US2046768A - Ignition system for oil burners and the like - Google Patents

Description

July 7, 1936. E. R. CAPITAA IGNITION SYSTEM FOR OIL BURNERS AND THE LIKE Filed May 6, 1952 Patented July 7, 1936 UNITED STATES IGNITION SYSTEM FOR OIL. BURNERS AND THE LIKE Emil R. Capita, New York, N. Y.

Application May 6, 1932, Serial No. 609,601

3 Claims.

My invention relates to a new and improved ignition system for oil burners and the like, and a new and improved method of controlling the ignition system or circuit of oil burners or the like.

One of the objects of my invention is to provide an improved ignition system for oil burners of the type in which the fuel is intermittently fed and ignited, it being understood however, that my invention applies toevery type of oil burner, viz the gun type, rotary or the like.

Another object of my invention is to provide a method of controlling the ignition in an oil burn er in which a blower motor is employed for atomizing and injecting oil into the fire-box, in which the transient reactance values of the different parts of the circuit causes a maximum'current to be initially supplied to the ignition device, said reactance being automatically changed when the blower motor is in full operation, so that the supply of current to the ignition device is maintained in order to produce continuous ignition of the oil. However, the invention is also applicable to oil burners in which the ignition.

circuit is interrupted after the flame has been produced. In either case, the major portion of the reactance of the circuit is supplied by the blower motor afterthe ignition has been secured and the blower motor is in full operation.

Another object of my invention is to provide a special system in which the oil will-b'e ignited by means of a concentrated heater resistance element (in contradistinction to a spark or arc) the circuit being so adjusted and the resistance element being so selected as to prevent any shorting of the heater resistance element.

Other objects of my invention are-to-provide improved safety devices whereby the circuit will be broken if the ignition device fails to operate or is thrown out of operation for any reason.

Other objects of my invention will be set forth in the following description and drawing which illustrates a preferred embodiment thereof, it being understood that the above general statement of the objects of my invention is intended merely to generally explain the same and not to limit in any manner.

Fig. 1 is a diagrammatic view illustrating, one embodiment of the invention;

Fig; 2 illustrates another embodiment, having a different form of safety device.

Fig. 3 illustrates a third embodiment of myin-e ventionhaving a third form of safety device.

Fig. 4 shows a fourth embodiment of my in-"- vention in which the ignition is secured by means of: a heater resistance element instead of utilizing the spark gap which is shown in Figs. 1-3 inclusive.

Fig. 5 is a diagrammatic view showing how a straight concentrated heater resistance element of special composition is employed instead of a wire heater resistance element of the type shown in Fig. 4.

Fig. 6 illustrates a different type of safety device.

It has heretofore been well known that the conventional jump spark oil burner electric ignition equipment consists of a set of electrodes forming an air gap directly in front of the nozzle or within the zone of the flame, supplied with high tension current from a high reactance. transformer connected'in parallel to the blower motor. With this method, the transformer is thrown across the supply line simultaneously with the motor.

It has been found that even though surplus voltage was supplied during normal operation, that on numerous occasions the spark failed to strike across the ignition electrodes, causing failure-ofignition and other complications. I have discovered that the reasons for these failures are as follows:-

Upon closing the line switch, the drop of line voltage'due to the large starting current of the blowerv motor resulted in a proportional drop of the transformer secondary voltage, so that the secondaryivoltage was insufiicient to strike across the gap. However, after the blower motor came up to speed and the voltage to normal, the air blast and oil vapor passing between the ignition electrode points raised the breakdown potential across the gap above the voltage which the transformer was able to supply.

As reference, it may beborne in mind that it requires a much higher voltage to jump across a non-ionized gap than to maintain an arc across the same gap subject to identical conditions.

With my method, as shown in Fig. 1, I connect the primary of a low reactance ignition transformer in series with the motor. In this installation the motor and transformer primary must be wound so as to operate at their rated voltampere input when the oilburner is in operation.

