US2814339A - Tunnel-type gas burner and double igni- - Google Patents

Description

F. B. AUBERT 2,814,339 TUNNEL-TYPE @As BURNER AND DOUBLE IGNITION yAND FLAME-sENsING PILOT MEANS Filed April I1, 1955 Nov. 26, 1957 INVENTOR. FRED B. AU BERT ATTORNEYS TUNNEL-TYPE GAS BURNER AND DOUBLE IGNI- TION AND FLAME-SENSING PILOT NIEANS Fred B. Aubert, Wellesley, Mass., assignor, by mesne assignments, to Detroit Controls Corporation, Detroit, Mich., a corporation of Michigan Application April 11, 1955, Serial No. 500,321 3 Claims. (Cl. 158-123) The present invention relates to gas burners, particularly those generally designated .as tunnel or block-type burners, and its obje-ct is to provide an improved burner permitting increased gas velocity and improved flame sta'bility, and in addition, to provide reliable and serviceable means by which the presence of 'a flame may be sensed and utilized through a greater range of modulation in combustion con-trol apparatus.

yBurners of the type with Iwhich -this invention is concerned generally include a nozzle formed of a ceramic burner block having a hollow cylindrical cavity forming an open ended .combustion chamber. A mixture of gas and air is introduced at the inner end of the chamber with combustion occurring partly within the chamber where the walls confine the base of the llame land direct it -generally outward from the chamber. Burners of this l type lare commonly .used Where a ame of high intensity is desired, since the gas and air mixture may be introduced at high velocities with combustion occurring within ra relatively conined space. Consequently, it is ordinarily desired that a tunnel burner be able to sustain the combustion of high velocity gas .and air streams to produce an intense hot relatively vsmall llame. However, even with burners of this type, the llame will drift out and away from the burner when the fuel is supplied at excessive velocities and improper `gas-air mixture rati-os.

Burners of the tunnel or block type have not realized their full potentialities in automatically controlled combustion systems employing a flame sensing device for controlling the operation of the burner because of the diiculty of reliably sensing when norm-al combustion conditions prevail. The extremely high temperatures e11- countered Within the cavity and 'the incande'scence to which its walls are heated render most ordi-nary llame sensing devices unreliable, either 'beca-use of their inability to withstand the inten-se heat, as would be the case with a probe type name detector, or because of the sustained emission of heat 'and light from the incandescent cavity walls lafter the fla-me has been extinguished, which causes unreliable operation of heat or lightsensitive means for sensing the presence of a flame.

This invention overcomes these difficulties by employing a pair of pilot burners insulated from each other so that ilame detection may be afforded by the existence of an electrical path through impinging llames issuing from the burners. Although the electrical path through impinging pilot llames has been utilized in combustion control systems in the past with generally good results, their use in tunnel-type burners has not heretofore been successful because of the difliculty of assuring such proper insulation of the burners from each other, that the only electrical .path between them is always through their dames. The necessity of these flames being within the combustion chamber requires that the burners also be directed into the chamber. However, the .walls of the chamber, although ceramic, become suliiciently conducting at high temperatures to preclude the mounting of niteci States Patent inner pilot burner tu'be 18 and the throat section 16 of the nice 2 the pilot burners in contact lwith them since they would provide :an electrical path between the burners in parallel with the .path through the flames.

In the burner of this invention, lone of the burners is electrically insulated not only from the other burner, but also from the ceramic block and is directed int-o the vblock through its throat where .the main gas and `air mixture is introduced. This pilot :burner provides a pilot flame at the very base of the main burner llame which serves not only to impinge with the other pilot flame, but also serves to stabilize the main llame within the combustion chamber and prevent its drifting out and away from the burner. With 'the pilot llame so oriented and directed, it has been found that significantly increased velocities of the incoming gas and air mixture may be used.

This invention will be -better understood from the following detailed description of a preferred embodiment selected for purposes of illustration yand shown in the accompanying drawing in which:

Fig. 1 is a longitudinal cross-section of the improved tunnel burner of -this invention; and

Figs. 2, 3, 4, and 5 are longitudinal cross-sections of the forward end of the burner showing the sequence of starting operations.

:In its general organization the improved burner of this invention consists principally of ya nozzle 10 fonned in a :ceramic burner 'block mounted on a flanged seat 11 at the forward end of a tubular body section 12 through which the fuel and air mixture is introduced, The nozzle is formed with a generally cylindrical cavity 13, open at its -forward or combustion end, and communicating at its inner end with the tubular body section 12 through an annular inlet 14 defined between an outer necked-.down body and an inner pilot 'burner tu'be 18 extending the length of the body.

The inner pilot burner tube 18 is insulated from the rest of the burner conveniently by mounting it in an insulating lbushing 19 bored to accommodate the rear end of the tube 18 which is retained therein by nuts 20 and 21 threaded to the tube Iand engaging opposite sides of the bushing. The bushing 19 is conveniently mounted between a flange 22 at the rear end of the body section 12 an-d a flanged lbonnet 24 through which a fuel-air mixture is supplied to the inner pilot vburner tube 1'8. -Electric-al connections to the inner pilot burner tube 18 is conveniently made 'by a terminal post 23 extending into the insulating bushing 19 .and into electrical contact with the inner pilot burner tube.

