Abstract
An experimental study of the behaviour of the oil in an engine crankcase was undertaken using advanced optical measurement techniques. The first objective of the study was to investigate the mechanisms of crankcase oil film dispersal from the leak point on the side of the crankshaft webbing at the main journal bearing. The second objective was to study the windage effect upon the oil aeration in the sump. To achieve these aims, an idealised crankshaft test rig was designed using production engine components. It was mounted in a transparent viewing chamber and rotated at crankshaft speeds of up to 6,000 pm. High-speed photography, Phase Doppler Anemometry (PDA) and Particle Image Velocimetry (PIV) techniques were utilised in the investigation. The results showed that the oil flow behaviour varied with spatial location, throughout an individual rotation, from one cycle to the next and with crankshaft rotational speed. The distribution of oil particle diameter and velocities varied greatly between the front and rear of the crank web. The frequency of the ejected oil particles varied with angular position. The ejected particles formed a thick, broad film of oil on the inner surface of the shroud. The force of the induced air motion pushed oil clear of the surface of the baffled windage tray. Three break-up regimes were identified for speeds from idle to 1800, 4200 and 6000 rpm. The first regime was typified by ligament break-up. At greater speeds, discrete particles were observed as the ligaments became increasingly elongated and distorted. At the highest speeds, a fine aerosol of oil particles filled the crankcase. Measured particle diameters varied in the range of between 20 and 120 μm depending upon location within the crankcase. The maximum oil particle velocities were of the order of 25 m/s. Increased aeration of the surface of the sump oil, funnelling and foaming were also observed.