A combustion engine system based on continuous internal combustion, comprising sequentially arranged, mutually separate mechanical arrangements for compression of combustion air, combustion and expansion, wherein cooling and exhaust-gas cleansing are integrated in the expansion stage. The system is characterized in that the compression arrangement includes at least two displacement compressors (7, 9, 11) arranged in series and of which the last compressor (11), as seen in the flow direction of the combustion air, forms a pressure barrier between the compression pressure and the combustion pressure; in that the combustion arrangement is comprised of a combustion chamber (13) into which one or more fuel delivery devices (14, 15) discharge; in that the expansion arrangement comprises at least two mutually sequential displacement-type expansion rotors (16, 17) which are coupled mechanically to form an output drive shaft of the combustion engine system; in that at least the walls of the expansion rotor (16) located nearest the combustion chamber are cooled by means of a liquid coolant (21); and in that there is arranged downstream of the last expansion rotor (17) as seen in the flow direction of the exhaust gases a condenser (19) which functions to cool the exhaust gases and to condense the vapour phase of the liquid coolant present therein.