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 eta* 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 eta* is bounded from the upper side by a function of the Carnot efficiency eta(C) 1 - T-c/T-h as eta* <=.eta(C)/(2 - eta(C)). We demonstrate the validity of our theory by showing that the low-dissipation Carnot engine can easily be described by our theory. Copyright (C) EPLA, 2012