A feed injector system comprises a movable central member, a first member substantially concentric with the central member to define a first channel for conveying a first fluid oxidizer stream, a second member substantially concentric with the first member to define a second channel for conveying a fuel feed, and a third member substantially concentric with the second member to define a third channel for conveying a second fluid oxidizer steam. The first member and the second member are configured to enhance instability in the fuel feed emanating from the second channel.