Boiling Heat Transfer Research On Bridge Zone In Water Jacket Of Gasoline Engine Cylinder Head

With the development of vehicle industry, it has become a necessary tool for people to travel. Engine is the core part of the vehicle, whose performance factors such as power and economical performance have very important effect. The requirements for the performance of engine have exigent, ensure that engine has a compact structure, meanwhile it can also output higher power. The improvement of engine power faces a very important problem, whose thermal load is high, the requirements for the performance of cooling system has exigent. In the development trend, the high temperature cooling is paid attention to by people, the traditional convective heat transfer is difficult to meet the requirements of the cooling system, high heat transfer capability of boiling heat transfer arouses people’s attention.In this paper, boiling heat transfer on bridge zone in water jacket of gasoline engine cylinder head is studied, the main research contents include that the bridge zone of cylinder head water jacket is simplified into a T-type duct, the influence factors of boiling heat transfer are analyzes through simulating T-type duct; the boiling experiment of cylinder head water jacket is finished, and observes coolant flow of the cylinder head water jacket under different rotational speed and measures temperature of engine measuring points; the simulation of flow filed and temperature field under the condition of considering the boiling is finished.The calculation formula of boiling heat transfer that is summarized by Chen is chose, simulate coolant boiling of water jacket through writing UDF(User-Define Function) program. In order to verify the accuracy of the simulation method, the paper establishes rectangular channel, whose size is the same with boiling experiment by Tao Bo, the calculation results are compared with the experimental data, and the results are in good agreement, so the method could simulate boiling heat transfer. Heat load is high in the bridge zone of cylinder head, and its structure is very complex, the paper simplifies the bridge zone into a T-type duct, FLUENT software is used to finish numerical simulation. The influence factors of boiling heat transfer are analyzed, such as coolant flow rate, pressure, temperature. When the engine works, it will produce vibration, research has shown that vibration can enhance heat transfer, engine vibration is regarded as harmonic vibration, harmonic vibration formula is written into vibration UDF, and combines with boiling UDF to analyze the effect of vibration on the boiling heat transfer.The paper finishes boiling experiment of the cylinder head water jacket. The innovation of this paper is that inserts endoscope in exhaust side of cylinder head, the flow of coolant in water jacket at different speeds is observed by the endoscope. Through observation, coolant occurs boiling at the 5500 r/min condition. Several measure points are set in cylinder head and cylinder block to finish temperature measurement. The temperature measurement can be used to evaluate the working condition of the engine cooling system, comparing with experimental data could analyze the accuracy of simulation results.The 5500r/min condition of engine is simulated through FLUENT software. First, the paper simplifies off small threaded hole and chamfering of engine. The engine model is divided into multiple parts for meshing. Then, the related boundary conditions are set, for temperature boundary conditions, GT-POWER is used to establish engine one-dimensional model, calculation results are imparted into FLUENT. Simulate flow field of water jacket in the first place, opens energy equation after convergence, simulates temperature field. The same measure points are obtained from the simulation results, compare with experimental data, have good agreement with the experimental results.