The trend towards using turbochargers in various engines continues. In some applications, including engines of light duty trucks, city buses and even tractors and harvesters, the warranty of long life is demanded because turbochargers are subject to high cyclic loading and on consequence the turbochargers can determine the lifetime of the whole engine. The replacement of the aluminium compressor wheel for a titanium one significantly improves the turbocharger lifetime, but since a titanium alloy has about 60 % higher density than an aluminium alloy, the mass and the moments of inertia of the wheel increases, which further leads to changes in natural frequencies, rotor stability and power losses in bearings assuming the same bearing system as for the rotor with the aluminium wheel is employed. In this article the influence of the increased mass properties are discussed. AVL EXCITE and in-house developed model are used for the construction of Campbell diagrams and stability maps and for the obtaining of detailed information about the behaviour of the oil films in floating bearings.

The screw compressor inversion is carried out in cooperation of the university UWB in Pilsen with the firm ATMOS Chrast and OTH Amberg-Weiden (Bavaria-Czech Cooperation Project). ATMOS produces screw compressors flooded with oil, which, unlike non-oiled, where only bearings and gears between screws are lubricated, have a more thorough oil machinery. Its importance rises with the expander. The oil must be thoroughly separated from the working medium behind the expander, where it has lower pressure and temperature than in the expander input. Since the oil must return to the expander inlet, both parameters need to be increased by the oil pump and in the heat exchanger to the inlet level in order to prevent cooling of the working medium and hence efficiency reduction. This creates an auxiliary oil cycle in addition to the main cycle with organic medium (ORC). The inversion of the compressor to the expander is not only about turning the rotation of the screws and the direction of flow, but also about optimizing the shape of the screwing to achieve acceptable efficiency. This problem is solved by numerical simulation, the results will be verified experimentally. From a structural point of view, it is necessary to solve a number of details that will prevent the unacceptable release of working organic media into the environment. This applies mainly to the expander and the circulation pump, where shaft seals cannot completely prevent leakage of liquid or gaseous phase of organic matter. An important design task is the perfect filtration of the lubricating oil from organic liquid substance. The cyclone commonly used here must be supplemented with another fine filter equipped with scavenge line. There is also a problem with the research facility how to manage electricity produced by the electrodynamic brake of the order of 100kW. It can either be returned to the power grid (expensive investment) or to the electric boiler of the organic cycle, or liquidated in resistive coils by heat conversion.

This paper aims at creating a mathematical model of a bending oscillation rotor system which enables to execute a dynamical analysis of its vibration including the influence of nonlinear bearing characteristics. More specifically, using the finite element method the model of rotating system supported by four hydrodynamic bearings was created. The basic dynamical analysis of the rotor system was performed and the eigenvalues, eigenvectors and stability conditions were evaluated.

This article describes the results of a project whose task is to research and develop a screw expander through the inversion of a screw compressor. The article summarizes aspects of the construction of an experimental device that works with an oil-flooded air screw expander. The expander was subjected to experimental and numerical analysis, the results of which are presented in the article. Numerical analysis to examine the expansion process is performed both on the basis of the analytical geometric description of the working chamber of the expander and on the basis of the geometry obtained from a 3D scan of a real machine. The results of experimental and numerical analysis will be used to integrate an oil-flooded screw expander into an energy unit for the use of low-potential heat, for example in ORC systems.