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Research Papers: Gas Turbines: Aircraft Engine

Unified Applicable Propulsion System Performance Metrics

[+] Author and Article Information
Oliver Schmitz

Researcher in Advanced Motive Power
Visionary Aircraft Concepts,
Bauhaus Luftfahrt e.V.,
Munich 80807, Germany
e-mail: oliver.schmitz@bauhaus-luftfahrt.net

Mirko Hornung

Executive Director Research and Technology
Bauhaus Luftfahrt e.V.,
Munich 80807, Germany
e-mail: mirko.hornung@bauhaus-luftfahrt.net

The naming “inner” instead of “thermal” efficiency is chosen in agreement with literature (compare Ref. [16], p. 64) and offers a better meaning for both the purely heat engine-based systems but also entire electrically-powered or hybrid systems.

Exhaust massflow m·exh might differ from inlet massflow m·inl due to fuel injection, bleed off-take, leakage, etc.

According to Ref. [17], DE is either defined as ratio of the power supplied electrically Psup,electric to the total power supplied Psup at a particular point or as ratio of the installed electrical energy to the total installed energy in an aircraft.

The complete energy conversion process is typically composed of a series of conversion processes, e.g., chemical energy into thermal energy into kinetic energy into mechanical energy. This can also include the inflight generation of electricity, e.g., a gas turbine-driven electric generator.

Contributed by the Aircraft Engine Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 28, 2013; final manuscript received July 17, 2013; published online September 17, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(11), 111201 (Sep 17, 2013) (9 pages) Paper No: GTP-13-1201; doi: 10.1115/1.4025066 History: Received June 28, 2013; Revised July 17, 2013

Progress in the development of electrical storage and conversion technology progressively attains focus in aerospace motive power research. Novel propulsion system concepts based on hybrid or even entirely electrical energy sources are seriously considered for aircraft design. To this point, unified figures of merit are required in order to allow for consistent comparative investigations of existing combustion engines and future electrically-based propulsion systems. Firstly, this paper identifies the shortcomings of conventional performance metrics used for nonthermal electrical conversion processes and then approaches exergy-based loss methods as means of metrics extensions. Subsequently, energy source-independent figures of merit based on exergy analysis are derived and embedded into the well-known performance definitions. Finally, the unified metrics are demonstrated through application to a conventional turbofan, a parallel-hybrid turbofan, a novel integrated-hybrid turbofan concept, and an entirely electrical fan concept.

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References

Figures

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Fig. 1

Enthalpy-entropy-diagram with generic propulsion system inlet and exhaust conditions with associated exergy values

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Fig. 2

Dual-spool unmixed flow turbofan station designations (according to Ref. [18])

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Fig. 3

Parallel hybrid core engine

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Fig. 4

Integrated hybrid core engine [19]

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Fig. 5

Comparison of concept-specific inner efficiency losses

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Fig. 6

Comparison of concept-specific availability efficiency, conversion efficiency, and inner efficiency

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