US3584987A

US3584987A - Fuel burner ignition

Info

Publication number: US3584987A
Application number: US819284A
Authority: US
Inventors: Leonard H Michaels
Original assignee: Harper Wyman Co
Current assignee: Harper Wyman Co
Priority date: 1969-04-25
Filing date: 1969-04-25
Publication date: 1971-06-15
Anticipated expiration: 1988-06-15

Abstract

A system for igniting a fuel burner includes an electrically operated solenoid valve for controlling the flow of fuel to the burner, the valve having a pair of windings. An electric resistance heating element having a positive coefficient of resistance relative to temperature is mounted adjacent the burner in order to ignite fuel flowing from the burner. A control circuit operates to connect the heating element and one coil of the solenoid winding in series for simultaneous energization of the valve and the heating element. In order to assure operation of the valve when the heating element is initially in a hot, high resistance condition, the other coil of the solenoid winding is connected in series with a variable resistance having a negative resistance coefficient relative to temperature.

Description

United States Patent [72] Inventor Leonard H. Michaels 3,454,345 7/1969 Dyre 431/66 La Grange, 11]. 3,488,133 1/1970 Perl..... 431/66 [21] 2 1969 Primary Examiner-Frederick L. Matteson f 1971 Assistant Examiner-Robert A. Dua

3 t Assignee nupebwymm p y Attorney Kolehmainen, Rathburn and Wyss and Mason Hinsdale, Ill.

[54] FUEL BURNER IGNITION ABSTRACT: A system for igniting a fuel burner includes an electrically operated solenoid valve for controlling the flow of 7 Claims, 1 Drawing Fig.

fuel to the burner, the valve having a pair of windings. An UeS. .Q

electric resistance heating element having a positive coefii. 123/32 cient of resistance relative to temperature is mounted adjacent Ill!- the burner in rder to ignite fuel flowing ftgm the burnen A [50] Field ofselldl 431/66, 6, tr l ircuit operates to connect the heating element and 123/32 one coil of the solenoid winding in series for simultaneous f energization of the valve and the heating element. In order to [56] Re cream cued assure operation of the valve when the heating element is ini- N ED STATES PATENTS tially in a hot, high resistance condition, the other coil of the 2,316,910 4/1943 Weber 431/66X solenoid winding is connected in series with a variable re- 2,382,2l6 8/1945 Eskin et al. I 431/66X sistance having a negative resistance coefficient relative to 3,282,324 11/1966 Romanelli 431/66 X temperature.

12 40 36 :t M2 0 a 2 2. -.2*-

\ I l f 3e 3e 3e 34 a 32B" (I INVENTOR LEONARD H. MICHAELS By WW,MWQ14 Attornevs FUEL BURNER IGNITION The present invention relates to apparatus for the electrical ignition of fuel burners.

In the copending application of Leonard H. Michaels, Ser. No. 742,577, filed July 5, 1968 there are disclosed and claimed fuel burner ignition systems capable of providing safe operation without the use of pilot burners, safety valves and the like. Although the type of system disclosed in that application is satisfactory for many fuel burner applications, when a solenoid valve is used to control gas flow and when the electrical igniter element is of the type which exhibits a positive coefficient of resistance with respect to temperature, a problem may be uncountered in rapid cycling systems or the like wherein it is desired to operate the main burner shortly after the ignition element has been deenergized. More specifically, if the solenoid winding and the ignition element are, for example, connected in series and the ignition element is in a relatively hot condition, the relatively high initial resistance of the igniter may reduce the initial current to such an extent that the solenoid valve does not open.

In order to overcome this difficulty, it is not desirable merely to increase the voltage supplied to the igniter and valve to such an extent that the valve will open even when the igniter is initially in a hot, high resistance condition. An important safety feature of the ignition system is that the solenoid valve does not open if the supply voltage decreases to a level at which the igniter does not operate reliably to provide ignition. Thus the minumum energization level for opening the solenoid valve should correspond to the minimum desired supply voltage level with the igniter in its relatively cold, low resistance condition. Increasing the voltage supplied to the igniter and valve would result in loss of this important safety feature.

Among the objects of the present invention are to provide an improved fuel burner ignition system of the type disclosed in the above-identified copending application; to provide an ignition system capable of fast cycling operation; and to provide an ignition system wherein fuel is supplied to the main burner only when the supply voltage is sufiicient to produce reliable ignition, the system not being adversely affected by the initial resistance condition of the igniter element.

