A fuel oxidizer system is operated in a first operating mode. In the first operating mode, a mixture that includes fuel from a fuel source is compressed in a compressor of the fuel oxidizer system; the fuel of the compressed mixture is oxidized in a reaction chamber of the fuel oxidizer system; and the oxidized fuel is expanded to generate rotational kinetic energy. The fuel oxidizer system is operated in a second operating mode. In the second operating mode, fuel from the fuel source is directed to bypass the compressor, and the fuel that bypassed the compressor is oxidized in the reaction chamber.