Abstract: An internal combustion engine and a method of operation thereof in which a plurality of compressors are connected through check valves with the inlet means of the working chambers of the engine while the working chambers are connected through control valves and gas turbines, each of which drives a respective compressor. The control valves are arranged to open sequentially as engine speed increases and to close sequentially as engine speed decreases with the opening of each control valve taking place more rapidly and at a higher engine speed than the closing thereof. In starting the engine, only one of the turbine is supplied with gas to initiate a supply of compressed air for use in starting the engine.