In brief, fuel burner ignition apparatus constructed in accordance with the present invention may comprise an electrically operated valve for controlling the flow of fuel to the burner, together with an electrical ignition element disposed in ignition relation to the burner and exhibiting a positive resistance coefficient relative to temperature. The apparatus includes a variable resistance having a negative resistance coefficient relative to temperature, and a control circuit is provided for coupling the electrically operated valve to a source of power through both the electrical ignition element and the variable resistance to the end that the energization level of the valve is substantially a function of the supply voltage and is not adversely affected by the initial resistance condition of the electric ignition element.

The invention together with the above and other objects and advantages may be best understood from consideration of the following detailed description of an illustrative embodiment of the invention illustrated diagrammatically and schematically in the single figure of the drawing.

Referring to the drawing, there is illustrated a new and improved ignition system constructed in accordance with the principles of thepresent invention and designated as a whole by the reference numeral 10. The ignition system serves au tomatically and safely to ignite the fuel flowing from a fuel burner 12, and in accordance with an important advantage of the present invention the system 10 is capable of reoperating the burner 12 shortly after its operation ,has been discontinued, thereby to produce a rapid cycling operation or the like.

Fuel is supplied to the burner 12 from a manifold or supply 1 by way of a conventional manually operated shutoff valve 16 and a normally closed electrically operated valve generally designated by the reference numeral 18 under the control of the ignition system 10. The valve 18 is a solenoid valve diagrammatically illustrated as including a housing 20 having an inlet 22 and an outlet 24 separated by a valve seat 26. A valve member 28 is movable between closed and open positions under the control of a solenoid plunger 30 operated by a solenoid winding 32. Fuel flowing to the burner 12 when the valves 16 and 18 are open enters the burner in the usual manner through an inlet fitting 34 and mixing tube 36 and emerges from the burner through a series of burner ports 38.

In order to ignite fuel flowing from the burner ports 38, the

ignition system 10 includes an electrically operated igniter 40 mounted adjacent the burner 12 in or near the path of fuel flowing from the burner ports 38. The igniter 40 comprises an electric resistance heating element preferably in the form of a length of wire made of molybdenum disilicide with ceramic additives, available under the name Kanthal-Super" from the Kanthal Corporation of Bethel, Connecticut.

The igniter element 40 formed of this material is capable when energized of rapidly reaching an elevated temperature in excess of 2500 or so reliably to ignite fuel flowing from the burner 12. in addition, the igniter element 40 formed of this material has a long life so that it is practical to provide a system wherein the igniter element 40 is continuously energized whenever fuel is supplied to the burner 12. The material of the igniter element 40 exhibits a positive coefficient of resistance with respect to temperature. More specifically, when the material of the igniter element is relatively cool the resistance of the igniter element is extremely low. The resistance of the igniter element in creases with increasing temperature and when the igniter element reaches an operating temperature in the neighborhood of 2500 or so, its resistance is substantially increased. For example, the preferred Kanthal-Super" material increases in resistivity by a factor of about 16 in a roughly linear fashion when its temperature is increased from 68 F. to 3100 F.

Proceeding now to a description of the ignition system 10, in general the system serves simultaneously to supply fuel to the burner 12 and to produce an ignition condition at the burner. The system is designed to protect against a variety of possible situation s which otherwise might result in the emission of unignited fuel from the burner, thereby to provide positive proof of ignition. Thus the system prevents opening of the valve 18 if the igniter 40 is broken or short circuited, if the circuit for energizing the valve is grounded or shorted at some point, or if the supply voltage falls to a level which is not sufficient to assure reliable ignition by the igniter 40. In accordance with an important feature of the invention, this sage operation is achieved in a system that is capable of rapid cycling operation because the system operation is not adversely affected by the initial temperature and resistance condition of the igniter.

Operating power for the ignition system 10 is provided by a pair of

power supply terminals

42 and 44 adapted to be connected to a suitable alternating current voltage source. The system 10 includes a transformer 46 having a primary winding 48, and when it is desired to operate the burner 12, the primary winding is connected to the power supply by operation of a switch 50, which switch may be a manually controlled switch or a thermostatically controlled switch. When the switch 50 is moved from its illustrated open condition to its closed condition, either manually or automatically in response to a demand for heat, the system serves to energize the igniter 40 and to open valve 18 to admit fuel to the burner 12. The fuel emerging from the burner ports 38 is ignited by the igniter 40 and the burner continues in operation until such time as the switch 50 is returned to its open condition.

In accordance with the present invention, the valve 18 is operated ata level of energization substantially dependent on the supply voltage level and substantially i dependent of the initial resistance condition of the igniter 40. This is accomplished by supplying operating current to the winding 32 through the igniter 40 and also through a compensating element 52 effective to counteract the positive resistance effect of the igniter 40. In the illustrated embodiment of the invention the element 42 is a self heating variable resistance element, or thermistor, having a negative coefficient of resistance relative to temperature.

