A constant volume Carnot engine cycle

An engine is presented such that its total volume is constant and whose cycle is the Carnot cycle as presented in the entropy-temperature picture, not as presented (by many textbooks) in the pressure-volume picture. The isothermal expansion and compression are replaced by an isothermal heat transfer between the surroundings and the engine such that there is a mass transfer between two gas reservoirs. The two reservoirs are always at the same temperature. The adiabatic expansion and compression are replaced by an adiabatic and reversible transfer of gas from one reservoir to another. Although the focus is on the working fluid being an ideal gas, the thermodynamic analysis presented can be extended easily to possible thermal electrochemical engines having a Carnot cycle characteristic. A heat engine, discussed by G.B. Baranescu (31st IECEC Conf., vol. 3, p. 713-718, 1996), is shown to be essentially one step of the present engine cycle.