US3625196A

US3625196A - Burner cap assembly

Info

Publication number: US3625196A
Application number: US36907A
Authority: US
Inventors: Albert F Craver
Original assignee: W J SCHOENBERGER CO
Current assignee: W J SCHOENBERGER CO
Priority date: 1970-05-05
Filing date: 1970-05-13
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07

Abstract

A combination of a steel burner cap, a burner cap mounting plate and a mixing tube. One end of the tube is adapted for connection to a gas manifold and the other end is connected to the mounting plate. Unobstructed openings intermediate the ends of the tube allow air to be aspirated when gas is injected from the manifold. The cap may be crimped to the plate for assembly tightness. Gas and primary air pass from the tube into the cap for further mixing while flowing radially out within the cap and subsequently through a plurality of ports. Ledges on the cap both above and below the ports extend radially outwardly to provide a flame shielding annular recess at the outer extent of the ports.

Description

llnited States Patent [72] Inventor Albert F. Craver Bay Village, Ohio [21] Appl. No. 36,907 [22] Filed May 13, 1970 [45] Patented Dec. 7, 1971 [73] Assignee The W. J. Schoenberger Co.

Cleveland. 01110 [54] BURNER CAP ASSEMBLY 9 Claims, 6 Drawing Figs.

[52] U.S. Cl 126/39 11, 126/214 R [51] Int. Cl F24c 3/00 [50] Field of Search 126/38, 39, 39 H, 39 N, 39 K, 44, 214, 40, 50; 239/559, 561, 567

[56] References Cited UNITED STATES PATENTS 1,196,230 8/1916 Graves 126/39 UX 2,642,934 6/1953 Gunther et a1 126/40X 2,781,779 2/1957 Kindl 26/39N UX 3,236,461 2/1966 Kindl et a1. 239/559 Shnidman, Gaseous Fuels, I954, pgs. 133- 154.

Primary Exam/new"hurles J. M yhre Ar!urney-Fay, Sharpe and Mulholland ABSTRACT: A combination of a steel burner cap, a burner cap mounting plate and a mixing tube. One end of the tube is adapted for connection to a gas manifold and the other end is connected to the mounting plate. Unobstructed openings intermediate the ends of the tube allow air to be aspirated when gas is injected from the manifold. The cap may be crimped to the plate for assembly tightness. Gas and primary air pass from the tube into the cap for further mixing while flowing radially out within the cap and subsequently through a plurality of ports. Ledges on the cap both above and below the ports extend radially outwardly to provide a flame shielding annular recess at the outer extent of the ports.

PATENTEU DEC 71971 $1625; 196

sum 2 or 2 52 FIG.5

FIG. 6 (PRIOR; ART) 'INVENTOR.

ALBERT F. CRAVER M S/xaape MM ATTORNEYS BURNER CAP ASSEMBLY BACKGROUND OF THE INVENTION The inventor intended to develop a new gas burner for the gas range industry which would be economical in cost, have the proper configuration for the aesthetics of the housewife and overcome certain undesirable operational features of conventional gas burners.

Gas burner construction has not changed substantially in years or so. Basically each burner includes (a) a gas supply unit, (b) a primary air inlet through a mixing tube connected to the gas supply, (c) an air shutter for regulating the size of the air inlet, (d) a venturi section in the mixing tube, (e) a burner base attached to the end of the mixing tube and (f) a burner head having ports about its periphery being mounted on the burner base.

Voluminous American publications have described techniques and set standards for gas burners over the past 50 years. Thus, much empirical data and technical formulas are available and recommended by various technical groups. Substantially all such data are directed to slight modifications of the above-listed basic elements.

Notwithstanding all of the previously recommended design techniques, the inventor decided to try something new. Because it was his intent to minimize cost he decided to eliminate the most expensive portion of the conventional gas burner which is the burner base. Conventional burner bases are cast iron or die-cast aluminum alloy or steel drawn cup structures of relatively large mass which serve as both a heat sink and a mixing chamber for the gas and primary air. The inventor eliminated the burner base altogether and substituted a tube of substantially uniform cross-sectional area from the gas manifold to the burner head.

