US3060997A - Oil burner and control system therefor - Google Patents

Description

Oct. 30, 1962 F. J. MANEY OIL BURNER AND CONTROL SYSTEM THEREFOR Filed Dec. 14, 1961 nunon* United States Patent Office 3,060,997 011, BURNER AND CNTRL SYSTEM THEREFQR Francis J. Maney, Mahwah, NJ., assigner, by mesne assignments, to Emerson-White-Rodgers Company, a corporation of Missouri Filed Dec. 14, 1961, Ser. No. 159,411

5 Claims. (Cl. 158-28) rl`his invention relates to a high pressure gun-type oil burner having a combustion improving grid element spaced outward from the burner fuel spray nozzle, an igniter arranged so as to ignite the fuel spray between the spray nozzle and grid element, and control means which responds instantaneously to the appearance of combustion ame to render the igniter inoperative and responds instantaneously upon subsequent flame failure to reinstate operation of the igniter.

The primary object of the invention is to provide an irnproved high pressure gun-type oil burner with an automatic control system therefor including ignition means, in which: improved combustion and desired ame pattern are achieved through a controlled turbulence of the fuel-air mixture -issuing from the burner tube which is accomplished by the provision of a grid element mounted in spaced relationship with the fuel spray nozzle and the discharge end of the burner tube; in which spark ignition means is arranged to ignite the fuel-air mixture at a point between the discharge end of the burner tube and the grid element; in which flame responsive means operates instantaneously to stop operation of the igniter when flame is established, thereby to preclude fouling of the grid element with carbon accumulation which would otherwise occur rapidly if ignition of the fuel between the spray nozzle and grid element persisted; and in which the flame responsive means also operates to reinstate operation of the igniter instantaneously if combustion subsequently fails.

Other objects and advantages will appear lfrom the following description when read in connection with the accompanying drawing.

The single FIGURE of the drawing is a diagrammatic illustration of a high pressure gun-type oil burner with a combustion improving grid ignition means and a control system constructed in accordance with the present invention.

Referring to the drawing, the primary elements of the system are: a high pressure gun-type oil Aburner generally indicated at 10, a space thermostat 12, a main relay having a winding 14 and normally open relay contacts 14a and 14h, an ignition relay having a `winding 16 and normally closed relay contacts 16a, a ame detector relay having a winding 18, ystationary contacts 18a and 18b, and a double-throw switch blade 18C normally in closed contact engagement with stationary contact 18a, a thermal time switch (safety switch) 20, a resistance heater 22 for operation of switch 20, a voltage step-do-Wn transformer having a primary winding 24 and a secondary winding 26, a voltage step-up ignition transformer having a primary winding 28 and a secondary winding 30, ignition spark electrodes 32, a photoconductive element 34, and power supply leads 36 and 38 for connection with a suitable power source.

The oil burner is provided with the usual blower and fuel supply pump which are driven by a motor 40, and which when driven by motor 40 supply air to the burner blast tube 42 and fuel to a spray nozzle 44 located at the discharge end of the blast tube from which the fuel issues in a generally conical spray and mixes with the formed draft of air issuing from the end of blast tube 42. Supported on the yburner tube in any A'suitable manner is a grid element 36 spaced from the discharge end of tube 42 and spray nozzle 44. The grid element 46 is arranged perpendicular to lthe axis 0f burner tube 42 and effects a predetermined turbulence in the fuel-air stream issuing from tube 44, which achieves greater total surface contact between the atomized liquid fuel and combustion supporting air and results in substantially improved combusti-on in the desired llame area.

in order to protect the ignition electrodes from constant impingement and erosion by flame during burner operation, they are positioned adjacent the spray nozzle 44 and between spray nozzle 44 and grid element 46.. The spacing of the grid element with respect to the end of blast tube 42 is such that when a combustible mixture is being supplied and the igniter is operating, the mixture is flashed in the area between the end of burner blast tube 42 and grid 46 and immediately begins to burn in complete combustion in a desired flame pattern on the side of grid 46 remote lfrom the burner tube, and continues to do so normally without further operation of the igniter or combustion between the end of the blast tube and the grid element. It has been found that continued operation of the igniter results in a relatively rapid build up of carbon on the burner side of the grid element due to the incomplete combustion which occurs in this area, and that any appreciable accumulation of carbon on the grid element distorts the flame pattern and defeats the intended purpose of the grid element. It is imperative, therefore, that operation of the igniter be cut oi instantaneously when combustion llame is established on the remote side of the grid element. Normally, combustion on the remote side of the grid is established within a fraction of a second after the mixture is flashed on the igniter side so that, normally the required operation o=f the igniter under conditions of a full volume of mixture flow is in the order of one second or less. lt has been found that to prolong operation of the igniter under normal conditions a mere fifteen (l5) seconds may result in a carbon accumulation on the grid element which greatly distorts the flame pattern on the remote side of the grid element.

