The invention concerns a piston internal-combustion engine with separate compression (K) and expansion (E) chambers and a compressed-gas transfer device (7) which feeds compressed gas from the compression chambers to the expansion chambers at the beginning of ignition. A control unit (7) is provided which, depending on the mode of operation, feeds the compressed gas either to the expansion chambers or to a pressure accumulator (10) from which the expansion chambers can also be operated in a pure compressed-air mode.