Surprisingly, although the flames emanating from the resulting burner head were not perfect in many respects, they did give promising results which warranted further investigation. The main drawback to the initial trial was the high velocity through the burner ports which resulted in substantial blowoff", excessive noise from improper ignition and inadequate combustion.

The variable parameters of a burner assembly for a conventional gas range are relatively well settled. The industry over the years has obtained many designs which have proved to be successful in meeting the standards set by the gas industry and government regulations. Because of the many parameters involved, modification of one will tend to change the results obtained. Customarily, what burner designers do is modify one portion of a burner assembly to obtain a particular result and then manipulate the other variables to obtain combustion at an acceptable standard.

Thus, it is not surprising that'the elimination of one of the parameters (namely, the burner base shown in FIG. 6) gave results which were immediately unsatisfactory by current standards. What was surprising and unexpected was that the results obtained gave promise that further modifications might be made to obtain acceptable burning characteristics.

Elimination of the burner base increased the internal pressure at the ports because the gas-air mixture was delivered directly to the burner cap without any intermediate obstruction or any substantial pressure drop.

With a conventional burner base the gas-air mixture from the mixing tube enters a mixing chamber which results in a relatively large pressure drop. Then from the mixing chamber it is distributed to the burner cap. The burner base conventionally has a volume of about six times that of the burner cap and the elimination of this volume from the burner assembly is a great saving in materials.

Because of the elimination of the burner base and the reduction of the downstream back pressure, the combustible gas injected from the gas manifold tends to aspirate more primary air through the air holes intermediate the ends of the mixing tube. The increased primary air in the gas-air mixture tends to increase flame ignition and cause further instability in the flames.

After modifying several of the variable parameters and innovating a combination of structural elements, the inventor was able to obtain a satisfactory flame with acceptable combustion and operating characteristics. This was accomplished by 1) eliminating the venturi section of the mixing tube, (2) designing a new cap with a new port configuration and (3) in some cases eliminating the air shutter at the primary air inlet to the mixing tube.

First, the elimination of the venturi section in the mixing tube was contrary to all technical recommendations and the known art of present day burner construction. The venturi section formed in accordance with mathematical formula has always been thought necessary in order to aspirate enough primary air for the initial gas-air mixture. The elimination of the burner base caused greater gas velocity past the air openings and greater air aspiration. In turn, elimination o the venturi section reduced the amount of air aspirated through the air openings. Thus, as acceptable balance was maintained, notwithstanding that the prior art advises otherwise.

Second, it was conceived that what was needed in the burner port configuration to minimize blowoff was something to coalesce the flames from the ports. The inventor concluded that this might be accomplished by a cooperative port configuration consisting of large and small ports where the small or secondary ports were located in such a position that the flames from small or secondary ports coalesced directly with the flames from larger or primary ports. In the final analysis and design, the result was a plurality of secondary ports to stabilize the ring of flame around the periphery of the burner cap and other secondary ports to carry over" the flame from one primary port to another.

Third, prior burner designs increased gas velocity by a venturi section in the mixing tube for the purpose of aspirating larger amounts of primary air and then reduced the velocity with the voluminous mixing chamber in the burner base. Eliminating the burner base eliminated the need for the venturi section. Hence, with the elimination of the burner base and the venturi section the inventor was able to standardize the size of the openings in the mixing tube and eliminate the conventional air shutter BRIEF DESCRIPTION OF THE INVENTION A thin-walled tube having openings intermediate its ends for the aspiration of primary air is connected at one end to a manifold. Combustible gas fed to the manifold could be any conventional heating or cooking gas commercially supplied, such as natural gas or liquified petroleum gas as is sometimes used in cooking appliances in mobile homes and campers. The other end of the tube is connected to a burner cap mounting plate and a flat topped burner cap is affixed to the mounting plate.

