Even after use of intermal combustion to increase the temperature, the CO2 cycle remained unexplored However, the concem of reducing CO2 emissions to atmosphere has brought attention to fuel combustion in a mixture of O2 and flue gases (H2O, CO2 or both) 3 Efficiencies of 35-45% seem possible in spite of power use for O2 production. The main benefit of these cycles is zero-emission, ie. no exhaust gases, Liquid co2 is the only effluent.