Study on cylinder liner hot deformation of turbocharged inter-cooled diesel engine

Abstract: Deformation of the cylinder liners, which was caused by inhomogeneous mechanical and thermal loads, mainly affects the performances of sealing, lubrication and wearing between piston assembly, and the cylinder liners and emission performance. It is significantly important for reducing oil consumption, oil emissions, and improving friction properties to control cylinder liner deformation and out-of-roundness. The characteristics of deformation caused by mechanical load was researched in the author's previous work. Therefore, there is a need to find out the distortion of liner caused by thermal load. In the present study, a coupled heat transfer model of the cylinder heads, the cooling water jacket, the cylinder liners, and the engine body of four cylinders, in-line, water cooling, turbocharged inter-cooled diesel engine was established by using the fluid-solid coupling heat transfer method. In this model, the external boundary conditions, which are difficult to determine on the fluid and solid contact faces, were translated into internal boundary conditions. The heat transfer in the solid and fluid was coupled by coupling the surfaces of the solid and fluid. Thus, the expected results of temperature distribution and coolant flow can be computed. The flow characteristics of coolant and the key point temperatures of the cylinder liners and cylinder heads were tested to correct the boundary conditions of flow and heat transfer. On the basis of correctional boundary conditions of heat transfer, the flow characteristics in the water jacket and heat transfer in the cylinder liners and cylinder heads were analyzed. Then, the steady-state heat transfer temperature distribution and the characteristics of thermal deformation of the cylinder liners were obtained.The results indicate that the coolant flow and cooling are uneven due to the difference of water jackets for each cylinder. The flow velocity is gradually reduced from the first to the fourth cylinder, and the temperature is gradually increased. The temperature of the exhaust side is higher than that of the intake side. The temperature distribution of each cylinder liner is uneven because of inhomogeneous coolant flow and thermal load. The temperature of the top of the cylinder liners, which is located between two adjacent cylinders, is higher than the other parts of cylinder liner (the highest temperature is 195℃, which is located at the top of the third and fourth cylinder liners). Temperature gradually decreases from the top to the bottom of the cylinder liners. The temperature at the top of the liners, which has contact with the bodies, is high, and the temperature gradient is large. The temperature gradient decreases in the middle area of the liners surrounded by coolant. The temperature and gradient at the bottom area of the liners for each cylinder liner, which is located under the bottom dead center of the pistons, are similar. The synthetic thermal deformation of each cylinder liner is not uniform; deformations of the first and the fourth cylinder liner are larger. The maximum expansion of hot deformation is 0.216mm and located at 90° of the fourth cylinder on the flywheel end. The largest shrinkage deformation is -0.131mm and located in between the first and second cylinder. The trend of deformation at the radial section of the liners is different from the trend of synthetic deformation. The middle area of the liners, surrounded by coolant, mainly presents expansion deformation. Expansion deformation of the top and bottom of each liner, constrained by the body, is smaller. Each cylinder shows inhomogeneous radial deformation, which is just like the shape of a pea, and there is a symmetry between the second and the third cylinders, and between the first and the fourth cylinders respectively. Deformation of main and minor thrust face for each cylinder liner is relatively less, and the difference of deformation of each liner is also smaller.