Optimization of a dual cycle cogeneration system based on a new exergetic performance criterion Yasin Ust a , Bahri Sahin a, * , Ali Kodal b a Department of Naval Architecture and Marine Engineering, Yildiz Technical University, Besiktas, 34349 Istanbul, Turkey b Department of Aeronautical Engineering, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey Received 13 October 2006; received in revised form 9 April 2007; accepted 21 April 2007 Available online 19 July 2007 Abstract An ecological performance analysis for an irreversible dual-cycle cogeneration system has been performed. The objective function is called as the exergetic-performance coefficient (EPC) and defined as the ratio of total exergy output to the loss rate of availability. The general and optimal performances of the irreversible dual-cycle cogeneration system, having a finite-rate of heat transfer, heat leak and internal irreversibilities based on the EPC objective function have been investigated. Comparisons with respect to the optimal total-exergy output are also provided in order to establish the utility of the new exergetic-performance coefficient. The analyzed results of the dual-cycle cogen- eration system considered, working at maximum EPC conditions, have a significant advantage in terms of entropy-generation rate and can be used for the selection of optimal design parameters. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Ecological optimization; Dual cycle; Cogeneration; Performance analysis; Exergetic performance 1. Introduction The optimization studies for air-standard reciprocating cycles, i.e., Otto, Diesel and dual cycles, with rate-dependent loss mechanisms have appeared as early as in the 1980s in the physics literature. In the fundamental analysis of modern Diesel engines, the dual cycle is 0306-2619/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2007.04.004 * Corresponding author. Fax: +90 212 236 4165. E-mail address: sahinb@yildiz.edu.tr (B. Sahin). Applied Energy 84 (2007) 1079–1091 www.elsevier.com/locate/apenergy APPLIED ENERGY