The whole assembly is supported by a bracket connected to the mixing tube and with its distal end resting on the upper surface of the oven of a gas range or the bottom of the burner box.

Ports are provided in the burner cap which are directed substantially radially outward of the cap and ledges are provided both above and below the ports to provide a flame shielding recess at the outer terminus of the ports. The bottom ledge serves generally to prevent turbulence in the port area which would cause blowoff and lifting. The upper ledge tends to retain the ring of flame at the low turndown" or minimum output of the burner.

Objects of the invention will be obvious from a detailed reading of the description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a prospective view of a gas range FIG. 2 is an enlarged fragmentary plan view of a single burner from FIG. 1 and incorporating the novel burner cap assembly of this invention.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

FIG. 4 is a prospective view of the burner cap assembly of this invention.

FIG. Sis a sectional view taken along line 55 of FIG. 4. FIG. 6 is a sectional view of a conventional burner as found in the prior art.

DESCRIPTION-OF THE PREFERRED EMBODIMENT FIG. 6 is illustrative of the prior art as relates to burners. Conventionally the burner cap assembly 10 includes a mixing tube 12 leading from a manifold (not shown) to a burner base 14.

The mixing tube 12 would, of course, include a venturi section (not shown) somewhat along the lines shown in the patents to Vixler, US. Pat. No. 2,638,976, Blanzy, US. Pat. No. 3,l3 1,752 or Fulmer, U.S. Pat. No. 3,219,098.

A holding plate 16 may be welded to the venturi tube 12 and attached to the burner base 14 by screws 18. Conventionally, a gasket 20 must be used to prevent gas leakage at the joint. Three to six assembly screws or bolts are conventionally used in the assembly.

The gaseous mixture from the mixing tube 12 is fed directly into a large mixing chamber 22 and subsequently into an annular channel 24 which serves to feed and equally distribute the gaseous mixture to a burner cap 26.

The type of conventional burner construction and assembly illustrated in FIG. 6 has been thought necessary so that the burner itself will be sufficiently flexible to satisfactorily burn all commercial gases under standard variable heating values and distribution pressures, and at the same time meet the exacting standards for such burners as required by most state and local ordinances and such national perfonnance requirements as may be demanded by the American Standards Association and Underwriters Laboratories.

The large internal gas volume of the conventional burner was considered necessary to give an even distribution and equal pressure to the gas at the burner cap ports 28, to obtain satisfactory flame stability and give good flame definition under conditions of standard commercial distribution. Commercial gas may vary greatly in B.t.u. content, specific gravity and pressure. The burner assembly may be required to perform with commercial gases where the required heating input capacity may vary from approximately 500 to 12,000 B.t.u.s per hour.

As is evident, the large volume of the conventional burner base and burner cap in combination leaves a substantial volume of unburned gas when the supply is turned off. It is ax iomatic to say that the greater the volume of the unburned gas, the greater are the hazards from so called flashback", noise of flame extinction and odors of unburned gas.

The odors of unburned gas are not really hazards, in fact. But they are truly hazards to commercial sales. As is well known in the art, the odor one perceives with unburned commercially available gas is not, in fact, the odor of the gas itself. Natural gas is generally odorless. The odoriferous additive is incorporated in the natural gas to serve as a safety feature for gas ranges for housewives. However, the resulting odor from the added ingredient in natural gas is a disquieting factor from the psychological standpoint in the home and it is extremely important that such odors be minimized. Thus, there is a real need to minimize the volume of unburned gas.

The burner assembly of this invention minimizes some of the prior hazards as well as the volume of the burner cap assembly. FIG. 1 illustrates a conventional gas range 30 having a burner box 31 and an oven 32 located below a plurality of gas burning units 34 on the top of the range. The top ofa conventional range usually includes an enameled, stamped sheet metal top 36 having apertures 38 for the burner assemblies as shown in FIG. 3. A pan 40 having an opening 42 in its center sits in each aperture 38. A grate 44 is mounted over each aperture 38 above the pan 42 and a flat-bottomed utensil 46 (shown in phantom in FIG. 3) is supported by the grate 44.

