Michael Lang, Christian Bechter, Thomas Amann, Sebastian Schurl, Niko Bretterklieber, Raimund Almbauer

Research output: Chapter in Book/Report/Conference proceedingConference paperpeer-review


Within the wide range of possible waste heat recovery (WHR) technologies (cf. Feulner (2008)), the Rankine Cycle showed to be widely applicable and established on the market, but mainly for high power systems; if used for smaller applications, either efficiency or costs of the system are often not satisfying. This is mostly caused by the characteristics of the used expansion engine types, mainly being reciprocating piston engines or turbines. Whereas the first show good part load performance and are well suited for small power, they suffer from lubrication problems and life time issues. Turbines, on the other hand, are preferably used for high power and can do without elaborate lubrication, but suffer under part load conditions and are quite costly.

Especially for medium power systems, i.e. waste heat fluxes between 200 and 400 kW, a novel concept for the expansion engine within a Rankine steam cycle was conceived. The aim was to combine the advantages of reciprocating piston engines and of turbines at reasonable costs. The so-called rotational wing-piston expander uses two pivoting shafts, each holding two wing-like pistons, within one housing, that are performing a cyclic movement relative to one another. This way, four working chambers with varying volumes are resulting, each experiencing repetitive compression and expansion. The conversion of the cyclic changing angular velocity to a constant rotation at the output shaft is done via a non-circular gear. This solution offers the possibility of sealing the lubricated gearbox against the steam-flooded section containing the working chambers via rotational seals, being much easier than the sealing within a conventional reciprocating piston engine.

This paper starts with treating the design and layout of this novel expansion engine concept, followed by mechanics development. The strategy for creating a robust and effective expansion engine design as well as the most important findings and insights gained during the experimental investigations of the engine are shown.
Original languageEnglish
Title of host publicationProceedings of the 5th International Seminar on ORC Power Systems
PublisherThe National Technical University of Athens (NTUA)
Number of pages8
ISBN (Electronic)ISBN: 978-90-9032038-0
Publication statusPublished - 10 Sept 2019

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