GB799898A - Improvements in ignition devices, especially applicable to combustion chambers of engines and propulsion units - Google Patents

Abstract

799,898. Vapour burners. SOC. NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION. Feb. 10, 1956 [March 28, 1955], No. 4287/56. Classes 75(1) and 75(3) [Also in Groups XII and XXVII] In an ignition device for a jet propulsion unit operating by means of a torch-like flame produced by an auxiliary combustion chamber 5 connected with the combustion zone of the jet unit through one or more outlet ducts 8 and supplied with air or other combustion supporting gas under pressure through a restricted inlet 12 and with liquid fuel for mixing with the air, and having means for igniting the mixture, an electric heating resistance 17, Fig. 7, extends in the air path upstream of the igniting means and another electric heating resistance 16 extends in the path of the liquid fuel for vaporizing the fuel whereby a mixture of heated air and vaporized fuel is passed over the igniting means. The ignition means is a plug 11 having sparking electrodes 13. The first resistance 17 for heating the air is wound over the insulating body of the plug and is enclosed in the plug outer casing 18 which has an air entrance aperture 19. The second resistance 16 for vaporizing the fuel is connected in series with the first resistance 17 and projects from the end of the plug into the auxiliary combustion chamber 5. The fuel is supplied by an injector 10. The auxiliary combustion chamber 5 has either a circular or a V-shaped cross. section and is placed between the screens 6, Fig. 2, of two adjacent burners 9 in the annular combustion chamber of the jet propulsion unit so that the two outlet ducts 8 discharge towards the central parts of the two burners 9. The restricted air inlet 12 is a diaphragm provided in an air admission pipe 7 opening on the delivery side of the air compressor of the jet propulsion unit. The transverse cross section of the auxiliary combustion chamber is large with respect to that of the air admission pipe 7 and to that of each outlet duct 8. An additional air heating resistance 20 may be disposed in the admission pipe 7. In a modification the ignition plug is not provided with the air and fuel heating resistances but instead an air heating resistance is disposed in the admission pipe 7 and a fuel vaporizing resistance is disposed below the sparking electrodes of the plug. In the modificed construction shown in Fig. 1, the auxiliary combustion chamber is divided into two parts 5a, 5b by a partition 45. The part 5a forms the combustion chamber and contains the fuel injector 10 and the ignition plug 11. The other part 5b serves as an air passage and is supplied with air through the air inlet 12 and through a pipe 48 connected; to a reservoir. Air passes into the combustion chamber 5a through an orifice 12a and through holes 46 in the partition 45. The combustion discharge pipes 8a are preferably perforated and are surrounded by pipes 8 connected to the air passage 5b. Fig. 10 shows a device according to the invention detachably secured to the combustion chamber 22 of a pulse jet unit. The discharge pipe 8 enters a hole 24 in the combustion chamber wall normally closed by a spring urged pivoted tongue 25 and studs 29 on the pulse jet unit enter holes in lugs 28 on the ignition device. Spring controlled levers 30 pivotally mounted on the ignition device and having an operating handle 33 lock the device on the studs. The volume of the combustion chamber 5 of the ignition device can be modified by a wall 34 displaceable by a screw 35. A device according to the invention may be used for igniting the pilot burner of a ram jet unit intended to be cast-off from an aircraft. The device is secured to the aircraft and has a short discharge pipe passing into a hole in the ram jet unit closed after casting off by a spring actuated tongue. In the construction shown in Fig. 13 the combustion chamber 5 of the ignition device is on the downstream side of the central body of a ram jet unit and air is supplied to the combustion chamber 5 from the air flowing through the ram jet and enters the combustion chamber 5 through an annular orifice 12a. In a modified construction, the combustion chamber of the ignition device is mounted in the interior of the central body of a ram jet unit and is supplied with air from an auxiliary source.