Research On Heat Transfer Of Cylinder Head For 4-cylinder Diesel Engine

With the development of diesel engine, the heat transfer and thermal loading of cylinder head is of great importance increasingly. 4-cylinder diesel engine is researched from the perspective of project application in this paper,all-sided research is made around the heat transfer of cylinder head for diesel engine. The FEA (Finite element analysis) model of cylinder head, combustion computing model and coolant jacket model are set up, heat transfer coefficient(HTC) and Temperature of combustion gas side can be obtained by gas-solid coupled analysis method, respective head boundary condition is provided by liquid-solid coupled analysis method, preprocessor and postprocessor software is used and calculation program is writed, the temperature field and heat stress field of cylinder head is evaluated for each simulation model. The calculation results with different boundary for coolant jacket side and combustion gas side are compared , primary research is made for taking into account the boiling how to influence the HTC of coolant side.Using Flowmaster2 software, perfonn 1-D cooling computation analysis for the whole cooling system of diesel engine and together with combining the VB program language of excel software to to analyze its matching situation and finally the parameter's matching reaches reasonable.The dissertation is divided into seven chapters, briefed as follow:Review the engine coolant jacket's research work at home and abroad which place an extremely importance role in the heat transfer of cylinder head and the development of CFD (computational fluid dynamics) software technology, introduce CFD and FEA business software, and propose the main research work in this essay. Aim to the heat transfer of cylinder head's research work at home now, the coolant jacket is given emphasis to research by CFD analysis method, the temperature analysis of cylinder head is realized by liquid-solid coupled analysis.Introduce the CFD analyzing process of diesel engine coolant jacket, which includes the establishment of 3-D geometric analysis model, the division of computing gridding, the selection of fluid dynamics governing equations and turbulence and its computation approaches, and after defining the physical models, computing approaches and boundary conditions, obtain a result, which is treated after being converged, and then assess computing results.Make a detail analysis about the 4-cylinder diesel engine coolant jacket. Analyze the cooling fluid flowing and cooling characteristics according to flux distribution, temperature distribution, HTC and pressure loss. According to the velocity field, identify the stagnation area and the area with velocity of big difference; according to temperature distribution, analyze the possible bubble location caused by boiling; according to HTC distribution, assess the cooling performance of coolant jacket; according to pressure distribution, display the area with the most loss. And through the brief fluid field test observe the flow at the top of cylinder head and compare with the CFD results.According to the CFD calculation results, propose all kinds of improved schemes, which includes: changing the cylinder fluid's lengthwise flowing into transverse flowing,and improving the diameter of water hole in each gasket to reach a better evener. Finally computing and comparing each improved schemes through CFD analysis means to find out the relative reasonable one.Heat release characteristics being used in calculation is calibrated by using exist performace test results, OD calculation is made to provide boundary condition for FEA calculation and 3D combustion calculation.3D combustion calculation model is set up for combustion calculation, and gas-solid coupled analysis is made to provide more actual heat boundary for gas side of cylinder head. CFD calculation is made for cylinder head coolant jacket if boiling is taken into account or not, thus different heat boundary of coolant jacket side is provided for cylinder head temperature field analysis, the first time temperature calculation is made.Wall temperature of coolant jacket which is obtained by FEA analysis in each case is made as real wall boundary of further CFD calculation, more actual heat boundary of coolant side are mapped,real Liquid-Solid Coupled analysis is realized, the temperature field of cylinder head is further assessed. The computed results show that it is the smallest between the test results and calculation results which is obtained by Liquid-Solid Coupled analysis On the base of the research method, the same Liquid-Solid Coupled analysis is made for the improved scheme, its temperature and heat stress are obtained and validated by the test of boiloff of engine to realize the goal of settling the heat crack fault of cylinder head.At last, to get the total evaluation of cooling system, the author uses the analysis result of 3D CFD as boundary conditions, and use Flowmaster2 software for 1D computation of cooling system, and together with combining the VB program language of excel software to assess the matching condition of whole cooling system so as to determine the reasonable parameters of fan, water pump and radiator.