A fuel flow control system includes a centrifugal pump, a gas inlet valve, and a control. The centrifugal pump has a fuel inlet, a gas inlet, and an outlet. The gas inlet valve is disposed upstream of the gas inlet and is responsive to valve position commands to move between a closed position, in which inert gas is prevented from flowing into the gas inlet, and a plurality of open positions, in which inert gas may flow into the gas inlet. The control is coupled to the gas inlet valve and is configured to supply the valve position commands to the gas inlet valve to command the gas inlet valve to selectively move to the closed position, such that the centrifugal pump is configured to operate as a fuel pump, or any open position, such that the centrifugal pump is configured to operate as a fuel-gas mixer.