Improved load carrying capacity of crosshead bearings (measurement of oil film thickness using LIF method)

Abstract

The crosshead bearing in large two-stroke diesel engines operates under severe lubrication conditions, because hydrodynamic action is limited by low amplitude, low velocity oscillation under high unidirectional load. The recent trend towards more compact engines with increased output raises the bearing specific load, thereby causing the lubrication severity to increase significantly. Thus it is very important to improve the load carrying capacity of the crosshead bearing. In the present study, experiments using a dynamically loaded bearing test apparatus were carried out to clarify how the oil film characteristics could be improved. The oil film thickness was accurately measured using a laser induced fluorescence (LIF) method. The major results are : (1) A decrease in the clearance ratio is generally effective in enhancing squeeze action on the entirety of the bearing pads. When the clearance ratio becomes too low, however, the ability to form an adequate wedge film is degraded, thereby causing the oil film thickness to decrease; (2) Even when the bearing has a very low clearance ratio, because incorporating the taper geometry on both sides of the oil-groove promotes wedge action, a significant improvement in the oil film characteristics can be expected; and (3) The minimum oil film thickness becomes a maximum when using the taper geometry with a subtended length of 5 degrees and a taper angle of 0.1 degree.