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Thermodynamic optimisation of a high-electrical efficiency integrated internal combustion engine – organic Rankine cycle combined heat and power system

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Title: Thermodynamic optimisation of a high-electrical efficiency integrated internal combustion engine – organic Rankine cycle combined heat and power system
Authors: Chatzopoulou, MA
Markides, C
Item Type: Journal Article
Abstract: Organic Rankine cycle (ORC) engines are suitable for heat recovery from internal combustion engines (ICE) in combined heat and power (CHP) systems. However, trade-offs must be considered between ICE and ORC engine performance in such integrated solutions. The ICE design and operational characteristics influence its own performance along with the exhaust-gas conditions available as heat source to the ORC engine, impacting ORC design and performance, while the heat-recovery heat exchanger (ORC evaporator) will affect the ICE operation. In this paper, an integrated ICE-ORC CHP whole-system optimisation framework is presented. This differs from other efforts in that we develop and apply a fully-integrated ICE-ORC CHP optimisation framework, considering the design and operation of both the ICE and ORC engines simultaneously within the combined system, to optimise the overall system performance. A dynamic ICE model is developed and validated, along with a steady-state model of subcritical recuperative ORC engines. Both naturally aspirated and turbocharged ICEs are considered, of two different sizes/capacities. Nine substances (covering low-GWP refrigerants and hydrocarbons) are investigated as potential ORC working fluids. The integrated ICE-ORC CHP system isoptimised for either maximum total power output, or minimum fuel consumption. Results highlight that by optimising the complete integrated ICE-ORC CHP system simultaneously, the total power output increases by up to 30% in comparison to a nominal system design. In the integrated CHP system, the ICE power output is slightly lower than that obtained for optimal stand alone ICE application, as the exhaust-gas temperature increases to promote the bottoming ORC engine performance, whose power increases by 7%. The ORC power output achieved accounts for up to 15% of the total power generated by the integrated system, increasing the system efficiency by up to 11%. When only power optimisation is performed, the specific fuel consumption increases, highlighting that high-power output comes at the cost of higher fuel consumption. In contrast, when specific fuel consumption is used as the objective function (minimised), fuel consumption drops by up to 17%, thereby significantly reducing the operating fuel costs. This study proves that by taking a holistic approach to whole-system ICE-ORC CHP design and operation optimisation, more power can be generated efficiently, with a lower fuel consumption. The findings are relevant to ICE and ORC manufacturers, integrators and installers, since it informs component design, system integration and operation decisions.
Issue Date: 15-Sep-2018
Date of Acceptance: 2-Jun-2018
URI: http://hdl.handle.net/10044/1/61095
DOI: https://dx.doi.org/10.1016/j.apenergy.2018.06.022
ISSN: 0306-2619
Publisher: Elsevier
Start Page: 1229
End Page: 1251
Journal / Book Title: Applied Energy
Volume: 226
Copyright Statement: © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/)
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Climate-KIC EIT PhD added value Programme
President's PhD Scholarships
UK Engineering and Physical Sciences Research Council
Funder's Grant Number: EP/P004709/1
Climate-KIC EIT PhD added value Programme
Award number: 1855813
Keywords: 09 Engineering
14 Economics
Publication Status: Published
Online Publication Date: 2018-07-18
Appears in Collections:Chemical Engineering
Faculty of Engineering