Efficiency at maximum power of minimally nonlinear irreversible heat engines

We propose the minimally nonlinear irreversible heat engine as a new general theoretical model to study the efficiency at the maximum power η* of heat engines operating between the hot heat reservoir at the temperature Th and the cold one at Tc (Tc≤Th). Our model is based on the extended Onsager relations with a new nonlinear term meaning the power dissipation. In this model, we show that η* is bounded from the upper side by a function of the Carnot efficiency ηC≡1−Tc/Th as η*≤ηC/(2−ηC). We demonstrate the validity of our theory by showing that the low-dissipation Carnot engine can easily be described by our theory.