CFD Analysis On Engine Cooling-Water Jacket And Cylinder-Head Heat Transfer

With the improvements of engine performance target and strength, the engine cooling system has become very important link in engine design, it's cooling department can have a direct impact on the engine work reliability and economy. As the important component of an engine, cylinder head has a complex structure, and endures high heat and mechanical loads in the process of engine working. It is easy to cause local overheat at the region where has a uneven or insufficient cooling, and give birth to crack under the high and low frequency thermal impact which can make the cylinder head invalid. Therefore the reasonable design engine cooling system can ensure its cooling effect and effectively improve the engine's efficiency and service life. As one important method of guiding engine cooling system design, CFD technology has high practical value and obtained the rapid development in recent years because of it's strong pertinence, short design cycle and high precision. This paper selects a gasoline engine as the research object, and establishes its precise 3d model in three-dimensional software UG, then conduct proper simplification and extract the cooling-jacket model on the basis of it. Import the cooling-jacket model with CATIA-v4 format to ICEM CFD, then establish a high quality hybrid grid through geometric topology, edit mesh. Then simulate and analyze it with ANSYS Fluent. The Velocity vector, temperature, heat transfer coefficient and pressure distribution, etc in the water jacket are obtained and evaluated. CFD analysis of the original water jacket shows that there exists stagnation zones in bottom zone of the third and fourth cylinders of cooling jacket. Firepower zone of 1st and 2nd head-cylinders of cooling jacket exist high temperature due to low flow and small heat transfer coefficient. Then improvement ideas are put forward according to the problem of cooling on the basis of analysis result and make best improvement scheme which can meet the cooling requirements to optimize engine cooling system. According to the CFD results comparison, the stagnation zones in bottom zone of the third and fourth cylinders of cooling jacket were improved obviously, the temperature of firepower zone of 1st and 2nd head-cylinders of cooling jacket were decreased, and uniformity of the cylinder head temperature is improved considerably.On the basis of numerical simulation of engine cooling-jacket, obtain the convective heat coefficient values. Then the temperature field of cylinder head is obtained. Compared with the original model, the highest temperature of bridge zones of cylinder head fire-face reduced by 7℃, and the results testified the cooling effect of the improved design.