US3782887A

US3782887A - Gaseous fuel burner

Info

Publication number: US3782887A
Application number: US00293050A
Authority: US
Inventors: R Brown
Original assignee: TRI MEN Manufacturing Inc
Current assignee: TRI MEN Manufacturing Inc
Priority date: 1972-09-28
Filing date: 1972-09-28
Publication date: 1974-01-01
Anticipated expiration: 1991-01-01
Also published as: CA985157A; JPS4993933A; GB1446952A; DE2348953A1

Abstract

A high capacity gaseous fuel burner of relatively short longitudinal dimension in which the fuel and combustion air are supplied at superatmospheric pressure and mixed in a widely flaring venturi section with the fuel admitted to the venturi throat in cross current fashion to the air flow and the mixture burned with a noiseless flame over a large area from a plate having numerous deep ports and located proximate the downstream mouth of the venturi. Means are also provided for adjusting the primary air-gas ratio entering the venturi and further means are provided for distributing secondary air to the base of the flame approximately in the plane of the downstream mouth of the venturi.

Description

United States Patent [1 1 Brown Jan. 1, 1974 GASEOUS FUEL BURNER Primary Examiner-Edward G. Favors [75] Inventor: Richard J. Brown, Mentor, Ohio Att0meyGeOrge Kaslk [73] Assignee: Tri-Men Manufacturing, Inc.,

Painesville, Ohio [57] ABSTRACT A hi h ca acit aseous fuel burner of relativel short 1 2 1972 g P Y g Y [22] Filed Sept 8 longitudinal dimension in which the fuel and combus- [21] Appl. NO-I 293,050 tion air are supplied at superatmospheric pressure and mixed in a widely flaring venturi section with the fuel 2 u 431 353, 432 222 admitted to the venturi throat in cross current fashion {2 i g F23d 12/02 to the air flow and the mixture burned with a noiseless [58] Fieid 326 328 flame over a large area from a plate having numerous 431/266. 432/222 deep ports and located proximate the downstream mouth of the venturi. Means are also provided for ad- [56] References Cited justing the primary air-gas ratio entering the venturi and further means are provided for distributing secon- UNITED STATES PATENTS dary air to the base of the flame approximately in the 2,72l.607 l0/l955 Damon et all 431/353 X plane f h downstream mouth f h i 3.709.473 l/l973 Ito et al. 43 l/353 X 9 Claims, 8 Drawing Figures GASEOUS FUEL BURNER BACKGROUND OF THE INVENTION This invention relates to gaseous fuel burners, particularly to relatively small size burners for use in space heating, as for example, the interior of mobile homes, marine craft and land vehicles. In applications of this sort, severe limitations are imposed on the heating equipment. It must be reliable and safe under adverse and widely varying ambient temperature conditions; it must be compact and require minimum power in its performance. It must be quiet in operation and economical (efficient) in the use of fuel. The subject burner is designed to meet these requirement.

Thus, a principal object of the invention is to provide a burner that is extremely compact but one that can produce a high output. For example, a typical burner of this invention may have the approximate dimensions of a three-inch cube and be able to produce an output of approximately 20,000 BTU perhour atan efficiency of greater than 80 percent. Not only is the burner of this invention able to perform with the above ability, but it does so in a reliable, safe and quiet fashion.

To accomplish this, the principle of supplying air and gaseousfuel at super-atmospheric pressure is used. Futhermore, the mixing of the primary combustion air and the gaseous fuel is effected by use of the venturi principle wherein the gaseous fuel is introduced into the throat of the venturi cross current to the flow of combustion air therethrough and the mixture rapidly expanded while still at super-atmospheric pressure and then burned off a deep-ported bumerplate over a relatively wide or large area.

It is a further object of the invention to divide the combustion air entering the burner into two parts: one part (as explained above) to be admitted to a venturi structure and mixed with the fuel gas; the second, and lesser,part to be used as a cooling medium andthence introduced into the combustion zone as secondary air for assisting in the complete combustion of the fuel. Throughout this description primary air shall be rdfined as that part of the combustion air that is intimately mixed with the gaseous fuel within the venturi structure; secondary air shall designate that part of the combustion air that is delivered to the burner head, but which is not mixed with the fuel in advance of the burner :ports.

Itis desirable and in fact an object of theinvention, tokeep the combustible, primary air gas mixture relatively cool prior to combustion, and so the downstream portion of the venturi opens at a widely divergent angle to allow rapid expansion of the gas mixture as it approaches the burner plate. This serves the further objective of securing maximum mixing of the fuel and air and further of reducing the (back) pressure against the venturi throat that could develop if the gases were heated substantially.

