US3454345A - Fuel igniting and flame sensing resistor with fuel feed control - Google Patents

Description

7 July 8, 1969 M. DYRE 3,454,345

FUEL IGNITING AND FLAME SENSING RESISTOR WITH FUEL FEED CONTROL Filed March 2, 1967 United States Patent Int. Cl. F23n 5/00; F23q 1/04, 7/12 US. Cl. 431-66 2 Claims ABSTRACT OF THE DISCLOSURE A flame ignitor and sensor made as an electrical resistor for continuously sensing the presence or absence of a flame and made of silicon carbide granules bonded by silicon oxy-nitride and used in conjunction with ignition and supervisory circuitry for igniting fuel from a burner and montoring the continuance of the burning of the fuel.

This invention relates generally to resistors and more particularly to a new and improved ignition and supervisory resistor for igniting a fuel and monitoring the continuance of ignition by continued sensing of the flame ignited.

Resistors which are exposed to high temperatures usually have a very short life. These resistors are attacked by oxidation and accordingly it is the practice to protect resistors, for example incandescent wires, from oxygen. Incandescent wires are protected from oxygen in incandescent lamps by partial evacuation of the envelope etc. The possibility of disintegration of such resistors is even greater when the resistor is introduced into a flame or allowed to remain therein. The possibility of disintegration increases because additional disintegration phenomena occur due to the combustion gases. Furthermore, the sudden increase of temperature to which these flame sensing resistors are subjected causes thermal stresses, particularly thermal shock, which greatly contribute to their destruction and disintegration. Accordingly resistors for introduction into or sensing of flames are generally made of chemically or thermally resistant rare metals. Nevertheless the life of these resistors is relatively short.

It is a principal object of the present invention to provide an electric resistor for introduction into a flame and sensing thereof and which has a long life.

Another object of the present invention is to provide an electric resistor for use in gas or oil-fired installations.

A feature of the resistor in accordance with the invention is that it is made of silicon carbide bonded by means of a bonding agent which provides a strong mechanical adhesion of the carbide granules not hitherto achieved. The mechanical adhesion of the granules continues even though the resistor is subjected to large temperature swings and changes and protects the silicon carbide granules from oxidation and other chemical effects. Hitherto it had not been known that the bonding agent, silicon oxy-nitride, according to the invention does not impair the electrical properties of the silicon carbide and results in a resistance substance of excellent electrical properties which have a long operating life even when introduced directly into a flame and allowed to remain therein for long periods of time.

Another feature of the invention is that the bonding agent and resistor material are formed in the shape of a.

thin rod resistor having a resistance such that direct connections to alternating current means, for example 220 volts is permissible.

Silicon carbide which is electrically conductive, has

been used in the past for making heating resistors. However, it has not been possible heretofore to manufacture resistors from silicon carbide which are sufliciently resistant to a flame so as to have a long life. Moreover, the resistor made in the manner of the invention is unaifected by oxidation and other chemical affects in a flame and is extremely resistant to thermal influence particularly thermal shock. Resistors made in the manner of the invention have a specific resistance in an unheated or cold state in the order of ohms cm. and in a heated state when energized in the order of 2 to 3 ohms cm. Thus resistors according to the invention have a negative coefiicient of electrical resistance.

Another feature of the resistor in accordance with the invention is that it may be used as an incandescent ignitor for igniting a fuel, for example oil or gas, and the negative temperature coeflicient of the resistor can be used to render the resistor incandescent and in the absence of ignition and the existence of a flame the negative temperature coeflicient can be used to reduce electric current in a supervisory circuit for cutting off fuel supply to a burner.

Still another feature of the resistor is that it can be used in a multiplicity of applications such as ignition apparatus, flame sensing and apparatus for measuring flame temperature and the like.

