For some time now, the research area Design has been dealing with systems for the recuperation of engine waste heat in the commercial vehicle sector. Until now, the main focus has been on the layout, simulation and design of expansion engines for use in mobile Clausius-Rankine steam cycles (Fig. 1). In the course of these activities, various reciprocating piston steam expanders were brought up to prototype status, but their function could not be tested in-house due to the lack of an appropriate test facility.

The aim of this project, entitled "Construction and operation of a hot steam test bench", is to set up a test facility for various components of a steam cycle for the waste heat recovery of commercial vehicle engines.

In the intention of reducing complexity and concentrating on the circuit components to be tested, the heat source, which is provided in real vehicle operation by the exhaust gas of the combustion engine, is electrically represented in the test. Instead of the exhaust gas mass flow, air is thus heated, which in turn evaporates the operating medium via heat exchangers.

The steam cycle is modular in design to provide maximum flexibility and to examine not only the expansion engine but also many other cycle components such as evaporator, pump, valves or switching elements.

Due to the large number of working media under discussion for ORC systems, the test bench is designed for operation with both water and organic media (e.g. refrigerants and alcohols), which is associated with additional expenditure in terms of safety. A 4-quadrant brake and indexing systems are available for measuring expansion engines.