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Journal of Non-Equilibrium Thermodynamics

Founded by Keller, Jürgen U.

Editor-in-Chief: Hoffmann, Karl Heinz

Managing Editor: Prehl, Janett / Paul, Raphael

Ed. by Michaelides, Efstathios E. / Rubi, J. Miguel

IMPACT FACTOR 2018: 2.083

CiteScore 2018: 1.84

SCImago Journal Rank (SJR) 2018: 0.564
Source Normalized Impact per Paper (SNIP) 2018: 0.876

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Volume 39, Issue 3


Optimal motion trajectory for the four-stroke free-piston engine with irreversible Miller cycle via a Gauss pseudospectral method

Jiming Lin / Siqin Chang / Zhaoping Xu
Published Online: 2014-06-27 | DOI: https://doi.org/10.1515/jnet-2014-0003


A four-stroke free-piston engine with internal and external irreversibilities of finite combustion rate of the fuel, heat transfer and friction is investigated in this paper. Under the condition of the fixed fuel consumption per cycle, the optimal piston motion trajectory for maximizing the net work output of different cases is derived by applying optimal control theory. Considering the path constraints and boundary conditions of this free-piston Miller cycle, a Gauss pseudospectral method (GPM) is presented for solving optimal motion trajectory. The results show that the optimal piston trajectory improves the efficiency by more than 10% and also suitably reduces the heat transfer losses compared to the conventional piston motion. By optimizing the piston motion around the top dead center (TDC), the in-cylinder gas pressure and temperature have a remarkable improvement while the heat transfer losses have a suitable reduction. The effects of other parameters, such as combustion duration and the frictional coefficient on the piston trajectory, are also investigated. It is shown that optimizing the piston motion trajectory is a good approach for the free-piston engine to improve the efficiency and it can provide guidelines for the optimal control of the practical free-piston engine.

Keywords: Free-piston engine; thermodynamic; Miller cycle; engine efficiency; optimization; piston motion

About the article

Received: 2014-02-11

Revised: 2014-05-01

Accepted: 2014-05-12

Published Online: 2014-06-27

Published in Print: 2014-09-01

Funding Source: National Natural Science Foundation of China

Award identifier / Grant number: 51207071

Funding Source: Postdoctoral Science Foundation of China

Award identifier / Grant number: 2012T50476

Funding Source: Zijin Intelligent Program, Nanjing University of Science and Technology

Award identifier / Grant number: 2013-ZJ-0202

Funding Source: Innovation Program of Postgraduates in Jiangsu Province

Award identifier / Grant number: CXZZ12_0181

Citation Information: Journal of Non-Equilibrium Thermodynamics, Volume 39, Issue 3, Pages 159–172, ISSN (Online) 1437-4358, ISSN (Print) 0340-0204, DOI: https://doi.org/10.1515/jnet-2014-0003.

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