The benefits of an inverted Brayton cycle bottoming cycle as an alternative to turbo-compounding

Research output: Chapter in Book/Report/Conference proceedingConference contribution

8 Citations (Scopus)

Abstract

The exhaust gas from an internal combustion engine contains approximately 30% of the thermal energy of combustion. Waste 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 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 an air-standard, irreversible Otto-cycle and the inverted Brayton cycle using finite-time thermodynamics (FTT) is presented to study heat recovery applied to an automotive internal combustion engine. The other two alternatives power cycle, the pressurized Brayton cycle and the turbo-compounding system, are compared with the Inverted Brayton Cycle (IBC) to specify the strengths and weaknesses of three alternative cycles. In the current paper, an irreversible Otto-cycle model that includes an array of losses is used as a basis for the bottoming cycle. The deviation of the turbomachinery from the idealized behavior is described by the isentropic component efficiencies. The performance of the system as defined as the specific power output and thermal efficiency is considered using parametric studies. The results show that the performance of the inverted Brayton cycle can be positively affected by five critical parameters – the number of compression stages, the cycle inlet temperature and pressure, the isentropic efficiency of the turbomachinery and the effectiveness of the heat exchanger. There exists an optimum pressure ratio across the IBC turbine that delivers the maximum specific power. In the view of the specific power, installing a single-stage of the inverted Brayton cycle appears the best balance between performance and complexity. Three alternative cycles are compared in terms of the thermal efficiency. The results indicate that the pressurized and Inverted Brayton Cycle can improve the performance of the turbocharged engine only when the turbomachinery efficiencies are higher than a critical value which changes with the operating condition. High performance of the IBC turbomachinery is required to ensure that the turbocharged engine with the inverted Brayton cycle is superior to that with turbo-compounding system.
Original languageEnglish
Title of host publicationProceedings of ASME Turbo Expo
Subtitle of host publicationTurbine Technical Conference and Exposition, 2015. Volume 8 - Microturbines, Turbochargers and Small Turbomachines; Steam Turbines
Place of PublicationMontreal, Canada
PublisherAmerican Society of Mechanical Engineers (ASME)
PagesV008T23A006
Number of pages15
ISBN (Print)9780791856796
DOIs
Publication statusPublished - 2015
EventASME Turbo Expo, 2015 - Palais de Congres, Montreal, Canada
Duration: 15 Jun 201519 Jun 2015

Conference

ConferenceASME Turbo Expo, 2015
CountryCanada
CityMontreal
Period15/06/1519/06/15

Fingerprint

Brayton cycle
Turbomachinery
Waste heat utilization
Otto cycle
Exhaust gases
Internal combustion engines
Thermodynamics
Engines
Thermal energy
Heat exchangers
Power plants
Turbines

Cite this

Copeland, C. D., & Chen, Z. (2015). The benefits of an inverted Brayton cycle bottoming cycle as an alternative to turbo-compounding. In Proceedings of ASME Turbo Expo: Turbine Technical Conference and Exposition, 2015. Volume 8 - Microturbines, Turbochargers and Small Turbomachines; Steam Turbines (pp. V008T23A006). Montreal, Canada: American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/GT2015-42623

The benefits of an inverted Brayton cycle bottoming cycle as an alternative to turbo-compounding. / Copeland, Colin D.; Chen, Zhihang.

Proceedings of ASME Turbo Expo: Turbine Technical Conference and Exposition, 2015. Volume 8 - Microturbines, Turbochargers and Small Turbomachines; Steam Turbines. Montreal, Canada : American Society of Mechanical Engineers (ASME), 2015. p. V008T23A006.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Copeland, CD & Chen, Z 2015, The benefits of an inverted Brayton cycle bottoming cycle as an alternative to turbo-compounding. in Proceedings of ASME Turbo Expo: Turbine Technical Conference and Exposition, 2015. Volume 8 - Microturbines, Turbochargers and Small Turbomachines; Steam Turbines. American Society of Mechanical Engineers (ASME), Montreal, Canada, pp. V008T23A006, ASME Turbo Expo, 2015, Montreal, Canada, 15/06/15. https://doi.org/10.1115/GT2015-42623
Copeland CD, Chen Z. The benefits of an inverted Brayton cycle bottoming cycle as an alternative to turbo-compounding. In Proceedings of ASME Turbo Expo: Turbine Technical Conference and Exposition, 2015. Volume 8 - Microturbines, Turbochargers and Small Turbomachines; Steam Turbines. Montreal, Canada: American Society of Mechanical Engineers (ASME). 2015. p. V008T23A006 https://doi.org/10.1115/GT2015-42623
Copeland, Colin D. ; Chen, Zhihang. / The benefits of an inverted Brayton cycle bottoming cycle as an alternative to turbo-compounding. Proceedings of ASME Turbo Expo: Turbine Technical Conference and Exposition, 2015. Volume 8 - Microturbines, Turbochargers and Small Turbomachines; Steam Turbines. Montreal, Canada : American Society of Mechanical Engineers (ASME), 2015. pp. V008T23A006
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N2 - The exhaust gas from an internal combustion engine contains approximately 30% of the thermal energy of combustion. Waste 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 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 an air-standard, irreversible Otto-cycle and the inverted Brayton cycle using finite-time thermodynamics (FTT) is presented to study heat recovery applied to an automotive internal combustion engine. The other two alternatives power cycle, the pressurized Brayton cycle and the turbo-compounding system, are compared with the Inverted Brayton Cycle (IBC) to specify the strengths and weaknesses of three alternative cycles. In the current paper, an irreversible Otto-cycle model that includes an array of losses is used as a basis for the bottoming cycle. The deviation of the turbomachinery from the idealized behavior is described by the isentropic component efficiencies. The performance of the system as defined as the specific power output and thermal efficiency is considered using parametric studies. The results show that the performance of the inverted Brayton cycle can be positively affected by five critical parameters – the number of compression stages, the cycle inlet temperature and pressure, the isentropic efficiency of the turbomachinery and the effectiveness of the heat exchanger. There exists an optimum pressure ratio across the IBC turbine that delivers the maximum specific power. In the view of the specific power, installing a single-stage of the inverted Brayton cycle appears the best balance between performance and complexity. Three alternative cycles are compared in terms of the thermal efficiency. The results indicate that the pressurized and Inverted Brayton Cycle can improve the performance of the turbocharged engine only when the turbomachinery efficiencies are higher than a critical value which changes with the operating condition. High performance of the IBC turbomachinery is required to ensure that the turbocharged engine with the inverted Brayton cycle is superior to that with turbo-compounding system.

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