The burner cap assembly 48, best seen in FIGS. 4 and 5, includes a mixing tube 50 supported by a bracket 52, a burner cap mounting plate 54 fixed to one end of the tube and a burner cap 56 crimped to the plate. It is not absolutely necessary that the cap be crimped to the plate but it is preferred where the range is in a mobile home or camper.

The mixing tube 50 is conventionally connected to a manifold and metering device (not shown) which feeds combustible gas into the tube. Openings 58 allow the aspiration of primary air as the combustible gas is injected into the tube past the openings.

As seen in FIG. 3, the bracket 52 may be bolted at 60 to the upper surface 62 of the oven 32. While the top of the over is shown as a single metal plate it is obvious that this is merely illustrative because any conventional oven includes insulation, etc.

The connection between the mixing tube 50 and the burner cap mounting plate 54 comprises a shoulder 64 crimped into the mixing tube and an upper flanged section 66 which is staked down on the plate 54 after it is assembled on the shoulder 64.

A drop-on-type burner cap 56 slips down over the periphery of the mounting plate 54 and may be crimped or staked at 68. A continuous flat top 70 on the cap 56 bridges the space across the annular vertical wall 72.

A mixing chamber 74 is formed by the cap and plate 54 which serves to further mix the combustible gas and primary air delivered by the mixing tube 50. The gaseous mixture will flow through the tube 50 upinto the chamber 74 and will be caused to change its flow direction by the flat top 70. The result will be a rolling, boiling, mixing type of motion creating turbulence within the chamber 74 as the gas-air mixture progresses outwardly toward the ports in the vertical wall 72.

The particular port pattern shown in FIGS. 3, 4 and 5 is effective to prevent flame blowing at the relatively high port velocity which results from the direct feed by the tube 50 into the chamber 74. Larger ports 76 are the primary exit means for the gas-air mixture. They are preferably round, approximately 0.078 inches in diameter and alternately spaced around the cap 56 with a spacing of approximately 0.3 I25 inches between centers. Smaller ports 78 are interspaced between the larger ports 76 and are of approximately 0.055 inches in diameter. Ports 78 have been added to give consistency of flame carry over between the primary ports 76, particularly at low gas inputs.

Other secondary ports 80 of approximately the same size as secondary ports 78 are aligned below the primary ports 76. When gas burns at ports 80, the resulting flame will coalesce with the flame emitted from ports 76 and will provide support and stability to the larger flame, thereby preventing blowing or lifting due to high gas velocity. The distance between the centers of

ports

76 and 80 may vary from three thirty-seconds to three-sixteenth inches.

A ledge 82 is formed in the cap 56 below the ports to help shield the flames 86. Turbulent air passing through the aperture 42 in the pan 40 tends to lift the flames from the port areas. An upper ledge 84 is provided above the ports to help shield the port area and the flames at low "turndown.

Because of the particular configuration of the burner cap assembly 48. on the low output end of the burner operating range the burner cap 56 will be heated to somewhere around 1,150 F. Experiments have shown that aluminum tends to deteriorate at these temperatures. Thus, steel is the preferred material for the cap.

It is preferable that the burner cap 56 have a diameter of approximately 2% inches and that the ports be directed through the wall 72 approximately radially of the burner cap. The flames emanating from the ports will tend to curl slightly upward near their ends around the upper ledge 84. However, when a cooking utensil is placed on the grate 44, such as illustrated in FIG. 3, the flat bottom of the utensil 46 will tend to cause a different flow pattern for the flame 86. Because of the velocity of the gas-air mixture ejected from the ports, the flat top cap construction, the lack of secondary air above the cap, and the radial direction of flow of the secondary air which flows through the aperture 42 in the pan, the flames 86 will stand almost horizontally outward from the burner cap 56,

' substantially parallel with the flat bottom of the utensil 46.

