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Research Papers: Gas Turbines: Cycle Innovations

Modeling and Simulation of an Inverted Brayton Cycle as an Exhaust-Gas Heat-Recovery System

[+] Author and Article Information
Zhihang Chen

Mem. ASME
Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: zc311@bath.ac.uk

Colin Copeland

Mem. ASME
Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: C.D.Copeland@bath.ac.uk

Bob Ceen

Axes Design Ltd.,
Worcestershire WR14 4JU, UK
e-mail: bobceen@hotmail.co.uk

Simon Jones

HiETA Technologies Ltd.,
Bristol BS16 7FR, UK
e-mail: simonjones@hieta.biz

Alan Agurto Goya

Jaguar Landrover Ltd.,
Coventry CV3 4LF, UK
e-mail: aagurto@jaguarlandrover.com

1Corresponding author.

Contributed by the Cycle Innovations Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 21, 2016; final manuscript received December 16, 2016; published online March 21, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(8), 081701 (Mar 21, 2017) (10 pages) Paper No: GTP-16-1544; doi: 10.1115/1.4035738 History: Received November 21, 2016; Revised December 16, 2016

The exhaust gas from an internal combustion engine contains approximately 30% of the thermal energy of combustion. The exhaust-gas heat-recovery systems aim to reclaim a proportion of this energy in a bottoming thermodynamic cycle to raise the overall system thermal efficiency. The inverted Brayton cycle (IBC) considered as a potential exhaust-gas heat-recovery system is a little-studied approach, especially when applied to small automotive power-plants. Hence, a model of the inverted Brayton cycle using finite-time thermodynamics (FTT) is presented to study heat recovery applied to a highly downsizing automotive internal combustion engine. IBC system consists of a turbine, a heat exchanger (HE), and compressors in sequence. The use of IBC turbine is to fully expand the exhaust gas available from the upper cycle. The remaining heat in the exhaust after expansion is rejected by the downstream heat exchanger. Then, the cooled exhaust gases are compressed back up to the ambient pressure by one or more compressors. In this paper, the exhaust conditions available from the engine test bench data were introduced as the inlet conditions of the IBC thermodynamic model to quantify the power recovered by IBC, thereby revealing the benefits of IBC to this particular engine. It should be noted that the test bench data of the baseline engine were collected by the worldwide harmonized light vehicles test procedures (WLTP). WLTP define a global harmonized standard for determining the levels of pollutants and CO2 emissions, fuel consumption. The IBC thermodynamic model was simulated with the following variables: IBC inlet pressure, turbine pressure ratio, heat exchanger effectiveness, turbomachinery efficiencies, and the IBC compression stage. The aim of this paper is to analysis the performance of IBC system when it is applied to a light-duty automotive engine operating in a real-world driving cycle.

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References

Figures

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Fig. 1

(Left) Turbocharging and turbocompounding and (right) inverted Brayton cycle

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Fig. 2

WLTP driving cycle

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Fig. 3

Time distribution of engine operating points on the engine map

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Fig. 4

Exhaust mass flow rate

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Fig. 5

Exhaust temperature

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Fig. 6

Schematic of three-stage IBC system

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Fig. 7

Temperature and entropy diagram of three-stage IBC system

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Fig. 8

The benefits of single-stage IBC

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Fig. 9

Heat transfer rate in the heat exchanger

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Fig. 10

Average BSFC improvement due to various stages IBC versus IBC expansion ratio

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Fig. 11

Comparison between optimized IBC with that of fixed expansion ratio

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