More specifically, the transformer 46 includes a pair of secondary windings 54 and 56 coupled to a pair of additively connected

winding sections

32A and 32B of the solenoid 32 respectively by the igniter 40 and by the variable resistance element 42. The point between the

solenoid windings

32A and 32B is coupled to the secondary windings of the transformer 46 by a fuse 58. Since the valve 18 is energized at a level determined by the initial conditions of both the igniter 40 and the variable resistance element 52, whether the igniter 40 and element 52 are both relative cool or both relatively hot the valve 18 is opened upon closing of the switch 50 if the supply voltage level is at a predetermined level.

The advantages of the improved system may best be understood in connection with its operation under a variety of circumstances. if the system has been inactive for a period of time when the switch 50 is closed, the .components of the system are in a cool condition. Thus the resistance of the igniter 40 is initially at a negligible, low level and the resistance of the variable resistance element 52 is at a relatively high level. Consequently the current flowing initially through the solenoid winding 32A is at a relatively high level and the current flowing through the solenoid winding 32B is at a relatively low level. Assuming that the supply voltage is within a range sufficient to produce operation of the igniter 40 above a safe ignition temperature, the plunger 30 is moved in response to the inrush current to open the valve 18.

Thus in an initially cool condition the valve 18 opens practically instantaneously upon closure of the switch 50. The igniter 40 heats rapidly, and within a short period of time such as a second or less it reaches an operating temperature in the neighborhood of about 2500 in order to ignite fuel escaping from the burner 12. Although the resistance of the igniter 40 increases substantially after the valve 18 is opened as the operating temperature is reached, there is no tendency for the solenoid to reclose since the current required to hold a solenoid valve open is substantially less than the current required initially to open the valve.

Due to the long life of the igniter 40 and in order to provide a continuing ignition without the necessity of a pilot burner or the like, the igniter 40 is maintained in its energized condition while the burner 12 operates. In order to discontinue operation of the burner, the switch 50 is moved to its illustrated open condition thereby discontinuing current flow to the

windings

32A and 32B and permitting the valve 18 to close.

In accordance with an important feature of the invention it is possible to operate the system 10' once more as soon as desired. The time required for the igniter 40 to cool to its low resistance condition depends upon its construction and mounting, and may be about 2 minutes or so. In some situations it may be desireable to cycle the burner 12 off and on more rapidly.

[f the switch 50 is closed while the igniter 40 remains in a relatively hot, high resistance condition the initial inrush current flowing to the winding portion 32A is decreased and alone may be insufficient to open the valve 18. However the variable resistance element 52 is also in a relatively hot condition at this time, and its resistance is consequently relatively low. The increased current flow thus made available to the winding section 32B augments the effect of the current flow through the igniter 40 and causes the valve 18 to open.

Due to variation s in the supply voltage, a condition may arise wherein the voltage available for energization of the igniter 40 is not sufficient to assure that a reliable ignition temperature will be reached. Under such circumstances it is not desirable to admit fuel to the burner 12. The valve 18 including the winding

sections

32A and 32B is designed so that if the supply voltage is below a predetermined level the magnetic force produced by the

windings

32A and 32B is insuflicient to open the valve. The

windings

54, 56, 32A and 32B are designed in relation to the resistance-temperature characteristics of the igniter 40 and variable resistance element 52 so that for any initial temperature condition the valve opens only if the supply voltage exceeds the predetermined level producing satisfactory ignition.

As noted above, the safety features of the systems disclosed in the above copending application are included in the system 10. 1f the igniter 40 burns out, breaks or otherwise is open circuited, current is not supplied to the winding 32A. The winding 32B alone is incapable under any initial temperature condition of opening the valve 18, and as a result fuel is not admitted to the burner 12.

If the igniter 40 is disabled by a short circuit across its input terminals, the valve 18 is not maintained open. More specifically, a short circuit of igniter 40 causes a continuous increased current to flow through the fuse 58, and the fuse produces an open circuit. The resistance of the element 52 is thus placed in series with the igniter and with windings 32A and 328, thus decreasing the current flow below the level required to open or to hold open the valve 18.

ln addition, due to the use of the transformer 46, grounding or shorting of the secondary circuit cannot cause the valve 18 to be opened when the igniter 40 is not energized.

