Maximum irreversible work and efficiency in power cycles

The concept of the efficiency of a process is used to analyse various thermodynamic power cycles with ideal gases. The Otto cycle is treated by considering irreversibilities coming exclusively from expansion and compression processes. For this cycle, the maximum irreversible work and the maximum efficiency are obtained in terms of the isentropic efficiencies and of the maximum and minimum temperatures of the reversible cycle. The results obtained are easily applicable to the Brayton cycle and have some similarities with those obtained from finite-time thermodynamics. The expression found for the efficiency of the Otto cycle for irreversible maximum work is similar to that obtained by maximizing the irreversible work in the Curzon-Ahlborn-Nokivov engine.