柴油机气缸套瞬态温度场移动边界方法分析

摘要

In the finite element analysis of a diesel engine liner, transient thermal boundary conditions have essential influence on the temperature distribution calculation.To analyze the temperature fields and thermal load of the liner of a medium-speed diesel engine, the transient temperature fields of the liner were analyzed based on a moving boundary method.The working process of a diesel engine was simulated with a 1-D working cycle simulation, whereby the transient temperature and heat transfer coefficient of the working fluid were obtained.With the combination of transient piston position, the liner surface area was divided into three major areas: working fluid contacting area, piston assembly contacting area, and crankcase air contacting area.The transient thermal boundary conditions of these areas were applied separately.With the application of a cyclically varying thermal load on the liner, the transient temperature fields of the liner were calculated.The results show that under stable operating conditions, the liner surface temperatures present cyclical variation.The maximum liner surface temperature and the highest temperature fluctuation appear on the top of the liner.The amplitudes of the temperature fluctuations decrease along the cylinder axial.In addition, the temperature fluctuations in the liner decrease rapidly along the radial direction.%在柴油机缸套有限元分析中,瞬态热边界条件对缸套的温度场分布计算结果起决定性作用.为了分析某型号中速柴油机气缸套的温度场及热负荷状态,采用移动边界方法进行了气缸套温度场瞬态分析.通过一维工作循环数值模拟得到缸内工质瞬时温度和换热系数,选取燃气数据变化关键时间点,结合该时刻的活塞位置对缸套内表面进行区域划分并分别求得不同区域瞬时热边界条件,进而对气缸套进行周期性载荷施加,计算得到稳定工况下循环瞬态温度场分布情况.计算结果表明:在稳态工况运行时,气缸套表面温度呈波动状态,最大波动幅值出现在气缸套上部,该位置的热负荷也最为严重.气缸套表面温度波动幅值沿气缸轴线向下止点方向不断减小,缸套内部温度波动幅值沿径向方向迅速衰减.