Power, efficiency, ecological function and ecological coefficient of performance of an irreversible Dual-Miller cycle (DMC) with nonlinear variable specific heat ratio of working fluid

Finite time thermodynamic (FTT) theory is applied to perform performance analysis for an air-standard irreversible Dual-Miller cycle (DMC) based on the power output (P), thermal efficiency (η\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\eta$\end{document}, ecological function (E) and ecological coefficient of performance (ECOP) criteria by considering nonlinear variable specific heat ratio, piston friction loss, heat transfer loss and other internal irreversible losses. Relationships between different performance characteristics are obtained via numerical calculations. Effects of pressure ratio and stroke length on each criterion are analyzed, and performance characteristics with different optimization objective are compared. The results show that pressure ratio has little influence on performance characteristics, but stroke length has great influence on performance characteristics. Moreover P, η\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\eta$\end{document}, E and ECOP decrease with increasing stroke length, but when stroke length increases to a certain value, E is less than 0 whatever value of compression ratio takes. Choosing the E and ECOP as optimization objectives is more significant by comparing with other performance indexes.