Methodology for Piston Ring Oil Accumulation and Oil Film Separation 2022-01-5023

Investigating the oil transport mechanisms of a combustion engine is essential to decrease engine losses and optimize overall performance. As explained in [1] the amount of oil at predefined positions can be investigated by mixing the engine oil with a specific dye. Therefore, the technology of laser-induced fluorescence (LIF) is used. Fiber optics are assembled flush to the cylinder wall and give the possibility of inducing the dye locally by means of a laser. The emitted light intensity correlates with the amount of oil between the cylinder wall and piston ring. The oil film thickness of the piston ring running surface can therefore be determined for each crank angle (CA). However, the emission signal measured does not always correlate to the complete barrel shape of the piston ring. Major causes of this are the boundary conditions that define how much of the piston ring running surface is covered by oil and how the connection between the ring surface and residual oil film on the liner is shaped. In this regard, a methodology has been developed that is based on surface tension and energy minimization. This methodology does not only allow a proper accumulation of oil in the lead area but also a boundary condition for the oil separation in the trail area. As a result, the oil coverage of the piston ring can be determined based on the ring design, the amount of available oil, and general conditions such as engine speed and load.