A Study Of Heat Transfer Characteristics About Piston Oil Gallery Of Diesel Engine

The piston is one of the important parts of internal combustion. In addition to great mechanical load, its top surface supports periodic heating effect by high temperature gas so that piston becomes one of the most fault parts in the engine. Too high temperature of the piston will cause piston ring stuck, lubricating oil sticking, local fracture or deformation of piston and so on. Therefore the research of the piston oscillation cooling a nd temperature field is very necessary.In the paper, the combination of experiment and numerical simulation studies some factors that impact on the flow and heat transfer characteristics of cooling gallery. And the paper does comparative study about different shapes of cooling gallery which are designed. Finally, temperature field about piston which has or doesn’t have cooling gallery and has different shape s of cooling gallery is analyzed. The results are as follows:Firstly, the experiment and numerical simulation study the oil flow under different injection pressures about 4D piston of the diesel engine and the result of numerical simulation is verified by the experimental result. The result of study shows that, as crankshaft rotation changes, the amount of oil through oil gallery firstly shows increase then decrease under different injection pressure s; the relative error of test value and simulation value is controlled under 6%, so the numerical simulation results have a certain of credibility; oil rate of the front cross-section of cooling gallery is less than the back cross-section; oil volume fraction of the front cross-section wall is higher than the back cross-section.Secondly, the study about piston oscillating cooling shows that, with the increase of engine speed, oil capture rate and filling rate decrease, but cyclic average heat transfer coefficient of cooling gallery wall increases, so high-frequency oscillation can enhance heat transfer; as oil injection rate rises, oil capture rate and filling rate increase, the average heat transfer coefficient of cooling gallery wall rises on the whole; with the increase of oil temperature, oil capture rate and filling rate rise, but the range of oil capture rate is not big, the average heat transfer coefficient of cooling gallery wall will decrease; with the increase of oil outlet cross-section’s area, oil dynamic capture rate and the average heat transfer coefficient of cooling gallery wall rise on the whole, but oil filling rate will decline; if the geometrical shape of oil inlet is more reasonable, oil capture rate, filling rate and the average heat transfer coefficient of cooling gallery wall will become higher; compared with crowned shape cooling gallery, the heat transfer of cylinder shape cooling gallery is better; the comparative study about the heat transfer of ordinary and special cooling gallery shows that, the waved 2 is greater than the general and the general is greater than the wave 1. By comparing five different shapes of oil gallery’s heat transfer effect, the cylinder shape is greater than the waved 2, the waved 2 is greater than the general, the general is greater than the crowned shape, and the crowned shape is greater than the waved 1. But usually the cylinder shape will not be used in the practical engineering.Thirdly, the temperature field analysis about piston with ordinary and waved 2 cooling gallery and without cooling gallery show that, from top to bottom the whole temperature distribution of the three kinds of piston reduce gradually and the gradient of temperature is also less, the temperature about the top of piston is higher which is contrast with other parts, the maximum and minimum temperature distribute in the edge of combustion chamber and the inside of skirt’s bottom; compared with piston that does not have cooling gallery, the part of heat is taken away through oil gallery, piston cooling effect is enhanced by after casting cooling gallery, the decrease temperature about the shore of ring and the second ring groove is maximum, the decrease temperature of combustion chamber and the top of inner chamber is less relatively, the decrease temperature of skirt’s bottom is minimum; compared with piston that has ordinary cooling gallery, the temperature of the piston with waved 2 coolin g gallery reduce 3℃ in general. With the improvement of the engine strengthening degree, it is recommended that an engine company changes the structure of 4D piston oil gallery for the waved 2.