The cycle of operation with the series connected circuit is as follows:

When the circuit is closed, the circuit of the r secondary'coil is open. The impedance of the transformer is then greater than the impedance of the motor, because the rotor of the motor is then stationary or operating at very low speed. The motors which are generally used in these devices are split-phase motors, which have a low starting torque. At this moment, the voltage drop across the transformer is greater than the voltage drop across the motor, so that a transient and very high secondary voltage is induced at the ignition electrodes. As the motor speeds up its impedance is increased. After the spark strikes across the ignition electrodes, the path is highly ionized and an arc is formed. This in turn practically short-circuits the secondary coil of the transformer reducing its impedance and the voltage drop across the primary windings. The reduction of transformer impedance results in a higher voltage drop across the motor, causing the same to start rotating. The rest of the cycle is as usual.

With the series circuit as shown in Fig. 1, the spark or are is strongest during the moment of starting and the spark or are is formed before the motor starts rotating and before the air blast and oil vapor are able to increase the break-down potential difference between the ignition electrodes.

The safety gap between auxiliary electrodes GI and G2, connected across the secondary winding of the transformer, is adjusted to strike below maximum secondary voltage and above the required operating voltage for producing the spark or are at the ignition electrodes. A fuse wire F is connected in series with the supply line located just above the safety gap and within its arc path so that the fuse wire is melted by the auxiliary arc, thus opening the line current, should the striking potential at the ignition electrodes exceed a predetermined value.

In Fig. l, the current is supplied through line wires L and L Fig. 2 shows the connection in series of the blower motor and transformer circuit. Connected across the secondary of the ignition transformer is a magnetic relay connected in series with a safety gap which breaks the blower motor circuit, should the potential across the ignition electrodes exceed the safe operation of the system;

The primary circuit during normal operation (Fig. 2) is as follows:-

Supply current enters from LI and passes through lead I3, through spring contact II, through contact I2, through flexible .pigtail I0, through lead I4, through primary 11 of transformer I, through blower motor 2 and back to line L2.

The secondary circuit is as follows:-

Electrodes 3A and 3B are connected to the high tension ends of the secondary IS of transformer I. The relay circuit is as follows: Starting with one end of the secondary, going through relay winding 5 connected at I6 to relay core 4, through relay armature I5, through gap 6, through lead I, and back to other pole of the secondary windings of the ignition transformer. The cycle of operation is as follows:

Should the potential across 3A and 3B exceed the safety limit, high tension current will flow through coil 5 to connection I6, through core 4, through armature I5, through safety gap 6, returning through lead I to the transformer secondary. A magnetic field in core 4 will attract armature I 5 which is pivoted at point 8, causing a lifting action of insulator bar 9, which, having a hook-shaped contact I2 attached to it will release spring blade I I, and thus break the'primary line circuit between circuit-breaker blade I I and contact I2, causing blade I I to assume position indicated by. reference numeral36. The breaking of the circuit by this relay will indicate the necessity of cleaning and adjusting the ignition electrodes. This relay is manually reset.

Fig. 3 also shows the series connection of the transformer and blower motor in the oil-burner ignition circuit, in which I use a thermo blade relay in series with. a safety gap connected across the transformer secondary output for the purpose of breaking the line current in case of excessive potential difference acrossthe igniter electrodes.

The primary circuit: Line current from LI passes through 22, through blade 2I, through junction 26, through thermo blade 20, through mounting stud 26, through lead 23, through primary IP of transformer I, through blower motor 2, and back into L2. This is the operation of the system under normal conditions. However, should the potential across 3A and 3B exceed the limits of safe operation, a gap between IT and I8 will strike causing an arc to form which in turn will heat the thermo blade 28. This thermo blade,

which has a hook 26 at its free end, is adjusted so that the heat applied to it will cause same to warp away from blade 2I, opening the primary circuit at this point, by permitting spring blade 2I to assume the position indicated by reference numeral 37. A mica insulator I9 or any suitable insulator is placed above auxiliary gap and below thermo blade 20 for providing electrical insulation between the primary and secondary circuits.

