Impact of oil-water emulsions on lubrication performance of ship stern bearings

During maritime operations, extreme events such as explosions, grounding, and seal failures can cause water ingress into lubricant compartments, forming oil-water emulsions that significantly affect the lubrication performance of ship stern bearings. Existing studies mainly focus on low water content, with limited exploration of the impact of high water content on lubrication performance. To address this gap, viscosity measurements of oil-water mixtures were conducted, and an emulsification viscosity equation applicable to varying water contents was derived. A thermal elastohydrodynamic lubrication model for stern bearings, incorporating rough surface contact and emulsification viscosity, was developed. Numerical results reveal two flow regimes of oil-water mixtures-water-in-oil (W/O) and oil-in-water (O/W)-each exhibiting distinct lubrication behaviors. In the high-viscosity W/O regime, water contamination increases lubricant viscosity, raises minimum oil film thickness, and lifts the journal, but significantly increases the friction coefficient and power consumption. The high specific heat capacity of water mitigates the temperature rise caused by increased viscosity. In the low-viscosity O/W regime, the mixture shows lower temperature rise and friction power under high-speed light-load conditions. However, under low-speed heavy-load conditions, the lubrication transitions to the boundary regime, leading to sharp increases in friction and temperature detrimental to bearing performance. This study highlights the critical influence of water content in oil-water emulsions on stern bearing lubrication, providing valuable insights for improving bearing design and operational reliability.