Abstract: A readily reversible, rotary type internal combustion engine which is selectively operable as a compressor and capable of several basic modes of operation, wherein an expansible combustion chamber or volume cyclically initiated from zero volume is chargeable, directly from a contractible compression volume, with compressed gaseous fluids in real-time as the combustion chamber is cyclically formed and expands from a selectively small volume, said volumes being formed within a housing between intermeshing rotors. The flow of compressed and expanding gases within the apparatus is controlled primarily by said rotors.