Fluctuations in heat engines

At the dawn of thermodynamics, Carnot's constraint on efficiency heat engines stimulated formulation one most universal physical principles, second law thermodynamics. In recent years, field acquired a new twist due to enormous efforts develop and describe microscopic machines based systems as small single atoms. microscales, fluctuations are an inherent part dynamics thermodynamic variables such work fluctuate. Novel probabilistic formulations imply general symmetries limitations for fluctuating output power engines. Will their complete understanding ignite similar revolution discovery law? Here, we review known results concerning in performance To make discussion more transparent, illustrate main abstract findings exactly solvable models provide thorough theoretical introduction newcomers field.