An aircraft propulsion system comprising: an internal combustion engine using intermittent combustion during operation; a propeller for propelling the aircraft, the propeller being drivingly engaged with the internal combustion engine ; a heat engine (20; 120; 220) using supercritical carbon dioxide (sCO 2 ) as a working fluid to convert heat into mechanical energy; and a first heat exchanger to facilitate heat transfer between exhaust gas downstream of a turbocharger turbine and the sCO 2 ; characterised by further comprising: a turbocharger associated with the internal combustion engine , the turbocharger including: the turbocharger turbine configured to be driven by a flow of exhaust gas from the internal combustion engine ; and a turbocharger compressor drivingly engaged with the turbocharger turbine and configured to compress combustion air for the internal combustion engine ; and a second heat exchanger to facilitate heat transfer between a coolant fluid of the internal combustion engine and the sCO 2 , the second heat exchanger being operatively disposed upstream of the first heat exchanger relative to a first flow of the sCO 2 in the first and second heat exchangers . an internal combustion engine using intermittent combustion during operation; a propeller for propelling the aircraft, the propeller being drivingly engaged with the internal combustion engine ; a heat engine (20; 120; 220) using supercritical carbon dioxide (sCO 2 ) as a working fluid to convert heat into mechanical energy; and a first heat exchanger to facilitate heat transfer between exhaust gas downstream of a turbocharger turbine and the sCO 2 ; characterised by further comprising: a turbocharger associated with the internal combustion engine , the turbocharger including: the turbocharger turbine configured to be driven by a flow of exhaust gas from the internal combustion engine ; and a turbocharger compressor drivingly engaged with the turbocharger turbine and configured to compress combustion air for the internal combustion engine ; and a second heat exchanger to facilitate heat transfer between a coolant fluid of the internal combustion engine and the sCO 2 , the second heat exchanger being operatively disposed upstream of the first heat exchanger relative to a first flow of the sCO 2 in the first and second heat exchangers . a turbocharger associated with the internal combustion engine , the turbocharger including: the turbocharger turbine configured to be driven by a flow of exhaust gas from the internal combustion engine ; and a turbocharger compressor drivingly engaged with the turbocharger turbine and configured to compress combustion air for the internal combustion engine ; and the turbocharger turbine configured to be driven by a flow of exhaust gas from the internal combustion engine ; and a turbocharger compressor drivingly engaged with the turbocharger turbine and configured to compress combustion air for the internal combustion engine ; and a second heat exchanger to facilitate heat transfer between a coolant fluid of the internal combustion engine and the sCO 2 , the second heat exchanger being operatively disposed upstream of the first heat exchanger relative to a first flow of the sCO 2 in the first and second heat exchangers . <EOS>