The Application Of CFD In Designing Multi-cylinder Diesel Engine Cooling System

The cooling medium's three-dimension flow in cooling system of diesel engine directly influences the cooling efficiency of diesel engine, thermal load of high temperature components, heat distribution and energy utilization of diesel engine, especially to the high intensified multi-cylinder diesel engine, it also influences cooling uniformity of each cylinder, which is not only concerned with power performance and fuel economy of diesel, but also with reliability and durability of diesel, so the cooling medium's three-dimension flow is always the focus of diesel design. Test research and numerical simulation are available for cooling system flow research of diesel engine. As the structure of multi-cylinder diesel cooling system is complex and closed in the inside of engine block, also the mechanism of cooling medium flow is complicated, it is hard to test and research the three-dimension flow and heat transfer in cooling fluid jacket, also the detail information of three-dimension flow is not easy to obtain with test. Recently, with the development of computer and computational fluid dynamics (CFD), three-dimension flow numerical simulation of diesel cooling system applies widely, especially when optimization design diesel cooling system. This paper optimization designed the cooling system of the CA6DE series diesel engine by using of CFD software STAR-CD and proved the validity and veracity of numerical simulation through test.Geometry model includes the whole cooling system (cylinder block water-jacket, cylinder head water jacket, oil cooler water-jacket, etc.) in research of cooling system flow and heat transfer, which is capable of reflecting the performance of whole cooling system. With discontinuous unstructured calculation grid for body model and body fitted anisotropic mesh for wall model, the geometry surfaces of cooling system are fitted well and the grid quality was also guaranteed farther. The method of locally adding mesh density was applied to improve the grid of important area. Thermal boundary conditions was available and the temperature distribution of the cylinder block, cylinder head, piston were also calculated by cylinder head- piston assembly-cylinder liner coupling heat transfer numerical simulation software, thereby the wall temperature was more accurately calculated. The cooling water flow assignment of each cylinder, the whole and partial flow field and pressure field and the wall heat transfer coefficient assignment were available by CFD numerical simulation, and then evaluated the designing effect of the whole cooling system.The designs defects were discovered and improve projects were put forward by three-dimension numerical simulating and researching to the diesel engine. Results showed that cooling effect was more uniform of each cylinder after improved; triangle region flow velocity increased a lot and was more uniform; the dead time at the bottom of cylinder block water-jacket was disappeared, which made the formation of steam ballonet impossible; top flow field velocity increased largely and formed circle flow, which met design require. Thus it can be seen by method of three-dimension numerical simulation it is well evaluated the advantage of improvement design to multi-cylinder diesel cooling system and proved the practicability of design project, as well as discovered the problem of structures after improvement designing.At last, this paper proved the validity and veracity of numerical simulation through test.With the applications of three-dimension numerical simulation to optimizing designsmulti-cylinder diesel cooling system, improvement design evaluation, structure parameters and performance are available, which lead the design method and theory to a new development stages.