It is an object of the invention to provide a burner that produces aluminous, quiet and soft flame of relatively short lenght and that burns to completion without significant unburned, residual products (suct as carbon monoxide) or other hazardous, or pollutant type products. To this end the flame from the subject burner is found to burn clean.

Although other types of burners (e.g. Bunsen) have employed the venturi principle (primarily to inspirate combustion air) they do not develop the burning rate capacity of the subject burner of comparable size. Furthermore, the prior artburners of this type have all had a relatively long and narrowly divergent venturi. Length limitations are severe in the application of the subject burner and could not be met with the aforesaid prior art structures. In addition, while the use of superatmospheric introduction of the fuel has been employed in prior art structures (to achieve high capacities i.e., burning rates) the nature of the prior art burners have been notoriously noisy in operation. Blow torches and gun burners are typical of this construction. In the present application, wherein the heating apparatus maybe close to confined living quarters, for example in a mobile home, the heating apparatus must operate quietly, so thatbumers ofthe prior art sort are intolerable.

A further object of this invention is to provide a burner having an ignition means (preferably of the continuous spark variety) that is safe and dependable in operation andis designed to have along life. In this respect, the igniterforthe subjectburneris so situated as to be cooled by the incoming air and air-gas mixtures and is further arranged to have its parts, particularly the electrode tip, out of the intense zone of combustion, but proximate the zone or plane where combustion initiates.

"BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal view, partially in section, showing theburner applied to a combustion chamber. FIG. 2 is a cross-sectional view looking upstream from the mouth of the burner, essentially along line 11-41 of FIG. 1.

FIG. 3 is afragmentary section across the throat of the venturi at the gaseous fuel admission orifices and on the plane of line III-III.

FIG. 4 is a'longitudinal schematic view of the venturi assembly, the supporting flange, combustion chamber, illustrating the air and 'gas flow and the combustion process.

FIG. 5is an end view of the upstream end of the venturi showing the distribution of primary air intake openings at the fixed primary air plate.

FIG. 6 is a detail of the air shutter adjusting means.

FIG. 7 is a fragmentary detail of the igniter structure.

FIG.8 is a schematic representation of a heating system embodyingthe subject burner.

DESCRIPTION OF THE PREFERRED EMBODIMENT Thepreferred embodiment of this invention includes a burnerbody B enclosing a venturi assembly V, gas admission means G, combustion air admission means A and an igniter assembly I.

Referring to FIG. 1, the burner body is cup-shaped with an open mouth and includes an end wall'2 and peripheralwall 3 having a flange 4 for attaching the burner to a combustion chamber designated generally as H. The end wall is provided with a boss 6 bored and threaded to receive a gas supply fitting 7 and a primary air adjustment crank pin 8 and its lock nut 9. A gas spud 12 is threaded into the end wall (in communication with the gas supply fitting 7) on the axis of the burner and has gas orifices 13 directed radially and in a plane lying about one-half the depth of the burner cup. A flange member 15 having a cylindrical skirt l6 is clamped by screws 18 between the face of the burner flange 4 and the combustion chamber H.

Welded to and supported by the skirt 16 is a venturi member, designated generally by the reference character V. The upstream mouth 20 of the venturi supports a primary air admission and adjustment means 40, described infra, in spaced relation to the end wall 4 and has its throat portion 22 located in the plane of the gas orifices 13; the abruptly flared downstream portion 26 of the venturi terminates just beyond the mouth of the burner body. Thus the venturi V divides the interior of the burner body B into two zones, namely; (1) the volume within the venturi that comprises a mixing zone in which a portion of the combustion air is mixed with the gaseous fuel and (2) the space surrounding the venturi over which passes the remaining combustion air to feed a concentric series of small (secondary) air openings 17 in the face of the flange 15. Preferably, these openings 17 are placed near and just outboard the juncture of the skirt 16 and the flange 15. In addition to furnishing necessary air to complete the combustion process, these openings furnish air that cools the venturi structure and burner plate structure, as will be shown in greater detail infra.

Within skirt 16 and just downstream from the end 26 of the venturi is positioned a relatively thick burner plate 30 having a large number of deep ports 32, uniformly distributed over the face of the plate, forming discharge openings for the mixture of fuel, gas and primary air delivered from venturi V. In the preferred embodiment, the ratio of port diameter to port depth is in the range of 1:4; for a burner plate having a 2-inch diameter, approximately 250 ports each having a l/l6 inch diameter may be provided.