The photoconductive element 34 is a solid state type photo-cell which has an extremely high resistance to the flow of electrical current in the absence of combustion flame, but becomes sufficiently conductive to permit energization of the series connected flame detector relay winding 18 when combustion flame exists. The element 34 may be mounted within the burner casing and arranged to see the light of burner flame through burner blast tube 42 either directly or by reflection A detailed showing and description of the mounting and positioning of element 34 in the burner casing is disclosed in the present assignees copending application of Bernardus J. Staring, Serial No. 33,050, filed May 2,1, 1960. The normally closed safety switch 20 is of the bimetal blade type which when heated by the resistance heater 22 for a predetermined period of time opens and locks open, requiring manual resetting.

Main relay winding 14 is initially energized upon closure of the thermostat 12 through a pull-in circuit which may be traced from one side of the transformer secondary winding 26 through a lead 48, the normally closed llame detector relay contacts 18C and 18a, a lead 50, the safety switch resistance heater 22, a lead 52, main relay winding 14, a lead 54, space thermostat 12, a 'lead 56, safety switch 20, and a lead 58 to the other side of secondary winding 26. When relay winding 14 energizes, its contacts 14a close to complete a holding circuit for 14 through a portion only of transformer secondary winding 26 and the now-closed contacts 14a. This holding circuit, which bypasses the llame detector relay contacts 13C and safety switch heater 22, may be traced from a mid-tap on the transformer secondary 26 through a lead 60, the relay contacts 14a, a lead 62, the relay winding 14, the lead 454, the thermostat 12, the lead 56, the safety switch 20, and the lead 58 to the lefthand side of secondary winding 26. This holding circuit maintains a somewhat lower level of energization of the winding 14 than does the pull-in circuit which includes all of the secondary winding 26, but this lower level of energization Vis suicient, however, to hold in the main relay contacts 14a and 14h once they have been pulled in.

When the main relay winding 14 is energized upon closing of the thermostat through the` described pull-in circuit, its contacts 14h also close and the burner motor 40 and the igniter transformer primary 28 are energized by circuits connecting these elements directly across the power source. The motor circuit extends from power source lead 36 through a lead 64, main relay contacts 14b, a lead 66, motor 40, and a lead 68 to power source lead 38. The circuit for the ignition transformer primary winding 28 extends from power source lead 36 through lead 64, a lead 70, the normally closed contacts 16a of the ignition relay, a lead 72, ignition transformer primary winding 28, a lead 74, and lead 68 to power source lead 38.

The ignition relay winding 16 is energized by a circuit extending from transformer secondary winding 26 through lead 48, the blade 18o and contact 13b of the llame detector relay when these are closed, a lead 76, the winding 16, a lead 78, lead 54, thermostat 12, lead 56, safety switch 20, and lead 58 to the other side of secondary 26.

The llame detector relay winding 18 is energized through a circuit extending from transformer secondary 26 through lead 48, a lead 80, the winding 18, a lead 82, the photoconductive element 34, a lead 84, a lead 56, safety switch 20, and lead 5S to the other side of secondary 26. It will be noted that the flame detector relay winding and photoconductive element 34 are not connected through the space thermostat 12.

Operation During normal operation when space thermostat 12 closes, a pull-in circuit is completed connecting the main relay winding 14 across the entire transformer secondary winding 26 through llame detector relay contacts 18a- 18e. When this occurs main relay holding contacts 14a and motor and ignition contacts 14h close. The closing of main relay contacts 14b initiates operation of the burner motor 40 and the igniter 32. The closing of main relay contacts 14a completes a parallel branch forming the holding circuit for the main relay winding 14 via the transformer secondary mid-tap lead 60 which includes the safety switch 20, but bypasses the safety switch resistance heater 22 and the llame detector relay contacts 18a-186. When normal combustion is established photoconductive element 34 becomes suciently conductive to permit energization of flame detector relay winding 18 through the circuit described. Energization of flame detector winding 18 causes its contacts 18a-18e to separate and contacts 18c-18b to close. The parting of contacts 18a-18e breaks the main relay pull-in circuit and de-energizes safety switch heater 22. The thermal timing means comprising the safety switch and resistance heater 22 is now inoperative.

The closing of llame detector relay contacts 18e-13b completes the described circuit for energization of ignition relay 16 which, upon being energized, opens its normally closed contacts 16a to break the circuit at that point for ignition primary winding 2S, thereby rendering the igniter 32 inoperative. Normally, combustion will now persist until space thermostat 12 opens. If, however, combustion llame fails for any reason, photoconductive element 34 instantly becomes non-conductive causing the llame detector relay winding to be de-energized and its contacts 18o- 1812 to separate and its contacts 13a-18e to close. The

separation of contacts 18e-18h de-energizes ignition relay 16 permitting its contacts 16a to close, thereby rendering the igniter 32 again operative, and the closing of contacts 18a-18e again completes the main relay puilin circuit which includes the safety switch heater 22. If combustion llame is re-established within the time required to open safety switch 26, normally operation of the burner will again continue; if not, both the main relay pull-in circuit and the holding circuit are broken at safety switch 29 and burner operation is stopped.

