Thermodynamic Optimization for an Endoreversible Dual-Miller Cycle (DMC) with Finite Speed of Piston

Power output (P), thermal efficiency (η) and ecological function (E) characteristics of an endoreversible Dual-Miller cycle (DMC) with finite speed of the piston and finite rate of heat transfer are investigated by applying finite time thermodynamic (FTT) theory. The parameter expressions of the non-dimensional power output (P), η and non-dimensional ecological function (E) are derived. The relationships between P and cut-off ratio (ρ), between P and η, as well as between E and ρ are demonstrated. The influences of ρ and piston speeds in different processes on P, η and E are investigated. The results show that P and E first increase and then start to decrease with increasing ρ. The optimal cut-off ratio ρopt will increase if piston speeds increase in heat addition processes and heat rejection processes. As piston speeds in different processes increase, the maximum values of P and E increase. The results include the performance characteristics of various simplified cycles of DMC, such as Otto cycle, Diesel cycle, Dual cycle, Otto-Atkinson cycle, Diesel-Atkinson cycle, Dual-Atkinson cycle, Otto-Miller cycle and Diesel-Miller cycle. Comparing performance characteristics of the DMC with different optimization objectives, when choosing E as optimization objective, η improves 26.4% compared to choosing P as optimization objective, while P improves 74.3% compared to choosing η as optimization objective. Thus, optimizing E is the best compromise between optimizing P and optimizing η. The results obtained can provide theoretical guidance to design practical DMC engines.