Patent GB-1206343-A (GB)
Title: Self-cleaning gas oven system
IPC: F23C3/00
Filed: 1968-02-29
Abstract: 1,206,343. Gas ovens. AMERICAN GAS ASSOCIATION Inc. 29 Feb., 1968 [1 March, 1967], No. 9791/68. Headings F4T and F4W. A cooking oven system comprises an oven cavity 12, forced-draught gas-burner means 16 communicating with said oven cavity and operable to produce pyrolytic-cleaning temperatures in said cavity, fresh air inlet means 20 and gas-moving means 22 for supplying a pressurized flow of secondary air to said burner means 16, vent means for removing a proportion of the oven gases, and recirculation means for circulating oven gases from the bottom of said cavity through conduit means 36 extending through the centre of said burner and back to the top of said cavity. Gaseous fuel supplied to the oven system via a gas line 40, is passed through supply lines 44, 46 to the burner means 16, primary and secondary air for combustion entering through the louvres 20, and passing to the burners via duct 28 under the action of the impeller 22. As shown, the burner head 60 defines a generally cylindrical combustion chamber 62 therein, the upper end of which chamber is closed by a top wall 64 and the lower end of which is open except for a screen 50, the recirculation conduit 36 being arranged concentrically within the chamber 62. Three gas nozzles 68, 70 and 72 extend into the annular combustion chamber to direct a gaseous fuel mixture counter-clockwise around the chamber. The burner head 60 also comprises an inlet duct 110 for supplying secondary air to a manifold 112, a plurality of narrow rectangular slots 124, 128 extending through the sidewalls of the combustion chamber directing the secondary air from the manifold 112 into the combustion chamber circumferentially, thus providing a strong swirling motion of the air-gas-flame mixture in the combustion chamber and satisfactory combustion in the region above the screen 50. Primary air for all three burner nozzles is supplied from the secondary-air inlet duct 110 by way of a pipe 150, a distributing manifold pipe 152 and individual primary-air supply pipes 154, 156, 158. When the burners are to be operated at a low level for baking and roasting purposes, gaseous fuel is supplied only to the line 44, hence only to the nozzle 68, while for broiling or pyrolytic cleaning purposes fuel is supplied to both the lines 44 and 46 so that all three nozzles are supplied. A conventional sparking plug 160 is used for ignition purposes. The recirculation system includes an opening 32 in the bottom of the oven with an impeller 30, suitably connected to the impeller 22 and a driving motor 322, for circulating the oven gases via a conduit 34 to a manifold 202 extending around the top wall 64 of the combustion chamber and in communication with the conduit 36, and a disposing plate 52. A minor percentage of the recirculated gases pass into the inlet 510 of a vent duct 58 travelling through a generally circular portion of the latter duct which is scrubbed at its outer wall by the burner flame, the vent gases passing to the vent pipe 56 and vent louvres 54, whence the hot gases are discharged. The oven system is suitably operated by a control system such that turning a selector knob 306 to any of the BAKE, BROIL or CLEAN positions applies an alternating current to the primary of a transformer 410, the secondary of which then operates the sparking plug 160. A flame electrode 420, positioned in the flame zone for the flame 162 senses the presence or absence of the flame 162 and is connected to a flame-sensing and delay circuit 422. The blower motor 322 is connected across the line voltage source 406 whenever the knob 306 is turned from its OFF position, so that the primary and secondary air and recirculation gases are delivered to the system.