GB2147361A

GB2147361A - Igniters for gas turbine engines

Info

Publication number: GB2147361A
Application number: GB08424616A
Authority: GB
Inventors: Gregory Neil Burland; Chandra Mohan Kler
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1983-10-01
Filing date: 1984-09-28
Publication date: 1985-05-09
Also published as: GB8424616D0; GB2147361B; GB8326368D0

Abstract

The electrical igniter (40) has a cavity (47), formed by a tubular semiconductor pellet (50) which, is contacted by an electrode (52) at one end, and by the outer shell (43) of the igniter at its other end, forming the other electrode. The cavity (47) opens through an aperture (48) in the shell (43) at the operative tip (41) of the igniter. The aperture (48) is inclined away from the axis of the igniter, such that, when the electrodes (52 and 43) are energised, discharge is produced in the cavity (47) and a plasma jet (60) is projected through the aperture away from the axis of the igniter, towards the region in which it is desired to produce ignition. The aperture may be axially aligned but provided with a deflector to direct the plasma jet. The semiconductive pellet may be omitted and a high voltage used to produce the plasma jet. <IMAGE>

Description

SPECIFICATION Electrical igniters and engines This invention relates to electrical igniters and engines.

The invention is more particularly, but not exclusively, concerned with igniters for use in gas-turbine engines.

The location of igniters in an engine is dictated by the design of the engine and commonly the igniter is not located at the best position for ignition of the fuel-air mixture. Because of this, difficulties can be experienced in ignition.

It is an object of the present invention to provide an igniter and an engine that can be used to alleviate these difficulties.

According to one apsect of the present invention there is provided an electrical igniter of generally elongate form, said igniter having a cavity, first and second electrodes arranged when energised to cause discharge within said cavity, and an aperture which opens from said cavity at the operative tip of said igniter, through which is projected a plasma jet produced by discharge within said cavity, wherein said aperture is arranged such that said plasma jet is directed away from the axis of said igniter.

With this form of igniter the plasma jet can be directed to a preferred part of the combustion region within the engine even though the igniter itself is not aligned with the region.

The igniter preferably has an outer shell forming one electrode of the igniter, the aperture at the operative tip of the igniter being formed in the outer shell. The igniter may include a semi-conductive surface within the cavity over which the discharge occurs, the semiconductive surface being formed on the inner surface of a tubular member which may be of semiconductive material. The aperture is preferably inclined away from the axis of the igniter.

An igniter for a gas-turbine engine in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows schematically the engine and the igniter; and Figure 2 is a partly sectional side elevation of the igniter to a larger scale.

With reference first to Fig. 1, the gasturbine engine has a compressor 1 at its inlet end 2 which produces a flow of air and of a fuel-air mixture along the engine to its outlet end 3. The engine has an outer casing 20 within which there is supported an inner wall 21 spaced from the casing so as to define an annular passageway 22. The region immediately downstream of the compressor 1, within the inner wall 21, forms the combustion chamber 30 of the engine where ignition and combustion of the fuel-air mixture occur. Cooling air is directed (as shown by the arrows 31) around the annular passageway 22, to cool the outer surface 23 of the wall 21.

Some of the cooling air also passes through openings 32 in the wall 21 along its inner surface 24.

Ignition within the combustion chamber 30 is brought about by means of an igniter 40 whic h projects through the outer casing 20, and across the annular passageway 22. The operative tip 41 of the igniter 40 is exposed to the combustion chamber 30 through an opening 25 in the inner wall 21. As so far described, the configuration of the engine is entirely conventional.

The construction of the igniter 40 and its mounting with the engine will now be described in greater detail with reference to Fig.

2. The operative tip 41 of the igniter is located at one end of a substantially cylindrical nose portion 42 of a tubular metal shell 43 that provides the external surface of the igniter. The shell 43 beyond the nose portion 42 is of enlarged diameter to provide a head portion 44 having two screw threads 45 and 46 that are for use, respectively, in mounting the igniter and in the establishment of electrical connection with it.

The igniter has a cavity 47 at its operative tip 41 within the nose portion 42. The cavity 47 opens at the tip of the igniter through an aperture 48 that is inclined away from the axis 49 of the igniter. A tubular semi-conductive pellet 50 is located axially within the cavity 47, the pellet being contacted at its forward end by the end of the shell 43 and its rear end by the forward end of a metal rod 52. The rod 52 extends axially of the igniter and is insulated from the shell 43 by a tubular ceramic insert 53. The rod 52 provides an inner electrode of the igniter whilst its shell provides an outer electrode.

In operation, application of a low voltage, high energy source across the outer and inner electrodes causes discharge within the cavity 47, over the exposed, curved surface of the pellet 50. This produces a plasma jet 60 of hot gases that is projected through the aperture 48 at an angle directed away from the axis of the igniter. The inclination of the aperture is selected such that the plasma jet 60 is directed towards the most favourable region for ignition of the fuel-air mixture in the combusion chamber. The aperture 48 may be straight, curved, or otherwise shaped to produce a plasma of the desired characteristics. The aperture itself may be axially aligned but may be provided with a deflector or other means to appropriately direct the plasma jet.

In this way ignition efficiency can be improved where the design of the engine requires the igniter to be aligned away from the most favourable region for ignition in the combustion chamber, since by appropriately designing the aperture, the plasma jet iteslf can be directed towards that region.

The igniter need not have a semiconductive surface over which discharge occurs, instead, a high voltage could be used to produce a plasma jet by discharge within a cavity.

Claims

1. An electrical igniter of generally elongate form, said igniter having a cavity, first and second electrodes arranged when energised to cause discharge within said cavity, and an aperture which opens from said cavity at the operative tip of said igniter, through which is projected a plasma jet produced by discharge within said cavity, wherein said aperture is arranged such that said plasma jet is directed away from the axis of said igniter.

2. An igniter according to Claim 1, wherein the igniter has an outer shell forming one electrode of the igniter, and wherein the aperture at the operative tip of the igniter is formed in the said outer shell.

3. An igniter according to Claim 1 or 2, including a semiconductive surface within the cavity over which the discharge occurs.

4. An igniter according to Claim 3, wherein the semiconductive surface is provided on the inner surface of a tubular member.

5. An igniter according to Claim 4, wherein the tubular member is of a semiconductive material.

6. An igniter according to any one of the preceding claims, wherein the said aperture is inclined away from the axis of said igniter.

7. An igniter substantially as hereinbefore described with reference to the accompanying drawings.

8. A gas-turbine engine including an igniter according to any one of the preceding claims.

9. A gas-turbine engine substantially as hereinbefore described with reference to the accompanying drawings.

10. Any novel feature or combination of features as hereinbefore described.