Study On Oscillating Cooling Effect Of High Intensified Piston Inner Cooling Cavity

Piston is one of the important parts of a diesel engine.When the piston is subjected to a large mechanical load,the top surface is also heated by the high temperature gas,and the high thermal load makes it become one of the most fault parts in the engine.If the piston temperature is too high,problems such as stuck fault of piston rings,lubricating oil coking,over local deformation or fracture of the pistons may occur,so cooling operation is needed for the piston.Cooling characteristic for piston is one of the key factors that affect the durability,reliability and economy of the engine.Therefore,the oscillation cooling characteristics of the closed oil cooling gallery of the piston are studied in this paper.Numerical simulation of oscillation cooling process of the internal oil cooling gallery is carried out by using the dynamic mesh technology and VOF multiphase flow model in the software FLUENT.The oscillation cooling effect of three kinds of inner oil cooling gallery,whose cross sections are circle,oval and water drop shapes,is respectively simulated under different crank angle,speed and stroke conditions.The simulation results show that the average heat transfer coefficient of the water drop shaped oil cooling gallery is the largest,and the cooling effect is the best.The transient oscillation flow and average surface heat transfer coefficient of oil in water drop shaped gallery were studied by numerical simulation,and the relationship between the heat transfer coefficient and the crank angle was obtained.The influence of rotating speed,stroke and oil filling rate on the oscillating cooling effect was studied.The relationships between the surface heat transfer coefficient and the speed,stroke and oil filling rate were obtained.Finally,the orthogonal design analysis of speed,stroke and oil filling rate is carried out,and the range analysis of the orthogonal test results is carried out.Through orthogonal analysis,the influence degrees of the three parameters for the cooling effect are determined,and the best design scheme is obtained.Taking the cooling effect as the goal and also considering the economic and safety conditions,the optimum oil filling rate is 20%,and the shape of the oil gallery should be slender.This design method can reduce fuel consumption and guarantee higher oscillation cooling effect.The related research in this paper provides the basis for the optimization design of the piston inner oil cooling gallery.