An internal combustion engine has a plurality of engine units, each having a working space, in which two rotary pistons are arranged so as mesh with each other and thereby divide the working space into an inflow region and an outflow region. Each engine unit has a closable inlet opening to the inflow region and a closable exhaust gas outlet opening. The internal combustion engine further includes a feed-line pipe to the inlet openings and an exhaust gas collection pipe connected to the exhaust gas outlet openings, so that the engine units are connected in parallel with each other. The internal combustion engine further includes exhaust gas lines which connect the engine units with each other in series. In certain cases, a control device operates some of the engine units either as internal combustion engines, or as expansion engines.