Thermodynamic cycles with nearly universal maximum-work efficiencies

Important thermodynamic heat engine cycles can be regarded as special cases of a more universal 'generalised' cycle. For specific choices of a continuously variable parameter, this generalised cycle reduces to the Carnot, Otto, Joule-Brayton, Diesel and other known cycles. Of particular interest is the thermal efficiency when characteristic temperatures between the highest and lowest operating temperatures (T + and T - ) are chosen to maximise the work output per cycle. This maximum-work efficiency is found to be equal to, or to be well approximated by, the Curzon-Ahlborn efficiency, eta CA identical to 1-(T - /T + ) 1/2 for a broad spectrum of cycles and temperatures.