The Behaviour of Some Working Fluids Applied on the Trilateral Cycles with Isothermal Controlled Expansion

This work studies the behaviour of some working fluids to be applied on trilateral thermal cycles characterised by the conversion of heat into mechanical work undergoing controlled isothermal expansion path functions. The considered trilateral cycles are relevant because of its ability to operate at very high efficiency when the working fluid operates within the vicinity of its critical point. Strategies to keep a constant temperature along the expansion stroke of a single effect reciprocating engine undergoing a corresponding pressure to ensure the desired path function are proposed and validated.
An analysis of the trilateral cycle undergoing isothermal expansion has been carried out and the thermal efficiency compared with that of a Carnot engine operating under a similar ratio of temperatures. Results revealed that for some working fluids, there exists a special region in the vicinity of the critical point that exhibits the best conditions to achieve high thermal efficiency when the conversion of heat to mechanical work is carried out undergoing an isothermal expansion.