Thermal Efficiency for a Curzon and Ahlborn Engine

Usually classical thermodynamics text books are devoted some parts to heat engines and their cycles. Most of these text books pay attention to Carnot cycle and index diagram, therefore the others diagrams and cycles often missed. Although the Carnot cycle has an important role in the evolution of the second law of thermodynamics from historical point of view, the other cycles like Brayton cycle, Otto cycle, Atkinson cycle [1], and recently Curzon and Ahlborn (C-A) cycle [2] are appreciable and must be regarded.