A Study On Flow And Heat Transfer In Piston Inner Cooling Gallery Of A Heavy Duty Diesel Engine

With the development of high duty,compact,lightweight of diesel engine,heat load problem of the key components of diesel engine is increasingly severe and sharp.Piston,as one of the key components of the diesel engine,has particularly serious heat problem,which can seriously affect the reliability and durability of diesel engines.Therefore,the problem of reducing the temperature field of the piston is particularly urgent.So the requirements of the piston cooling effect is also getting higher and higher.The method of forced oscillation cooling of inner cooling gallery in piston achieve a significant drop in the piston temperature by cooling oil with the piston reciprocating motion in the internal cold oil field oscillate intensely,and take away a lot of heat via the impacting of the inner cooler gallery wall.It is necessary to study the flow and heat transfer process of the internal cooling oil passage when the piston is injected and the oscillation is forced to be used as an effective means to reduce the working temperature of the piston.Forced oscillation cooling of inner cooling gallery in piston can reduce the working temperature of the piston.Thus,it is necessary to study the flow and heat transfer process in inner cooling gallery when pistons inject and oscillate cooling.In this paper,a supercharged diesel engine piston is used as the object of study,and the experimental study and numerical simulation of the temperature field of the original piston are carried out.On this basis,inner cooling gallery is added to the original machine,the cooling process of piston injection oscillation cooling is studied,and the temperature field distribution of the inner cooling gallery in piston is obtained.The main contents and conclusions are as follows:(1)The piston temperature field test-bed is built and tested under the declared working condition of diesel engine.The temperature of 25 key points of piston surface is measured by hardness plug temperature measurement.The test results showed that the maximum temperature of the top surface is 358 ?,which is close to combustion chamber throat,and the temperature of the measuring point is also thehighest temperature of the temperature field test.The temperature of the temperature measuring point which is close to the combustion chamber throat lap is higher than the temperature on the periphery.The temperature of the center of the combustion chamber is different from the temperature at the bottom of the combustion chamber.As the height of the piston side decreases,the temperature is gradually reduced.(2)The piston geometric entity is established and the piston calculation model is obtained by the meshing method.The initial thermal boundary condition of the piston is obtained by AVL-Boost simulation analysis and empirical formula.Based on the results of the piston temperature field test,the thermal boundary conditions of the piston surface were determined by keeping debugging.The results show that absolute error is less than 5% of the piston temperature field calculation results compared with its test results,which indicates that the model is established with certain accuracy.(3)The model of piston shaker cooling is established,and the calculation model is obtained by meshing.The influence of oil grid size,multi-phase flow model and turbulence model on the accuracy of piston CFD simulation results and the process of oil flows in the inner cooling gallery is investigated.The results show that the grid size is 1.0mm,multi-phase flow model is CLSVOF model and the turbulence model is Realizable k-? model,the calculation accuracy is the best.The movement trend of oil in the inner cooling gallery is the same,and the oil filling rate and the wall heat transfer coefficient in the inner cooling gallery are consistent with the change of crank angle under different parameter models.(4)Three different shapes of the inner cooling gallery are added in the original piston of diesel engine according to the design requirements of inner cooling gallery in piston.The influence of the shape and cross-sectional area of the inner cooling gallery on the cooling effect of the piston is analyzed.The results show that the shape of the inner cooling gallery has little effect on the temperature field of the piston.Under the same cross-sectional area,the contact area between the inner cooling gallery surface and the piston is bigger and the cooling effect is better.The cross-sectional area of the inner cooling gallery has a great influence on the cooling effect of the piston,and the cross-sectional area of inner cooling gallery and coolingeffect are not linear.