The burner is designed to burn a wide variety of combustible gases, ranging in heating value from 500 to 2500 BTU or more; to accomplish this in a efficient manner, control of the primary combustion air is necessary. In the preferred embodiment, this control is obtained by fixing a primary air plate 41 in the upstream end 20 of venturi V, FIG. 5. This plate has a series of air admission openings 42 the effective size of which are controlled by a movable shutter plate 44 having a matching series of openings 45. The shutter is positioned by and rides on a shoulder 2a (part of the burner end wall 2) and is actuated by crank pin 8 joumaled in end wall 2 and having a slotted flange 52 which receives a pin 46 carried by the shutter, FIG. 6. Rotational movement of the crank causes the shutter to rotationally shift with respect to the air plate and allows the desired adjustment of the primary air admission openings. The crank is fixed in the desired position by lock nut 9.

The igniter I consists of an electrode 60 sheathed in an insulating sleeve 62 that is mounted in an opening through the top of the burner and held in place by lock nut 63. The working end of the igniter is positioned near the axis of the burner just downstream of the burner plate 30 and is adapted to continuously are against said plate. With reference to FIG. 7, it will be noted that the igniter electrode tip 64 terminates at the downstream face of burner plate 30 proximate a pocket 38. Arcing occurs from the tip 64 to the pocket wall. Some of the burner ports intersect the wall of the pocket 38 and thereby introduce the combustible mixture to the confines of the pocket across which the arc 56 occurs. This assures positive ignition, for it occurs in a confined zone, slightly ahead of the main flame front and provides a pilot light for the front. By locating the electrode tip 64 ahead of the main flame, i.e., upstream therefrom, it operates at a cooler temperature which assures a longer operating life. High tension voltage is applied to the electrode (from a source not shown) and burner plate 30 provides the return path for the electrical current; for this purpose, it is desirable to have the plate welded or brazed in firm contact with the flange skirt 16. It will be noted that the bell portion 26 of the venturi and the burner plate 30 are cut out to make a close fitting opening 26a and 34, respectively, for the accommodation of the igniter element 60. A typical application of the burner of this invention is schematically illustrated in FIG. 8, wherein it is used as a source of heat for a heating system S. The burner B is applied to a combustion chamber-heat exchanger H, served with an exhaust line H1, and enclosed in a shroud T to which ventilating air is suppleid by a fan F driven by motor M. This same motor may drive a separate blower A which furnishes combustion air to the burner through air line Al. Gaseous fuel is supplied through line G from a source at superatmospheric pressure (eg 8 to l3 inches of water column). The burner igniter is shown at I, and has a convenient source of constant high tension voltage (not shown) during burner operation. The entire system may be enclosed in a casing having appropriate heated air outlet openings S1 and air inlet openings S2. The overall dimensions of such an installation may only be 14 inches long, 13 inches wide and 9 inches high, with the unit capable of delivering in excess of 15,000 BTU per hour at better than percent efficiency. To accomplish this, the novel burner of the invention, being less than three inches in diameter and about two inches deep, is able to provide an efficient flame for a 7-inch long combustion chamber to effect the above output. Not only does the burner accomplish the above output, but in operation it is quiet, clean burning and safe.

MODE OF OPERATION AND PRINCIPLES INVOLVED The subject burner is designed for constant spark ignition and is generally operated under a control system (not shown) that provides for a start up, run and shutdown cycle, with thermostatic and safety control features. The gaseous fuel supply at super-atmospheric pressure is introduced in a cross-current fashion to throat 22 of the venturi through orifices 13, preferably at a line pressure of 8 to 13 inches water column (see FIG. 3). At the same time combustion air is brought tangentially into the head through opening 10 at a pressure of one to two inches of water column. This air divides into two portions: the major part of it passes through the

primary air openings

42 and 45 to enter the interior of the venturi bell section 20 and the remainder passes around the venturi and out through the secondary air holes 17. The air that enters the venturi is funneled into the throat portion 22 and due to its increased flow velocity, tends to draw the fuel gas leaving orifices 13 into the stream and inter-mix it thoroughly with the combustion air. This construction is an important feature of the design, since variation in the rate of air flow through the throat (which may be due to changes in the delivery rate of the blower because of external factors, such as line voltage variation, etc.) automatically adjusts the inspiration of gas to maintain a constant airgas ratio in the mixture discharged from the throat. Thus, the greater the air flow through the throat 22, the greater is the gas injection effect, and vice versa. As the gas-air mixture leaves the throat 22, it is expanded rapidly and further mixing takes place, so that a uniform, combustible mixture is presented to the burner plate 30.