This serves the useful purpose of preventing the flame from impinging on the grate 44. Flame impingement on the grate tends to increase both the unburned gas and the carbon monoxide content of the resulting combustion products which is obviously undesirable.

In the design of the burner cap it was found that the metal walls of the cap 56 should be relatively thin, being about 0.035 to 0.050 inches in thickness, and that the cap may be formed by stamping, diecasting or other conventional mean. The thinwalled cap aspect of the invention and the high operating temperature the cap have apparently contributed to an increased burning efficiency of the gas-air mixture, as will be graphically illustrated subsequently. It is believed that one of the reasons for the increased efficiency is the heat which may be transmitted to the gas from the flat upper surface 70 of the cap.

As best seen in FIG. 5, when the gas-air mixture exits from the tube 50 it will tend to impinge against the flat upper surface 70 of the cap and the gas-air mixture will tend to absorb heat from the metal top 70. The fact that turbulent flow will be caused by the change in flow direction of the gas-air mixture will tend to further increase the heat transfer to the gas-air mixture. As is well known in the gas burning industry, part of the heat of combustion goes to heat the adjacent gas to ignition temperature. Thus, the heated gas from cap 56 will be initially hotter at the ports and absorb less heat from the adjacent flames. This unique heat transfer feature is clearly not the only reason for the increased efficiency of the instant burner but it is one of the reasons.

The increased temperature on the top surface of the burner also serves another useful purpose. With conventional burners the burner top may attain a temperature of about 900 F. The increased burner cap temperature (l,l50 F.) of the instant invention helps to incinerate and vaporize spills and droppings from the cooking utensils. The cap will thus require less cleaning and there will be a resulting lower percentage of the ports clogged by spilled food.

Another important feature of this invention is the openings 58 intermediate the ends of the mixing tube 50. Because the conventional air shutter has been eliminated, the inlets are less susceptible to closure from lint, dirt and grease. However, it is obvious that while the air shutter has been eliminated in the preferred embodiment, an air shutter could be included without departing from the spirit or scope of this invention.

To show the increased efficiency of the burner cap assembly of this invention the testing requirements, procedures and standards of the American Standard Association and the American Gas Association Testing Laboratories were used. In essence the standard requirement states that on gas ranges the carbon monoxide produced under certain test conditions must not be greater than 0.08 percent air free and under the same test conditions the efficiency of the burner shall not be less than 48 percent for natural gas and 50 percent for liquified petroleum gas.

In any particular burner assembly used for a gas range there is usually a direct relationship between the amount of carbon monoxide produced and the efficiency obtained. That is, some happy medium exists for the distance of the burner from the bottom of the cooking utensil where both the CO content and efficiency standards are met. Under the various test conditions required by the national standards, the latitude between allowable carbon monoxide produced and the required efficiency is quite small. Where a gain is desired in one of these two factors a sacrifice must generally be expected in the other. With conventional burners what generally happens is, the burners are placed as far away from the bottom of the cooking utensil as possible to meet the minimum efficiency requirements. This will generally give satisfactory results on carbon monoxide. Burner heights under these conditions usually fall within the limits of 1% to l l/l6 inches. The term bumer heights" as used herein is intended to mean the spacing between the upper surface of the grate and the centerline of the uppermost line of ports.

The test conditions and requirements are quite sensitive and in order to pass them it is common practice on standard burners and assemblies to closely proportion all adjustments such as the air shutter, orifice size, burner port size. secondary air distribution and burner heights. For example, on many burners the air shutter cannot be opened too far or the flames will blow and lift from the ports. If the shutter is closed too far the flames are too soft and will produce carbon monoxide. In other words, everything has to be adjusted proportionately or some failure will result.

