A New Cavitation Algorithm to Support the Interpretation of LIF Measurements of Piston Rings 2020-01-1091
To investigate oil transport mechanisms under real engine conditions, laser induced fluorescence (LIF) is used. The engine oil is mixed with a dye that can be induced by a laser. The emitted light intensity from the dye correlates with the residual oil at the sensor position and resulting oil film thicknesses can be determined in high detail for each crank angle. However, the general expectation is not always achieved, e.g. an exact representation of piston ring barrel shapes. In order to investigate the responsible lubrication effects of this behavior, a new cavitation algorithm for the Reynolds equation has been developed. The solution retains the mass conservation and does not use any switch function in its mathematical approach. In contrast to common approaches, no vapor-liquid ratio is used, but one or several bigger bubbles are approximated, as have been observed in other experiments already. As a result, not only the known boundary conditions for the Reynolds equation become unnecessary, but the solution also gives a clearer idea about the shape of the cavitation bubble. The combination of simulated oil film thicknesses, the resulting cavitation bubbles and the fixed field of view from the LIF-sensor allows a reproduction of the measurement signal. The comparison of measurement and simulation shows a high correlation and thus enables a deeper knowledge and understanding about the real conditions inside a combustion engine. On the other hand, it can be seen, that effects such as a decrease of LIF-signal in the cavitation area is much less than what is expected in the literature.
Fabian H. Ruch, Georg Wachtmeister
Technical University of Munich / Tenneco