in a prefereed embodiment, for a burner with a twoinch diameter burner plate, the venturi may have an inlet cone that is inch deep with sides converging at an included angle of 120, a throat one inch in diameter and inch long and a downstream bell 26 diverging at an included angle of 90. The volume of the downstream conical section or hell 26 is larger than the corresponding upstream structure to allow for the increased volume of gases (the added fuel gas) and the expansion thereof at higher temperature in proximity to the combustion zone. It is desirable to maintina the internal pressure uniform throughout the venturi, except at the throat where the pressure drop is designed to assist in the injection and mixing of the gaseous fuel. This is accomplished by proper sizing of the primary air openings 42 and balanced by the size and number of burner port openings 32.

The space within the burner head 1 and exterior of the venturi structure is maintained at essentially the same pressure (e.g. one and be inch water column) as that inside the venturi bell portions 22 and 26. This air is given a spiral motion, sweeps the venturi structure tending to cool the same, and is discharged through the secondary air openings 17 in the flange 15. Based on the ratio of the area of the primary air openings 42-45 to that of the secondary air openings 17, approximately three-fourths of the combustion air enters the venturi as primary air and the balance, or one-fourth, of the combustion air A is discharged through openings 17 as secondary air. The purpose of the secondary air is twofold: (1) it is supplied to the combustion chamber H to assure complete and properly controlled combustion and (2) it is used to ventilate or cool the burner parts including the burner wall 3, the venturi structure V, the burner plate 30 and the igniter I. Whereas the gas-air mixture presented to and leaving the burner ports 32 is a readily combustible gaseous medium (thus assuring proper ignition and burning at the ports), the introduction of secondary air permits a softer flame from the ports 32 and assures completion of combustion in a quiet manner within a short distance from the burner plate 30. It has been found in practice with the subject burner, that the primary air-gas mixture first burns in soft jets at and off the burner face; these jets combine into a uniform, rapidly burning, hydroxylating flame or inner mantle of a length approximately lrfi times the diameter of the burner plate and this flame is surrounded by a blue outer mantle, filling the combustion chamber H and assuring complete combustion within a distance of three times the diameter of the burner plate. By maintaining a substantial pressure head in the venturi section 26 on the upstream side of burner plate 30 in combination with a relatively thick and cooloperating burner plate and deep ports 32, the possibility of flash back through the ports is eliminated even though the air-gas mixture is readily combustible. This permits burning directly ofl" the face of burner plate 30 and shortens to a minimum the length of the flame required for complete combustion.

I claim:

1. A gaseous fuel burner comprising a cup-shaped burner head including an end wall and a cylindrical wall enclosing an air cavity with an open mouth, means for introducing combustion air at super-atmospheric pressure tangentially to the interior of the head near the end wall, means for introducing gaseous fuel under pressure through ports oriented in a radial direction at a point along the longitudinal axis of the burner and spaced from the end wall, a restrictor flange attached to and partially closing the mouth of the head member and terminating in a cylindrical sleeve portion extending downstream, a sharply flaring venturi structure supported at its downstream end by said sleeve and having its throat portion in the vicinity of the gas ports and its upstream end spaced from the end wall, a perforated plate across the upstream end of the venturi to allow primary air to enter the venturi and a multi-ported burner plate supported across the downstream portion of the sleeve and spaced from the diverging wall of the venturi.

2. The burner of claim 1, including electrical ignition means carried by the head and operative at the downstream face of the burner plate.

3. The burner of claim 2, wherein the burner plate is provided with a pocket and the ignition means is adapted to create a spark in said pocket for igniting the gaseous mixture to be burned.

4. The burner of claim 1, including an air shutter for regulating the flow of primary air entering the venturi.

5. The burner of claim 4, wherein means are provided for adjusting the air shutter from a point exterior of the burner head.

6. The burner of claim 1, wherein the restrictor flange is provided with a concentric ring of secondary air ports at the mouth of the cavity along the outer surface of the sleeve.

7. The burner of claim 5, wherein the air shutter adjustment means is a crank pin carried by the end wall of the burner.

8. The burner of claim 3, wherein the ignition means is a high tension spark electrode that is mounted on the head, extends through the cavity and terminates in the pocket at essentially the central axis of the burner.

9. The burner of claim 1, wherein the ratio of port diameter to port length in the burner plate is in the range of 0.25 to 0.33.