Every thermodynamics cycle needs to do negative work to the environment, which lower its total positive work. For example, in Carnot cycle, the most efficiency possible: 1/ Engine receives heat from hot reservoir, expands and do positive work to surround 2/ Surround does work to engine, compresses it and heat is rejected to cold reservoir. The usable work is positive work from process 1 minuses negative work in process 2, and thus limit the efficiency to n = (Th - Tc) / Th, where Th and Tc are absolute temperatures of hot and cold reservoirs. All thermodynamics cycles do this kind of negative work. So why don't we increase efficiency by ignoring process 2, i.e. don't do negative work by compressing gas every cycle? For example, let see this example, we burn oil to heat air. Air is heated and pressure is raised. Let this heated air runs through a turbine vertically, so the inlet of turbine is hot air with high pressure, and the outlet of turbine is cool ambient air with low pressure While hot air expands through the turbine, energy is extracted from hot air, temperature and pressure are dropped. Cool air is fed naturally below in the inlet of the turbine and is heated to high pressure. The cycle is completed and reapeated. If we assume ideal conditions, e.g. no friction... then all received heat will be converted to work. There isn't any negative work wasted to the environment, i.e. no air is recompressed like in the classical thermodynamics cycles. So why doesn't every thermodynamics cycle choose this approach but instead they all need to do negative work on the environment? What is wrong with my approach?