A burner nozzle comprises a tubular body (18) defining a chamber (22). Fuel jet (29) enters at aperture (24) and is separated from the chamber wall. The jet reattaches itself asymmetrically (30) to the inside wall surface (17). The jet precesses (37) about the nozzle axis as it is deflected (32) when emerging from the outlet port (26). The precession enhances mixing of fuel with air (34, 35) from the exterior of the chamber (22). Flow control means (40) directs further flow of fluid through an orifice. This flow forms a secondary jet (45) aligned along the axis about which the primary jet precesses. The momentum of the secondary jet (45) influences flame shape. By controlling the secondary jet, the overall flame shape can be controlled. A diversity of flame shapes, e.g. a short radiant flame or a long convective flame, can be obtained.
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