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 T h and the cold one at T c ( T c ⩽ T h ). 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 η C ≡1− T c / T h as η * ⩽η C /(2−η C ). We demonstrate the validity of our theory by showing that the low-dissipation Carnot engine can easily be described by our theory.