GB2164432A

GB2164432A - Gas igniter

Info

Publication number: GB2164432A
Application number: GB08522605A
Authority: GB
Inventors: Ronald Gordon Bunch
Original assignee: BUCCLEUCH ENGINEERING Ltd
Current assignee: BUCCLEUCH ENGINEERING Ltd
Priority date: 1984-09-12
Filing date: 1985-09-12
Publication date: 1986-03-19
Also published as: GB8522605D0; GB8422965D0

Abstract

A gas igniter particularly for use as a pilot ignition device incorporates an electrical heating coil (2) at least partially encapsulated in a refractory insulating envelope (1) and connected to exposed terminals (3). The operative life of the heating coil (2) is greatly extended by the protection it receives from oxidation and other deleterious effects by the refractory envelope (1) and the support it receives from the refractory envelope (1). <IMAGE>

Description

SPECIFICATION Gas igniter The subject of this invention is a gas igniter intended primarily for use as a pilot igniter in a gas-consuming appliance.

The original form of pilot lighter used in gas-consuming appliances was a pilot flame which burned constantly. This suffered from the disadvantage that in order to avoid excessive consumption of gas the flame was necessarily small and thus could readily be extinguished either by being blown out or by the fine nozzle becoming blocked. If the main gas supply were turned on while the flame was extinguished unburned gas issued from the appliance resulting in a continuous outflow of unburned gas.

To prevent this occurrence many gas authorities have required that any gas appliance incorporating a pilot flame should also be fitted with a flame failure device usually incorporating a thermocouple which, on extinguishment of the pilot flame, was arranged to operate and close the main gas supply valve so that no gas could then issue from the gas appliance.

A later development to replace a pilot flame has been an electrical heating device. This can take the form of a heating coil or an electric spark producing device. Such devices are not only more reliable but their running costs are usually considerably less than that of a gas pilot and no flame failure precautions require to be made. Spark igniters using a high tension alternating or interrupted current have been favoured but a difficulty has arisen with the increasing prevalence of electronic apparatus. It will be understood that a spark gap in operation acts as a minature transmitter of radio waves and it has been found that the radiation from spark igniters is sufficient to cause malfunction and other difficulties in electronic equipment such as computers.The problem is becoming of increasing importance with the increasing use of electronic equipment both in industry and in the home.

It is an object of the present invention to provide a gas igniter which does not suffer from any of the described disadvantages.

A gas igniter according to the invention comprises an electrical resistance heating coil connected to two terminals and an envelope of refractory insulating material at least partially encapsulating the heating coil but leaving the terminals exposed.

The envelope of refractory material may completely encapsulate the heating coil so that no portion of the coil is exposed. Alternatively the envelope of refractory material may only partially encapsulate the heating coil leaving a segment of the coil exposed.

The refractory insulating material may be an alumina composition and may be applied to the heating coil by forming a slurry containing alumina and moulding the slurry around the heating coil then causing the alumina composition to set.

The heating coil may be formed of a refractory alloy such as a platinum alloy.

The terminals may comprise tabs arranged to engage spring clips mounted on the appliance and connectible to a source of low voltage electric current.

Practical embodiments of the invention are illustrated in the accompanying drawings in which Fig. 1 is a section of an igniter with totally encapsulated heating coil taken through the line 1-1 in Fig. 2 and Fig. 3 is a section of an igniter with a partially encapsulated heating coil taken through the line 3-3 in Fig. 4.

In the drawings 1 denotes an evelope of refractory insulating material surrounding a resistance heating coil 2 connected to tabs 3 constituting terminals for the heating coil 2. In the embodiment of Figs. 1 and 2 the heating coil 2 is totally encapsulated. In the embodiment of Figs. 3 and 4 the heating coil 2 is partially encapsulated, a small segment of the coil being left exposed.

In operation, and with particular reference to Figs. 1 and 2, when current is supplied to the tabs 3 it flows through the heating coil 2 and causes the heating coil to attain a temperature sufficient to ignite gas. The heating coil heats the refractory envelope surrounding the coil and provides a hot portion hot enough to ignite gas from the gas appliance. A heater as described cannot blow out and can be left connected to its electricity supply during all the time the gas appliance is in operation because since the coil 2 is completely protected from contact with the atmosphere no deterioration of the wire of the coil can take place.In particular the material of the coil cannot volatilize and even if some grain growth takes place in the coil material since the coil is completely supported by the refractory envelope the weakening effect on the wire is not of importance and the coil will not break down from that cause. Since the flow of current is continuous there is no electromagnetic radiation from the igniter and the magnetic field emanating from the coil is too weak to have any effect outside of the gas consuming appliance.The small time lag incurred when the igniter is switched on before it attains operating temperature is advantageous because when a previously inoperative gas consuming appliance is switched on the gas first issuing from the main burners is usually mixed with too much air and provides momentarily an explosive mixture but the time lag before the igniter operates to ignite the gas allows this situation to pass and the gas supply to be stabilized before the igniter operates to ignite the gas so that smooth ignition of the gas occurs.

The embodiment of Figs. 3 and 4 may be employed where the time lag occurring with a completly encapsulated coil is unacceptable.

This construction provides most of the advantages of the construction of Figs. 1 and 2 but the exposed segment of the coil does not have to heat the refractory material so that it provides a heating area capable of igniting gas virtually without delay, while the amount of the coil exposed is not sufficient to reduce the life of the coil to an unacceptable extent or to reduce appreciably the support provided by the refractory envelope.

Claims

1. A gas igniter which comprises an electrical resistance heating coil connected to two terminals and an envelope of refractory insulating material at least partially encapsulating the heating coil but leaving the terminals exposed.

2. A gas igniter as claimed in claim 1 in which the heating coil is completely encapsulated by the refractory insulating material.

3. A gas igniter as claimed in claim 1 in which a segment of the coil projects from and is not convered by the refractory insulating material.

4. A gas igniter as claimed in claim 1 in which the refractory insulating material is an alumina composition.

5. A gas igniter as claimed in claim 4 in which alumina composition is applied to the heating coil by forming a slurry containing alumina and moulding the slurry around the heating coil then causing the alumina composition to set.

6. A gas igniter as claimed in claim 1 in which the heating coil is formed of a platinum alloy.

7. A gas igniter as claimed in claim 1 in which the terminals comprise tabs arranged to engage spring clips mounted on the appliance and connectible to a source of low voltage electric current.