The Research On Heat-fluid-solid Coupling And Structural Improvement Of Diesel Engine Cylinder Head

As the core components of the diesel engine, cylinder head is of the largest members to bear the load, and it is also a key part of the combustion chamber, its structure and shape are more complex. When the cylinder head works, it’s environment is severe, not only suffer the effects of high temperature by heat gas load, but also bear the stress from the bolt preload. Because of the heating effect and cooling effect on the cylinder head temperature gas coolant is not very uniform, which makes some of the high-temperature parts of the cylinder head can not be well cooled and cylinder head overheating phenomena occur, affecting its normal work. Therefore, the cylinder head were analyzed under mechanical and thermal loads to investigate the improvement measures have a very important practical significance. Therefore this theory in computational fluid mechanics, heat transfer theory, basic theory and thermal stress on the contact theory of multi-field coupling head finite element simulation. Firstly according ANSYS-CFX software combinations head and the coolant inside the research object to stream- solid coupling calculation based on the calculation results of the analysis of the temperature field and the distribution of the various parts of the flow field, for its cavity flow Road structural improvements to provide a reference. Secondly, carries on the cylinder head numerical simulation using the finite element method under different conditions, according to the results of the stress state in the cylinder head are analyzed under different conditions, and to determine the location of stress concentration, and then clear it at work situation. Finally, in different conditions of the finite element simulation results, discuss measures to improve its structure according to the cylinder head. Specific analysis of the implementation process and conclusions are as follows:(1)Using ANSYS-CFX software to the cylinder head and its internal coolant for the study were coupled fluid-structure calculations, and analysis of the impact of its various parts for the temperature field and flow field, the analysis shows that: Cylinder Head coolant in the coolant flow rate within the exhaust passage close to the lowest, the nose region of the exhaust passage, and exhaust passage of the exhaust gas temperature of the high temperature so that the temperature rise of the cylinder head here, not a reasonable cooling here will affect the normal operation of the cylinder head, and therefore should be close to the exhaust passage structure suitably modified to facilitate the flow velocity of the coolant is increased here, enhance the cooling effect here; exhaust passage and near the nose region of the the flow rate is too low, a small coolant flow, not a good way to cool the exhaust near the area, resulting in high temperature exhaust gas path at. The cylinder head coolant only near the surface near the cylinder head inlet firepower were cooled, and the cooling effect of the road near the fire near the surface of the exhaust is very poor, which would make the fire near the surface of the exhaust channel at high temperatures phenomenon.(2)By analyzing the stress field shows that: the cylinder head, the cylinder head bolt boss, cylinder head intake and exhaust tract nose firepower surface area, the cylinder head bolt holes at the bottom near the wall chamfer at the regional waterways and easily to cause stress concentration phenomenon.(3)According to the cylinder head in its raised edge at the bolt, the exhaust passage near the nose area, rounded at the cylinder head internal water chamber tends to cause stress concentration. Through different degree of influence in different details of its cylinder head, four corresponding proposed improved method, namely: to increase the diameter of the hole of the cylinder head Above the water hole reducing the thickness of the bottom surface of the cylinder head, increase the diameter of the hole cylinder head Above the water hole while reducing the thickness of the bottom surface, the bottom surface of the cylinder head machining relief groove in order to achieve the effect of strengthening the cylinder head cooling purposes and to reduce the stress concentration caused by fatigue failure and concluded as follows: increasing the diameter of the cylinder head and side by Above the water hole while the large diameter thinning head Above the water hole underside surface where the panel thickness of the cylinder head cooling firepower better; Above the water hole to increase the diameter of the hole so that the outlet of the flow rate of the exhaust tract nose at significantly increased; modification The average velocity impact Above the water hole diameter on the outlet of the flow rate of greater diameter modify Above the water Road to the average velocity of the exhaust nose at a greater impact, modify, Above the water hole diameter of the cooling water chamber intersection than great. Above the water hole while increasing hole diameter and the thickness of the bottom panel to reduce cylinder head, cylinder head can obviously make overall, head firepower surface, cylinder head exhaust ports and inlet temperature.