A method is provided for operating a volume-controlled internal-combustion engine having an intake tract and an exhaust system. An expansion machine is arranged in the intake tract in the flow direction of a combustion air in front of an inlet valve of the engine. An output shaft of the expansion machine is coupleable with an output shaft of the engine. A heat exchanger is arranged in the exhaust system. Before combustion air flows through the expansion machine, it is heated in the heat exchanger by exhaust gas of the internal-combustion engine. The method achieves an efficiency improvement in an internal-combustion engine with a volume-controlled load control at partial load.