Fig. 4 shows an ignition system for oil burners in which a heater resistance wire is located within the zone of the flame. This heater resistance is connected in series with the blower motor. The function of this system is as follows: When line current from LI and L2 is supplied, the blower motor rotor now being initially stationary, will represent a very small proportion of the impedance in this circuit. Hence the largest portion of the voltage drop, and the large wattage consumption will take place across terminals 34 and 35 of the igniter resistor, which during the starting of the motor, will be heated to a temperature high enough to ignite the vaporized oil. Directly after the rotor of the motor comes up to normal speed, the increase of impedance in the motor will result in a reduction of current flow which in turn will reduce the heating effect of igniter resistor 29, thus automatically producing a high temperature in the ignitor resistor before the atomized oil is blown into the fire box, and automatically reducing the current flow through the resistor during operation. Should the resistor in this circuit burn open, the opening of same will break the motor circuit, making the system inoperative and therefore avoiding the possibility of pumping into the furnace a quantity of vaporized fuel, thus eliminating fire hazards. The fuelsupply pipe 21 has the usual outlet 28.

Fig. 5 shows an ignition system for oil burners in which a straight heater resistance element is held between clips 38 and 39, and is connected in series with the blower motor. The function of the system is as follows:

When line current is supplied through LI and L2, the blower motor rotor, being initially stationary, will represent a very small proportion of the impedance in this circuit, causing the largest proportion of voltage drop and therefore large wattage consumption to take place across terminals 38 and 39 of the igniter resistor. During the starting of the motor this resistor will be heated to a temperature high enough to ignite the vaporized oil. Directly after the motor comes up to.normal speed, the increase of impedance in the motor will result in a reduction of current flow which in turn will reduce the heating effect of igniter resistor 40, thus automatically producing a high temperature in the igniter resistor before the atomized oil is blown into thefire box, and automatically reducing the current flow through the resistor during operation. Should the resistor in this circuit burn open, the opening of the same will break the motor circuit, making. the system inoperative and therefore avoidingv the possibility of pumping into the furnace a quantity of vaporized fuel with the resultant fire hazard.

The resistor 40 may be made of any suitable silicon carbide (carborundum) or carbon graphite composition having a high resistancewithin a relatively small mass so that the momentary high wattage consumed therein will cause the same to attain a temperature above the ignition requirements of theato-mized oil and air mixture. Preferably, the resistor 40 is made in a straight piece in order to avoid. excessive heating which results when a helically wound wire resistor is used, in which case carbon deposits between adjacent turns. tend to short circuit these turns. I also take advantage of the negative resistance characteristics of the resistor 40 as from my observation, when some of these materials were brought to a high temperature their resistance was reduced causing less wattage to be consumed with same.

Fig. 6 shows the series connection of the blower motor and transformer circuit. Connected across the secondary of the ignition transformer is a relay actuated through the burning apart of a string or the like, should the potential across the ignition electrodes exceed the safe operation potential of the system.

The primary circuit during normal operation (Fig. 6): Current enters at L1, passes through wire 4|, through blade 42, through contact 43, through wire 44, through primary coil IP, through blower motor 2, returning to L2.

The secondary circuit during normal operation (Fig. 6): Electrodes 3A and 3B are connected to the high tension ends of the secondary coil IS. The relay circuit is as follows: Starting with one terminal of the transformer secondary coil IS, hence to safety gap electrode 45, through gap 46 to electrode 41 and returning to other terminal of transformer secondary IS. A piece of string (this string member may be made of any combustible material) is fastened to the support 50. This string member passes through the arc zone of the safety gap 46 and it holds the blade 42 in the full line position shown in Fig. 6.

Should the potential across 3A and 3B exceed the safety limits, an arc will strike between safety gap electrodes 45 and 41 causing member 49 to burn apart, thus permitting the blade 42 to spring to the dotted line position 42A and opening the supply line circuit.

While I do not wish to be limited to the constants stated herein, I can give the following as the result of some practical experiments.

Utilizing a popular make of oil burner, the current momentarily consumed when the line circuit was closed was approximately 18 amps. At full motor speed, the current diminished to 3.5 amps. Hence, when the system began to operate, there was a consumption of 1800 watts in the resistor described in Figs. 4 and 5, and this diminished to 60 watts; resistor 28 has a total resistance of about 5 ohms when it.is.cold and it had. acquired a temperature of about 2400" F. with the momentary starting current of 18 amps.

