A fuel injection system for a gas turbine engine (10) comprises; a pilot fuel injector section (22, 23) and a main airblast fuel injector section (25, 26, 27, 28, 29), the main airblast fuel injector section having an aft end (29) facing a combustion chamber (30). A surface of the injection system exposed to air flow through an injection system is non-axisymmetric or non-planar in a reference circumferential plane and/or is configured to generate controlled and varying acoustic impedance at or adjacent the aft end where, in use, the air flow collides with an oncoming acoustic wave.