Multi-dimensional Flow Numerical Simulation Of Cooling System And Working Process Of Diesel Engine

Flow in diesel engine is the key problem in design all the time, of which the flow in cooling system and working process is the most important because flow and heat transfer in cooling system directly affect cooling efficiency of diesel engine, heat load of high temperature component, heat distribution and energy use in diesel engine, especially for high intensive multi-cylinder diesel engine, the cooling uniformity of each cylinder as well. While flow in working process directly affects charging efficiency, fuel mixing, burning, flame propagation, heat transfer, emission formation etc. So flow in diesel engine affects dynamic performance, fuel economy, burning noise and emission formation etc, moreover directly affects reliability and durability of diesel engine. In the research of diesel flow problem, some parameters can also be measured by instrument, however, it is due to the complicated construction of diesel engine that the related details cannot be obtained. In comparison with test that studying flow problem by using multi-dimensional numerical simulation cannot only greatly decrease research cost, save labor and material resource, shorten development period, but also get some data which is unmeasured by experiment and flow information in detail.Considering the importance of flow in diesel engine and the advantage of numerical simulation, in this paper flow problems both in cooling system and working process are simulated.Three-dimensional steady-state numerical simulation of flow and heat transfer in cooling system of an in-line six cylinders diesel is performed. Geometry model including whole six cylinder cooling system(cylinder block water jacket, cylinder head water jacket, oil cooler water jacket) is established which can reflect the performance of the whole cooling system. Meshes are built which mainly are uncontinuous, complete unconstructed hexahedron, partially unconstructed polyhedron, near wall boundary layer mesh is adopted which can fit complicated geometry surface of cooling system well and guarantee mesh quality, in addition partial refinement technology is used to make mesh better in some key location. Heat boundary condition, the temperature distribution of cylinder head, cylinder block and piston is calculated by a cylinder head-piston group-cylinder liner coupling heat transfer numerical simulation software and furthermore wall temperature distribution is obtained accurately. By numerical calculation the whole and partial flow field, pressure field distribution are presented, and as well as wall heat transfer coefficient, moreover cooling water fluxdistribution of each cylinder is obtained which can evaluate the design of whole cooling system.Multi-dimensional transient numerical simulation of flow in single cylinder working process of a 6110 diesel is performed. Geometry model including spiral inlet channel, offset combustion chamber, tangential exhaust channel, cylinder and intake and exhaust valve is established which involves the main part of the whole working process, the geometry and position of valve model is accurate. Meshes are built which mainly are uncontinuous, complete unconstructed hexahedron, including the moving mesh that is necessary for simulating the movement of valve and piston. Boundary conditions adopt both moving boundary and static boundary to deal with moving mesh, flow boundary condition adopts the outlet pressure of intake and exhaust channel, as for valve boundary regarding cylinder, valve and channel as one, namely the calculation domain is including the whole valve area and partial channel area and is solved by multi-dimensional method. Through multi-dimensional transient numerical simulation, gas flow field and pressure field distribution during inlet-compressure process, the influence of fuel injection to in-cylinder flow field, flow field distribution during discharging process are analyzed, in addition the influence of initial boundary condition to the whole calculation, especially to early intake process are analyzed too.Through multi-dimensional numerical simulation of flow in cooling system and working process of diesel engine, it cannot only provide theory for construction optimization of cooling system, intake channel, cylinder, combustion chamber and exhaust channel, but also provide guidance for setting the position of fuel injection nozzle, inlet delay angle, valve overlap angle. Consequently the type of diesel engine, construction and performance parameters would be optimized and the design method and theory research would enter into another new stage.