A system for the gradual oxidation of fuel is disclosed. The system includes an oxidizer that has a reaction chamber with an inlet and an outlet. The reaction chamber is configured to receive a fluid comprising an oxidizable fuel through the inlet. The oxidizer is configured to maintain a flameless oxidation process. The system also includes a heating chamber with an inlet and an outlet. The inlet of the heating chamber is in fluid communication with the outlet of the reaction chamber. The heating chamber is configured to receive the fluid from the reaction chamber and selectably heat the fluid.