,Referring tothe embodiments utilizing a spark gap, under. normal operating conditions and at normal speed, the motor had a total impedance of substantially 28 ohms. This consisted of a reactance of 26.9- ohms and a resistance of 7.6

ohms. The insertion of the ignition transformer in series increased the resistance component to 12.44 ohms, thusincreasing the impedance to 29.6 ohms. When the motor is operating at normal speed, its impedance largely consists of its reactance, and the addition of 4.84 ohms to the resistance component of the reactance, did not produce any noticeable difference in the normal operatingspeed. of the motor.

In the ignition. system now used, the starting current is in excess of amps. According .to my improved method, the starting current is brought down to approximately 18 amps.

For the purposes of this specification, the resistors 29 and 40, and, the separated ignition electrodes-may be referredto as an ignition device. Ineach of theembodiments specified herein, it may be stated that the ignition device is coupled in series to the blower motor, because the transformer is in effect an inductive coupling.

When the circuit of the ignition system is closed, it will be noted that the full line voltage is simultaneously impressed upon the motor and upon the ignition device. Likewise, the voltage drop'across the ignition device has a transient value and this transient value varies in such mannor as to reduce the voltage drop across the low tension supply of said ignition device, when the motor has reached its normal predetermined speed.

In the shunt circuit system which is now in use, it is customary to use a transformer having a high reactance, as for example, a reactance of 100%. In the series circuit which I have devised, I prefer to use a transformer having a reactance which is as low as commercial construction will permit. As is well-known, a low reactance transformer has very close coupling between its primary and secondary coils, so that the stray flux is minimized. Hence, the power factor of the transformer which I utilize is much higher than the power factor of the type of transformer which is now used in the shunt circuit. For example, I utilize a transformer having a power factor which is substantially unity, whereas the power factor of the transformer used in shunt is seldom as high as 70% and ordinarily rates between 40% and 50%.

Another characteristic of my circuit is that the impedance of the blower motor acts as the reactive or current-limiting component of the circuit of the ignition transformer. That is, the impedance of the blower motor acts in effect as a choke coil to limit the current supplied to the spark or arc which is formed across the terminals of the secondary coil. It has been assumed for the purposes of this specification that ordinary commercial alternating current is utilized.

According to my invention, I can temporarily overload the transformer at the moment when the line switch is closed and before the blower motor begins to turn, and during the period while the blower motor is attaining its normal predetermined speed. From this viewpoint as well as Referring to Fig. 4, the.

from other viewpoints, the use of a low reactance transformer is an important feature, because it permits the motor to attain and to keep its normal predetermined speed while the oil isbeing injected and ignited.

I claim:

1. A control system for .an oil burner having a blower motor and a spark ignition means, comprising a motor circuit having a main control switch and. the primary coil of a transformer connected in series with the blower motor, ignition electrodes connected to the terminals of the secondary coil of said transformer, auxiliary electrodes connected in parallel with said ignition electrodes and forming an auxiliary gap materi ally greater than the gap between said ignition electrodes, and control means operable in response to the passage of current across said auxiliary gap to open said main switch.

2. A control system for an oil burner having a blower motor and a spark ignition means, comprising a motor circuit having a main control switch and the primary coil of a transformer connected in series with the blower motor, ignition electrodes connected to the terminals of the secondary coil of said transformer, auxiliary electrodes connected in parallel with said ignition electrodes and forming an auxiliary gap materially greater than the gap between said ignition electrodes, and control means operable in response to the passage of current across said auxiliary gap to open said main switch, said transformer having a reactance which is sufiiciently low in relation to the reactance of the motor so as to cause said transformer to be overloaded during the period in which said motor is attaining its normal predetermined speed.

3. A control system for an oil burner having a blower motor and a spark ignition means, comprising a motor circuit having a main control switch and the primary coil of a transformer connected in series with the blower motor, ignition electrodes connected to the terminals of the secondary coil of said transformer, auxiliary electrodes connected in parallel with said ignition electrodes and forming an auxiliary gap materially greater than the gap between said ignition electrodes, and control means operable in response to the passage of current across said auxiliary gap to open said main switch, the impedance of the motor exceeding fifty per cent of the total impedance of the circuit when the motor is operating at normal speed and the spark ignition means are operative.

EMIL R. CAPITA.

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