Under conditions wherein no combustion llame exists and main relay contacts 14a and flame detector relay contacts 18a-18C are both closed, which condition normally exists immediately after the closing of the space thermostat, the energization of safety switch heater 22 is continued through section B of secondary winding 25 and hold-in energization of the main relay winding 14 is maintained through section A of this secondary winding.

Under conditions wherein photoconductive element 34 is defectively conductive or has been improperly installed so as to be rendered conductive by light energy other than that of combustion llame, the main relay winding will not be energized upon closing of thermostat 12. This is so because, under these conditions, flame detector relay contacts 18a-18e will be separated due to energization of ilame detector relay winding 18 which is not connected through the space thermostat. In the event of a failure of the electrical power source, all elements of the circuit return instantly to their normal starting positions.

l claim:

l. In a pressure type oil burner having a combustion Vair blast tube and a fuel discharge nozzle at the discharge end of said tube, a grid element arranged perpendicular to the axis of said blast tube and being so constructed and so spaced from said discharge end of said tube that once a combustible mixture issuing from said blast tube is ignited combustion llame is sustained on that side of said grid element remote from said end of said blast tube without continued operation of ignition means, electric.

spark ignition means including a pair of spaced spark electrodes positioned between said grid element and said ldischarge end of said blast tube and arranged to ignite a combustible mixture in that area, an energizing circuit for said ignition means, and combustion llame responsive switching means including a photoconductive flame sensing element controlling said energizing circuit whereby otf and on control of the operation of said ignition means is caused to occur substantially instantaneously with the appearance and disappearance of combustion llame.

2. In a pressure type oil burner having a blast tube, a fuel discharge nozzle at the discharge end of said tube, and a grid element arranged perpendicular to the axis of said blast tube and being so constructed and so spaced from said fuel discharge nozzle that complete combustion occurs only on that side of said grid remote from said fuel nozzle and having been established persists without further operation of ignition means, spark ignition means including a pair of spaced spark electrodes positioned between said fuel discharge nozzle and said grid element to ignite the combustible mixture in that area, an energizing circuit or said ignition means, and means for eiecting the substantially instantaneous cut-olf of igniter operation upon the appearance of combustion flame thereby to minimize the period of incomplete combustion occurring in the ignition area, said last means comprising combustion llame responsive switching means including a photoconductive llame sensing element controlling said energizing circuit.

3. In a pressure type oil burner having a blast tube from which fuel and air are discharged and a grid element spaced from the discharge end of said tube, and said grid element being so constructed and arranged that complete combustion occurs only on that side thereof remote from said discharge end of said tube once combustion is established, an electric spark igniter including a pair of spark electrodes positioned between the discharge end of said tube and said grid element to elect ignition of the com- =bustible mixture in that area, electrically operated means operative when energized to cause the discharge of fuel and air from said tube, circuit connections including a normally open switch controlling energization of said electrically operated means, circuit connections including said normally open switch and a normally closed switch for controlling operation of said igniter, a rst Winding operative when energized to close said normally open switch and a second winding operative when energized to open said normally closed switch, a double throw flame sensitive switch, circuit connections including one pole of said double throw switch and its blade controlling energization of said first winding, and circuit connections including the opposite pole of said double throw switch and its switch blade controlling energization of said second winding, said double throw arne sensitive switch having a normal 11o-flame position wherein its blade engages said one pole and a flame responding position in which its blade engages said opposite pole, whereby energization of said rst winding may be completed only when said double throw switch is in a no-ame position and whereby energization of said second winding is completed when said double throw switch is in its flame position, thereby causing the opening of said normally closed switch and de-energization of said igniter, circuit connections including a second normally open switch operated to a closed position upon energization of said rst winding to complete a holding circuit for maintaining energization of said first winding when said double throw switch moves from 11o-flame to llame position, a third winding operative when energized to move said double throw switch -from its normal no-ilame to flame position and circuit connections including a solid state photoconductive flame sensing element arranged to be responsive to combustion flame controlling energization of said third winding.

4. An arrangement as set -forth in claim 3 in which the circuit connections controlling energization of said rst winding further include in series relationship a normally closed thermal time switch and a resistance heater therefor.

5. An arrangement as set forth in claim 3 in which the circuit connections controlling energization of said iirst winding include the entire secondary winding of a power source transformer, in which the circuit connections completing a holding circuit for said 'lrst winding parallel said time switch resistance heater and said `double throw switch and include only a portion of said secondary winding.

References Cited in the file of this patent UNITED STATES PATENTS 2,537,291 Wilson Ian. 9, 1951 2,585,221 BriSkin Feb. 12, 1952 2,966,619 Burckhardt Dec. 27, 1960 FOREIGN PATENTS 1,128,417 lFrance Ian. 27, 1956

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