Abstract
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 ρ o p t 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.