Studies of unconventional heat engine design, operation and efficiency: four-step quasi-Carnot cycles with a linear P/V transition

Abstract

Although the ideal Carnot engine rejoices in the largest efficiency of any heat engine operating between given temperature extremes, alternative closed-loop four-step cycles in which a variable-temperature, straight-line transition replaces the Carnot high-temperature isothermal expansion appear ostensibly to offer a higher thermodynamic efficiency. This arises from the fact that higher maximal temperatures are attained; the efficiency of the equivalent Carnot engine operating between such temperature extremes reinstates Carnot supremacy by slightly transcending the unconventional engine's efficiency. Our investigations stress the importance of the second, as well as the first, law of thermodynamics, and consider operating characteristics quantitatively for specimen engines of various design.