An internal combustion engine comprises a plurality of engine units (50A-50C), each having a working space (11), in which two rotary pistons (20, 30) are arranged so as mesh with each other and thereby divide the working space (11) into an inflow region (12) and an outflow region (13). Each engine unit comprises a closable inlet opening (62A-62C) to the inflow region (12) and a closable exhaust gas outlet opening (64A-64C). The internal combustion engine further comprises a feed-line pipe (60) to the inlet openings (62A-62C) and an exhaust gas collection pipe (66) connected to the exhaust gas outlet openings (64A-64C), so that the engine units (50A-50C) are connected in parallel with each other. The internal combustion engine further comprises exhaust gas lines (63A, 63B) which connect the engine units (50A, 50B) with each other in series. In dependence upon a desired power output, a control device (70) operates some of the engine units (50B, 50C) either as internal combustion engines, wherein the respective inlet opening (62B-62C) is opened, or as expansion engines, wherein respective inlet opening (62B-62C) remains closed and the respective rotary pistons (20, 30) are instead driven by exhaust gas flowing in via the respective exhaust gas line (63A, 63B).