The primary injection area contains axial gas lances (7) with multi-hole nozzles (12) at intervals round the periphery. The nozzle holes discharge at a set angle inclined radially outwards the lance axes, and on paths intersection those from adjacent lances. At the turbine side, the lances can pass through hollow guide vanes (8), typically so as to leave an annular gap (11) in each case of 1 to 2 mm. The lances are gimbal-mounted in a supporting ring (9). ADVANTAGE - Allows use of liquid or gaseous fuel or a combination of the two.