| With the continuous improvement of the internal combustion engine,as key components of high-power diesel engines,piston are belonging to high thermal loads bearing during operation.It needs to be effectively cooled and the heat load reduced to ensure the normal operation of marine diesel engines.In order to improve the heat transfer performance of the dual-cavity internal cooling gallery in high-power diesel engine pistons,and to reveal the oscillation-enhanced cooling mechanism in the internal cooling gallery,the author uses a combination of numerical simulation and visualization experiments.The main research contents and conclusions are as follows:Based on the three-dimensional model of the actual cooling gallery in the piston and the boundary conditions,a CFD model for oscillating cooling in the cooling gallery was established,and the numerical simulation method in this paper was explained.At the same time,a ZD270 piston oscillation cooling test stand with a height similar to that of a singlecylinder diesel engine was designed and built.The test stand was used to visually study the piston oscillation,and the oscillation flow image of the lubricating oil in the transparent piston was obtained,which was in good agreement with the numerical simulation.A series of model for changing the inlet area were calculated,and the optimization method of the cooling gallery in the piston was gradually found.According to the optimization direction of "multiple-in,multiple-out",through a series of univariate factor calculations,the best solution for greatly improving the heat transfer performance of the internal cooling gallery was obtained.The results show that the improved internal cooling cavity wall heat transfer coefficient is increased by 24% as a whole,and the optimization of the oscillation cooling capacity of a large marine diesel engine is completed.Finally,the oscillation-enhanced cooling mechanism of the double-chamber internal cooling chamber was studied,the oscillation cooling process was decomposed and analyzed,the specific composition of the convective heat transfer coefficient in the piston oscillation cooling was studied in detail,the influence of import and export flow rate,lubricant filling rate on heat transfer coefficient was revealed.Based on the data analysis of the calculation results,based on the convective heat transfer theory,a method for decomposing the convective heat transfer coefficient is proposed,which is convenient for quantifying the oscillating enhanced heat transfer and analyzing its influence laws.It has guiding significance for the structural optimization of the cooling gallery in the piston in the future. |
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