Thermal Fluid-structure Coupling Analysis Of Cylinder Head And Cylinder Liner Of Dual-fuel Low Speed Engine

Dual-fuel engines using natural gas and diesel can significantly reduce harmful emissions,which is an important measure for reducing emissions for marine diesel engines.Due to its higher combustion temperature and explosion pressure,dual fuel engines need to analyze its structural strength and operational reliability.The cooling and in-cylinder combustion of the dual-fuel engine have an important influence on the temperature distribution of the heated parts,and the temperature distribution has a decisive influence on the thermal stress and reliability of the structure.In this paper,a dual fuel low speed engine is simulated by thermo-fluid coupling simulation.The temperature field and stress field are analyzed in detail.At the same time,the deformation discipline of the inner wall of cylinder liner was studied,which provided a certain theoretical basis for the control of cylinder liner deformation.Firstly,the fluid calculation area and the solid calculation area were determined according to the three-dimensional numerical model file.A flow field calculation grid for cylinder liner,cylinder head and exhaust valve housing,and a finite element calculation grid for more than 20 heated components were generated.The CFD analysis was performed on the complex cooling flow field,and the initial heat transfer boundary conditions at the junction of the cooling water and the wall were obtained.According to the heat transfer boundary conditions on the cooling side and the combustion side,the finite element model was used to calculate the temperature field,and the distribution of the temperature field of the whole machine was obtained by thermal fluid-structure coupling.The analysis results show that the temperature distribution of the combustion chamber parts is relatively reasonable.Based on the analysis of the temperature field,the deformation and stress of the dual-fuel engine under the mechanical load,thermal load and thermo-mechanical coupling conditions were further analyzed.The cylinder liner deformation is critical to the operation of the piston-cylinder friction pair,axial and radial deformations under different loading conditions were analyzed.The calculation results show that the factors affecting the stress and deformation of the cylinder head and cylinder liner are: heat load>gas pressure>bolt pre-tightening force,and the thermal stress is larger at the location where the temperature gradient is larger,and the overall stress of the cylinder head is greater than the cylinder liner.The deformation of the cylinder head mainly occurs at the position of contact with the gasket and bolt.The axial deformation of the liner inner wall surface is generally cup-shaped,expanding outward in the area of the cooling jacket,and shrinking in the low portion.The radial deformation is slightly larger in the axial direction of the crankshaft,and the structural rigidity is relatively weak.In summary,the calculation of the thermal fluid-structure coupling of the heated parts of the dual-fuel engine cylinder head and cylinder liner can obtain the accurate temperature field and stress deformation distribution,which can provide the basis for the structural design and improvement of the dual-fuel engine.