Performance of Universal Reciprocating Heat-Engine Cycle with Variable Specific Heats Ratio of Working Fluid

Considering the finite time characteristic, heat transfer loss, friction loss and internal irreversibility loss, an air standard reciprocating heat-engine cycle model is founded by using finite time thermodynamics. The cycle model, which consists of two endothermic processes, two exothermic processes and two adiabatic processes, is well generalized. The performance parameters, including the power output and efficiency (PAE), are obtained. The PAE versus compression ratio relations are obtained by numerical computation. The impacts of variable specific heats ratio (SHR) of working fluid (WF) on universal cycle performances are analyzed and various special cycles are also discussed. The results include the PAE performance characteristics of various special cycles (including Miller, Dual, Atkinson, Brayton, Diesel and Otto cycles) when the SHR of WF is constant and variable (including the SHR varied with linear function (LF) and nonlinear function (NLF) of WF temperature). The maximum power outputs and the corresponding optimal compression ratios, as well as the maximum efficiencies and the corresponding optimal compression ratios for various special cycles with three SHR models are compared.

Mass Engine Cycle

A new thermodynamic cycle is proposed named mass engine cycle. In the proposed cycle, mass is transferred from a high mass concentration reservoir to the cycle, mass is rejected to a low mass concentration reservoir, and a net positive work is generated. This is similar to heat engine cycles where heat is transferred from a high temperature thermal reservoir (heat source) to the cycle; heat is rejected to a low temperature thermal reservoir (heat sink), and a net positive work is generated. The heat engine cycle uses heat exchangers to transfer heat between the cycle and the thermal reservoirs, while the mass engine cycle uses membrane mass exchangers which transfer mass between the cycle and the mass reservoir. These membrane mass exchangers transfer water through a semi-permeable membrane and reject other substances. The driving force for the mass transfer is the hydrostatic and osmotic pressure differences. Similar to Carnot limit of the thermal efficiency of the heat engine cycle, a theoretical limit is obtained for the proposed mass engine cycle under reversible thermodynamic conditions.

Thermodynamic Optimization Characteristics of a Type I Absorption Heat Pump within Finite Time

The absorption heat pump was studied with finite time thermodynamics. A four reservoirs model of absorption heat pump which is treated as an irreversible Carnot heat pump driven by an irreversible Carnot heat engine was established considering the heat resistance and the irreversibility of the internal cycle. A generalized optimization relationship between the main parameters and the corresponding conditions were derived. It is show that, two internal irreversibility parameters, the heat engine cycle and the heat pump cycle has different effects on system performance, and the reduction of the friction, heat loss, and internal dissipations of the equivalent heat pump cycle are more important than its reduction of heat engine cycle.