Process Of Boiling Heat Transfer In Engine Jacket And Stress Analysis Of Cylinder Head

In recent years,the heavy-duty internal combustion(IC)engine has been hit by the pressure of the market and the environment.Its rising power is getting higher,and the emission requirements are becoming stricter.In addition,advanced technologies such as high turbocharged,ultra-high pressure injection and precision intelligent control are the wide application has led to higher thermal loads of cylinder heads,resulting in cracking damage.Subcooled boiling heat transfer is gradually applied to the IC engines due to its high heat exchange efficiency.Compared with the traditional IC engine cooling,the subcooled boiling heat transfer can promote the uniform distribution of temperature,reduce the thermal stress of the cylinder head,improve the durability of the components,and prevent component failure.However,the development of subcooled boiling heat transfer in the IC engine is not mature.If the boiling control is not good,it will easily form excessive boiling,and cause damage to key components.In order to clarify the heat transfer characteristics of the boiling in the IC engine,and effectively utilize and control the subcooled boiling heat transfer process in the cylinder head to explore the subcooling use experiments and simulation calculations in a simple channel.And then to explore the subcool boiling heat transfer characteristics in the actual IC engine and its influence on the temperature field and stress field distribution of the cylinder head.The boiling test platform for heating the bottom of the rectangular section is designed to simulate the cooling passage of the cylinder head.The cooling system cooling parameters and operating conditions are simulated by adjusting the channel structure size,pressure,bottom side heating power and cooling medium type,flow speed and temperature.The temperature of the heating block was measured by thermocouple,and the influence of the above parameter changes on the surface temperature,the wall heat transfer heat flow and the flow boiling heat transfer characteristics were discussed.The superimposed Chen model is corrected and verified based on the experimental data.A transparent model of a high-power diesel engine is made by using acrylic materials in proportion,a high-speed camera is used to shoot the flow of key parts of the cylinder head,and MATLAB programming is used to digitally process the captured image to obtain the flow field distribution of key parts such as the nose cover of the cylinder head.CFD was used to calculate the flow field distribution in the cooling channel,and the calculated velocity value of the feature position was compared with the characteristic position velocity value measured by high-speed photography.The calculation model is used to calculate the flow field in the cooling water chamber of the actual IC engine by using the boundary condition of the water chamber wall surface of the actual IC engine and the corresponding operating conditions.A diesel engine test bench was retrofitted to achieve temperature measurement of the cylinder head and visualization of flow boiling in the cooling passage.The thermocouple was machined at a distance of 3 mm and 8 mm from the fire side,and the temperature in the nose of the cylinder head were measured.The high-speed camera is used to capture the boiling phenomenon in the water chamber through the endoscope,and the captured image is digitally imaged to obtain an average void ratio.Under different operating conditions of IC engine,the effects of cooling water temperature,flow rate change and pressure change of cooling circulation system on cylinder head temperature distribution and average void ratio were studied.Based on the simulation and experimental measurement of the one-dimensional working process of the IC engine,the fluid in the cylinder head and the fluid in the cooling water chamber are directly coupled to the solid-liquid,and the combustion cycle in the cylinder is sequentially coupled with the solid-liquid region of the cylinder head to establish the gas-solid-liquid three-phase coupling simulation model.The single-phase flow convection heat transfer,the single-phase flow boiling heat transfer and the two-phase flow boiling heat transfer model are respectively embedded in the fluid-solid coupling calculation of the cylinder head and the water chamber,and the calculated temperature values are compared with the experimental measurements.Find the most accurate heat transfer model in the cooling water chamber.The temperature distribution of the cylinder head is calculated by using the more accurate flow heat transfer model.Based on the calculation results,Abaqus is used to analyze the stress of the cylinder head to find out the position where the maximum stress is and the stress distribution of the cylinder head.The influence of cooling water temperature,cooling system pressure and flow velocity on the stress distribution of cylinder head is further discussed,and the most reliable way to utilize and control the subcooled boiling process in cylinder head is found to effectively improve the stress distribution of cylinder head.