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Proposing Institution

Lehrstuhl für Aerodynamik, TU München
Project Manager

Dr.-Ing. Steffen Schmidt
Boltzmannstr. 15
85748 Garching
Modern common rail injection systems exceed operating pressures of more than 2000 bar, with the aim to improve fuel injection efficiency and meet demanding emission standards. However, huge pressure drops cause the working fluid to cavitate. Cavitation is a phenomenon that occurs when the local static pressure in a liquid drops below the vapor pressure, resulting in the formation of vapor cavities. Vapor cavities are usually unstable, and after reaching a region with an increased pressure, they violently collapse – nearly constant vapor pressure in the cavity provides virtually no resistance to the surrounding liquid that accelerates towards its center. At the final collapse stage, pressure peaks with magnitudes of several GPa can be reached, and strong shock waves are emitted through the liquid. If those collapses occur in the vicinity of a solid wall, material can be removed from the surface, changing in this way the initial design. Cavitation erosion can thus severely affect engine performance, or even lead to the complete mechanical failure of an injector. However, in injection nozzles or discharge throttles, cavitation is inevitable. For theformer, it enhances spray mixing, whereas for the latter, it ensures constant mass flux and enables precise sequencing and fuel injection. The main focus of this project are instationary flow mechanisms in discharge throttles and injection nozzles for diesel applications and their connection to cavitation erosion. In the open literature there are no publications taking into the account the influence of turbulence and gas content on the cavity dynamics and accompanied erosion process under realistic operating conditions. In order to improve performance of diesel engines and to fulfill future emission legislations, profound knowledge of these aspects has to be gathered. Since experimental investigations at real operation conditions are rather limited, high fidelity numerical simulations are ideally suited for answering those questions.

Impressum, Conny Wendler