GB723726A - Improvements in and relating to air-cooled spark plugs - Google Patents

Abstract

723,726. Sparking plugs. BOEING AIRPLANE CO. Nov. 26, 1952, No. 29969/52. Class 7 (4). In a sparking plug for a continuous-combustion engine, such as a gas turbine, having a cooling air duct 36 adjacent to its combustion chamber 34, the plug comprising an annular body 10 that extends across the duct 36 to project the electrode end into the chamber 34, a tubular centre-electrode 16 co-acting with an earth electrode 20, an insulator 18, an aperture 40 in the body 10 facing against the air stream in the duct 36, and the electrode 16 having an aperture in alignment with the aperture 40 for entrance of cooling air by ram effect into the centre electrode, the ignition end of the latter is open to enable the air to flow through the electrode into the chamber 34. The plug casing 10, which is secured to the outer combustion-chamber wall 30 by a flange 22 and bolts 26, passes across the duct 36 and terminates level with or just beyond the flame tube 32 whilst the insulator 18 and centre electrode 16 extend into the combustion chamber 34, as does the earth electrode 20. An opening 42, smaller than aperture 40 but in alignment therewith, is incorporated in the insulator 18. Part of the air entering the aperture 40 flows into the chamber 34 through both the hollow electrode 16 and the space 38 between the insulator and casing thus cooling the plug and preventing fuel-laden air from entering space 38. The earthed electrode may be cooled by air from space 38 and electrode 16 or as shown, it may comprise a tubular element communicating with a further opening 44 in the casing 10 ; the electrode 20 may be shortened to enable the cooling air emerging therefrom to impinge upon the centre electrode 16.