Evaporation of an oil film is of critical importance in direct injection gasoline engines as it affects the particulate emissions. During operation, a thin film of engine lubricant is created at the cylinder wall, and its evaporation is, among other factors, sensitive to flow velocity in the piston and turbulence characteristics. The present work aims to characterize the effects of turbulence on the evaporation rate of a multicomponent liquid film, i.e., the oil film. Tests are performed in a channel where an oil film is deposited on a controlled sample (figure 12). The oil film is heated by a combination of cartridge and radiant heaters. Particle Image Velocimetry (PIV) and hot-wire anemometry are used to characterize the flow over the film sample. Grids with different characteristics are used to change the turbulence intensity and characteristics of the incoming flow. The results of this study will lead to a semi-empirical model for predicting evaporation rate of an oil film under engine conditions as a function of different turbulence intensities, inflow velocities, temperature, and film thicknesses.
Figure 12. Representative schematic of cylinder conditions and evaporation meachanisms of oil film shown with experimental setup.