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The paper has explored the solutions to the thermal overload in the cylinder head of a heavy-duty vehicle 6-cylinder diesel engine and the thermal cracks in the valve-bridge of the engine. The experiments include measuring the temperature of the cylinder head bottom and testing the flow distribution of coolant through the upper nozzles of cylinder head bottom. The follow-up analysis was conducted on the causes of the excessive thermal load of the cylinder head bottom, the thermal cracks in the valve-bridge region, and the rationality of the structure of the water jacket for the cylinder head. The mechanism of the water jacket of cylinder head was further inquired. Then 3-D CFD numerical simulation of water jacket in the sixth cylinder, which is in the worst cooling condition, is performed. To enhance the flow form in water jacket and lower the cost of enhancement, we proposed 4 schemes of water jacket and conducted the numerical simulations to these schemes. It was identified that all these schemes have efficiently improved the flow field in water jacket. In the typical proposed scheme 1 in which 6 nozzles of all the 10 upper nozzles were blocked, the coolant flow rate on the bottom of the water jacket and in the cylinder head valve-bridge region increased by about 68.73%. The measuring results of the cylinder head bottom temperature show that the maximum temperature in the valve-bridge region of cylinder head is reduced by 9.2 °C and the temperature gradient reduction is 19.55 percent, suggesting that the thermal load and thermal stress of the studied diesel engine cylinder head has been significantly lowered.

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Application of super elasticity theory and nonlinear theory, based on finite element method and the Abaqus software, the performance of Y ring rubber seal, such as the Von Mises stress, the sealing ring deformation and the contact pressure were simulated and analyzed under the influence of changeable hydraulic pressure. According to seal failure criterion, the effect of hydraulic pressure changes on the sealing performance were studied. Results show that, the maximum stress appears in the intersection of lips, the largest deformation area near the inner lip. The root has greater contact pressure, which would result in bitten phenomenon or aggravate wear.