Apparatus for a combustion turbine engine, comprising: a pre-mixing passage having an upstream inlet arranged to receive a flow of air to be mixed with fuel; a fuel-injecting lance disposed in the pre-mixing passage; at least a first fuel ejection orifice disposed at a first axial location of the fuel-injecting lance; at least a second ejection orifice disposed at a second axial location of the fuel-injecting lance, wherein a spacing between the first and second axial locations is arranged to effect oscillatory interference patterns in pockets comprising mixtures of air and fuel that flow towards a downstream outlet of the pre-mixing passage, wherein the at least first fuel ejection orifice is part of a plurality of fuel ejection orifices disposed in a row at the first axial location and the at least second fuel ejection orifice is part of a plurality of fuel ejection orifices disposed in a row at the second axial location, wherein the respective rows (R1, R2) of fuel ejection orifices comprise circumferentially-extending rows of fuel ejection orifices respectively spanning at least respective portions of a perimeter of the fuel-injecting lance, and characterized in that the circumferentially-extending row of fuel ejection orifices at the first axial location comprises fuel ejection orifices configured for fuel-rich injection, and the circumferentially-extending row of fuel ejection orifices at the second axial location comprises fuel ejection orifices configured for fuel-lean injection; or in that the circumferentially-extending row of fuel ejection orifices at the first axial location comprises fuel ejection orifices configured for fuel-lean injection, and the circumferentially-extending row of fuel ejection orifices at the second axial location comprises fuel ejection orifices configured for fuel-rich injection. a pre-mixing passage having an upstream inlet arranged to receive a flow of air to be mixed with fuel; a fuel-injecting lance disposed in the pre-mixing passage; at least a first fuel ejection orifice disposed at a first axial location of the fuel-injecting lance; at least a second ejection orifice disposed at a second axial location of the fuel-injecting lance, wherein a spacing between the first and second axial locations is arranged to effect oscillatory interference patterns in pockets comprising mixtures of air and fuel that flow towards a downstream outlet of the pre-mixing passage, wherein the at least first fuel ejection orifice is part of a plurality of fuel ejection orifices disposed in a row at the first axial location and the at least second fuel ejection orifice is part of a plurality of fuel ejection orifices disposed in a row at the second axial location, wherein the respective rows (R1, R2) of fuel ejection orifices comprise circumferentially-extending rows of fuel ejection orifices respectively spanning at least respective portions of a perimeter of the fuel-injecting lance, and characterized in that the circumferentially-extending row of fuel ejection orifices at the first axial location comprises fuel ejection orifices configured for fuel-rich injection, and the circumferentially-extending row of fuel ejection orifices at the second axial location comprises fuel ejection orifices configured for fuel-lean injection; or in that the circumferentially-extending row of fuel ejection orifices at the first axial location comprises fuel ejection orifices configured for fuel-lean injection, and the circumferentially-extending row of fuel ejection orifices at the second axial location comprises fuel ejection orifices configured for fuel-rich injection.