Blue-flame oil burner

An apparatus for burning oil and combustion air under relatively high pressure for producing a high-heat blue flame, comprising a burner having a chamber in which an oil atomizing device is located, means for introducing pressurized combustion air into said chamber for surrounding said oil atomizing device, an interior wall spaced from said oil atomizing device downstream therefrom, orifice means formed in said interior wall and communicating with said oil atomizing device, said oil atomizing device injecting oil under pressure therefrom for mixing with said combustion air, a flame tube joined to said interior wall in coaxial relation with respect to said oil atomizing device and defining the downstream portion of said burner, a mixing tube located interiorly of and coaxially with respect to said oil atomizing device and said flame tube and said orifice means and being disposed downstream of said orifice means and spaced from said interior wall, the area in said flame tube that is located downstream of the downstream end of said mixing tube and that is spaced inwardly of the discharge end of said flame tube defining a combustion zone which is the region of highest temperature in said flame tube, said mixing tube having opening means formed in the upstream end thereof, wherein the space between said interior wall and the upstream end of said mixing tube provides for reentry into said upstream end of a portion of the combustion gases that are discharged from the downstream end of said mixing tube for recirculation thereof, said recirculated combustion gases being those gases in which the oil has not been completely oxidized, said recirculated gases being drawn from the combustion zone toward the upstream end of said mixing tube by the velocity of the mixed atomized oil and combustion air passing into said mixing tube from said orifice means, the recirculated combustion gases providing for heating of the mixture of air and atomized oil entering the mixing tube from said orifice means whereby the atomized oil is vaporized, the upstream end of said flame tube being sealingly connected to said interior wall in which said orifice means is located, a freely open annular space being formed between the outer surface of said mixing tube and the inner surface of said flame tube, recirculation of the combustion gases occurring over substantially the entire length of said flame tube from said combustion zone to said mixing tube, the path of said recirculated combustion gases that emanate from the region of highest temperature in said flame tube being directed through said annular space into the upstream end of said mixing tube, the wall of said flame tube being relatively thin, wherein the freely open annular space as defined between said flame tube and said mixing tube is of sufficient dimension to provide for the free flow of said recirculating combustion gases therethrough to said mixing tube, said mixing tube having a ratio of length (L.sub.1) to diameter (D.sub.1) of between about 1.0 and 1.75, said flame tube having a ratio length (L.sub.2) to diameter (D.sub.2) of between about 2.0 and 5.0 and said flame tube being a diameter (D.sub.2) which is about 2-2.5 times the diameter (D.sub.1) of said mixing tube.