A method of operating an aircraft power plant having an interburner fluidly connected between a combustion engine and a turbine, includes: operating the combustion engine at an air-fuel ratio corresponding to a nominal air-fuel ratio to generate combustion gases; receiving the combustion gases generated by the combustion engine into the interburner; increasing a temperature of the combustion gases generated by a combustion chamber of the combustion engine by lowering the air-fuel ratio to an ignition air-fuel ratio lower than the nominal air-fuel ratio; injecting fuel into the interburner to cause ignition of a mixture of the combustion gases and the fuel received into the interburner; and after ignition of the interburner, increasing the air-fuel ratio above the ignition air-fuel ratio.