The forward end of the inner pilot burner tube 18 is in general alignment with the throat 16 at the inner end of the combustion chamber and serves as the plug frequently provided a-t the fuel inlet of burners of this type. lIn the operation of the burner of this invention, however, the pilot burner tube serves not only as an inner throat plug, but also provides an independently controllable flame at the base of the main flame which serves to stabilize the latter.

An outer pilot burner t-ube 26 through which 'is -provided a pilot llame impinging with th-e flame from the inner pilot burner 18, is .accommodated within a bore in the burner block 10 and is tted to the seat 11 through which it is electrically grounded. A spark plug 28 is threaded in the Wall of the outer pilot burner tube 26 and provides for initial ignition.

The burner above described is .admirably lsuited for use -in automatic combustion control systems of numerous types, suc-h as those described in -eopending application Ser. No. 412,162, iiled February 24, 1954, and U. S. Patent No. 2,386,648 in which the -circuit between the outer pilot burner 3 tube 26 (or ground) is utilized to control the operation of the combustion control device. In such devices, normal flow of fuel to the burner is continued only so long as th-is circuit between the pilot burners exists, and when this circuit opens, -as upon a flame failure, the fuel supply is cut off.

As shown in Figs. 2, 3, 4 and 5 starting up of the burner involves rst the ignition of the outer pilot by means of the spark plug 28 (Fig. 2). Thereafter, the inner pilot burner is ignited (Fig. 3) following which the main fuel valve is opened to deliver fuel to the annular fuel inlet 14 initially at low velocity as shown in Fig. 4. During this initial warming up period the pilot ames continue to impinge and a direct circuit through them is maintained. After the burner nozzle has heated, the fuel rate will normally be increased to provide a flame of the desired high intensity, as shown in Fig. 5. When this occurs the outer pilot ame will likely be blown and caused to deect by the high velocity main flame so as not to impinge directly on the inner pilot flame, in which case, however, the necessary circuit will be in series through the three flames.

With the inner pilot tube 18 electrically insulated from the rest of the burner, and separated at its tip by the annular inlet 14, the presence of a flame is essential to any circuit through the inner pilot burner tube, and any flame failure is occasioned by a simultaneous opening of that circuit. Thus, even though the ceramic burner block is hot enough to be conducting, it forms no part of the control circuit. Nor does its temperature or incandescence in any other way affect the functioning or condition of the detecting circuit provided through the inner pilot burner tube 18.

From the foregoing description it is believed apparent that this invention provides not only an improved tunnel or block type burner capable of operation at higher fuel rates than would otherwise be satisfactory, but also provides a flame detection system not heretofore achieved reliably and safely in burners of this type.

While arne stability is maintained at higher fuel velocities in burners embodying this invention, the normal low velocities frequently desired may also be used. In other words, the range of permissive velocities is increased by this invention to include higher velocities but without raising the lower end of the range. In this connection, it will further be noted that ame sensing at low velocities, when the rnain burner llame is extremely low, is adequately and reliably provided for.

Although this invention has been described in detail with reference to a preferred embodiment, it is contemplated that obvious modifications will occur to those skilled in the art and that they may be made without departing from the scope of the invention.

Having thus disclosed my invention and described in detail the preferred embodiment, I claim and ldesire to secure by Letters Patent:

l. A gas burner comprising a burner nozzle deining an open ended combustion chamber having a fuel inlet opening, an inner pilot burner of electrically conductive material directed into said chamber through said opening and spaced therefrom, to form an annular fuel inlet passage, an outer pilot burner of electrically conductive material directed into said chamber at an angle to said inner pilot burner, said burners being adapted to provide flames mutually impinging within said chamber, insulating means outside of said chamber to which said inner pilot burner is mounted, main fuel conduit means communicating with the fuel inlet opening, and pilot fuel conduit means communicating with said pilot burners.

2. A gas burner comprising a burner nozzle defining an open ended combustion chamber having a fuel inlet opening, a tubular body supporting said nozzle and dening a main fuel duct to said fuel inlet opening, an inner pilot burner tube of electrically conductive material extending the length of the tubular body concentrically therewith and terminating with its end within said opening to define an annular fuel inlet passage, insulating means outside said chamber mounting said inner pilot burner tube to said tubular body, an outer pilot burner tube of electrically conductive material directed into said chamber through said nozzle directed to provide a ame impinging the llame from said inner pilot burner tube, main fuel conduit means communicating with said tubular body, inner pilot fuel conduit means communicating with said inner pilot burner tube, and outer pilot fuel conduit means communicating with said outer pilot burner tube.

3. A gas burner comprising a burner nozzle defining an open ended combustion chamber having a fuel inlet opening, a body member defining a main fuel duct connecting with said fuel inlet opening, an inner pilot burner tube of electrically conductive material mounted within said body member and directed into said chamber through and spaced from said opening to form an annular fuel inlet passage, said pilot burner tube being electrically insulated from said body member, an outer pilot burner tube of electrically conductive material directed into said chamber through said nozzle directed to provide a ame impinging the ame from said inner pilot burner, main fuel conduit means communicating with said body member, inner pilot fuel conduit means communicating with said inner pilot burner tube, and outer fuel conduit means communicating with said outer pilot burner tube.

References Cited in the le of this patent UNITED STATES PATENTS

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