This is not true with the burner cap assembly of this invention. Although there are certain conditions, the operative range is much broader with fewer critical limitations. First, there is no air shutter at all in the preferred embodiment. Using fixed unobstructed air openings meets all normal operating conditions. This in itself is most unusual for this type of burner. In addition, no formed venturi section is used in order to aspirate sufficient primary air. And last, the heavy cast burner base has been eliminated as an unnecessary element to the acceptable burning operation of the instant burner assembly.

However, the most important feature of all is the wide range of burner heights allowable with the burner cap assembly of this invention. As can be seen from the following data, the instant burner cap assembly may be placed much closer to the cooking utensil (which results in much higher burner efficiencies) and while still maintaining allowable carbon monoxide concentrations.

As can be seen from the above test data the burner height of the instant invention is useful from five-eighths to IV: inches while the conventional burner cap is extremely limited in its efficiency and in its operating range.

The implications of this wide range of efficient uses for the instant invention may not be obvious to the layman. However, the implications will come home quickly to those in the gas range manufacturing business. Because there is such a critical limitation in burner heights with conventional burners it is customary to use supplemental means independent of the bottom of the burner box for the purpose of mounting the burner assembly. This is obviously an expensive operation which is totally eliminated by the instant invention.

The particular burner cap assembly of this invention may be mounted directly on the oven top. The expansions and contractions of the oven will not have the effect of raising or lowering the burner cap assembly of this invention out of the allowable burner height range. However, with conventional burners the critical spacing between the top of the grate and the centerline of the upper row of ports could be destroyed by flexing of the oven top when the oven is heated. Oven heat could cause an expansion of the walls and top surface of the oven or perhaps a buckling of the same. This might move the burner cap vertically as much as a quarter of an inch or in some cases perhaps even more. With the conventional burner this is obviously not permissible as may be observed from the test data. However, it is clearly within the allowable limits of the burner cap assembly of this invention.

Thus, this invention allows the burner cap assembly to incorporate a bracket 52 which may rest on the lower surface of the burner box or the top of a conventional oven and the elimination of all of the prior art mounting bars and brackets which support the burner assembly on the range top itself out ofdirect contact with the bottom of the burner box.

Preferably, the volume of the chamber 74 will be approximately in the range 1.0 to 1.5 cubic inches, the total port area will be in the range 0.2 to 0.3 square inches and the cross-sectional area of the mixing tube will be approximately in the range 0.24 to 0.36 square inches. Thus, the ratio of the burner head volume to the port area is approximately equal to 3.3 through 7.5 and the ratio of the burner head volume to the cross-sectional area of the mixing tube is approximately in the range 2.8 to 6.3. The particular volume and cross-sectional area limitations are critical to the gas range industry.

While the ports described and shown in the drawing are round it is obvious that other conventional shapes could be substituted; for example, crosses, slots, elongated circles, etc.

This invention claimed is:

1. In a gas range for cooking the combination of a steel burner cap, a burner cap mounting plate and a mixing tube,

said tube having opening means for the aspiration of air into the tube, said opening means serving to provide adequate aspirated air over the full burner operating range without means for adjusting the size of the opening means, said operating range being from a B.t.u. per hour output of about 500 to about l2,000,

one end of said tube being adapted to receive gas injected from a manifold and the other end being connected in an opening in the mounting plate, said connection including material integral with said tube and extending radially thereof forming an annular, substantially gas tight connection with said plate,

the cap being mounted on the plate,

said cap and plate in combination comprising a mixing chamber for combustible gas and air delivered by said tube,

said cap including a plurality of ports directed substantially radially of said chamber,

ledge means above and below said ports extending radially outward for providing flame shields at the outer extent of said ports.

2. The combination of claim 1 wherein the top of the cap is substantially flat and continuous inwardly of its periphery.

3. The combination of claim 1 wherein said tube is of substantially nondecreasing crosssectional area from said openings to said plate.

