活塞结构参数对柴油机活塞传热与温度场的影响分析

为了降低活塞热负荷,降低活塞热疲劳失效概率,以一款高压共轨柴油机活塞作为研究对象,结合活塞温度试验测试,建立了活塞传热仿真分析模型,采用单因素扫值法和正交试验分析了活塞销座长度、活塞销孔直径、第一环岸厚度以及回油孔距离4个结构参数对活塞温度场分布的影响。研究发现,活塞结构对活塞传热与温度场分布有一定的影响,第一环岸厚度对活塞传热与温度场的影响最大。活塞的最高温度随着第一环岸厚度增加而升高,最多升高13.8℃。第一环槽的温度随着第一环岸厚度增加而降低,最多降低16℃。销座和回油孔结构对活塞温度场影响较小。最优方案是销座长度72.5 mm、销孔直径35 mm、火力岸厚度8 mm、回油孔相距53 mm的活塞,可以使活塞最高温度降低至374.3℃。为优化活塞传热提供参考。

Influences of piston structural parameters on heat transfer and temperature field of diesel engine piston

In order to meet the requirements of increasingly more stringent regulations of energy conservation and emissions reduction for automotive engines, many new technologies have been applied, such as multi-valve structures, variable geometry turbochargers, exhaust gas recirculation (EGR), and electronic controlled high-pressure fuel injection systems. On the other hand, the strength of the diesel engine is higher and higher, and the temperature field distributions of the engine parts are more uneven, such as pistons and cylinder head. The optimized piston structure, the inner cooling gallery structure, and the surface coating technology have become main ways to decrease heat load and optimize the temperature distributions of piston. The phenomenon of the thermal stress concentration is caused by uneven distribution of temperature field of the piston of internal combustion engine. In order to further study the temperature field distribution of the piston, a piston of high pressure common rail diesel engine which met the emission limit of Level 5 in China was treated as the research object. Combined with the temperature test of the feature points of piston surface using hardness plug, a heat transfer model of the piston group was established by using the finite element method. The enchased ring and pin were considered in the simulation model. A temperature field of piston was obtained by using the simulation model. Through the analysis it was found that some key locations of piston were prone to thermal stress concentration, such as the upside of the pin boss, the pin hole, the piston head and the 2 oil holes. Therefore, the length of the piston pin boss, the diameter of the pin hole, the height of the top land and the distance of 2 oil holes were treated as structural parameters. The influences of piston structure on heat transfer and temperature field were analyzed by using the single parameter sweep method and the orthogonal experiment method. The study found that the temperature distribution of the piston was not uniform. The maximum temperature of 382.6 ℃ appeared at the bowl edge of combustion chamber, and the minimum temperature of 161.1 ℃ appeared at the bottom of piston skirt. The piston structures had some influence on heat transfer performance and the temperature field distribution of the piston. Among the 4 structural parameters in this study, the height of the top land had the most influence on heat transfer and temperature field, the oil hole position ranked the second, and the pin hole diameter had the minimum. The top land height had the major influences on the distribution of temperature field of piston head. The maximum temperature of the piston increased by 13.8 ℃ with the increasing of the height of the top land. On the other hand, the maximum temperature of the first groove decreased by 16 ℃with the increasing of the height of the top land of the piston. The pin boss structure had the major impact on the regions under the oil ring and the regions of pin boss. The oil hole position had a little effect on heat transfer and temperature field of piston. In addition, if a piston structural parameter was changed, heat quantity conducted from gas side still remained almost the same. Therefore, the variation of the structure parameter could only affect heat transfer and temperature distribution of the corresponding part instead of other regions. The optimal combination of 4 structure parameters was found by the orthogonal experiment. The corresponding optimal scheme was the pin length of 72.5 mm, the diameter of the pin hole of 35 mm, the height of the top land of 8 mm, and the distance of the 2 oil holes of 53 mm. Through the heat transfer analysis it was found that the optimal scheme could reduce the maximum temperature of piston to 374.3 ℃.