Other features and advantages of the resistor and circuitry in combination therewith in accordance with the present invention will be better understood as described in the following specification and appended claims, in conjunction with the following drawings in which:

FIG. 1 is a diagram of a resisttor, connected to ignition circuitry, according to the invention; and

FIG. 2 is a diagram of a resistor according to the invention and ignition and supervisory or monitor circuitry for flame sensing and monitoring.

As illustrated in FIG. 1 a burner 1 is provided with a fuel from a fuel supply source, not shown, under pressure, for example oil or gas. The fuel to the burner or nozzle 1 is of course controlled by means not shown and is ignited by an ignition resistor 2 made in accordance with the invention. The ignitor or resistor 2 comprises a thin rod bent in a U-shaped configuration and consists of silicon carbide granules (SiC) bonded by silicon oxynitride (Si ON or Si ON). The resistor material has already been used as a ceramic lining for furnaces, crucibles etc. and is sold by Norton International Inc. for example, under the trade name Crystolon 63 Silicon Carbide. The resistor 2 is in position for having the fuel discharged from the burner impinge thereon for ignition therefrom when the resistor is rendered incandescent by application of current thereto by closing of a switch 3 to apply current from terminals 4, connected to a current source, not shown. When the switch 3 is closed the element 2 can be made to glow and the controlled discharge of fuel from the burner can take effect once the element is heated. The current may then be interrupted once the fuel from the burner 1 is ignited and is burning.

In the embodiment illustrated in FIG. 2 a burner 11 has the application of fuel, for example gas or oil, thereto controlled by a normally closed electromagnetic valve 12 connected to control provision of fuel from a fuel source, not shown. A resistor 13 constructed in the manner of the resistor 2 is positioned adjacent the burner and is in series with an operating coil 14 of the electromagnetic valve 12 and a switch 15 connected to terminals 16 of alternating current mains of a network, not shown.

When the switch 15 is closed a large current flows in the circuit due to the decreasing resistance caused by the negative temperature coefficient of the element or resistor 13. This current energizes the operating coil 14 and keeps the valve 12 open while the flame burns. However, if the current flowing through the circuit is not sufliciently high enough the valve closes since its normal operating or rest position is in a closed condition, Thus if the flame becomes extinguished the resistance of the resistor 13 rises and the holding current for valve 12 is decreased so that it is closed. Thus the circuitry functions as ignition circuitry and supervisory circuitry in conjunction with the resistor 13.

The apparatus illustrated in FIG. 2 is provided with an operator 17, shown diagrammatically, for manually opening the valve 12 at the beginning of the operation of the system if desired.

While preferred embodiments of the invention have been shown and described it will be understood that many modifications and changes can be made within the true spirit and scope of the invention.

What I claim and desire to be secured by Letters Patent 1. In combination with a burner having discharge means for discharging fluid fuel therefrom, an ignition and flame monitoring system comprising, an ignition and flame monitoring resistor in the discharge path of fuel from said burner, an ignition and flame supervisory electrical circuit including said resistor rendering said resistor incandescent to cause ignition of said fuel to cause it to burn, said resistor comprising a negative resistance resistor comprising a siliconoxynitride bonded silicon carbide composition, a switch in said circuit to control supply of .4 energizing current to said resistor and said circuit including electrically energized means responsive to current flow in said supervisory circuit under control of current flow determined by the resistance of said resistor initiating turning off flow of fuel to said burner when the resistance of said resistor increases to a selected value in response to the absence of a flame being sensed by said resistor.

2. The combination according to claim 1, including an electromagnetically operated valve controlling flow of fuel to said burner, and said electrically energized means responsive to current flow in said supervised circuit comprising an operating coil in said valve.

References Cited UNITED STATES PATENTS 2,095,253 10/1937 Heyworth 317--79 2,596,729 5/1952 See 43 I66 2,968,530 1/1961 Forgeng et al 106--44 3,193,399 7/1965 Washburn 10644 3,248,346 4/1966 Amberg 252518 3,282,324 11/1966 Romanelli 43124 VOLODYMYR Y. MAYEWSKl, Primary Examiner.

US. Cl. X.R.

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