微小型发动机柱塞温度场和热变形的三维有限元数值模拟

3-D finite element numerical simulation of temperature distribution and deformation of piston in micro engines

对微型无人机用排气量在1ml以下的微小型发动机的柱塞组件进行了三维有限元热分析,并以0.33ml微小型机为例进行了实际计算,用热成像和易熔合金法进行了相关实验。根据实验数据利用反推法提高了模型精度,获得了微小型发动机的温度场和热变形的较准确结果。分析表明,排气系统等结构设计使柱塞的温度场和热变形轴向不对称,但差别很小;球铰的温度高,热应力大,容易发生失效。柱塞裙部轴向温度和变形呈指数分布,变形后形线内凹。高转速的强制冷却效果以及比表面积大的体积效应减少了热负荷,同时降低了热效率。本文建立的分析方法对1ml以下的微小型发动机具有通用性。

Thermal analysis has been carried out on piston of a micro engine with displacement of 0.33 ml by 3D finite element method (FEM).Related experiments were conducted by IR thermography and fusible alloy plugs.Precision of mathematical model was improved by inverse process from experimental data.Calculated results show that because of structure of exhaust system,temperature field and thermal deformation of piston appear minute axial asymmetry.Failure may happen in ball joint which suffers high temperature and stress.Axial temperature and deformation of piston shirt are in shape of exponential curve along piston wall.High speed cooling airflows and large engine surface area to volume ratio decrease both engine thermal load and efficiency.Presented methodology is universally suitable for micro engines with displacement less than 1 ml.