An engine comprising an isothermal air compressor (1) into which liquid is sprayed as the air is compressed. A combustion chamber (4) receives and expands the compressed air from which the liquid has been removed, to generate power. A precompressor (21, 27) compresses the air upstream of the isothermal compressor. The compressed air from the isothermal compressor receives heat from the exhaust gas from the combustion chamber in a primary heat exchanger (3). A secondary heat exchanger (31, 45) transfers heat recovered from a part of the engine to the compressed air from the isothermal compressor (1) upstream of the primary heat exchanger (3).