4. The combination of claim 1 including a grate mounted above said cap, a pan on said grate, the spacing between the top of said grate and the center line of the uppermost ports being in the range five-eighths to 1% inches, said combination operating within the range five-eighths to 1% inches giving off no more than an air free 0.08 percent CO and having a heat transfer efficiency to said pan of not less than 50 percent.

5. The combination of claim 1 including a bracket means adapted for mounting said combination on the top surface of an oven of a gas range.

6. The combination of claim 1 wherein the ratio of the volume of the mixing chamber to the cross-sectional area of the ports is ap roximatel in the range 3.3 to 7.5.

7. The com ination 0 claim 1 wherein the mixing tube [5 of substantially uniform cross-sectional area from end to end and the ratio of the volume ofthe mixing chamber to the cross-sectional area of the tube is approximately in the range 2.8 to 6.3.

8. In combination a mixing tube, a bracket, a burner cap mounting plate and a burner cap,

said tube having one end shaped for connection to a gas manifold and the other end connected to the mounting plate, an opening in said tube intermediate its ends for the aspiration of primary air, the cap and plate being joined to form a mixing chamber, the ratio of the volume of the mixing chamber to the cross-sectional area of the ports is approximately in the range 3.3 to 7.5,

the mixing tube being of substantially uniform cross-sectional area from end to end and the ratio of the volume of the mixing chamber to the cross-sectional area of the tube being approximately in the range 2.8 to 6.3,

the bracket being adapted for mounting said combination above a drip pan ofa gas range,

the cap being mounted on the plate,

said cap including a flat top, a plurality of ports about its periphery and ledge means below said ports extending substantially radially outward for providing a flame shield at the outer extent ofsaid ports.

9. The combination of claim 8 including a ledge on said cap both above and below said ports extending radially outward to provide an annular recess at the outer extent of said ports.

i t i i

Claims

2. The combination of claim 1 wherein the top of the cap is substantially flat and continuous inwardly of its periphery.
3. The combination of claim 1 wherein said tube is of substantially nondecreasing cross-sectional area from said openings to said plate.
4. The combination of claim 1 including a grate mounted above said cap, a pan on said grate, the spacing between the top of said grate and the center line of the uppermost ports being in the range five-eighths to 1 1/2 inches, said combination operating within the range five-eighths to 1 1/2 inches giving off no more than an air free 0.08 percent CO and having a heat transfer efficiency to said pan of not less than 50 percent.
5. The combination of claim 1 including a bracket means adapted for mounting said combination on the top surface of an oven of a gas range.
6. The combination of claim 1 wherein the ratio of the volume of the mixing chamber to the cross-sectional area of the ports is approximately in the range 3.3 to 7.5.
7. The combination of claim 1 wherein the mixing tube is of substantially uniform cross-sectional area from end to end and the ratio of the volume of the mixing chamber to the cross-sectional area of the tube is approximately in the range 2.8 to 6.3.
8. In combination a mixing tube, a bracket, a burner cap mounting plate and a burner cap, said tube having one end shaped for connection to a gas manifold and the other end connected to the mounting plate, an opening in said tube intermediate its ends for the aspiration of primary air, the cap and plate being joined to form a mixing chamber, the ratio of the volume of the mixing chamber to the cross-sectional area of the ports is approximately in the range 3.3 to 7.5, the mixing tube being of substantially uniform cross-sectional area from end to end and the ratio of the volume of the mixing chamber to the cross-sectional area of the tube being approximately in the range 2.8 to 6.3, the bracket being adapted for mounting said combination above a drip pan of a gas range, one end of said tube being adapted to receive gas injected from a manifold and the other end being connected in an opening in the mounting plate, said connection including material integral with said tube and extending radially thereof forming an annular, substantially gas tight connection with said plate, the cap being mounted on the plate, said cap including a flat top, a plurality of ports about its periphery and ledge means below said ports extending substantially radially outward for providing a flame shield at the outer extent of said ports.
9. The combination of claim 8 including a ledge on said cap both above and below said ports extending radially outward to provide an annular recess at the outer extent of said ports.