Friction model of a marine diesel engine piston assembly

In modern marine diesel engines, power output and in-cylinder firing pressures are constantly increasing, leading to higher friction in engine components and especially in the piston assembly. A good understanding of the friction contributions of the various engine components is needed, if mechanical efficiency is to be improved. A friction model for the engine piston assembly has been developed and is presented in this paper. The model, based on lubrication theory, considers the detailed engine geometry and the complete lubricant action, and thus can be applied to a wide range of engines. In detail, the analysis takes into account the friction components of compression rings, oil control rings, piston skirt and gudgeon pin of the engine piston assembly. The model was applied to a four-stroke (medium speed) marine diesel engine and the effect of engine speed and load on friction was examined and compared with results from other semi-empirical models. The engine friction was predicted at constant rotational speed (generator operation) and variable rotational speed (propulsion operation).