Currently, Combined Cycle Power Plants represent the most advanced technology in the domain of high and medium power generation units operating with fossil fuels. Consequently, the interest for their implementation in the propulsion systems field is justified. At this moment, Combined Cycle Units are used for propulsion only on ships (marine propulsion). The present study goes one step further by referring to a small scale Combined Cycle Unit configured for operation as terrestrial propulsion system and based on a two-pressure-levels Steam Cycle. The performances of this unit are analyzed function by the compressor pressure ratio and HRSG feed water temperature.

The functioning of a Vuilleumier heat pump with four variable-volume chambers and six heat exchangers was numerically simulated using a theoretical adiabatic physico-mathematical model. All four variable-volume chambers were assumed as adiabatic and the heat exchangers were considered as isothermal. The model uses the piston movement laws given by the mechanism and not simplified sinusoidal ones. The adiabatic functioning was described through thermodynamic diagrams showing pressure and temperatures cyclical variations inside the machine and inside each adiabatic chamber. The model allows to estimate the heat pump performances, highlighting the energy exchanged by the working agent inside heaters and coolers and the coefficient of performance. The adiabatic model is able to emphasize the energy transfer that appears between the branches of the machine, feature that simpler theoretical models do not have. This analysis of the functioning with the adiabatic model could be extended for a Vuilleumier heat pump that rejects heat at two different temperatures.