Development of a near-wall heat transfer model accounting for lubricating oil film effects in high-intensity marine diesel engines

Accurate prediction of wall heat transfer is critical for the reliability design of high-intensity marine engines, yet conventional models often neglect the thermal resistance introduced by lubricating oil films and the influence of near-wall turbulent heat transfer characteristics. To improve the engineering prediction capability of existing approaches, this study develops an engineering-oriented extension of the classical O'Rourke and Amsden wall heat-transfer model by incorporating two practical modifications: (1) coupling the thermal resistance of thin lubricating oil films on the piston, cylinder liner, and cylinder head surfaces, and (2) introducing a variable turbulent Prandtl number (Pr t ) that dynamically adapts to changes in the dimensionless wall distance (y+). The extended model is validated against experimental measurements under different operating conditions of a medium-speed, high-intensity marine diesel engine. Results demonstrate that the improved model enhances prediction accuracy, reducing the errors in peak in-cylinder pressure and heat transfer loss to 0.94% and 0.79%, respectively. Comparative analysis indicates that the lubricating oil film functions as an additional thermal resistance layer, reducing heat flux, while the variable Pr t provides a more accurate representation of near-wall thermal diffusion behavior. Furthermore, the model predicts that increasing oil film thickness from 2 μm to 5 μm leads to a non-monotonic variation in heat transfer, and that overload operation with higher injection pressure improves combustion performance but increases the piston heat transfer contribution to 49.2%. This study provides a validated engineering-oriented wall heat transfer model that offers a practical tool for thermal management and performance optimization of high-intensity marine engines. Further validation across different engine configurations is required to assess its broader applicability.