprised of stainless steel.