In a system constructed in accordance with the present invention, the primary winding 48 of the transformer 46 was energized with a standard 60 cycle ll5 volt AC supply, and the transformer was designed to produce about 4 volts across winding 54 and about 15 volts across winding 56 when the input voltage was volts. The winding 56 when the input voltage was 120 volts. The winding 32A included about 40 turns while the winding 328 included about 700 turns. The current flowing through the igniter 40 when it reached its operating temperature was about 5 amperes, the inrush current with the igniter in its cool condition being much higher. The current flowing through the variable resistance 52 in its relatively cool condition was about 0.10 ampere, and in its self-heated relatively hot condition this current increased to about 0.225 ampere. The fuse 58 was designed to produce an open circuit when subjected to a continuous current in excess of about 8 amperes. The solenoid valve 18 was designed not to open when the line voltage fell below about 84 volts, this being the minimum voltage producing satisfactory operation of the igniter 40. It should be understood that these specific figures are given only by way of illustration of one embodiment of the invention.

What I claim and desire to be secured by Letters Patent of the United States is:

1. Fuel burner ignition apparatus for use with an electrically operated valve for controlling the flow of fuel to the burner and comprising:

an electric ignition element adjacent the burner and having a positive resistance coefficient relative to temperature;

a variable resistance having a negative resistance coefficient relative to temperature;

and control circuit means for coupling the electrically operated valve to a source of power through both said element and said variable resistance so that the energization level of said valve is substantially a function of the supply voltage;

said electrically operated valve comprising a solenoid valve having winding means coupled to said element and to said variable resistance, the winding means including first and second winding segments, said control circuit means having a first circuit loop including at least said element and said first segment, said control circuit means having a second circuit loop including at least said variable resistance means and said second segment.

2. The apparatus of claim 1, said control circuit means including a transformer having a first secondary winding in said first loop and a second secondary winding in said second loop.

3. The apparatus of claim 2, said control circuit means including a fuse included in both said first and second loops.

4. A fuel burner ignition system comprising a valve adapted to communicate with the fuel burner to control the admission of fuel thereto; solenoid means for operating said valve; an igniter disposed adjacent the fuel burner for igniting fuel at the burner and including an electric resistance heating means having a positive coefficient of resistance relative to its temperature; and control means for simultaneously operating the igniter and the valve, said control means including:

first circuit means for energizing said solenoid means with a current flowing through said igniter;

a temperature responsive variable resistance means having a negative coefficient of resistance relative to its selfgenerated temperature;

and second circuit means for energizing said solenoid means with a current flowing through said variable resistance means to assure opening of said valve when said igniter is in a relatively hot condition and when the supply voltage is sufficient to produce operation of said igniter.

5. The apparatus of claim 4, the solenoid meansincluding first and second winding segments, said first circuit means comprising a first circuit loop including at least said igniter and said first segment, said second circuit means comprising a second circuit loop including at least said variable resistance means and said second segment.

6. The apparatus of claim 5, a supply transformer having a first secondary winding in said first loop and a second secondary winding in said second loop.

7. The apparatus of claim 6, said control circuit means including a fuse included in both said first and second loops.

Claims

1. Fuel burner ignition apparatus for use with an electrically operated valve for controlling the flow of fuel to the burner and comprising: an electric ignition element adjacent the burner and having a positive resistance coefficient relative to temperature; a variable resistance having a negative resistance coefficient relative to temperature; and control circuit means for coupling the electrically operated valve to a source of power through both said element and said variable resistance so that the energization level of said valve is substantially a function of the supply voltage; said electrically operated valve comprising a solenoid valve having winding means coupled to said element and to said variable resistance, the winding means including first and second winding segments, said control circuit means having a first circuit loop including at least said element and said first segment, said control circuit means having a second circuit loop including at least said variable resistance means and said second segment.

4. A fuel burner ignition system comprising a valve adapted to communicate with the fuel burner to control the admission of fuel thereto; solenoid means for operating said valve; an igniter disposed adjacent the fuel burner for igniting fuel at the burner and including an electric resistance heating means having a positive coefficient of resistance relative to its temperature; and control means for simultaneously operating the igniter and the valve, said control means including: first circuit means for energizing said solenoid means with a current flowing through said igniter; a temperature responsive variable resistance means having a negative coefficient of resistance relative to its self-generated temperature; and second circuit means for energizing said solenoid means with a current flowing through said variable resistance means to assure opening of said valve when said igniter is in a relatively hot condition and when the supply voltage is sufficient to produce operation of said igniter.

5. The apparatus of claim 4, the solenoid means including first and second winding segments, said first circuit means comprising a first circuit loop including at least said igniter and said first segment, said second circuit means comprising a second circuit loop including at least said variable resistance means and said second segment.