A gas turbine engine with a single stage combustor includes an external premixer to provide premixed fuel/compressed air to the combustor as well as compressed air for dilution; and an automatic controller to provide feedback control of the compressed air flow and fuel flow to the premixer in accordance with actual power versus power demand. The fuel/compressed air mixture is combusted in a combustor and the combustion gases and dilution air are expanded in a turbine. The engine further includes a bleed valve under control of the controller for diverting sufficient compressed dilution air past the turbine to induce increased fuel flow and compressed air flow to the premixer for delivery to, and combustion of, the combustor to compensate for the power deficit due to the bled air, to provide selected minimum premixer exit velocities during engine operation.